Design and Application of Flowable Fill

Copyright by ASTM Int'l (all rights reserved); Thu Feb 7 18:46:02 EST 2013Downloaded/printed byKarina Agama (Freyssinet+Tierra+Armada+Peru+S.A.C.) pursuant to License Agreement. No further reproductions authorized.

S T P 1331

The Design and Application of Controlled Low-Strength Materials (Flowable Fill)

Amster K. Howard and Jennifer L. Hitch, Editors

ASTM Stock #: STP1331

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Library of Congress Cataloging-in-Publication Data

The design and application of controlled low-strength materials (flowable fill) / Amster K. Howard and Jennifer L. Hitch, editors.

p. c m . - (STP ; 1331) Includes bibliographical references and index. ISBN 0-8031-2477-5 1. Fills (Earthwork)--Mater ia ls. 2. Soil cement.

I. Howard, Amster K. II. Hitch, Jennifer L., 1960- II1. Series: ASTM special technical publication ; 1331. TA750.D47 1998 625.7'33--dc21

3. Slurry.

98-4142 CIP

Copyright �9 1998 AMERICAN SOCIETY FOR TESTING AND MATERIALS, West Conshohocken, PA. All rights reserved. This material may not be reproduced or copied, in whole or in part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of the publisher.

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The quality of the papers in this publication reflects not only the obvious efforts of the authors and the technical editor(s), but also the work of these peer reviewers. The ASTM Committee on Publications acknowledges with appreciation their dedication and contribution of time and effort on behalf of ASTM.

Printed in Philadelphia, PA May 1998


Foreword

This publication, The Design and Application of Controlled Low-Strength Materials (Flow- able Fill), contains papers presented at the symposium of the same name, held on 19-20 June 1997 in St. Louis, Missouri. The symposium was sponsored by ASTM Committee D- 18 on Soil and Rock and its Subcommittee D18.15 on Stabilization with Admixtures, in cooperation with ASTM Committee A-4 on Iron Castings, ASTM Committee C-9 on Con- crete and Concrete Aggregates, the American Concrete Institute, and the National Ready Mixed Concrete Association. Amster K. Howard of Lakewood, CO and Jennifer L. Hitch of Pozzolanic Intl. in Mercer Island, WA presided as symposium chairpersons and are editors of the resulting publication.


Contents

Overview--A. K. HOWARD AND J. L. HITCH

CURRENT STATE OF TEST STANDARDS

Test Methods for CLSM: Past, Present, and Future~J. L. HITCH

I N G R E D I E N T S - - F L Y A S H

Comparison of Dry Scrubber and Class C Fly Ash in CLSM Applicationsm /3. DOCKTER

Design and Testing CLSM Using Clean Coal Ash--T. R. NAIK, R. N. KRAUS, R. F. STURZL, AND /3. W. RAMME

INGREDIENTS - - A G G R E G A T E S

Use of High-Fines Limestone Screenings as Aggregate for CLSMm L, K. CROUCH, R. GAM/3LE, J. F. BROGDON, AND C. J. TUCKER

Utilization of Recycled Glass as Aggregate in CLSMmT. R. OHLHEISER

ix

13

27

45

60

PROPERTIES

Development of Engineering Properties for Regular and Quick-Set Flowable F i l l m F . PONS, J. S. LANDWERMEYER, AND L. KEMS 67

Engineering Properties of Air-Modified CLSMmR. J. HOOPES 87

Long Term Strength Gain of CLSM--J. i. MULLARKY 102

Admixture Enhanced CLSM for Direct Underwater Injection with Minimal Cross ContaminationmH. K. HEPWORTH, J. S. DAVIDSON, AND J. L. HOOYMAN 108


Corrosion Activity of Steel in Cementitious CLSM versus That in Soi l - - A. ABELLEIRA, N. S. BERKE, AND D. G. PICKERING 124

C A S E HISTORIES

Innovative Uses of CLSM in Colorado--w. NOOK AND D. A. CLEM

Fly-Ash-Based CLSM Used for Critical Microtunnel ing Appl ica t ions- - B. H. GREEN, K. STAHELI, D. BENNETT, AND D. WALLEY

Construction of CLSM Approach Embankmen t to Minimize the Bump at the End of the Bridge--D. R. SNETHEN AND J. M. BENSON

Filling Abandoned Mines with Fluidized Bed Combustion Ash G r o u t - - D. D. GRAY, T. P. REDDY~ D. C. BLACK, AND P. F. ZIEMKIEMCZ

Developing CLSM to Meet Indust ry and Construction Needs--M. R. GARDNER

Flowable Fill Backfill for Use in Sequential Excavations in Contaminated SoiI--M. P. WALKER AND J. R. ASH

Use of Controlled Density Fill to Fill Underslab Void--T. r. MASON

Properties of Low-Strength Concrete for Meeks Cabin Dam Modification Project, WyomingmT. P. DOLEN AND A. A. BENAVIDEZ

137

151

165

180

194

200

210

213

C A S E H I S T O R I E S - - P I P E L I N E S

Ten Year Performance Record of Non-Shrink Slurry Backfill--D. BRINKLEY AND P. E. MUELLER

Field Test of Buried Pipe with CLSM Backfill--M. c. WEBB, T. J. McGRATH, AND E. T. SELIG

Flowable Fill Promotes Trench Safety and Supports Drainage Pipe Buried 6 0

ft (18.3 m) Under New Runway--J . R. HEGARTY AND S. J. EATON

Bedding Factors and E ' Values for Buried Pipe Installation Backfilled with Air-Modified CLSM--T. J. McGRATH AND R. J. HOOPES

Frost Penetrat ion in Flowable Fill Used in Pipe Trench Backfi l lD T. HARRY W. BAKER

231

237

255

265

275


SPECIFICATIONS, STANDARDS, AND TESTING

Proposed Standard Practice for Installing Buried Pipe Using Flowable Fill-- A. HOWARD

Specifications and Use of CLSM by State Transportation Agencies-- E. H. RIGGS AND R. H. KECK

Heat of Neutralization Test to Determine Cement Content of Soil-Cement or Roller-Compacted Concrete--R. SCAVUZZO AND B. A. KUNZER

APPENDIX--CLSM STANDARDS

Standard Test Method for Preparation and Testing of Controlled Low Strength Material (CLSM) Test Cylinders

Standard Practice for Sampling Freshly Mixed Controlled Low-Strength Material

Standard Test Method for Unit Weight, Yield, Cement Content, and Air Content (Gravimetric) of Controlled Low Strength Material (CLSM)

Standard Test Method for Ball Drop on Controlled Low Strength Material (CLSM) to Determine Suitability for Load Application

Standard Test Method for Flow Consistency of Controlled Low Strength Material (CLSM)

Author Index

Subject Index

285

296

306

319

323

325

329

332

335

337


OVERVIEW

The symposium on Design and Application o fCLSM (Flowable Fill) was held in St. Louis, Missouri on June 19-20, 1997. The symposium was sponsored by ASTM Committee D 18 on Soil and Rock in cooperation with Committee A 4 on Iron Castings, C 9 on Concrete and Concrete Aggregates and with the American National Ready Mix Concrete Association.

Over the last decade and a half, the use of Controlled Low Strength Material (CLSM) or flowable fill as it is more commonly known, has increased dramatically. The purpose of this symposium was to present new design procedures, new applications, and installation innovations to help assess the need for new or improved standards on flowable fill. As discussed by Jenny Hitch in her paper in the symposium, ASTM Subcommittee D 18.15 has recently developed four new standards on CLSM to bring the number of standards concerning CLSM to five.

CLSM is also known as flowable fill, flow fill, controlled density fill, soil-cement slurry, and K-crete, among others. It is a mixture ofcementitious material (portland cement or Class C fly ash), soil, water and sometimes fly ash and admixtures. CLSM is used in place of compacted backfill and the most common use has been for pipe embedment and backfill. However, CLSM has many uses as illustrated in the symposium by the papers by Hook and Clem, Green et al, Snethen and Benson, Gray et al, Gardner, Mason, and Dolen and Benavidez.

The symposium was divided into 5 parts to cover the wide range of new developments in the use of CLSM, as follows:

* Ingredients * Properties of CLSM * Test Methods, Standards, and Specifications * Case Histories * Pipeline Applications

INGREDIENTS

Fly Ash Two papers dealt with using fly ash in CLSM mixes: Bruce Dockter described testing to determine how fly ashes that do not meet

specifications for use in concrete can be used in CLSM. Tarun R. Naik, et al, discussed the development of mixture proportions of clean

coal ash from atmospheric fluidized bed combustion for acceptable u s e in CLSM mixtures.

Aggegate Two papers dealt with the use of non-traditional materials as aggregates in CLSM:

L. K. Crouch, et al, reported the successful use of limestone screenings with high fines (passing No. 200 sieve) content as an aggregate for flowable fill.

ix


X OVERVI EW

Todd R. Ohlheiser investigated the use of recycled glass to replace 100 % of the aggregate in flowable fill. The use of recycled glass has been approved by the Colorado Department of Transportation.

Other Gilbert Tallard addressed a flowable fill material composed ofattapulgite clay and a finely ground blast furnace cement. The resulting material has a very low unit weight and permeability.

PROPERTIES OF CLSM

Five papers dealt with the properties of flowable fill: Pons and Landwermeyer compared the bearing strength, diggability, and

subsidence of regular CLSM to a quick setting CLSM. Penetration resistance and compressive strength were also determined.

R. J. Hoopes concluded that air-modified low-water content CLSM retains the compressibility, shear, load bearing, and flowability characteristics of regular CLSM, while improving permeability, subsidence, bleeding, and freeze-thaw properties.

Jon Mullarky addressed the long-term strength gain of CLSM and described a two year study to evaluate mix parameters to control strength gain.

Hepworth, et al, investigated the use of wash out resistant CLSM as a stabilizing and entombing agent for the remediation of tanks containing contaminated materials.

Angel Abelleira, et al, described an experiment with steel coupons placed in soil or in CLSM to evaluate their effect on the corrosion of the steel.

TESTS METHODS, STANDARDS, AND SPECIFICATIONS

Amster Howard reported on a proposed ASTM standard practice for installation of buried pipe using flowable fill. This standard is currently being developed by Subcommittee D 18.15 and would apply to all types of pipe.

E. H. Riggs and R. H. Keck compared the specifications for flowable fill being used by transportation agencies in several southern states and gave recommendations for standard specification language.

Elizabeth Kunzer gave a paper authored by Robert Scavuzzo and herself that described a laboratory test to determine the cement content of CLSM by measuring the heat of neutralization created when adding acid to the CLSM. The test is faster and simpler that the current titration method.

Jenny Hitch related the history of CLSM testing and the current efforts of ASTM Committee D 18 to develop standards for test methods.

CASE HISTORIES

Many interesting uses offiowable fill were described by the following speakers: W. Hook reported on the use offlowable fill to backfill culverts used to replace

substandard bridges, to fill an abandoned culvert, in tilt-up construction, in foundation wall backfill, and in pipe bedding.

B. H. Green, et al, discussed the use offlowable fill to fill the void left by microtunneling machines when forced to abort the tunnel and withdraw. They also


OVERVIEW xi

described the use offlowable fill to stabilize the soil surrounding the sheet-piled shaft that would be used to launch a microtunnel boring machine.

Snethen and Benson evaluated the use of CLSM to construct the approach embankments to a bridge to minimize the bump that sometimes occurs when compacted soil embankments settle.

D. D. Gray, et al, described the trial use o fa CLSM composed o f a cementitious fly ash, bentonite, and water to backfill abandoned mines.

M. R. Gardner discussed the use of flowable fill to backfill over a bus tunnel, support a parking garage on a dumpsite, replace compacted soil to reduce the construction traffic, quickly backfill a water main under a railway minimizing any disruption to train traffic, and to encapsulate contaminated soil.

M. P. Walker and J. R. Ash reported on the use offlowable fill as backfill in sequential excavations.

T. Mason described how flowable fill was used to fill a void underneath a building slab.

Dolen and Benavidez related the development of a mix design for flowable fill to be used as a cutoffwall constructed in an existing dam to reduce foundation seepage through the dam.

PIPELINE APPLICATIONS

There were 5 papers that dealt specifically with using flowable fill for pipeline construction.

D. Brinkley and P. E. Mueller described the use of a zero-slump CLSM mixture that has a high void content. The material is easily excavated and is now required for all utility trench backfill in Prescott Arizona.

T. J. McGrath, et al, investigated the use of flowable fill for installing three types of pipe, reinforced concrete, corrugated HDPE, and corrugated metal. The study was part of an National Science Foundation research project on installation procedures for buried pipe.

Hegarty and Eaton reported on the use of flowable fill for the embedment of concrete pipe with 60 feet of backfill under an airport runway.

T. J. McGrath and R. J. Hoopes gave the results o f a finite dement study to develop the bedding factors and E prime values for buried pipe installations using flowable fill.

T. H. W. Baker addressed the potential problems associated with frost penetration when using flowable fill for pipe backfill.

The symposium papers were a reflection of the versatility of the rapidly growing use of flowable fill and its ingredients. Many useful ideas and comments were generated for the use of ASTM Subcommittee D 18.15 for their updating and development of CLSM.


xii OVERVIEW

ASTM STANDARDS ON CLSM

The Appendix to this STP contains the current ASTM Standards on CLSM developed by Committee I)-18 on Soil and Rock, as follows:

D 4832 Standard Test Method for Preparation and Testing of Controlled Low Strength Material (CLSM) Test Cylinders

D 5971 Standard Practice for Sampling Freshly Mixed Controlled Low Strength Material

D 6023 Standard Test Method for Unit Weight, Yield, Cement Content, and Air Content (Gravimetric) of Controlled Low Strength Material

D 6024 Standard Test Method for Ball Drop on Controlled Low Strength Material to Determine Suitability for Load Application

D 6103 Standard Test Method for Flow Consistency of Controlled Low Strength Material

ACKNOWLEDGMENTS

We wish to thank all the authors, reviewers, and session chairmen whose hard work made the symposium an interesting and very useful forum for discussing the current use and application of controlled low strength material. We would also like to thank the staff at ASTM for their help in organizing this symposium.

Amster Howard Symposium Co-Chair Consulting Civil Engineer Lakewood CO USA

Jenny Hitch Symposium Co-Chair Pozzolanic International Mercer Island WA USA


Current State of Test Standards

C o p y r i g h t b y A S T M I n t ' l ( a l l r i g h t s r e s e r v e d ) ; T h u F e b 7 1 8 : 4 6 : 0 2 E S T 2 0 1 3D o w n l o a d e d / p r i n t e d b yK a r i n a A g a m a ( F r e y s s i n e t + T i e r r a + A r m a d a + P e r u + S . A . C . ) p u r s u a n t t o L i c e n s e A g r e e m e n t . N o f u r t h e r r e p r o d u c t i o n s a u t h o r i z e d .

Jennifer L. Hitch ~

TEST METHODS FOR CONTROLLED LOW-STRENGTH MATERIAL (CLSM): PAST, PRESENT, AND FUTURE

REFERENCE: Hitch, J. L., "Test Methods for Controlled Low-Strength Material (CLSM): Past, Present, and Future," The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: Controlled low-strength material (CLSM) encompasses a variety of fill materials that are primarily used as replacements for compacted backfill. The history of CLSM tracing back to its inception as K-Krete| provides a basis for how test methods came into existence. The American Concrete Institute's (ACI) work assimilating all of the knowledge gained throughout history, including a working definition of CLSM, resulted in a state-of-the-art report which brought this new fill technology to the construction industry. It was ACI who originally recognized the need for test methods to be developed specifically for CLSM.

The testing of CLSM became important, and the role that ASTM Subcommittee D 18.15 on Stabilization with Admixtures played in creating standardized test methods is discussed. Background into how these test methods came into existence stems from experiences at the Bureau of Reclamation, the Ohio Ready Mixed Concrete Association, and Pozzolanic Northwest. The history of the current standard test methods for CLSM is rather short but quite important. Five ASTM standards currently exist specifically for CLSM which is just the beginning. Possibilities for additional test methods are explored.

KEYWORDS: controlled low-strength material (CLSM), K-Krete, CDF, flowable fill, fly ash, backfill, void filling, test methods

Many definitions exist for controlled low-strength material (CLSM) as well as many different names. In general, CLSM describes a fill technology that is used in place of compacted backfill. CLSM is lower in strength than concrete, which makes future excavation a possibility. The ingredients may vary, but typically, CLSM contains fly ash, portland cement, aggregates or soil, water, and sometimes chemical admixtures. It can be

1 Manager-Quality Assurance, Pozzolanic International, 7525 S.E. 24 tu St., Suite 630, Mercer Island, WA 98040.

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4 CONTROLLED LOW-STRENGTH MATERIALS

delivered as a fluid in a ready-mix concrete truck or even as a dry material in a dump truck. It can be proportioned to be self-leveling so it will not require compaction. It can be designed to meet specific strength criteria or density requirement. CLSM is an innovative fill technology that the construction industry is just beginning to use.

K-KRETE| AND CDF

The earliest documented cases of using soil-cement slurry date back to the 1960s (Howard 1996), however, it wasn't until the early 1970s that the use of CLSM became more prominent (Brewer 1994). During the Enrico Fermi II Nuclear Station project in Monroe, Michigan, engineers from the Detroit Edison Company (Detroit, Michigan) and the Kuhlman Corporation (Toledo, Ohio) began to examine the role of fly ash in concrete in an effort to increase its use in any way possible. The Detroit Edison Company was interested in reducing their stockpile of fly ash by increasing the volume used, while Kuhlman wanted to increase the production of their ready-mixed concrete trucks. The combination of these two goals prompted the initial research into low-strength materials.

Mr. William E. Brewer, who was working for Kuhlman Corporation, along with Mr. Frank Zimmer of Detroit Edison contracted with Edwin L. Saxer of the University of Toledo to run a series of laboratory tests to confirm that low-strength materials could be produced while maintaining some degree of product control. Being successful in their endeavor with the laboratory tests, both Kuhlman Corporation and Detroit Edison Company agreed to provide funding to develop a company known as K-Krete Inc. Representatives from both organizations were appointed corporate officers. The low- strength materials involved in these laboratory tests were named K-Krete| for which the company received trademark rights. Detroit Edison Company had stipulated before forming the new company that the mixtures and applications be protected; therefore, patents were developed. Four patent areas were chosen: mixture design, backfill technique, pipe bedding, and dike construction.

By 1974, K-Krete Inc. had franchises throughout the United States and one in Canada. K-Krete Inc. was sold in 1977 to a Minneapolis firm known as CONTECH which eventually sold the K-Krete Inc. rights. While in existence, the K-Krete patents never had the opportunity to be tested in a court of law. Currently, they are assigned to the National Ready Mixed Concrete Association (NRMCA) for general use which allows ready-mixed concrete producers and contractors to use materials similar to K-Krete without fear of any legal action (Brewer 1994).

The term controlled density fill (CDF) came about in an effort to avoid the patented K-Krete backfills while responding to the needs of the construction industry to develop other low-strength specialty fills for applications such as pavement bases, structural fills, and thermal fills. These first CDF mixtures were low strength in comparison to concrete and maintained a uniform density from the top to the bottom of the trench. Mixtures could be designed to meet any density criteria and compressive strengths. Initially, CDF mixes had 28 day strengths around 0.7 Mpa (100 psi). The mixes generally contained fly ash, portland cement, fine aggregates, and water (Cincinnati Gas & Electric Co. 1992).


HITCH/TEST METHODS 5

PROMOTION OF CLSM

By 1984, the technology regarding CDF had slowed. In an effort to increase awareness and disseminate more information on this subject, Mr. Brewer approached the American Concrete Institute (ACI) and suggested that a committee be formed for low- strength materials. That year ACI Committee 229 on Controlled Low Strength Materials (CLSM) was created, and Mr. Brewer served as the chairman for six years. The term CLSM was chosen over CDF because it was more general, covering more types of fill materials. The pioneering members of ACI 229 determined that the definition of CLSM was to be those materials with a 28-day compressive strength &less than 8.28 Mpa (1200 psi) regardless of the materials used to produce the mixture. The Committee then began the task of creating a state-of-the-art report on CLSM that would summarize the information known to the industry.

Ten years after the formation of ACI Committee 229, under the chairmanship of Wayne Adaska, the report on controlled low-strength material (CLSM) was completed. It appeared in the July 1994 edition of Concrete International (ACI Committee 229 1994a). Distribution of this document increased the awareness and understanding of CLSM The report which is a guide to CLSM, begins with an introduction containing a definition, other terms used, and a table explaining the advantages of using CLSM. It then describes applications in which CLSM can be used such as backfills, structural fills, insulating and isolation fills, pavement bases, conduit bedding, erosion control, and void filling. The material section describes requirements for the cement, fly ash, chemical admixtures, water, and aggregates. It also discusses the use of nonstandard materials. The various properties in the plastic and hardened state are reviewed. A section on mix proportioning includes a table containing different mix designs, some of which were specified by state departments of transportation. Suggestions on mixing, transporting, and placing are provided as well as quality control procedures that should be followed. The report also includes a section on low-density CLSM made with preformed foam.

In 1994, ACI published Report SP-150, "Controlled Low-Strength Materials" that contains papers presented at the 1992 ACI Spring Convention and the 1992 annual meeting of the Transportation Research Board (ACI 1994b). The papers discuss mix designs, physical properties, and case histories of CLSM.

The ACI 229 Report in the discussion on quality control acknowledges that there are a lack of test methods specifically for CLSM. Historically, testing required on CLSM was minimal. If anything was required, CLSM was treated as a "concrete-like" material with similar testing specified. Often convincing the producer that their own product was acceptable was the difficult part. Once they acquired confidence in the material, their experience was often relied upon quite heavily. As the use of CLSM increased, compressive strengths were perceived to be important, so in keeping with the concrete mentality, 28-day strengths were being specified. Occasionally, the producer supplying the job would make extra cylinders to monitor strength past 28 days, sometimes to a year or more. While this data on each mix was quite useful in tracking long-term performance, it was relatively useless in the developmental stages of the mix. CLSM mixes surpassing



strength criteria were being supplied, and nothing could be done to prevent it. Once long- term data on a particular mix was completed, adjustments could be made on future mixes. Unfortunately, strength information was not always used properly.

TEST M E T H O D H I S T O R Y

It was immediately apparent to anyone preparing CLSM cylinders that they were quite different from concrete cylinders. They were also much more fragile. Some cylinders could not survive the curing and stripping process. The method of capping was questioned. Testing the cylinders was also a challenge. Most concrete testing machines were not set up to measure low strengths accurately.

Slump was sometimes specified; however, the test would not provide useful information for very flowable mixtures. The flow test was suggested by members of ACI Committee 229 as a better measure of the flowability characteristics than the slump test. The flowability of certain CLSM mixtures differentiated it from concrete. It was discovered fairly quickly that flow could not be judged by the eye. By quantitatively measuring the spread diameter for flowable materials, it was possible to determine the relative performance of the CLSM mixture.

Occasionally, unit weights were specified, but once again the test procedure for concrete needed modifications. Experiences continued to show that CLSM did not perform exactly like concrete and therefore new procedures were desperately needed and the equipment would need to be evaluated. In addition, since CLSM was often used as a fill material, the engineering community became interested in how it compared to native soil or imported backfill which caused CLSM to be scrutinized by soil tests which were not always appropriate.

The ASTM Committee D18 on Soil and Rock was the was the first to respond to these needs. The ASTM Subcommittee D18.15, which was responsible for standards dealing with Stabilization with Admixtures, undertook the task of creating standards for this new material. Chairman Wayne Adaska appointed a task group to determine exactly which standards were needed and to begin standardizing test methods for CLSM.

One of the standards under ASTM Subcommittee D 18.15 jurisdiction was already suitable, but it required some modification. The ASTM Test Method for Preparation and Testing of Soil-Cement Slurry Test Cylinders (D 4832) had originally been authored by Amster Howard, formerly with the Bureau of Reclamation. It had come about from experiences that the Bureau of Reclamation had with some pipeline projects. In the 1960s, the Bureau of Reclamation had used a soil-cement slurry on the Canadian River project in Texas for bedding 476 km (296 miles) of pipe. The soil-cement worked quite well, however, future use was sporadic. It was not until the late 1970s that interest in soil- cement slurries increased within the Bureau of Reclamation. In the mid-1980s, the Bureau of Reclamation had a project in Gilroy, California in which soil-cement slurry was used to bed a pipe. On this project, the field laboratory technicians, through much trial and error, developed a test method for preparing and testing soil-cement slurry cylinders (Howard 1996). Mr. Howard documented the procedures and the standard was created. It was

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approved and became a full standard in 1988. CLSM was referenced in the Appendix; however, that is nonmandatory information. Mr. Howard revised the standard so that it was applicable for CLSM 2. In 1995, the revised standard was approved, including a title change and is now known as ASTM Test Method for Preparation and Testing of Controlled Low Strength Material (CLSM) Test Cylinders (D 4832).

The Ohio Ready Mixed Concrete Association (ORMCA) became an instrumental part of the standardization of ASTM Test Method D 4832 as well as three other test methods. They had recently revised some existing concrete standards in an effort to respond to the needs of their membership. CLSM, or flowable fill as it was known in Ohio, had been heavily promoted by ORMCA for many years. The evolution of flowable fill promotion in Ohio sprang from Mr. Brewer's work with K-Krete and CDF. A large electric utility company had done a number of ash utilization studies and requested that ORMCA begin aggressively promoting flowable fill. ORMCA responded to the request and began to work with the ready-mix community and the contractors so the material could be delivered to job sites. Both were quite receptive to the concept. ORMCA then began working with engineers within the Ohio Department of Transportation to get them to specify the material. The next step was to go to the County engineers. Following their success they then approached City engineers in an effort to get flowable fill specified. For the Public Works sector, the most significant benefit of CLSM was the lack of settlement. The market grew and flowable fill continued to be specified. The more it was used, the more it was scrutinized. Compressive strength testing began to be specified more often in an effort to assure quality, however, that made it difficult on the contractor. They were becoming disenchanted with flowable fill due to the extra work and associated costs that it required. In addition to those difficulties another situation arose which almost caused the demise of flowable fill. The ultimate strength of in-place flowable fill exceeded specified strength and excavation was extremely difficult. Unfortunately, in this particular case backup data had not been maintained. It was a losing situation for the ready-mix supplier, the contractor, and the reputation offlowable fill. Those events prompted suppliers to question the current test methods being used and to suggest that new methods be explored in order to save this new fill technology. ORMCA had the ability and the personnel to begin the investigation.

Warren Baas and John Paxton, both having backgrounds in concrete technology, began examining existing concrete test methods and found some ASTM standards that could be adapted for flowable fill. They incorporated current test methods being used in the field into these standards. By June 1994, they had revised four flowable fill standards which they titled "ORMCA FF 1-4 (94)." They also had prepared recommendations for producers and specifiers on "Diggable Flowable Fill." ORMCA provided copies to their members and also elicited comments from all of the ready-mix associations bordering the state of Ohio. They sponsored a series of demonstrations on flowable fill throughout the state using the new test methods. An article on the standards appeared in the November 1994 issue of Concrete Products (Intertec Publishing Nov. 1994) that helped focus on the need for current test methods for flowable fill 3.

2 A. K. Howard, Personal communication, Consultant, Lakewood, CO, 1997. 3 W. P. Baas and R. P. Jones, Personal communication, ORMCA, Columbus, OH, 1996.



About the time those 4 standards were being revised, the method for the ball-drop test was being developed in the Northwest. The Western Washington representative for Pozzolanic Northwest recognized the need for a test to determine if CLSM was ready to receive loads. In the field, he was witnessing the contractor stomping a few times on the hardened CLSM. If their foot did not settle and no water came to the surface, then they would make the decision to apply the final wearing surface 4. As crude as this test was, it worked quite well. To standardize that field test, the action of a stomping foot was simulated by a large weight dropped numerous times. A "Kelly-Ball," which had originally been used to measure slumps in the concrete industry, was selected by the author and her associate. The weight of the ball was 16 kg (35 lbs) and it came equipped with a frame to allow the weight to be dropped in the same spot numerous times. After many lab trials on CLSM mixes it was determined that the weight should be dropped five consecutive times onto the surface of CLSM. It was also discovered that if the surface remained free of water, even if a slight indentation appeared, then it was replicating what had been witnessed in the field and was ready to receive the final wearing surface. During these lab tests and subsequent field trials, CLSM which was not hardened was actually compacted by the "Kelly-Ball" allowing water to be pumped to the surface creating a sheen or even a puddle in the indentation. If the CLSM was hardened, it would withstand the weight without pumping water. The test method was then drafted into ASTM format and submitted to ASTM Subcommittee D 18.15 for approval.

ORMCA had also contacted ASTM Subcommittee D 18.15 and requested that three of their standards be rewritten to comply with ASTM format (one was already incorporated into ASTM Test Method D 4832). They worked closely with the author, who was the current task group chairman, editing the standards.

STATUS OF CURRENT TEST METHODS

In 1994, a request was made to the ASTM Committee D 18 that four standards be granted provisional status on the basis that there was a desperate need in the industry for ASTM test methods specifically for CLSM. Provisional standards are published for a limited time period of 2 years and require only subcommittee consensus. After the 2 year period they have either been reviewed and balloted to be elevated to a full standard or they are withdrawn from the Annual Book of ASTM Standards (ASTM July 1995). The request for provisional standards was granted and the following were issued: �9 ASTM Provisional Test Method for Flow Consistency of Controlled Low Strength

Material (PS 28) �9 ASTM Provisional Test Method for Unit Weight, Yield, and Air Content

(Gravimetric) of Controlled Low Strength Material (PS 29) �9 ASTM Provisional Practice for Sampling Freshly Mixed Controlled Low Strength

Material (PS 30) �9 ASTM Provisional Test Method for Ball Drop on Controlled Low Strength Material

to Determine Suitability for Load Application (PS 31)

4 R. R. Halverson, Personal communication, Pozzolanic Northwest, Mercer Island, WA, 1995.



The announcement of the new provisional standards appeared in the March 1996 edition of ASTM Standardization News (ASTM March 1996).

In 1996, under the chairmanship of Mrs. Jenny Hitch, the standards were revised and adopted as ASTM standards: �9 ASTM Practice for Sampling Freshly Mixed Controlled Low Strength Material (D

5791) �9 ASTM Test Method for Unit Weight, Yield and Air Content (Gravimetric) of

Controlled Low Strength Material (D 6023) �9 ASTM Test Method for Ball Drop on Controlled Low Strength Material to Determine

Suitability for Load Application (D 6024) �9 ASTM Test Method for Flow Consistency of Controlled Low Strength Material (D

6103)

Much discussion has ensued on the topic of additional test methods for CLSM. The construction industry is asking for tests to be developed to monitor in-place CLSM as opposed to testing lab mixes. A method which utilizes a penetrometer on hardened CLSM in the field has been investigated as it has shown promising results for testing in- place strength. A method of sampling the material insitu has been requested to determine among other things any voids or discontinuities but also to monitor field strength. There is a need for test methods for nonfiowable CLSM. Looking ahead a series of test methods for different varieties of CLSM may need to be developed. The path that will be taken on future test methods and practices will most likely be set according to the needs of the industry.

SUMMARY

The future for CLSM looks very promising. Test methods are continuing to be developed and refined as more experience is gained. This leads to an increase in confidence on the part of the producers of the material, which encourages them to gain even more experience and in essence continue to create a higher quality product. As engineers and architects become more familiar with CLSM and their confidence increases, they will call out for it more in specifications. Increasing confidence allows the advancement of technology surrounding CLSM. However, the industry must be cognizant that the technology does not become so complicated and restrictive that CLSM is disregarded and soil or rock backfill chosen in its place. The temptation is great to overtest the material but it must be remembered that CLSM is merely "strong dirt". The testing that is required should parallel that for ordinary compacted backfill answering questions such as:

ols the void completely filled? oWill there be any settlement ?

while also answering specific concerns related to CLSM, like:

ols the CLSM ready to receive the final wearing surface?



�9 Can it be excavated at a later date? �9 Is the material homogeneous throughout the area?

These are a few of the issues that must be responded to with established test methods. The construction industry with the help of ASTM Subcommittee D 18.15 is attempting to reply to those questions by utilizing existing test methods and refining

them where necessary and also by developing new test methods. The ultimate goal is to permit the evolution of CLSM so that it fills the needs of the construction industry well into the future.

REFERENCES

American Concrete Institute Committee 229, July 1994, "ACI 229R-94 Report: Controlled Low Strength Materials (CLSM)," Concrete International, Vol. 16, No. 7.

American Concrete Institute, 1994, Controlled Low-Strength Materials, SP-150, ACI, Detroit, MI.

American Society for Testing and Materials, 1995 Annual Book of ASTM Standards, Section 4, Volume 4.08, ASTM, Philadelphia, PA.

American Society for Testing and Materials, July 1995, Regulations Governing ASTM Technical Committees.

American Society for Testing and Materials, March 1996, "Four Standards on Controlled Low Strength Materials Published," ASTM Standardization News, pp. 9-10.

Brewer, W. E., 1994, "Durability Factors Affecting CLSM", Controlled Low-Strength Materials, STP- 150, American Concrete Institute, Michigan, pp. 41-43

The Cincinnati Gas & Electric Company, 1992, Special Report Controlled Low Strength Material (CLSM) for Ready Mixed Concrete Producers, Brewer & Associates, Toledo, Ohio.

Howard, A. K., 1996, Pipeline Installation, Relativity Publishing, Lakewood, CO.

Intertec Publishing, Nov. 1994, "ORMCA pitches flowable fill standards to ASTM, AASHTO," Concrete Products, pp. 8-10.


Ingredients Fly Ash


Bruce A. Dockter ~

COMPARISON OF DRY SCRUBBER AND CLASS C FLY ASH IN CONTROLLED LOW-

STRENGTH MATERIAL (CLSM) APPLICATIONS

REFERENCE: Dockter, B.A. ''Comparison of Dry Scrubber and Class C Fly Ash in Controlled Low-Strength Materials (CLSM) Applications'', The Design and Application of Controlled Low-Strength Materials (Flowable Fill)'', ASTM STP 1331, A.K. Howard and J.L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: Controlled low-strength material (CLSM) is a cementitious material, commonly a blend of portland cement, fly ash, sand, and water, that is usually flowable and self-leveling at the time of placement. It is generally used in nonstructural applications below grade where low strengths are desired. In these cases, the mature strength of the CLSM is intended to be no stronger than that of the surrounding soils.

KEYWORDS: controlled low-strength materials, flowable fill, controlled density fill

Two coal ash residues were compared in this study for use in controlled low-strength material (CLSM) applications. The first ash sample (FAI) was produced from a pulverized coal combustion system burning North Dakota lignite coal. The second ash (FA2) is described as a dry scrubber ash collected from a combustion system that burns subbituminous coal from the Powder River Basin in Wyoming and injects a lime absorbent in the form of crushed limestone to remove sulfur dioxide (SO2) emissions. Sample FAI is classified as a Class C fly ash according to American Society for Testing and Materials (ASTM) Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete (C 618) and has been marketed as a concrete additive for the past 20 years. The intent of this project was to compare two variable ash sources as well as proportions of ash, cement, sand, and water and determine their corresponding characteristics such as strength development, set time, and consistency. Coal ashes need not meet Specification ASTM C 618 for CLSM uses; thus; it is extremely advantageous to evaluate various types of coal combustion by-products for such applications. Of particular interest are the coal combustion by-products from advanced coal

~Manager, Materials Properties Research Laboratories, Energy & Environmental Research Center, University of North Dakota, PO Box 9018, Grand Forks, ND 58202-9018.

13

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technologies such as limestone injection and fluidized-bed combustion

ashes. These advanced coal technology by-products and many other

pulverized coal ashes that fail to meet specifications for use in

concrete could find a niche as a constituent material in a CLSM mixture.

INTRODUCTION

With support from the Coal Ash Resources Research Consortium

(CARRC) of the Energy & Environmental Research Center (EERC) and its

members, research was performed on two sources of coal ash in CLSM

applications~ CLSM is also known as controlled density fill, flowable

mortar, ready-mix flowable fill, lean mix backfill, and K-Krete| 2 CLSM

is a cementitious material, commonly a blend of portland cement, fly

ash, sand, and water, that is usually of a flowable and self-leveling

consistency at the time of placement. It is generally used in

nonstructural applications below grade for which low strengths are

desired. In these cases, the mature strength of the CLSM is intended to

be no stronger than that of the surrounding soils.

Coal combustion residues used in this study were supplied by CARRC

members. The first ash sample (FAI) was produced from a pulverized coal

combustion system burning North Dakota lignite coal. The second ash (FA2) is described as a dry scrubber ash collected from a combustion

system that burns subbituminous coal from the Powder River Basin in

Wyoming and injects a lime absorbent in the form of crushed limestone to

remove SO2 emissions. Sample FAI is classified as a Class C fly ash

according to ASTM Specification C 618 and has been marketed as a

concrete additive for the past 20 years. The chemical and physical analyses of both fly ashes are given in Table I. The ASTM Specification

C 618 for allowing the use of fly ash in portland cement concrete is

given in Table 2.

BACKGROUND

Beginning in the late 1960s, the Detroit Edison Company initiated

efforts to use a fly ash cement grout placed in a fluid consistency for

backfilling pipe trenches, culverts, and retaining structures and as a

subbase under building floors and paved areas. The desired product

characteristics included fluid placement, elimination of tamping or

compaction in layers, and stable support. Initial placement tests were

conducted at Detroit Edison Company's Greenwood Energy Center, located

in Avoca, Michigan (Brewer 1976).

This work culminated in the marketing of a product known as K-

Krete | controlled density fill. Early CLSM mixes designed for higher-

strength applications consisted of approximately equal percentages of

portland cement and fly ash, with most of the mix being sand aggregate.

In low-strength applications in which future excavation was possible,

2K-Krete, Inc., 7711 Computer Avenue, Minneapolis, Minnesota 55435.

A Contech Inc. company.


DOCKTER/DRY SCRUBBER AND CLASS C FLY ASH 15

CLSM mixes contained lower percentages of portland cement, the remainder

being fly ash without sand aggregate filler (Collins et al�9 1991) . In

1977, four patents for K-Krete | were issued to Brewer and others (Larsen

1990). They were then sold to Contech Inc., in Minneapolis, Minnesota,

which has since ceded the patent rights to the National Ready-Mix

Concrete Association with the stipulation that these rights may not be

used in a proprietary manner�9

TABLE 1--Coal ash characZerization results (ASTM Specification C 618)�9

coal Ash FA1 Coal Ash FA2

Chemical Composition, %

Silicon dioxide (SiO 2)

Aluminum oxide (AI2Q)

Iron oxide (FeO3)

Calcium oxide (CaO)

Magnesium oxide (MgO)

Sodium oxide (Na20)

Potassium oxide (K20) Sulfur trioxide (SO3)

Loss on ignition, %

Moisture content, %

Available alkalies

Physical Properties Fineness, % retained on

No�9 325 sieve

Strength activity index

with portland cement,

% of control at 28 With lime, psi (MPa)

Water requirement,

% of control

Autoclave soundness,

expansion, %

Specific gravity

1 620

44�9

15.60

7.60

21.00

1�9

0.44

0.02

0�9

28.50

15.30 2 90

24 20

3 20

2 i0

0 60

17 00

1 70

1 80

1 97

19�9 13�9

91 107

(ii.i) 2 160 (14�9

88 95

0.07 0.09

2.53 2.42

Since the initial marketing of K-Krete | CLSM mix formulations have

been independently developed by others, including utility companies and

state highway departments. Examples of typical mix designs are shown in

Table 3. Although CLSMs are referred to in numerous ways, all have the

same general definition: a 10w-strength material, mixed to a wet

flowable consistency, used as an economical fill or backfill material

placed by pouring it into the area to be filled�9 Slumps measured in

accordance with ASTM Standard Test Method for Slump of Hydraulic Cement

Concrete (C 143) are generally 8 in. (20 cm) or higher. The CLSMs have a

self-leveling consistency and can be placed with minimal effort and no

vibration or tamping�9 The American Concrete Institute (ACI) Committee

229 classes CLSM as a construction material having a maximum 28-day

compressible strength lower than 1200 psi (8.23 MPa) (National Ready-Mix

Concrete Association)�9 If the mixture is intended to be removed at a

possible later date, the design strength should be in the range of 30 to

150 psi (0.20 to 1�9 MPa) .



TABLE 2--ASTM SDecification C 618-92a chemical and Dhvsical

specifications.

Mineral Admixture Class

N F C

Chemical Requirements

Silicon dioxide, aluminum oxide,

iron oxide (SiQ + AI203 + Fe203) ,

min. % 70 70 50

Sulfur trioxide (SO~), max. % 4.0 5.0 5.0

Moisture content, max. % 3.0 3.0 3.0

Loss on ignition, max. % I0.0 6.0 a 6.0

Available alkalies as Na20, max. %b 1.5 1.5 1.5

Physical Requirements

Fineness, max. % retained on 325-

mesh sieve 34 34 34

Strength activity index with

portland cement

7-day, min. % of control 75 c 75 c 75 c

28-day, min. % of control 75 c 75 c 75 c

Water requirement, max. % of control 115 105 105

Autoclave expansion, soundness, max 0.8 0.8 0.8

a The use of Class F pozzolan with up to 12% loss on ignition may be

approved by the user if either acceptable performance records or

laboratory test results are made available.

b Applicable only when specifically required by the purchaser for

mineral admixture to be used in concrete containing reactive

aggregate and cement to meet a limitation on the alkali content.

c Meeting the 7- or 28-day strength activity index will indicate

specification compliance.

TABLE 3--Common CLSM mixture desians [I vd 3 (I.0 m 3) ] .

Iowa utility Subbase Erosion

DOT [~] Trench Backfill Control

Cement, ib(kg) i00 (59) i0 (5.9) 25 (14.8) 150 (89)

Fly Ash, ib(kg) 300 (178) 275 (163) 300 (178) 150 (89)

Sand, ib(kg) 2 600 (i 544) 2 780 (i 650) 2 740 (i 627) 2 790 (I 657)

Water, gal(kg) 70 (346) 50 (247) 50 (247) 40 (198)

Unconfined

Compressive

Strength, 100-150 120 120 1 i00

psi (kPa) (690-1 030) (830) (830) (7 580)

In 1979, the Office of Materials of the Iowa Department of

Transportation developed a flowable mortar backfill material consisting

of 212 ib (125 kg) of Type I portland cement, 505 ib (298 kg) of Class F

fly ash, 2 232 ib (i 317 kg) of sand, and 438 ib (258 kg) of water for a

l-yd 3 (l-m 3) mixture (Buss 1990). Using this flowable mixture material,

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granular backfill, and soil backfill, a comparison was set up within a

project in which nine culverts were being replaced. Comparison of the

three methods of bridge and culvert repair showed the flowable mortar to

be clearly superior. Final costs of using a flowable fill were less than

half of either of the other two methods.

CLSM has been used in the state of Minnesota 3 in the pipe bedding

for the Champion Corporation steam line and in the reconstruction of the

Robert Street Bridge piers, both in St. Paul. The cities of Minneapolis

and St. Paul include specifications for CLSM in their annual contracts

for concrete purchases. Use of CLSM has helped to prevent cave-ins under

approximately 160 dwellings in Fairmont, West Virginia (Tyson 1989). The

subsidence, resulting from underground coal mining activities that took

place around 1900, had caused sidewalks and pavements to crack, yards to

sink, and basements to collapse.

Flowable CLSM mixtures are clearly an economical alternative,

saving labor and time over placing and compacting soil or granular

materials. CLSM materials offer a number of advantages compared to the

placement of conventional earth fill materials that require controlled

compaction in layers. These advantages include the following:

�9 Ease of mixing and placement

�9 No special equipment required

�9 Ability to flow into hard-to-reach places

�9 Self-leveling placement �9 Negligible subsidence once material has attained final set

�9 Ability to support equipment within 24 h

�9 Can be placed under adverse weather conditions

�9 Reduction of water seepage by low permeability

Although CLSM mixtures provide numerous advantages compared to

conventional earth backfilling, some limitations must be considered when

these materials are used. Limitations include the following (Collins

et al. 1991):

�9 Need to anchor lighter-weight pipes

�9 Confinement needed before setting

�9 Higher-strength mixtures may not allow excavation

�9 Lateral pressure while in the fluid condition

with a broad range in CLSM engineering characteristics (for

example, unconfined compressive strength, density, and time of set) the

applications are limitless. Uses of CLSM include backfill (sewer

trenches, utility trenches, bridge abutments, conduit trenches, pile

excavations, and retaining walls), structural fill (foundation subbase,

subfooting, floor slab base, and pipe bending), and other miscellaneous

3 Letter with information on CLSM utilization by NSP from Kerry C.

Winslow, Northern States Power, to Richard Suanda, Minnesota Pollution

Control Agency, May 28, 1991.



uses (abandoned underground storage tanks, wells, abandoned utility

company vaults, voids under pavement, sewers, and manholes).

ENGINEERING CHARACTERISTICS OF CLSM

When a CLSM mixture is designed, a variety of engineering

parameters need to be evaluated prior to, during, and after placement in

the field. Optimum conditions for each parameter depend on the

application. Typically, the blends will be proportioned and the desired

characteristics will be tested according to the appropriate standard

procedures. Although not all parameters need to be evaluated, the

following are of major consequence to the effectiveness of the CLSM

mixture:

�9 Strength development

�9 Time of set �9 Flowability and fluidity, or consistency of the mixture

�9 Permeability �9 Consolidation characteristics

�9 California bearing-ratio test

�9 Freeze-thaw durability

Strenath Development

The proper control of strength development in CLSM applications is probably the single most important criterion in developing the design

mix (Diogoia Brendal 1992) o Not only must minimal strength development

be met to provide structure support, but maximum strength development

must usually be controlled also. The unconfined compression strength test is typically used to monitor strength development in CLSM mixtures.

The test can be performed either on cylindrical samples, usually having

a height-to-diameter ratio of 2:1 or on 2-in. (5-cm) mortar cubes. Most

of the information generated on CLSM applications pertains to testing

conducted on cylindrical samples.

Time of Set

The time of set is of interest to predict workability and

transportability. It can be defined in two separate stages. The first

stage is the initial set, such that it can support a person standing on

it within 3 to 4 hours (collins et al. 1991). The final time of setting

concerns stability of the placed product or its load-carrying

characteristics and usually occurs within 1 to 2 days. Class F fly ash

requires the addition of cement or lime to set. with poorly reactive fly

ash, set time may be too long for the mix to be useful. Set time is

especially important when backfill is placed in lifts.

Flowability and Fluidity

Typically, the flowability of a CLSM is such that it is to be

deposited and is expected to migrate under gravity or unconfined flow.

However, if the material is to be transported under pressure into

smaller voids and orifices, its fluidity is evaluated. Fluidity is a



measurement of the ability of the CLSM material to flow through a

standard flow cone apparatus in accordance with ASTM Standard Test

Method for Preplaced-Aggregate Concrete (Flow Cone Method) (C 939). A

"slump", as measured in accordance with ASTM C 143, that gives results

in the range of 4 to 6 in. (i0 to 15 cm) or less will provide a material

that will remain in place, while a slump of 7 to i0 in. (18 to 26 cm) or

more provides material that will flow long distances from its discharge

point, penetrating fine cracks and encapsulating anything in its path

(Diogoia and Brendal 1992). Ability to flow increases with water content

and decreases with aggregate content.

Permeability

Permeability can be determined using constant-head or falling-head

principles, much the same as for soils testing using a triaxial

apparatus. Because of possible volume changes in the CLSM mixture, it is

preferable to perform the testing in a membrane with an appropriate

confirming pressure. Note that in a laboratory setting, the best

possible continuous samples are tested. Often, discontinuity will occur in field applications with the formation of shrinkage cracking, which

can increase the effective permeability by several orders of magnitude

(Diogoia and Brendal 1992).

Consolidation Characteristics

As CLSM mixtures develop strength over time, their consolidation or compressibility characteristics improve. Iowa Department of

Transportation testing has indicated a potential settlement of ~-in.

(3.175 mm) per vertical linear ft (Zimmerman 1992). Negligible

settlement will occur once the CLSM mixture has set.

California Bearina-Ratio T@st

The california bearing-ratio test (CBR) is a measure of the in-

place bearing strength of a subgrade material compared to that of

standard crushed stone (Collins et al. 1991). The CBR value is often

used with unpaved thickness design determinations. Testing sponsored by

Baltimore Gas & Electric Company (Collins et al. 1991, American Stone Mix Inc.) has shown that CLSM fills have a CBR value in the 40% range.

Freeze-Thaw Durability

Freeze-thaw testing may or may not be appropriate for some

applications. If a CLSM mixture is used below the frost penetration

line, this test is not applicable. It is a measure of the ability of a

material to withstand climatic changes over time without loss of

strength. Freeze-thaw durability is often evaluated by means of the

vacuum saturation test procedure described in accordance with ASTM

Standard Specification for Fly Ash and other pozzolans for Use with Lime

(C 593). For road base composition, a minimum strength criterion of

400 psi (2.7 MPa) after vacuum saturation is preferred (American Stone

Mix Inc.)



RESEARCH PROGRAM

Although the technology of CLSM mixtures is not new to the

construction industry, there has been a lack of laboratory research to

determine optimum mixture designs and general engineering

characteristics. It is the intent of this study to assist in bridging

that gap in technical documentation and to examine high-volume use of

coal ashes.

There are essentially four basic raw materials used in a CLSM

mixture: coal ash, cement, granular mix (sand), and water. For this

research project, four areas of variability were examined: sand-to-coal

ash and cement ratio; water-to-total solids ratio; fly ash replacement

with cement; and, of course, the source of the coal ash. The test matrix

is given below. The final proportions for all 27 mixture designs are

given in Table 4.

Two sand-to-coal ash and cement ratios (3.0 and 7.0)

�9 The water-to-solids ratio (0.08 to 0.25)

Mix No.

TABLE 4--Mixture proportions (laboratory scale), a

Cement, g Coal Ash, g Sand, g Water, mL

1 0 3 750 ii 250 1 500

2 0 3 750 II 250 i 200

3 0 3 750 Ii 250 1 350

4 375 3 375 Ii 250 1 500

5 375 3 375 Ii 250 1 800

6 375 3 375 II 250 1 650

7 0 1 875 13 125 1 800

8 0 1 875 13 125 1 650

9 0 1 875 13 125 1 950

i0 187.5 1 687.5 13 125 1 800

ii 187.5 I 687.5 13 125 1 950

12 187.5 1 687.5 13 125 2 I00

25 0 7 500 7 500 2 190

26 0 Ii 250 3 750 3 000

27 0 15 000 0 3 690

13 0 3 000 9 000 1 920

14 0 3 000 9 000 2 040

15 0 3 000 9 000 2 280

16 300 2 700 9 000 2 040

17 300 2 700 9 000 2 280

18 300 2 700 9 000 2 400

19 0 1 500 10 500 2 160

20 0 1 500 i0 500 1 920

21 0 1 500 I0 500 1 680

22 150 1 350 I0 500 2 040

23 150 1 350 i0 500 1 800

24 150 1 350 I0 500 1 920

a Mixes 1-12 and 25-27 contain Class C fly ash (FAI).

Mixes 13-24 contain dry scrubber ash (FA2).



�9 Two levels of coal ash replacement with cement (0~ and 10%) Two sources of coal ash (FAI and FA2)

The coal ashes were discussed earlier. The cement was an ASTM Specification for portland cement C 150 Type I cement, and the sand was a single-washed sand obtained from a local ready-mix concrete supplier. A total of 27 mix designs were evaluated in this project (see Table 4). Mix Designs 25-27 were added at a later date. Mixing was performed in a metal 5-gal (19-L) bucket revolving about a central axis by an electric- powered, belt-driven mixer. The mixer was similar in design to a conventional laboratory concrete mixer. The total amount of dry materials for mixtures using the Class C fly ash was 15 000 g. The total amount of dry materials incorporating the dry scrubber ash was 12 000 g. The total amount of dry materials used in each instance was limited by the volume of the 5-gal mixer. The unit weight of the dry scrubber ash was significantly less than that of the Class C fly ash, 33.8 ib/ft ~ (0.54 g/cm ~) versus 71.1 ib/ft ~ (1.14 g/cm~), so smaller quantities of scrubber ash were required to produce a given volume of mixture.

Cylindrical samples measuring 3 by 6 in. (7.6 by 15.2 cm) were cast for testing. One of the objectives of this research effort was to examine long-term strength development; therefore sample specimens were cured and tested for unconfined compressive strength, beginning at 28 days of age and extending up to 1 year.

Flowability and fluidity, or consistency, were measured using two standard test procedures. One method was ASTM Test Method C 143, which is the standard test method for measuring the slump of hydraulic cement concrete. A second method of evaluation was through the use of a flow cone apparatus according to ASTM C 939. The time of set was evaluated according to ASTM Standard Test Method for Time of Setting of Hydraulic Cement by Vicat Needle (C 191). When a test mixture achieved an initial set within 24 hours of initial preparation using this procedure, it was duly noted in (Table 5). Also included in Table 5 are measurements for consistency and dry density.

RESULTS

Results of the unconfined compression strength tests indicated very little difference between varying water contents for a given mixture design of dry materials (such as Mixes 1-3). In most instances, the lowest of the three water contents indicated the highest unconfined compressive strength. The remaining two mixtures with higher water contents were relatively equal in strength. This could lead to the conclusion that mixtures with the lower moisture contents should be recommended to ensure the maximum potential compressive strength. However, this would be defeating a fundamental advantage of CLSM mixtures, which is their ease of application in the field. A better applied field specification would be to require a minimum flowability in the field, such as a 9- to 10-in. (23- to 26-cm) slump or a 30- to 40-s flow cone time. While the amount of water used to make a CLSM mixture is not a critically formulated value, it is possible to "overdose" with water. In such a case, the solids will not stay in solution well enough to create a stable mixture. The water will separate from the solids, and the solids will simply stack up at the discharge point.

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TABLE 5--Laboratory mixture characteristics, a

Mix No. Slump, in. (cm) Flow Cone, s

1 i1.5 (29.2) 27

2 9.25 (23.5) NA

3 11.25 (28.6) 40

4 10.75 (27.3) 92

5 11.5 (29.2) 18

6 11.5 (29.2) 17

7 ii.0 (27.9) NA

8 9.5 (24.1) NA

9 11.5 (29.2) 15

i0 9.5 (24.1) NA

ii 11.25 (28.6) NA

12 11.5 (29.2) 13

25 NA 28

26 NA 17

27 NA 18

13 10.5 (26.7) NA

14 10.75 (27.3) NA

15 11.25 (28.6) 32

16 Ii.0 (27.9) NA

17 11.25 (28.6) 25

18 11.5 (29.2) 14

19 11.75 (29.8) ii

20 11.25 (28.6) 85

21 ii.0 (27.9) NA

22 11.5 (29.2) 13

23 ii.0 (27.9) NA

24 11.25 (28.6) 20

a Wet densities would vary from i0 to 20

higher than the dry densities.

Dry Density, ib/ft 3 (g/cm 3)

131.4 (2.10)

132 9 (2.13)

129 2 (2.07)

133 5 (2.14)

130 1 (2.o8)

127 8 (2.05)

128 0 (2.05)

128 3 (2.06)

127 1 (2.04)

128 2 (2.05)

127 7 (2.04)

125 8 (2.02)

120.4 (1.93)

108.0 (1.73)

101.3 (1.62)

121.0 (1.94)

116.3 (1.86)

113.6 (1.82)

118.3 (1.89)

112.2 (1.80)

112.3 (1.80)

119.6 (i 92)

120.3 (i 93)

124.1 (I 99)

121.2 (i 94)

124.7 (2 00)

124.8 (2 00)

ib/ft 3 (0.16

Set Time,

< 24 h

Yes

Yes

Yes

Yes

Yes

Yes

No

No

No

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

No

No

No

No

No

No

to 0.32 g/cm 3)

Because of the relatively small differences in unconfined

compressive strength between water contents, the unconfined compressive

strength results were averaged for all three water contents in Figures 1

and 2. These graphs present the effects of using different levels of

sand and cement and different ash sources. Comparisons include the

effects of variable sand and cement levels for both the Class C fly ash

and the dry scrubber ash, as well as a comparison between the two ash

sources. Clearly, the addition of even small amounts of cement result in

significant increases of compressive strength, sometimes as much as

tenfold.

When the two coal ash sources were compared, the dry scrubber ash

(FA2) showed more cementitious reaction and less pozzolanic reaction

than the Class C fly ash (FAI). This is a useful characteristic,

uniquely desirable for CLSM application. The higher strength at an

earlier age will allow the construction contractor to expose the CLSM

mixture to overburden loads sooner. Also, negligible strength gain over

a period of time will allow for easier excavation if required.

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FIG. 1--Compressive strength of fly ash and dry scrubber ash, using a ratio of sand-to-dry powder (ash plus cement) of 3:1.

FIG. 2--Compressive strength of fly ash and dry scrubber ash, using a ratio of sand-to-dry powder (ash plus cement) of 7:1.



A comparison of the effects of using variable levels of sand and

Class C fly ash with no cement addition is presented in Figure 3. The

intent here was to determine the maximum attainable compressive strength

with the maximum level of fly ash used. The results indicate that for

this particular source of coal ash, no additional strength development

occurred for mix designs containing more than 50% fly ash as the total

solids content. The optimum CLSM mix design using this coal ash and no

cement would thus be dependent on the desired compressive strength and

the cost of the raw materials, coal ash and fine aggregate.

CONCLUSIONS AND RECO~D~ENDATIONS

The intent of this project was to establish a laboratory protocol

to evaluate effectively coal ashes for CLSM applications before

placement in the field. It is much more cost-effective to perform trial-

and-error designs in the laboratory than in the field. With this in

mind, as well as the fact that coal ashes need not meet ASTM

Specification C 618 for CLSM uses, it would be extremely advantageous to

evaluate different types of coal combustion by-products in the laboratory. Of particular interest would be the advanced coal technology

by-products such as limestone injection and fluidized-bed combustion

ashes. Many of these advanced coal technology by-products do show more

cementitious and less pozzolanic characteristics, a good design

characteristic for CLSM applications. Pulverized coal ashes that fail to

meet specifications for use in concrete could also find a niche in CLSM

applications.

One of the most frequent and unanswered questions about the use

of coal ash is the effect on the environment by way of surface runoff

3O0O

{3_ 2500

133 c 2000

1 5 0 0

if) ~ 1 0 0 0

E 0 5OO

o

0

..... I �9 100.0% Ash ............................................................................... ~ ...................................................

I " 7s.o% h . / 7 - J �9 5o.o% . ....

'-/ * 25.o . ........................................... 77-i " . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

0 50 100 150 200 250 300 350 Curing Time, days

FIG. 3--Compressive strength of Class C fly ash using variable amounts

of sand and fly ash and zero percent cement.



and groundwater infiltration. If noncompliance (according to ASTM

Specification C 618) coal ashes are to be evaluated and promoted, then

the environmental concerns should also be assessed in the laboratory

along with the engineering properties. A carefully laid out testing

program to evaluate the ash for major chemical constituents in leachate

should be incorporated into an effective ash management plan for

developing CLSM mixture designs.

Bottom ashes could also be examined for use as a granular filler

in place of fine aggregate. Many bottom ashes have a gradation similar

to that of aggregates used in the production of portland cement

concrete. Using bottom ash for filler would have the benefit of using a

second coal combustion by-product that currently requires stringent disposal practices.

Two field requirements that should be specified to ensure quality

control and ease of placement are a minimum level of flowability or

consistency and a specified method of measuring it. Measuring

flowability with the flow cone method is most applicable for grout

mixtures that use no aggregate filler. The discharge orifice of the flow cone is only i/2 in. (12.7 mm) in diameter. Unless a fine aggregate is

thoroughly sieved, larger pieces can disrupt the flow cone measurement.

Specifying the use of a consistency in the field is necessary. A maximum

flow cone measurement of 35 s or a minimum slump of 9 in. (23 cm) would be two practical design parameters. Other methods to specify CLSM

consistency have also been suggested. One such method is to fill a

hollow cylinder (3 by 6 in. [7.6 by 15.2 cm]) with the test mixture, lift the cylinder in a manner similar to that used for the slump cone, and

measure the increased diameter of the resulting "pie" (Ramme 1992). This

method is similar to ASTM Standard Test Specification for Flow Table for Use in Tests of Hydraulic Cement (C 230), which determines the

consistency, or flow, of mortar mixtures. CLSMs are in fact very wet mortars.

One final suggestion for further research is to evaluate the uses of chemical admixtures such as water-reducing agents, set retarders or

accelerators, and super plasticizers. One has to remain aware, however,

of the ACI classification of CLSM as a mixture design having a maximum 28-day compressive strength of 1200 Ib/in. 2 (8.2 MPa). Beyond this

level, the researcher is approaching the realm of low-strength concrete

and should be consulting references that more appropriately address that topic.

REFERENCES

American Stone Mix Inc., "Physical Properties of Flo-Ash," Towson, MD.

Brewer, W. E., "The K-Krete | Inc. Story," in ProceedinQs of the Fourth

International Ash Utilization Symposium, ERDA Report No. MERC/5P- 76/4, St. Louis, MO, March 1976.



Buss W.E., "Iowa Flowable Mortar Saves Bridges and Culverts," Presented

at The Next Generation of Ash Utilization Workshop, Bismarck, ND,

30-31 Aug. 1990.

Collins, R. J., Colussi, J. J., and Ruggiano, L. M. "Physical

Considerations with Design, Mixing and Placement of Flowable Fill

Materials," in Proceedings of the Ninth International Ash

Symposium, EPRI GS-7162 VI, Orlando, FL, Jan. 1991.

Digioia, A. M. Jr. and Brendal, G. F., Fly Ash Desian Manual for Road

and Site Applications, Vol. 2: Slurried Placement, EPRI

TR-I00472, April 1992.

Larsen, R. L., "Sound Uses of CLSM's on the Environment," Concrete International July 1990.

National Ready-Mix Concrete Association, "What, Why, and How? Flowable

Fill Materials," CIP 17, IOM/3-91.

Ramme, B. W., "Report for Wisconsin Electric Power Company," presented

at the Ash Utilization Workshop, Minneapolis, MN, i0 June 1992.

Tyson, S. S., "Flowable Mixtures with Coal Fly Ash," presented at the National Ready-Mix Concrete Association Annual Convention,

Washington, DC, 26 Feb. - 2 March 1989.

Zimmerman, L. G., "Practical Considerations for the Formulation and

Usage of Flowable Fill Materials," Presented at the Coal Ash Manager Certification Program, Michigan State University,

1-5 June 1992.


Tarun R. Naik I, Rudolph N. Kraus 2, Raymond F. Sturzl 3, and Bruce W. Ramme 4

DESIGN AND TESTING CONTROLLED LOW-STRENGTH MATERIALs (CLSM) USING CLEAN COAL ASH

REFERENCE: Naik, T. R., Kraus, R. N., Sturzl, R. F., and Ramme, B. W., ''Design and Testing Controlled Low-Strength Materials (CLSM) Using Clean Coal Ash,'' The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: The major objective of this project was to develop mixture proportions for controlled low-strength material (CLSM) using clean coal ash obtained from atmospheric fluidized bed combustion (AFBC). A clean coal ash is defined as the ash deiived from SO x and NO x control technologies. The specific ashes used for this project were: (i) circulating fluidized bed boiler fly ash and bottom ash and (2) stoker- type boiler fly ash and bottom ash. These two coal ash samples were characterized for physical and chemical properties. Chemical properties and water leaching tests were also performed on the hardened CLSM. Many initial CLSM mixtures were developed by blending the two types of ash.

Tests conducted on the final three selected CLSM mixtures included compressive strength, bleeding, setting and hardening, settlement, length change of hardened CLSM, permeability, mineralogy, and chemical water leach testing. Results show that acceptable CLSM material can be developed by blending the fluidized bed boiler ash with the stoker boiler ash. Recommendations for a pilot scale manufacturing application of the three CLSM mixtures were made based upon the lab test results.

KEYWORDS: controlled low-strength material (CLSM), mixture proportion, compressive strength, permeability, shiinkage, leachates, fluidized bed boiler, coal ash

The project objective was the development of controlled low- strength material (CLSM), namely manufactured dirt, and mixtures using clean coal ash obtained from AFBC boilers. A clean coal ash is defined as ash derived from SO x and NO x control technologies. Two types of ash material were used for this project: Ash A, a stoker-type boiler fly ash and bottom ash and Ash B, circulating fluidized bed boiler fly ash and bottom ash. This paper summarizes results of the laboratory research

I Director, Center for By~Products Utilization and Associate Professor, Department of Civil Engineering and Mechanics, the University of Wisconsin-Milwaukee, Milwaukee, WI 53211.

2 Research Associate, Center for By-Products Utilization, University of Wisconsin-Milwaukee, Milwaukee, WI 53201.

3 Electric Production Manager, Manitowoc Public Utilities, Manitowoc, WI 54221.

4 Manager, Combustion By-Products Utilization, Wisconsin Electric Power Company, Milwaukee, WI 53201.

C o p y r i g h t �9 1 9 9 8 by ASTH I n t e r n a t i o n a l

27

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activities for the project. No cement was used for CLSM mixtures using Ash B because of the cementitious nature of the fluidized bed boiler ash, and to make better use of these by-products.

CLEAN COALAND CONVENTIONALASHMATERIAL

Two different types of ash were used in this project: (I) Ash A, a conventional fly ash and bottom ash obtained from stoker type boilers and (2) Ash B, a clean coal ash obtained from fluidized bed boilers.

Ash A was obtained from the combustion residues of three stoker- type boilers. A Hazard/Elkhorn blend of coal was used for these units. Fly ash and bottom ash from these boiler units were combined and stored in a silo.

Ash B consisted of ash produced from a 20-MW circulating fluidized bed boiler. This fluidized bed boiler burns a coal blend consisting of 20% Southern Illinois bituminous coal and 80% of petroleum coke. Ash B is classified as a clean coal ash. Calcium carbonate in the form of limestone or dolomite (Basu and Fraser 1991, Podolski 1984, Tung and Williams 1987, and Yerushalmi 1986) was injected into the fluidized bed boiler during combustion of the coal/coke combination to act as a sorbent for SO 2 emissions. The limestone breaks down to an oxide form while heated (Podolski 1984):

CaCO 3 ~ CaO + CO 2

The calcium oxide then reacts with the SO 2 which is produced duling coal combustion to form calcium sulfate:

CaO § SO 2 + 1/2 02 ~ CaSO 4

The advantages of the fluidized bed boiler are a significant reduction (85 to 98%) (Tung and Williams 1987, and Yerushalmi 1986) of SO s emissions without the utilization of a wet scrubber system typically used in flue gas desulfurization (Podolski 1984), and reduced NO• emissions since coal combustion temperatures are lower than those typically found in a pulverized coal boiler (Tung and Williams 1987, and Yerushalmi 1986). Ash B material consisted of the spent limestone material and bottom ash along with fly ash fiom the fluidized bed boiler unit.

Characterization of Ash Materials

Physical test results on each source of ash are shown in Table i. The tests results given in Table 1 are those typically required by ASTM Specification for Coal Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Concrete (C 618). Table 2 shows the results of the sieve analysis of the ashes. Ash A material had larger size fractions (approximately 6% retained No. 4 sieve) and was more uniformly gladed than Ash B. Seventy percent of Ash B material was between No. 50 and No. 200 sieve. Both Ash A and Ash B contain approximately 20% material finer than No. 200 sieve.

Elemental Analysis of Ash A and Ash B

The results of the elemental analysis of Ash A and Ash B samples are given in Table 3. These ashes were analyzed using instrumental neutron activation analysis. The neutron activation analysis method exposes the sample to neutrons which results in an activation of many elements. This activation consists of radiation of various elements. For the ashes used for this project, gamma ray emissions were detected.

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NAIK ET AL./CLEAN COAL ASH 29

Many different elements may be detected simultaneously based on the gamma ray energies and half-lives.

TABLE 1--Physical test iesults.

TEST Ash A Ash B

ASTM C 618 SPECIFICATIONS

Class C Class F

Retained on No.325 sieve, (%) 66.5 54.8 34 Max 34 Max

Strength Activity Index with Cement at 7 days, (% of 54.4 49.2 75 Min 75 Min Control)

Strength Activity Index with Cement at 28 days, (% of 57.5 53.5 75 Min 75 Min Control)

Water Requirement (% of Control) 130 103 105 Max 105 Max

Specific Gravity 2.00 2.58

(%) Variation from Mean, Fineness (R325) Specific Gravity

1.3 2.7

5 Max 5 Max

3,5 2.0

5 Max 5 Max

TABLE 2--Sieve analysis of ashes.

Sieve Size Percent Passing

Ash A Ash B

12.5 mm 97.8

9.5 mm 97.0 i00

4.75 mm (No. 4) 93.6 99.4 95-100

2.36 mm (No. 8) 89.6 99.2 80~I00

1.18 ~n (No. 16) 83.7 98.6 50-85

600 Hm (No. 30) 65.9 95.1 25-60

300 pm (No. 50) 46.3 91.9 10-30

150 pm (No. i00) 33.9 63.9 2-10

75 pm (No. 200) 21.1 21.9

ASTM C 33 Specifications

for Fine Aggregates



TABLE 3--Elemental analysis of ashes.

ELEMENTAL (BULK CHEMICAL) ANALYSIS (mg/kg unless noted otherwise)

Element Ash Type

Ash A Ash B

Aluminum (A1) 90472.3 11708.3

Antimony (Sb) 7.9 2.9

Arsenic (As) 306.0 113.7

Barium (Ba) 187.4 61.7

Beryllium (Be) 3.7 19.0

Boron (B) 79.0 78.0

Cadmium (cd) <1520.5" <585.6*

Calcium (Ca) 594.6 40581.5

Chloride (CI) 65.5 1781.0

Chromium, Total (CI) 75.5 26.7

Cobalt (Co) 46.4 7.0

Copper (Cu) 233.1 282.1

Fluoride (F) 2.5 13.0

Iron (Fe) 22610.0 13525.0

Lead (Pb) 33.0 18.0

Magnesium (Mg) 6101.8 2098.2

Manganese (Mn) 607.8 1561.8

Mercury (Hg) 27.3 4.0

Molybdenum (Mo) <66.3* 125.7

* Less than detection limit noted.

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TABLE 3 (Cont.)--Elemental analysis of ashes.

ELEMENTAL (BULK CHEMICAL) ANALYSIS (mg/kg unless noted otherwise)

Ash Type Element

Ash A Ash B

Nickel (Ni) 2097.0 54055.0

Nitrogen, Soluble 1.8 1.7 NO 2 + NO 3

Phosphorous (P) 340.0 200.0

Potassium (K) 14385.0 2894.5

Selenium (Se) 673.0 223.3

Silicon (Si) 3900.0 9300.0

Silver (Ag) 18.5 3.3

Sodium (Na) 1166.5 4552.5

Strontium (St) 123.3 <11.2"

Thallium (TI) 1.3 <0.3*

Tin (Sn) 260.6 103.4

Vanadium (V) 200.8 3086.8

Zinc (Zn) 12.9 I0.i

* Less than detection limit noted.

The elemental composition of the two types of ash differed considerably. Ash B contained higher quantities of beryllium, calcium, chloride, flouride, manganese, molybdenum, nickel, silicon, sodium, and vanadium and lower amounts of aluminum, arsenic, barium, cadmium, chromium, cobalt, iron, lead, magnesium, mercury, potassium, selenium, strontium, and silver. They contained comparable amounts of antimony, boron, copper, nitrogen, phosphorus, thallium, tin, and zinc.

The elemental analysis of ash is dependent on the type of coal used, combustion process, additives, and so forth. Although general elemental composition is of interest, the elements that may leach are of greater relevance. Leachate results of the hardened CLSM are discussed later in this paper.

Ash A and Ash B - Oxides, Sulfite, Loss of Iqnition, and Mineraloloqy

A summary of the oxides, sulfite, and loss on ignition (LOI) analysis is given in Table 4. Ash A had a very high LOI, approximately 25% by weight. Ash B also had a high (15%) LOI. Although the high LOI ashes would not be suitable for use in structural concrete, the high LOI should not affect its application to CLSM since air entraining admixtures are generally not required to be used for manufacturing CLSM.



TABLE 4--Analysis for oxides, sulfite, and loss on iqnition.

Analysis Parameter Ash A, % Ash B, %

ASTM C 618 Requirements

Class C Class F

Silicon Dioxide, SiO 2 41.1 6.3 . . . .

Aluminum Oxide, AI203 23.5 3.0 . . . .

Iron Oxide, Fe203 3.4 1.7 . . . .

SiO 2 +AI203 +Fe203 68.1 ii.i 50.0 Min 70 Min

Calcium Oxide, CaO 1.2 37.2 -- -

Magnesium Oxide, MgO 0.6 0.8 . . . .

Titanium Oxide, TiO 2 1.3 0.0 . . . .

Potassium Oxide, K20 1.3 0.2 . . . .

Sodium Oxide, Na20 0.3 0.6 . . . .

Sulfite, SO 3 0.7 32.3 5.0 Max 5.0 Max

Loss on Ignition, LOI 24.8 15.0 6.0 Max 6.0 Max

Moisture, % 0.6 0.4 3.0 Max 3.0 Max

Water requirement for the ash with high LOI generally is higher, but again, this should not impact its use for CLSM. The very high value of LOI of these ashes may be due to incomplete combustion or low temperature combustion characteristics of a typical low-mix boiler. A visual examination of Ash A material revealed that there were pieces of incompletely burned coal which were partially covered with slag. This is not unusual for the bottom ash material of stoker boilers.

Mineralology of the Ash A and Ash B are shown in Table 5. The mineralogical composition of the two ashes are different. This is to be expected since two different types of boilers (fluidized bed and stoker) produced these ashes. Ash B also contained a significant amount (42%) of anhydrite CaSO 4. This is not a mineral typically found from pulverized coal ash boilers. Ash B anhydrite CaSO 4 is due to the use of limestone as a sorbent for controlling SO x emissions in the fluidized bed boiler. Ash B also contained calcite, 13.2%; portlandite, 1.5 %; and quartz, 2.1%. The free lime (CaO) content was only 2.3%. Oxide analysis (Table 4) indicates a total lime (CaO) of 37%. The total lime content indicates the total calcium (Ca § ions and oxide (O) ions present. The combination of Ca" and 0 ~ can occur in minerals other than free lime such as anhydrite, calcite, and portlandite. Free lime indicates the quantity of lime in a compound form alone, without other elements. Some of these minerals may not be sufficiently cementitious.

Ash A contained quartz, 4.5%; mullite, 24.1%; and the remaining amounts as amorphous (glass phases) materials of 71.5%. The mineralogical composition of Ash A indicates that this ash may not have sufficiently independent cementitious properties.



TABLE 5--Minezaloqy of ashes.

MINERALOLOGY, % by Weight

Analysis Parameter Ash A Ash B

Quartz, sio 2 4.5 2.1

Mullite, AI2SiO 5 24.1 *

Gypsum, CaSO4.2H20 * *

Anhydrite, CaSO 4 * 42.1

Bassanite, CaSO4,O-5H20 * *

Ettringite, CaAI 2 (SO4,SIO4,CO 3) * , (OH) I2.26H20

Calcite, CaCO 3 * 13.2

Portlandite, Ca(OH) 2 * 1.5

Lime, CaO * 2.3

Amorphous 71.5 38.7

* Not detected.

CLSM MIXTURES

Although CLSM may have strengths as high as 8.3 MPa at the 28-day age, a CLSM mixture that is considered to be excavatable at a later age using hand tools should have a compressive strength lower than 0.7 MPa at the 28-day age (American Concrete Institute 1994, American Coal Ash Association 1995, Canadian Portland Cement Association 1990, Kraus and Naik 1996, Naik and Ramme 1990, 1994, Naik et al. 1991, and Ramme et al. 1995). Mechanical equipment such as a backhoe is required for excavation at a later age for a mixture with compressive strengths higher than 0.7 MPa up to as high as 1.4 MPa. A mixture with compressive strength higher than 1.4 MPa may require jackhammers fol excavation at a later age or may be chipped loose with a backhoe bucket.

Based upon the test results of a preliminary test phase (Kraus and Naik 1996), three mixtules weIe selected for furthel development and testing. They ale:

(i) 100% Ash B, Mix 1 and 2, (2) 50% Ash B + 50% Ash A, Mix 3 and 4, and (3) 25% Ash B + 75% Ash A, Mix 5 and 6.

An exothermic reaction takes place when water is added to ash produced by the fluidized bed boiler. Free calcium oxide and calcium sulfite/sulfate produce the exothermic reaction (Basu and Fraser 1991):

CaO + H20 ~ Ca(OH) 2 + 15.6 kCal/g mol CaSO 4 + 2 H20 ~ CaSO 4 ,2H20 + 4.22 kCal/g mol

This exothermic reaction was particularly evident in the 100% Ash B mixtures.



Bench scale mixtures of approximately 0.13 m 3 were mixed for each of these test mixtures. Mixture proportions and theological properties for these six mixtures are given in Table 6. The reported mixture proportions were adjusted based upon the actual yield of the test batch. Density of the CLSM decreased as the amount of Ash A was increased in the mixture. Water required was approximately the same for all mixtures. Flow/spread was measured in accordance with ASTM Provisional Test Method for Flow Consistency of Controlled Low Strength Material (PS 28). The water-to-cementitious materials ratio for bench scale mixtures was 0.56 • 0.08.

Compressive Strenqth of CLSM Mixtures

Compressive strength test results for the CLSM are shown in Table 7. Three 150- by 300-mm cylinders were tested in accordance with ASTM Test Method for Preparation and Testing of Soil-Cement Slurry Test Cylinders (D 4832) at each test age. The 28-day compressive strength test results range from 0.7 to 4.5 MPa. The mixtures containing 75% Ash A (Mixes 5 and 6) had the lowest compressive strength of 0.7 MPa, and the 100% Ash B mixture (Mixes 1 and 2) had the highest values at 3.3 and 4.5 MPa. A range of values for compressive strength at the 28-day age of the CLSM mixture should be one of the considerations when specifying it for a given application if excavation is required. The CLSM mixture with the 28-day compressive strength of 0.7 MPa is considered to be easily excavated at the later day age. Excavation of a mixture of 4.5 MPa would involve a significantly higher cost.

Settinq and Hardening of CLSM Mixtures

Setting and hardening characteristics measurements of the CLSM mixtures are reported in Table 8. The values reported are the average of three measurements taken from three 150- by 300-mm cylinders for each mixture. To evaluate their setting and hardening characteristics, the test specimens were left in the molds and not covered for the entire 14- day measurement period.

Setting characteristics of the CLSM mixtures were measured by applying a 4.5-kg force on a 50-m m-long seven penny nail and then measuring the depth of the nail penetration. The CLSM mixtures generally hardened slowly as the quantity of Ash A increased. These nail penetration measurements were taken from the test cylinders where the bleedwater was not removed periodically. Therefore, these setting times axe considered a worst case for the CLSM mixtures for field use because the bleedwater will generally drain off to the surrounding soil from a CLSM mixture placed at a project site.

Bleedwater measurements were negligible for the mixture containing 100% Ash B, Mix 2. The maximum amount of bleedwater was for the mixtures with 75% Ash A + 25% Ash B, Mixtures 5 and 6, which had a 20-ram depth of bleedwater on the top of the 150-mm-high cylinder mold at the age of 1 h.

Settlement values, reported in Table 8, are the measurement to the "solids" portion of the CLSM mixture with respect to a datum (that is, top of the cylinder mold) taken as the original height of the cylinder. These settlement values are not indications of how the material may behave when a load is applied. Positive settlement (or an increase in the settlement) measurements of the CLSM indicate that the CLSM material actually expanded when hardening. The CLSM mixtures containing 100% Ash B (Mixes 1 and 2) exhibited expansion.



TABLE 6--Mixture proportions and fresh CLSM test results for bench scale mixtures.

~ixtureNo 11 I 2 13 1 4 I 5 I 6

Ash A, Content (%) 0 0 50 50 75 75

Ash B, Content (%) i00 i00 50 50 25 25

Ash A (kg/m ~) 0 0 485 485 670 665

Ash B (kg/m 3) 1150 1177 485 485 220 220

Cement (kg/m 3) 0 0 0 0 0 0

Water (kg/m') 555 570 550 550 560 555

Water-to- 0.48 0.48 0.57 0.57 0.63 0.63 Cementitious

Materials Ratio

Flow/Spread ([am) 230 355 230 280 245 255

Slurry Temp. (~ 32 36 31 30 26 29

Air Temp. (~ 22 24 19 24 24 24

Air Content (%) 1.6 1.5 3,0 3.4 3.9 4.9

Slurry Density 1710 1750 1520 1530 1450 1430 (kg/m 3)

Test Mixture 0.13 0.05 0.13 0.05 0.13 0.13 Yield(m 3)

TABLE 7--Compressive strenqth test results - bench scale CLSM mixtuIes.

Mixture No.

Ash A Content (%)

Ash B Content (%)

Cement Content (%)

1 I 2 I 3 I 4 I 5 I 6

0 0 50 50 75 75

I00 100 50 50 25 25

0 0 0 0 0 0

Test Age (days) Compressive Strength (MPa)

3 1.7 i.i*

7 2,1 1.2 1.7 0.3

14 2.6

28 3.3 4.5 2.2 2.6

0.3 0.2

0.6 0.3

0.7

* Test at five day age.



TABLE 8--Settinq and hardeninq chalacteristics - CLSM mixtules.

50-mm Nail Ash Mixture Test penetlation, Bleedwater, Settlement,

Age mm ram mm*

l~ 50 0 0

l-Day 5 0 +3

Mix 2 3-Day 2 0 +5

(100% Ash B) 5-Day 0 0 +5

7-Day 0 0 +3

14-Day 0 0 +3

l-HouI 50 16 -16

l-Day 50 8 -16

3-Day 24 3 -0.5

5-Day i0 0 -14

Mix 4

(50% Ash A +

50% Ash B) 7-Day 5 0 -13

14-Day 2 0 13

l-Hour 50 20 -20

1-Day 50 14 -13 Mix 5 & 6

3-Day 24 i0 -16 (75% Ash A

+ 5-Day i0 6 -16 25% Ash B)

7-Day 5 3 -14

14-Day 3 0 -14

* Settlement values of the CLSM are taken from a datum level at the oliginal cast height of the CLSM.

TABLE 9--Permeability of CLSM mixtures.

Mixture No.

Ash A Content,

%

Ash B Content,

%

Specimen Test Age, Permeability, x 10 .6 cm/s

No. days Actual Average

1 31 1.0 1 0 i00 2 31 2.1 1.3

3 31 0.9

1 40 3.4 3 50 50 2 3.5

3 40 3.7

4 50 50 1 28 2. i 2.1

1 35 3.2 6 75 25 2 35 3.1 3.1

3 35 3.0



Permeability of Hardened CLSM Mixtures

Permeability of the CLSM mixtures was measured at the age of approximately 30 days. Results are reported in Table 9. Three i00- by 100-mm cylinders were cast from each mixture for permeability measurements. At the age of seven days, the test specimens were immersed in 23~177 2~ lime-saturated water until the time of testing. A falling head parameter was utilized for these tests per ASTM Test Method for Measurement of Hydiaulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter (D 5084). Typically, permeability of the CLSM increased as the amount of Ash A increased in the mixture, 1.3 x 10 ̀6 cm/s for the 100% Ash B (Mix I), to 3.1 x i0 -6 cm/s for the 75% Ash A + 25% Ash B (Mix 6). These values are consistent with i00 x I0 6 to 10 x 10 .6 cm/s for a compacted granular backfill and 0.i x i0 ~ cm/s or less for compacted clays. Differences in permeability between Mixes 3 and 4 can be attributed to the small quantity of CLSM utilized for the test (0.0008 m3). Permeability of the mixtures is not expected to increase at later ages.

Oxides, SO~ and Loss on Iqnition of Hardened CLSM Mixtures

The hardened CLSM material was also analyzed for oxides, sulfite, loss on ignition, and moisture content. The results of the analysis, Table i0, show that the composition of the hardened CLSM material varies with the ash composition of the CLSM. A comparison with the oxide analysis of the ash material (Table 4) shows that the approximate oxide

TABLE 10--Hardened CLSM mixtures - analysis for oxides, sulfite, and loss on iqnition.

CLSM Mix 3, CLSM Mix 5, Analysis CLSM Mix i, 50% Ash B + 50% 25% Ash B + Parameter 100% Ash B, % Ash A, % 75% Ash A, %

Silicon Dioxide, SiO 2 8.5 17.1 26.0

Aluminum 4.5 10.0 15.5

Oxide, AI203

Iron Oxide, 1.8 2.4 2.8 Fe203

Calcium Oxide, 30.4 19.7 12.0 CaO

Magnesium 0.7 0.7 0.6 Oxide, MgO

Titanium Oxide, TiO 2 0.I 0.4 0.7

Potassium 0.2 0.5 0.8

Oxide, K20

Sodium Oxide, 0.4 0.5 0.5 Na20

Sulfite, SO~ 25.3 17.7 11.4

Loss on 25.6 27.9 30.4

Ignition, LOI

Moisture, % 28.5 1.5 31.6



composition of the hardened CLSM material could be obtained by appropriately blending the two ash types. These test data are logical because the CLSM is produced by mixing the Ash A and Ash B materials with water without any other ingredients.

Mineraloloqv of the Hardened CLSM

Mineralogy of the hardened CLSM matelial is presented in Table ii. Mineral formation of the CLSM mixtures are very different compaied to the minerals of the ash used. The CLSM using 100% Ash B (Mix i) is primarily composed of gypsum (-60%), amorphous glass phases (36%), and ettringite (5%). The CLSM mixture of 25% Ash B and 75% Ash A (Mix 5) has a much different composition with nearly 70% of the material amorphous, about 15% mullite, and 10% bassanite. With a high percentage of the 100% Ash B CLSM (Mix i) being gypsum (Table ii), there may be potential for the Ash B material for uses other than CLSM where gypsum is desired.

TABLE ll--Mineraloqy of CLSM mixtures.

MINERALOLOGY, % by Weight

CLSM, Mix 3 CLSM Mix 5 Analysis Parameter CLSM Mix i, ' ' 100% Ash B 50% Ash B + 25% Ash B +

50% Ash A 75% Ash A

Quartz, SiO 2 0.5 1.7 2.9

Mullite, AI2SiO 5 -- 6.5 14.7

Gypsum, 58.9 16.9 - - CaSO 4, 2 H20

Anhydrite, CaSO 4 -- 6.5 0.5

Bassanite, - - 6.2 9.4

CaSO4,O- 5H20

Ettringite, CaAl2 (S04 ,Si04 ,C03) 5.0 . . . . (OH) 12,26H20

Calcite, CaCO 3 -- 7.8 5.3

Portlandite, Ca(OH) 2 -- 1.6 --

Lime, CaO . . . . .

Amorphous 35.5 52.7 67.2

Leachate Results of Hardened CLSM

The leachate results of the three mixtures tested are given in Table 12. The three mixtures are: 100% Ash B, Mix I; 50% Ash A + 50% Ash B, Mix 3; and 25% Ash B + 75% Ash A, Mix 5. The leachate parameters shown are the elements which the Wisconsin Department of Natural Resources have identified in their interim guidelines for waste reuse in CLSM. Leachate results for pH, sulfate, total alkalinity, and total dissolved solids were relatively high, but the results are consistent with leachate from other circulating fluidized bed boiler ashes (Basu and Fraser 1991).

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NAIK ET AL/CLEAN COAL ASH 39

TABLE 12--Leachate analysis of hardened CLSM mixtures.

LEACHATE RESULTS, mg/l unless noted otherwise

CLSM Ash Mixture

Leachate Parameter Mix i, 100% Ash B

Mix 3 50% Ash A + 50%

Ash B

Total Alkalinity 2300 1600 66

Aluminum (AI) 0.024 0.026 0.Ii0

Antimony (Sb) <0.004* <0.004* <0.004*

Arsenic (As) <0.005* <0.005* <0.005*

Barium (Ba) 0.190 0.130 0.ii0

Beryllium (Be) <0.001- <0.001" <0.001-

Boron (B) <0.004* <0.004* <0.004*

Cadmium (cd) <0.0001" <0.0001" <0.0001"

Calcium (Ca) 1600 II00 640

chloride (CI) 34 37 20

Chromium, Total 0.0021 0.0016 0.0027 (Cr)

Cobalt (Co) <0.008* <0.008* 0.008

Conductivity ii000 umhos/cm 7900 umhos/cm 2600 umhos/cm

Copper (Cu) <0.002* <0.002* <0.002*

Fluoride (F) 0.92 0.61 <0.25*

Total Hardness 4100 2700 1600

Iron (Fe) <0.006* <0.006* <0.006*

Lead (Pb) <0.005* 0.006 <0.005*

Magnesium (Mg) <0.02* <0.02* 0.32

Manganese (Mn) <0.002* <0.002* <0.002*

Mercury (Hg) <0.0002* <0.0002* <0.0002*

Mix 5 25% Ash B + 75%

Ash A

* Less than detection limit.



TABLE 12(Cont.)--Leachate analysis of hardened CLSM.

LEACHATE RESULTS, mg/l unless noted otherwise

Leachate Parameter Mix i,

100% Ash B

Molybdenum (Mo) 0.650

Nickel (Ni) <0.008*

Nitrite & Nitrate 1.9

pH 12.60 S.U.

Phosphorous (P) <0.i*

Potassium (K) 16

Selenium (Se) <0.0008*

CLSM Ash Mixture

Mix 3, 50% Ash A + 50%

Ash B

Mix 5 25% Ash B + 75%

Ash A

Silicon (Si) 0.16

silver (Ag) <0.0004* <0.0004* <0.0004*

Sodium (Na) 36 49 33

Strontium (St) 0.910

Sulfate (SO 4) 1600

Thallium (TI) <0.001"

Tin (Sn) <0.40*

Total Dissolved 4200 Solids

TOC 2

TOX 0.O52

Vanadium (V) 0.076

0. 0073 Zinc (Zn)

0.610 0.380

<0.008* <0.008*

4.5 0.5

10.36 S.U. 10.74 S.U.

<0.1" <0.I*

35 40

<0.0008* <0.0008*

0.30 9.4

1.500 2.100

1300 1600

<0.001" <0.001-

<0.040* <0.040,

3400 2600

2 2

0.180 0.089

0.Ii0 2.9

0. 012

* Less than detection limit.

0.0038

SUMMARY OF MIXTURE TEST RESULTS

The following is a summary of these results.

Three bench scale mixtures were selected for detailed testing based upon preliminary tests (Kraus and Naik 1996) for this project. None of the mixtures used cement. The three mixtures developed are:

(i) 100% Ash B, Mix i, (2) 50% Ash B and 50% Ash A, Mix 3, and (3) 75% Ash A and 25% Ash B, Mix 5 or 6.

Density of the fresh CLSM increased as the amount of Ash B increased.

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Compressive strength of the CLSM mixtures range from 0.7 MPa for the 25% Ash B + 75% Ash A mixture to 4.5 MPa for the 100% Ash B mixture. If the CLSM is expected to be excavated in the future, a lower strength CLSM at the 28-day should be used to minimize cost of excavating a mix with a compressive strength above 0.7 MPa at the 28-day age. Ash B, when mixed with water, was found to be expansive. This expansion was readily apparent for the 100% Ash B CLSM mixture. The expansive properties of the CLSM may be desirable in certain applications, for example, filling abandoned tunnels or tanks in which assurance of complete and tight fill would be desirable.

Permeability of the CLSM was low, approximately I0 to i00 times lower than that of compacted sand. The length change values after 7-day age show some expansion but not to the extent of the material at ages at less than 7 day (as measured by settlement values of the cylinders in their molds).

Oxide analysis of the hardened CLSM indicates that the oxide composition of the material is approximately the same as what would be obtained by blending the ashes. Minerals present in the CLSM materials are different than the original minerals depending upon the ash type as a result of amorphous glass materials in the ashes. The CLSM containing 100% Ash B contained nearly 60% gypsum, while nearly 70% of the material for the 25% Ash B + 75% Ash A mixture was amorphous (glass phase).

PROPOSED USAGE OF CLSM

Mixtures deve loped for this project could have distinctly diffeient applications because of the variation in compressive strength Also, as a result of the expansive nature of the 100% Ash B mixture, applications of this material should be judiciously evaluated to take into account for this characteristic. Expansion of the CLSM would be desirable for applications in which complete fill must be ensured such as tanks or abandoned tunnels. The 100% Ash B mixture should only be used where excavation would not be expected (because of high compressive strength of the mixture of 4.5 MPa at 28-day age).

If the potential for leaching is desired to be minimized, applications of the CLSM used in this study may be capped with concrete or asphalt or the CLSM may be used in a confined area.

Typical usage of this CLSM material will be for roadway sub-bases backfilling of utility trenches; excavation for walls and buildings; filling abandoned sewer and tunnels; support for foundations; in addition to others.

REFERENCES

ACI 229R-94 Report, July 1994, "Controlled Low-Strength Materials (CLSM)," Concrete International, pp.55-64

American Coal Ash Association, Dec. 1995, Fly Ash Facts for Hiqhway Enqineers, Alexandria, VA

Basu, P., and Fraser, S. A., 1991, Circulatinq Fluidized Bed Boilers - Desiqn and Operations, Butterworth-Heinemann, Stoneham, MA

Canadian Portland Cement Association, 1990, "Unshrinkable Fill for Utility Trenches in Streets," Concrete Information CPOO4.02P

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Kraus, R. N. and Naik, T. R., Feb. 1996, "Development of Controlled Low Strength Materials ("Manufactured Dirt") Utilizing Manitowoc Public Utilities Ash," CBU Report to Manitowoc Public Utilities, Milwaukee, WI

Naik, T. R., and Ramme, B. W., Oct. 1990, "Low Strength Concrete and Controlled Low Strength Material (CLSM) Produced with High-Lime Fly Ash," in Proceedinqs of the CANMET/EPRI International Conference on Fly Ash in Concrete, Published by CANMET, Ottawa, Ontario

Naik, T. R., Ramme, B. W., and Kolbeck, H. J., Sep. 1991,"Controlled Low-Strength Material (CLSM) Produced with High-Lime Fly Ash," in Proceedinqs of the International Conference on the Utilization of Fly Ash and Other Coal Combustion By-Products, Shanghai Building Science Research Institute, Shanghai, China

Naik, T. R., and Ramme, B. W., 1994, "Low Strength Concrete and Controlled Low Strength Material (CLSM) Produced with Class F Fly Ash," in Controlled Low-Strenqth Materials, ACI SP-150, W. S. Adaska, Ed., American Concrete Institute

Podolski, W. F., 1984, "Fluidized Bed Combustion," in The Science and Technoloqy of Coal and Coal Utilization, B. R. Cooper, and W. A. Ellingson, Eds., Plenum Press, New York

Ramme, B. W., Naik, T. R., and Kolbeck, H. J., June 1995, "Construction Experience with CLSM Fly Ash Slurry for Underground Facilities", in Plpceedinqs of the Fifth CANMET/ACI International Conference on Fly Ash, Silica Fume, Slaq, and Natural Pozzolans in Concrete, Milwaukee, WI

Tung, S. E., and Williams, G. C., Jan. 1987, Atmospheric Fluidized Bed Combustion - A Technical Source Book, The Massachusetts Institute of Technology, Cambridge, MA

Yerushalmi, J., 1986, "An Overview of Commercial Circulating Fluidized Bed Boilers," in Circulatinq Fluidized Bed Technoloqy, P. Basu, Ed., Pergamon Press, Ontario, Canada

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Ingredients~Aggregates


L. K. Crouch, I Rod Gamble, 2 James F. Brogdon, 3 and Charles J. Tucker 3

U S E OF H I G H - F I N E S L I M E S T O N E S C R E E N I N G S A S AGGREGATE FOR CONTROLLED LOW-STRENGTH MATERIAL (CLSM)

REFERENCE: Crouch, L. K., Gamble, R., Brogdon, J. F., and Tucker, C. J., ''Use of High-Fines Limestone Screenings as Aggregate for Controlled Low-Strength Material (CLSM),'' The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: Before the development of performance-enhancing admixtures, flowable fill mixes bled off excess mix water to consolidate after placement. The presence of significant amounts of material finer than 0.075 mm in the aggregate impeded bleeding, and therefore, most specifying agencies limited the percentage allowed to less than ten. New performance-enhancing admixtures limit strength, prevent segregation, and enhance workability by entraining large percentages of stable air bubbles in flowable fill mixtures. Flowable fill mixtures containing these admixtures do not bleed and, therefore, could possibly use aggregates containing greater than 10% finer than 0.075 mm. It was determined that aggregate containing up to 21% finer than 0.075 mm could be used to produce a flowable fill mix meeting National Ready Mixed Concrete Association performance recommendations.

KEYWORDS: controlled low-strength material (CLSM), flowable fill, mix proportioning, fine aggregate, air-entrainment, flowability, compressive strength

IAssociate Professor of Civil Engineering, Tennessee Technological University, Cookeville, TN 38505,

2Area Manager, Rogers Group, Inc., Algood, TN 38506,

3Graduate Teaching Assistants, Civil and Environmental Engineering Department, Tennessee Technological University.

45

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American Concrete Institute (ACI) 229R-94 (ACI 1994) defines controlled low-strength material (CLSM) in part as "a self-compacted, cementitious material used primarily in lieu of compacted fill." However, there are a variety of CLSM types available for various engineering purposes. Perhaps the most obvious distinction between these types is the possible need for future removal. Most researchers agree that CLSM excavatability is dependent on many factors including binder strength, binder density, aggregate quantity, aggregate gradation, and the excavating equipment used. Researchers differ on the exact limits of excavatability.

The National Ready Mixed Concrete Association (NRMCA) recommends that excavatable CLSM mixes have a 138+ kPa compressive strength at 3 days, a 207+ kPa compressive strength at 28 days, and ultimate compressive strength less than 1034 kPa. Compliance with these recommendations is typically established with cylinder compressive strength tests. Minimum strength requirements/recommendations are to assure that the CLSM has adequate bearing capacity and does not settle (deform) excessively under load. Maximum requirements/recommendations are to assure that CLSM can be removed with conventional excavating equipment (NRMCA 1989).

Most researchers agree that the correct consistency of CLSM depends on the particular application. Consistency is measured by filling a 75-by-150 mm open-end cylinder or pipe with CLSM on a level surface and then raising the cylinder to allow the CLSM to flow out. For most applications, the Tennessee Department of Transportation (TDOT) requires a patty wit h a minimum 200-mm diameter and no visible segregation (TDOT 1995).

Air-entrained, excavatable CLSM has several advantages over non-air-entrained excavatable CLSM mixes. Flow and resistance to segregation must be provided by cementitious materials in non-air-entrained mixes. Unfortunately, additional cementitious materials increase the cost of the mix and jeopardize achieving long-term strength goals for excavatability. ACI reports acceptable long-term performance with class F fly ash contents up to 207 kg/m 3 (ACI 1994). However, Meade (et al. 1994) caution that including significant amounts of fly ash may result in ultimate strengths 4 to 5 times the 28-day strength. In properly designed air-entrained, excavatable CLSM mixes, performance- enhancing admixtures limit strength, prevent segregation, and enhance workability by entraining large percentages of stable air bubbles in the CLSM mixtures.

RESEARCH SIGNIFICANCE

A Center for Aggregate Research (CAR) industry survey


CROUCH ET AL./HIGH-FINES LIMESTONE SCREENINGS 47

indicated that the greatest challenge faced by aggregate producers dealt with by-product fines, often referred to as screenings (CAR 1994). The National Aggregates Association and National Stone Association concur that by-product fines are one of the industry's highest priorities. Industry leaders estimate more than 90 million tons of quarry by- products were generated in 1993 (CAR 1994). It is difficult to find viable uses for by-product fines, which account for 15 to 25% of aggregate production since most construction and highway material specifications limit the percent finer than 0.075 mm to six or less.

The combination of large supply and small market has resulted in millions of tons of screenings accumulating in stockpiles. These huge stockpiles not only pose an environmental problem, but also result in lost revenues for the aggregate producer. CAR identified flowable fill as a very promising potential use for high volumes of by-product fines (CAR 1996).

If high-fines limestone screenings prove to be a viable flowable fill aggregate, the benefits would be very significant. Environmental benefits include cost of disposal, storage, and watershed protection saved in addition to the more efficient use of a dwindling natural resource. Economic benefits include increased revenues for aggregate manufactures and decreased material costs for ready-mix producers and end-users of flowable fill.

EXPERIMENTAL PROGRAM

To determine if high-fines limestone screenings were a viable flowable fill aggregate, multiple batches of flowable fill containing limestone screenings with 0, 7, 14, 21, and 28 % finer than 0.075-mm were mixed using mix designs recommended by the admixture manufacturers. The plastic and hardened properties of each batch were characterized and compared to NRMCA strength recommendations and TDOT flow requirements.

Several subsequent attempts were made to produce economical mixes conforming to NRMCA and TDOT performance recommendations with each admixture and percent passing the 0.075-mm combination. For each subsequent round, the results of the previous round were analyzed, mix proportions were adjusted, and new batches were mixed. The performance and cost of the final resulting mix designs were compared to an air-entrained mix using river sand aggregate and a non-air- entrained traditional flowable fill mix containing manufactured sand and Class F fly ash.



Materials

Manufactured limestone screenings obtained from Rogers Group Algood Quarry were used as aggregate for all variable mixes in the study. The gradation, as determined per the ASTM Test Method for Sieve Analysis of Fine and Coarse Aggregates (C 136) and the ASTM Test Method for Materials Finer than 75 ~m (No. 200) Sieve in Mineral Aggregates by Washing (C 117), of the material was determined using three samples of approximately 1.5 kg each. The results of the gradation tests as well as the AASHTO M43 #i0 screenings aggregate specifications (AASHT0 1995) are shown in Table I. Samples S-I and S-2 met AASHTO M 43 #i0 specifications. However, Sample S-3 failed to meet AASHTO M43 #i0 specifications because of 6.5 g retained on the 3/8-in. (9.5-mm) sieve. In the judgement of the authors, the minor deviation from AASHTO specifications did not significantly affect the aggregate's performance.

TABLE 1--Gradation results and specifications (% passing).

Size,mm S-I S-2 S-3 Average AASHTO M43 #i0

9.5 100 i00 99.6 99.9 i00 4.75 87.0 87.6 88.2 87.6 85 - i00 2.36 55.8 57.3 58.2 57.1 ... 1.18 38.4 39.6 40.3 39.4 ... 0.60 29.3 29.6 29.8 29.6 ... 0.30 22.5 22.5 22.3 22.4 ... 0.15 17.8 17.7 17.4 17.6 i0 - 30 0.075 14.6 14.6 14.1 14.4 ...

Table 2 shows the gradations used in the study. Any gradation with more material passing the 0.075-mm size than the "28" gradation is unlikely to meet AASHTO M43 #i0 specifications. The "14" gradation is the as-received gradation, the values shown are the average of the three samples from Table i. "0," "7," "21," and "28" gradations were constructed to approximately parallel the "14" gradation and contain the desired percentage passing the 0.075-mm sieve. "0," "7," "21," and "28" gradations were produced by dividing the as-received screenings into component sizes by sieving and washing and subsequently recombining the sized components in the correct proportions to produce each desired gradation.

Three specific gravity and absorption tests, performed in accordance with ASTM Test Method for Specific Gravity and Absorption of Fine Aggregate (C 128), were used to

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characterize the portion of the screenings coarser than 0.075-mm. The average bulk (dry) specific gravity was 2.651 and the average absorption was 1.17%. The results of the three tests met ASTM Test Method C 128 precision criteria. Similarly, three specific gravity tests, performed in accordance with ASTM Test Method for Specific Gravity of Soils (D 854), were used to characterize the portion of the screenings finer than 0.075-mm. The average apparent specific gravity was 2.697. The results of the three tests also met ASTM Test Method D 854 precision criteria.

TABLE 2--Aggregate gradations used (% passing).

Size,mm "0" "7" "14" "21" "28"

9.5 4.75 2.36 1.18 0.60 0.30 0.15 0. 075

I00 85 0 48 0 28 0 17 0 9 0 4 0 0 0

I00 86.0 53.0 34.0 23.0 16.0 ii.0 7.0

I00 87 6 57 1 39 4 29 6 22 4 17 6 14 4

i00 89.0 61 0 45 0 35 0 29 0 24 0 21 0

i00 90.0 65.0 50.0 41.0 35.0 31.0 28.0

A method proposed by the Asphalt Institute (AI 1993) for determining asphalt demand of fine particles was used to obtain an estimate of the extra water needed to coat the particles finer than 0.075-mm.

A locally available river sand and a manufactured limestone sand from a previous research project (Crouch et al. 1996) were used as aggregates for the air-entrained and traditional comparison standard mixes, respectively. The bulk (dry) specific gravity and absorption values, determined as per ASTM Test Method C 128 were 2.579 and 0.79% for the river sand and 2.658 and 1.0% for manufactured limestone sand. The gradations for the two aggregates and ASTM Specifications for Concrete Aggregates (C 33) are shown in Table 3. Although the river sand was slightly outside the specification limits, in the judgement of the authors, the minor deviation from ASTM specifications did not significantly affect the aggregate's performance. In addition, a Class F fly ash from a previous project was used to enhance the flow of the traditional mix.

In addition to limestone screenings, Type I portland cement, tap water, and a performance-enhancing admixture were used in each variable batch. The two commercially available flowable fill performance-enhancing admixtures



selected for the study were W.R. Grace Construction Products Darafill (WRG) and Master Builders Technologies MB AE 90 (MBT). Darafill and MB AE 90 entrain large volumes of stable air bubbles in the flowable fill. The large volumes of stable air bubbles reportedly enhance performance by limiting strength, minimizing segregation, reducing bleeding, and increasing flow in properly designed flowable fill mixes.

TABLE 3--Comparison aqgreqate qradations and specifications.

Size,mm River Sand Manufactured Sand ASTM C 33 FA % passing % passing % passing

9.5 i00 i00 i00 4.75 98.0 98.6 95 - i00 2.36 91.8 87.5 80 - I00 1.18 80.4 53.6 50 - 85 0.60 57.5 31.1 25 - 60 0.30 9.4 15.9 I0 - 30 0.15 0.8 8.2 2 - i0 0.075 ... 5.4 0 - 7

Procedure

The comparison and manufacturers' recommended mix designs used in the study are shown in Table 4. The research team made a 0.229-m 3 batch of each mix in Table 4 except the "TRAD" mix. Data for the "TRAD" mix, a non-air-entrained used for cost comparisons, were already available from a previous research project (Crouch et al. 1996).

TABLE 4--Mix desiqns for 1 m 3.

Component RS AE TRAD MBT Rec. WRG Rec.

Type I PC (kg) 89.0 21.4 44.5 59.3 Fly ash "F" (kg) ... 267.0 . . . . . . R. sand (kg,ssd) 1454.8 ... *~ *~ M. sand (kg,ssd) ... 1530.7 *~ *~ Water (kg) 201.7 284.8 148.3 148.3 MB AE 90 (mL) 1582.6 ... 1582.6 ... WRG Darafill (mL) . . . . . . . . . 67.8

*~ = aggregate mass required to produce 1 m 3.



Each batch was mixed in a 1.529-m 3 capacity electric drum mixer. MBT batches were mixed 4.5 min, allowed to rest 4.5 min, and finally mixed again for 3 min. For the WRG batches, all the components except one quarter of the mix water were placed in the drum. The components were then mixed 4.5 min, allowed to rest for 4.5 min, and then mixed again for 3 min. At the conclusion of the 3-min mixing cycle, the Darafill admixture was washed down into the zero- slump mixture using the remaining mix water. Following the admixture addition, the mixture was mixed for another i0 min as per WRG recommendations (Grace 1996).

The consistency of each batch was characterized using an open-end-cylinder flow test as per TDOT specifications (TDOT 1995). In addition, ASTM Test Method for Air Content of Freshly Mixed Concrete by the Volumetric Method (C 173) and ASTM Test Method for Unit Weight, Yield, and Air Content (Gravimetric) of Concrete (C 138) procedures were conducted on each batch. Twenty 50-by 100-mm cylinders were cast from each batch. All specimens were cast by pouring in the CLSM to overfill the mold, consolidated by tapping lightly on the mold, and subsequently stuck off.

All cylindrical strength specimens were capped with a plastic bag fixed with a rubber band and allowed to cure in the molds at approximately 21~ until the testing date or 28 days, whichever came first. Following the 28-day tests, at least 6 cylinders from each batch were demolded and placed in a lime water bath at approximately 23~ The remaining cylinders (if any) were allow to cure in laboratory air until the 60-day test. Three of the six cylinders placed in the 23~ tank were transferred to an approximately 35~ tank on about Day 46. The intention of the 35~ tank was to simulate long-term or ultimate strength by curing at elevated temperatures.

Three 50-by 100-mm cylindrical strength specimens from each batch were tested at 3, 7, and 28 days except when precluded by cylinder damage from demolding, similarly, three 50-by 100-mm cylindrical specimens from each batch were tested from the 23~ tank and the 35~ tank at 60 days. In addition, several remaining air-dry specimens (if available) were tested at 60 days.

Strength specimens with compressive strengths less than 1 MPa were tested on a screw-type, electrically driven unconfined compression test frame equipped with a 2.22-kN proving ring. The deformation rate on the screw-type load frame was set to 12.7 mm/min with no load on the platens as required by ASTM Test Method for Compressive Strength of Cylindrical Concrete Specimens (C 39). The strength specimens with compressive strengths greater than 1 MPa were tested on a 1.78-MN hydraulic load frame equipped with a digital load display. All cylinders tested on the hydraulic



load frame were loaded as near as possible to the 0.14 to 0.34 MPa/s rate prescribed by ASTM Test Method C 39. However, several cylinders failed before the prescribed rate could be achieved. All cylinders in the study were tested without caps.

INITIAL RESULTS

The results of the open-end-cylinder flow, volumetric air content, and unit weight tests for the manufacturers' recommended and comparison mixes (RS AE and TRAD) along with TDOT flow requirements are shown in Table 5. Variable gradation mixes were assigned designations by the following method: first three letters - admixture used, first two numbers - percent aggregate passing 0.075 mm, and last number - mix attempt.

The average compressive strength results for each batch at each age along with NRMCA recommendations are shown are shown in Table 6. The ultimate strength column refers to the average compressive strength cylinders from the 35~ bath. Because of a high percentage of cylinder destruction during demolding, no 60-day air-dry strengths are available for these batches.

MIX ADJUSTMENT

Mixes were adjusted primarily by altering the water and portland cement contents, although some attempts were made to adjust mixes by varying the admixture dosage or introducing a different admixture. It was known from previous research (Crouch et al. 1996) that the primary factors effecting strength development of air-entrained CLSM mixes were portland cement, air , and water contents. Flow was primarily dependent on air and water content and, to a somewhat lesser degree, on portland cement content.

Economy was primarily a function of portland cement content, admixture dosage, and aggregate cost. Therefore, the research team concentrated on producing mix designs that met N~CA recommendations and TDOT requirements with minimum portland cement and admixture contents. However, the research team was not able to entrain a significant percentage of air in mixes containing aggregate with 28% passing 0.075-mm.

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CROUCH ET AL./HIGH-FINES LIMESTONE SCREENINGS

TABLE 5--Plastic properties of initial mixes.

Mix Flow,mm Air Content,% Unit Weight,kg/m 3

53

MBT001 133 28.5 1507 MBT072 102 15.0 1721 MBTI41 <i00 9.5 2031 MBT211 <i00 3.5 2164 WRG001 229 32.0 1538 WRG071 197 34.0 1461 WRGI41 203 36.0 1405 WRG211 181 34.5 1423 WRG281 <i00 3.0 2262 RS AE 203 16.5 1631 TRAD 324 . . . . . . REQ'D 200 . . . . . .

TABLE 6--Compressive strength of initial mixes (in kPa).

Mix 3-Day 7-Day 28-Day 60-Day Ultimate

MBT001 30 51 86 70 61 MBT071 108 171 262 201 188 MBTI41 282 299 734 448 391 MBT211 502 607 1244 738 636 WRG001 78 117 214 15 16 WRG071 X ~ 51 81 30 38 WRGI41 i0 X ! X ~ X ~ X ~ WRG211 5 23 17 7 4 WRG281 969 1041 1389 1345 981 RS AE 138 160 487 490 567 TRAD ... 234 296 414 ... REC'S >138 ... >207 <1034 <1034

X a = cylinders accidentally destroyed during demolding.

FINAL RESULTS

The final adjusted mix designs are shown in Table 7. The results of the open-end-cylinder flow, volumetric air content, and unit weight tests for the final adjusted mixes along with NRMCA flow recommendations are shown in Table 8. The average compressive strength results for each batch at each age along with NRMCA recommendations are shown in Table 9. The ultimate strength column refers to the average compressive strength cylinders from the 35~ bath or the average compressive strength of the air-dry cylinders, whichever was greater. However, it is important



TABLE 7--Final adjusted mixes for 1 m 3.

Mix Type I PC,kg Water,kg Agg.,kg,ssd Admix.,mL

MBT003 89 220 1453 1583 MBT072 89 220 1455 1583 MBTI46 89 237 1411 1583 MBT215 74 237 1430 1583 WRG003 89 166 1489 34 WRG072 89 190 1427 68 WRGI48 89 190 1432 68 WRG213 89 178 ~ 1469 68

! +8-kg/m 3 water after i0 min mix cycle to increase flow.

TABLE 8--Plastic properties of final adjusted mixes.

Mix Flow,mm Air Content,% Unit Weight,kg/m 3

MBT003 289 22.0 1554 MBT072 260 21.0 1632 MBTI46 260 14.5 1743 MBT215 298 9.5 1802 WRG003 330 28.0 1546 WRG072 305 22.5 1661 WRGI48 210 22.5 1612 WRG213 210 20.5 1639 REQ'D 200 . . . . . .

TABLE 9--Compressive strength of final mixes (in kPa).

Mix 3-Day 7-Day 28-Day 60-Day Ultimate

MBT003 138 212 329 392 390 MBT072 170 317 415 518 532 MBTI46 368 530 669 712 753 D ~ MBT215 277 388 825 778 825 WRG003 355 505 940 422 830 D ~ WRG072 276 374 858 714 971 D ~ WRGI48 211 324 518 352 381 WRG213 233 272 349 368 559 D ~ REC'S >138 ... >207 <1034 <1034

[9 = air-dry condition stronger than 35~ condition.



to point out that as a result of occasional cylinder damage during demolding, air-dry specimens were not always available. The last two air-dry cylinders of Mix WRG072 had strengths of 1042 kPa at 60 days. The testing of the first cylinder from that mix was begun on the small 2.22-kN load frame. When it became evident that the cylinder would exceed the capacity of the small load frame it was transferred to the larger 1.78-MN load frame. It is possible that previous testing on the small load frame lowered the strength of Cylinder i. However the authors do not believe this is a problem for three reasons:

(i) the average strength of the 35~ bath cylinders was 510 kPa,

(2) the average strength of the 23~ bath cylinders was 714 kPa, and

(3) it is unlikely that CLSM would achieve an air-dry condition under a functional pavement.

ANALYSIS OF RESULTS

The proper air content in a well-designed mix limited strength, generated proper flow, eliminated segregation, and greatly reduced bleeding by producing a cohesive homogeneous mixture. The proper air content is a function of many factors, but air contents of 14 to 30% worked well in this study. If the air content is below 14%, there is a good chance that the ultimate strength of the mix may exceed the desired level. In addition, a low air content may produce a bleeding mix with inadequate flow. If the air content exceeds 30%, it will be difficult to achieve early strength goals with portland cement contents less than 120 kg/m 3.

Air contents of the mixes in this study appear to be a function of five factors. These factors, in apparent order of importance, are:

(i) admixture type or brand, (2) percent of aggregate passing 0.075 mm, (3) water content of the mix, (4) aggregate particle shape, and (5) admixture dosage.

WRG Darafill entrained higher percentages of air than MB AE 90 for every gradation. The difference in percent air entrained increased from the "7" gradation to the "14" gradation and even more dramatically from the "14" gradation to the "21" gradation.

In general, air content decreased as the percentage of the aggregate passing 0.075 mm increased. This effect was much more pronounced for MB AE 90 than for WRG Darafill. However, the research team was unable to entrain a



significant air content in a mix containing aggregate with 28% passing 0.075 mm with either admixture.

The dependence of air content on water content was the most perplexing and time-consuming lesson learned in the study because the two admixtures used in the study reacted very differently to changes in mix water content. Above a certain minimum water content, WRG Darafill entrained less air as water content increased. However, MB AE 90 entrained more air as water content increased. After these facts were understood, they proved very useful to the research team, actually allowing the successful completion of the project. The research team was having difficulty producing mix designs that would meet NRMCA recommendations with aggregates containing 21% passing 0.075 mm. Using the lessons stated above, the WRG mix was batched and mixed rather dry to generate a higher air content. Following the generation of a high air content, a small amount of water was added to increase the flow to the desired level. Similarly, faced with a MBT mix with a low flow, low air content, and a sticky consistency, the water content was increased to increase air content and flow.

From the limited use of rounded aggregates in this project, and from discussions with admixture manufacturers, it was determined that angular (crushed) aggregates entrain significantly higher air contents than rounded aggregates for similar mixes. This increase in air content partially offsets the reduction in air content as a result of increasing the percent of the aggregate passing 0.075 mm. However, the effect of percent passing 0.075 mm rapidly supersedes the effect of angularity as the percent passing 0.075 mm increases.

Admixture dosage rate appeared to have the least effect of the five factors provided that the dosage rate was above a certain minimum. An approximate double dose of MB AE 90 actually lowered the air content obtained in similar mixes. Some success was obtained in lowering the air content of certain mixes by halving the dosage of WRG Darafill. Until further definitive research is available, the authors recommend using a dosage rate from 50 to 100% of the manufacturers' recommendations for WRG Darafill and using 100% of the manufacturers' recommended dosage of MB AE 90.

As previously stated, the primary factors affecting strength development of air-entrained CLSM mixes were portland cement, air, and water contents. If a proper air content (14 to 30%) cannot be obtained, strength can be reduced by increasing the water content and decreasing the portland cement content, as in Mix MBT215. However, caution must be exercised to ensure the mix does not segregate and achieves early strength goals.

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Ideally, proper flow should be achieved with a proper air content (14 to 30 %) and a water content as low as possible to minimize segregation and bleeding. However, flow may also be increased by increasing the water content or, to a lesser degree, by increasing the portland cement content. Again, caution should be exercised. All the engineering properties of the mixture are interrelated, any alteration of one property almost always has collateral effects.

In summary, the mixes contained herein are meant as a good starting point for producers or testing laboratories to design mixes for specific applications using locally available materials. The mixes provided are not intended as universal "recipes" for properly performing excavatable CLSM.

Material cost data are provided in Table i0 for the final adjusted mixes and the two comparison mixes for two different market assumptions. Component cost assumptions for two markets are as follows: in both markets Type I portland cement is 68.04 $/Mg, Class F fly ash is 19.96 $/Mg, MB AE 90 is 0.63 $/I, WRG Darafill is $ 40.38 $/i, and water cost is negligible; in Market A, river sand is 10.89 $/Mg, manufactured sand is 8.16 $/Mg, and screenings are 3.63 $/Mg; in Market B, all aggregates are 2.72 $/Mg. In Market A, the final adjusted mixes are economically attractive because of the high cost of other aggregate options. However, in Market B in which all aggregate cost are equal, the final adjusted mixes are still competitive.

CONCLUSIONS

Based on the limited results of this study, the following conclusions can be drawn.

i. High-fines limestone screenings containing up to 21% finer than 0.075 mm can be used as aggregate to produce a flowable fill mix meeting NRMCA performance recommendations and TDOT requirements.

2. The proper air content in a well-designed mix limited strength, generated adequate flow, eliminated segregation, and greatly reduced bleeding by producing a cohesive homogeneous mixture. The proper air content for flowable fill mixes containing high-fines limestone screenings as aggregate appears to 14 to 30%.

3. Environmental benefits of using screenings as flowable fill aggregate include cost savings for disposal, storage and water shed protection in addition to the more efficient use of a dwindling natural resource.

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TABLE 10--Cost of mixes ($/m 3) based on SSD aqqreqates.

Component Cost Market A Cost Market B

TRAD 23.43 13.30 RS AE 28.32 13.89 MBT003 15.49 13.89 MBT072 15.49 13.88 MBTI46 15.30 13.75 MBT215 14.15 12.57 WRG003 16.55 14.91 WRG072 18.89 17.32 WRGI48 18.90 17.32 WRG213 19.07 17.45

4. Economic benefits of using screenings as flowable fill aggregate include increased revenues for aggregate manufactures and decreased material costs for ready-mix producers and end-users of flowable fill.

5. Flowable fill mixes containing high-fines limestone screenings containing up to 21% finer than 0.075 mm can be economically attractive in markets were other aggregates are expensive. In markets in which river sand is inexpensive, flowable fill mixes containing high-fines limestone screenings are competitive in price.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the support of the Rogers Group Inc. The authors appreciate the donation of materials and the advice provided by W.R. Grace Construction Products and Master Builders Technologies. The authors also wish to thank the following individuals for providing technical assistance with project:

Mr. William E. Brewer, ACI Committee 229 Mr. R. Wayne McCamey and Mr. Larry Clouse, Master Builders

Technologies Mr. Doug Poe and Mr. Ken Nelson, W. R. Grace Construction

Products Mr. Barry N. Whitten, Mr. Jason Burgess, Mr. Jason Laxson,

and Mr. Richard Maxwell, Tennessee Technological University



REFERENCES

American Concrete Institute, 1994, Controlled Low Strenqth, Materials (CLSM) ACI 229R-94, Box 19150 Redford Station, Detroit, MI 48219.

American Association of State Highway and Transportation Officials, 1995, Standard Specifications for for Transportation Materials and Methods of Sampling and Testing, Seventeenth Edition, Part 1 Specifications, 444 North Capitol St., N.W., Suite 249, Washington, D.C. 20001.

Asphalt Institute, 1993, Mix Design Methods For Asphalt Concrete and Other Hot-mix Types, MS-2, sixth ed., Lexington, KY, pp 125-131.

Center for Aggregates Research, 1994, "Industry Concerns Revealed in Preliminary Survey" in Aggregate Views, Volume 2 Number i, The University of Texas, Bldg. ECJ5.200, Austin, TX 78712-1076.

Center for Aggregates Research, 1994, "Fine Ideas for Quarry By-products" in Aggregate Views, Volume 2 Number 2.

Center for Aggregates Research, 1996, "CAR Responds to Industry Need: Finding Uses for Fines" in Aggregate Update, Volume 1 Number i.

Crouch, L. K., Charles J. Tucker, and James F. Brogdon, 1996, "Development of an Improved Controlled Low Strength Material (CLSM) Mix Design for Cleveland Utilities," Unpublished Research Report for Cleveland Utilities Water Division, Cleveland Tennessee.

Grace Construction Products, 1996, Darafill Flowable Fill Performance Additive, Available from W.R. Grace & Co.- Conn.,9303-E Monroe Road, Charlotte, NC, 28270, 1-800- 954-7676.

Meade, Bobby W., David Q. Hunsucker, and Michael D. Stone, 1994, "Use of Flowable Fill (CLSM) for Trench Backfill", Research Report KTC-94-24, Kentucky Transportation Center, College of Engineering, University of Kentucky, Lexington, Kentucky.

National Ready Mix Concrete Association, 1989, "What, Why & How ? Flowable Fill Materials," Concrete in Practice, CIP 17, 900 Spring St., Silver Spring, Maryland 20910.

Tennessee Department of Transportation Standard Specifications for Road and Bridge Construction, James K. Polk Bldg., 505 Deadrick St., Nashville, TN 37243, 1 March 1995.


Todd R. Ohlheiser

UTILIZATION OF RECYCLED GLASS AS AGGREGATE IN CONTROLLED LoW-STRENGTH MATERIAL (CLSM~

REFERENCE: Ohlheiser, T. R., "Utilization of Recycled Glass as Aggregate in Con- trolled Low-Strength Material (CLSM)," The Design and Application o f Controlled Low- Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: Incoming glass from curbside recycling programs is successfully being utilized as aggregate replacements. The colored glass that can not be used by local bottle manufacturers is crushed to a ~/i in. (12.5mm) material and used in various construction projects. The most successful use of processed glass aggregate (PGA) to date, has been in replacing up to 100% of the aggregate in controlled low-strength material (CLSM). It has proven to be successful and has gained acceptance by contractors in the Boulder, Colorado area.

KEYWOROS: CLSM, flowable fill, back fill, construction, pipe, glass, recycling, recycled glass, PGA.

In late 1994, Boulder County' s recycling outlet, Eco-Cycle, was informed that Coors Brewing Company's glass division would soon stop accepting the mixed colored glass at their Golden, Colorado facility. Until this time, Coors had been purchasing 100% of the non-profit organization's glass (Lombardi, Eric 3/1/95). Eco-Cycle's Executive Director, Eric Lombardi, immediately formed a "glass task force" to find alternative outlets for the incoming green glass and unsortable fragments of broken glass collected in local curbside recycling programs (Fig. 1). The processed glass aggregate (PGA) pro~am that followed is a direct result of the work of this team, consisting of Eco-Cycle, the City of Boulder and the author's company, a local aggregate and concrete producer.

1 Vice President - GeneralManager, Western Mobile Denver Aggregate Division, Denver, CO 80221.

60


OHLHEISER/RECYCLED GLASS 61

The team first explored safety issues with handling this type of product. The first concern-silica, was addressed thoroughly in the "Clean Washington" study, to the satisfaction of the team. This study concludes that the PGA material does not pose the threats inherent to silica (Dames & Moore, 3/937. The next concern was the risk of cuts and injuries caused by handling the glass particles. Testing and experiments proved that once the glass was pulverized into small pieces and ran through a sizing screen, the result was a PGA that could be safely handled without gloves (Fig. 2). The safe material handling aspect of the project was key to the success of the PGA project.

Fig. 1 - Glass collected from curbside recycling program being loaded into pulverizer.



Fig 2 - PGA material as it appears in inventor.. This product can be handled without ~pecial equipment or protective gear.

Once the research was completed, addressing the issues of material handling and silica, a small crushing and material processing operation was installed at a local concrete plant. The material was processed to a 1A in. (12.5mm) and smaller size while caps and labels were separated from the finished product (Fig. 3). This unwashed material can then be utilized in variety of ways. The most successful use of PGA has proven to be a replacement for virgin aggregate in controlled low-strength material (CLSM). The original mix design for 1 cubic yard of glass CLSM was as follows:

Glass CLSM U.S. Measure Metric Measure

1/2" minus glass 3000 lbs. 1,361 kgs Type C Fly Ash 120 lbs. 54.4 kgs Cement 60 lbs. 27.2 kgs Air Entraining Agent varies varies Water 30 gal. 113.5 litres


OHLHEISER/RECYCLED GLASS 63

Fig. 3 - Glass pulverizing equipment crushing glass to �89 in. (12. 5ram) material and separating caps and labels.

Field tests for flowability proved that the glass CLSM performed better than or equal to the original CLSM utilized by the author's company. With the initial performance results complete on the project, the emphasis switched to gaining statewide acceptance and usage. With this as an end, mix designs and material samples were submitted to the Colorado Department of Transportation (CDOT) Engineering Department for approval.

Once sufficient testing was complete, the CDOT issued a revision of section 206, structure backfill (Table 1), to allow recycled broken glass as an acceptable replacement for part or all of the aggregate.

With the CDOT acceptance of glass as an aggregate replacement, customers in the area were willing to use the product. They now have a choice of ordering "recycled" or "virgin" aggregate in their CLSM. Many prefer to assist in the recycling effort and request the PGA mix, even though the price is similar to that of the original mix.

The utilization of glass as an aggregate replacement in CLSM has brought a heightened level of awareness to the aggregate and CLSM industry. By partnering in local recycling efforts, partnerships can be successfully established in order to expand the C.LS.M. industry while providing a community service at the same time.



Table I - *Eco-cycle does not accept glass containing toxic or hazardous substances. 10% is by volume.

REVISION OF SECTION 2 0 6 STRUCTURE BACKFILL (FLOWFILL)

STRUCTURE BACKFILL (FLOWFILL) MEETING THE FOLLOWING REQUIREMENTS SHALL BE USED

TO BACKFILL BRIDGE ABUTMENTS AND TO BACKFILL PIPES WHEN SPECIFIED IN THE CONTRACT.

INGREDIENTS LBs. /C.Y. KG/M3

CEMENT

COARSE AGGREGATE (AASHTO No. 57 OR 67) FINE AGGREGATE (AASHTO M 6) WATER (39 GALLONS) (147 L)

50 30 1700 1009 1845 1095 325 (OR AS NEEDED) 193

(oR AS NEEDED)

THE CONTRACTOR MAY SUBSTITUTE 30 LBs./C.Y. (18 KG/~f3) OF CEMENT AND 30 LBs./C.Y. (18 KG/M3) OF FLY ASH FOR 50 LBS/C.Y. (30 KG/M3) OF CEMENT OR MAY SUBSTITUTE 60 LBS./C.Y. (36 KG/M3) OF CEMENT AND 60 LBS./C.Y. (36 KG/M3) OF FLY ASH FOR 100 LBS./C.Y. (60 KG/M3) OF CEMENT.

RECYCLED BROKEN GLASS (GLASS CULLET) IS ACCEPTABLE AS PART OR ALL OF THE AGGREGATE. AGGREGATE INCLUDING GLASS MUST CONFORM TO THE REQUIRED GRADATIONS. ALL CONTAINERS USED

TO PRODUCE THE CULLET SHALL BE EMPTY PRIOR TO PROCESSING. CHEMICAL, PHARMACEUTICAL,

INSECTICIDE, PESTICIDE, OR OTHER GLASS CONTAINERS CONTAINING OR HAVING CONTAINED TOXIC OR

HAZARDOUS SUBSTANCES SHALL NOT BE ALLOWED AND SHALL BE GROUNDS FOR REJECTING THE GLASS

CULLET. THE MAXIMUM DEBRIS LEVEL IN THE CULLET SHALL BE 10%.* DEBRIS IS DEFINED AS ANY

DELETERIOUS MATERIAL WHICH IMPACTS THE PERFORMANCE OF THE FLOWFILL INCLUDING ALL NON-

GLASS CONSTITUENTS.

tLombardi, Eric, Eco-Cycle Community-Based Recycling Since 1976, Al ternat ive Recycled Glass Marke t s Developed, 3/1/95. 2Dames & Moore, Clean Washington Center, Glass Feedback Evaluat ion Projec t Task 1

Repor t Testing P r o g r a m Design, 3/93. 3Mauro, Ken, Colorado Department o f Transportation, Revision of Section 206 St ruc ture Backfill (Flowfill), 8/3/95.


Properties


Femando Ports, 1 John S. Landwermeyer ,1 and Larry Kerns 2

DEVELOPMENT OF ENGINEERING PROPERTIES FOR REGULAR AND QUICK-SET F L O W A B L E FILL

REFERENCE: Pons, F., Landwermeyer, J. S., and Kerns, L., "Development of Engineering Properties for Regular and Quick-Set Flowable Fill," The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: The purpose of this paper is to report relationships that have been developed in a study performed in Tulsa, Oklahoma, for bearing strength, diggahility, and subsidence for regular and quick-setting flowable fills. The bearing strength parameters measured were California bearing ratio (CBR) and subgrade modulus (k). These parameters are typically used in the design of engineered backfill, subgrades, and pavement bases. More easily measured parameters such as hand-held mortar penetration resistance and 3 by 6-in. (76 by 152-mm) cylinder unconfined compressive strength through 365 days were also determined. Aggregate base CBR test values are presented to serve as benchmarks for comparing to CBR values offlowable fills since aggregate base has been used extensively and CBR values are widely known and used in the engineering and construction communities. This paper also presents an economic analysis and a controlled full-scale diggability assessment of regular and quick-set flowable fills. The results of our testing program, excavatability assessment, and economic analysis demonstrate the advantages of quick-setting flowahle fills over regular flowable fills for use in street/cut repair applications.

KEYWORDS: controlled low-strength material (CLSM), flowable fill, California bearing ratio (CBR), modulus of subgrade reaction, diggability, backfill, aggregate base, bearing, strength, subsidence

In the last few years, the City of Tulsa, Oklahoma has successfully used quick- setting flowable fill in numerous street cut/repair and infxastructure rehabilitation projects as an alternate to more conventional backfill materials such as soil and aggregate base. The City of Tulsa Public Works Department has implemented materials and construction

Senior Geotechnical Engineer and Senior Materials Engineer, respectively; Law Engcneering and Environmental Services, Inc., 1540 N 107 ta E Ave, Tulsa, OK

2 Special Projects Engineer; City of Tulsa Public Works Department, 2317 S Jackson, Tulsa, OK

67



specifications such that typical street cut/repair and infrastructure rehabilitation projects are routinely completed and opened to traffic within 24 h, regardless of weather conditions. Because of this success, the estimated annual flowable fill market in Tulsa for the 1995- ! 996 calendar year grew to approximately 20 000 yd 3 (15 000 m3), and is expected to exceed this amount in 1997~

For the City of Tulsa, Oklahoma, quick-setting flowable fill has proven to be an ideal backfill material for use on street cut/repair and infrastructure rehabilitation projects; namely, because they develop high early penetration resistance, have low shrinkage and compressibility characteristics, are economical, are not labor intensive, are diggable at any age, and are not adversely efl~cted by varying moisture contents. Although the advantages of quick-setting flowable fills were evident, known correlations between strength characteristics and geoteclmical parameters had not been established to date.

The purpose of this study was to develop engineering properties for flowable fills and to assist in developing new City of Tulsa construction specifications for regular and quick-set flowable fills. For that purpose, an extensive research, field and laboratory testing program, conducted by Law Engineering and Environmental Services, Inc. and commissioned by the City of Tulsa Public Works Department [1], included laboratory placements in trench mock-ups, field bearing strength tests, field tracking of ongoing flowable fill projects in the City of Tulsa, diggability/excavatability tests, laboratory void studies, and economic analysis.

This paper describes our field and laboratory testing program, excavatab'dity assessment, and economic analysis and presents our test results and conclusions. Throughout this paper, flowable fill and controlled low strength materials (CLSM) are used interchangeably.

FLOWABLE FILL MIXES USED

In the Tulsa area, flowable fill generally consists of cement, fine aggregate, and water. Depending on the mix design, other constituents have historically included fly ash, air-entraining agents, accelerators, and retarders; but may also include other industrial by- products used as fine-aggregate or pozzolans or both.

The mix designs used for this study are those typically specified by the City of Tulsa Public Works Department and are listed in Table 1. These CLSM mixes are designated as:

Mix 1 for Regular (normal setting) CLSM, Mix 2 for Master Builders Quick-Set CLSM, Mix 3 for CTS Quick-Set CLSM, and Mix 4 for CTS Quick-Set with 2 % Retarder CLSM.


PONS ET AL./ENGINEERING PROPERTIES 69

This terminology is used throughout all work items in this paper. Table 1 contains the constituents and proportions for 1 yd 3 (0.8 m 3) of CLSM for each of the four mix designs used.

TABLE 1--Flowable fill mixes used. a

Material Regular Quick-Set CLSM Quick-Set CLSM Quick-Set CLSM CLSM (Mix 2) (Mix 3) w/2% retarder (Mix 1) (Mix 4)

Cement 60 lbs. (Type I) 100 lbs. (Type I) 100 lbs. (Rapid 100 lbs. (Rapid Set (b)) Set ~b) )

Fly ash Type C 290 lbs. 0 lbs. 0 lbs. 0 lbs. Sand, ASTM C 2750 lbs. 2925 lbs. 2970 lbs. 2970 lbs. 33 Water 458 lbs. 585 lbs. 500 lbs. 500 lbs. Admixture none 2 oz. air -

entraining agent

Water/cement 1.31 ratio (a) a 1 lb = 0.45 kg,

80 oz. accelerator (Pozzutec 20 (~ ASTM C 494 Type C & E 5.90 5.00

b Rapid Set is a proprietary product of CTS Cement Manuthctunng Co. ~ Pozzutec 20 is a proprietary product of Master Builders, Inc. Water/cement ratio is defined as total flee water and liquid admixture divided by cementitious materials

2% citric acid retarder (2 lbs)

5.00

FIELD AND LABORATORY TEST PROCEDURES

Laboratory Mock-Up Trench Placements

Four 1-yd 3 (0.8-m3), open, perforated wood boxes were constructed to simulate field trench conditions. The 1-yd 3 (0.8 m 3) wooden boxes were constructed with 3/4 in. (19-mm) plywood and lined on the inside with a 4-oz/yd z (136 g/m 2) nonwoven geotextile. One-half-in. (13-mm) diameter perforations were drilled in the sides and the bottom of the wooden boxes at 4 in. (102 mm) on-center to simulate worst case conditions of an earthen trench, allowing a high degree &bleeding fhrough the "'sidewalls." Mixes 1, 2, 3, and 4 were batched by ready-mix concrete suppliers and transported to the laboratory in transit-mix concrete trucks in accordance with AASHTO Standard Specification for Ready-Mixed Concrete (M 157). The quick-setting cement was added to Mix 3 at the laboratory because the initial set occurs within 12 to 23 min in this mix.

Once the mixes were placed in the boxes, a Soiltest CT-421A mortar penetrometer was used to measure the penetration resistance at the open surface of each CLSM mixture. The CT-421A mortar penetrometer measurement involves forcing the



penetrometer's shaft into the CLSM to a depth of I in. (2.54 cm) at a constant rate. The resistance in pounds per square inch (psi) is shown on the penetrometer's direct-reading scale. The psi values obtained from the mortar penetrometer are not equivalent to the psi values obtained from unconfined compressive strength tests. Generally, the mortar penetrometer is used for determining the rate of hardening for mortars containing no coarse aggregate~ In conjunction with penetration resistance measurements, subsidence of the mixtures were obtained from a baseline established across the tops of the boxes.

During placement of the mixtures, 3-in. (76-ram) diameter by 6-in. (152-mm) long cylinders were cast, and the temperature, air content, unit weight, and flow consistence of the mixtures was measured. Testing and sampling offlowable fill was performed in general accordance with Ohio Ready Mixed Concrete Association (ORMCA) Flowable Fill Standards FF(1) through FF(4). Unconfined compressive strength tests were performed on cylinders through 365 days.of age. Flow tests were performed using an open-ended 3-in. (76-ram) by 6-in. (152-ram) cylinder, in general accordance with ORMCA FF2 (94) and the ASTM Provisional Test Method for Flow Consistency of Controlled Low Strength Material (PS 28). Alternatively, flow tests were attempted using a flow cone in accordance with the ASTM Test Method for Flow of Grout for Preplaced- Aggregate Concrete (Flow Cone Method) (C 939). This testing was discontinued due to incomplete flow (no air space resulted through the neck of the cone).

Finally, the laboratory boxes were partially dismantled approximately six weeks after the CLSM was placed. Six-inch square (39-cm 2) cubes were removed from each of the mixtures at depths of 1 to 2 ft (30 to 60 cm) below the surface with a hand-held spade to determine if the mixtures were diggable.

Field Trench Placements and Bearing Strength Tests

Four experimental trenches were excavated on City o f Tulsa property and backfllled with the flowable fill mixtures to perform field tests to determine the in-place bearing strength of the fill. Excavation of the trenches and placement of the mixtures were performed expeditiously on the same day to minimize drying of the trench wall soils. The soils encountered at the trench sites were classified in accordance with the Unified Soil Classification System and AASHTO. In general, the soils consisted of clayey sand to sandy clay fill soils with gravel and other construction rubble (asphalt and concrete pavement, rebar, and so forth), which are typical of soils encountered in street cut repair and rehabilitation projects in Tulsa.

CLSM Mixes 1, 2, and 4 were batched and transported to the site in transit-mix concrete trucks in accordance with AASHTO M 157. Mix 3 was not placed in the field since its initial set occurs within 12 to 23 rain and can logistically only be placed in the field using volumetric batching and continuous mixing methods as described by the ASTM Specification for Concrete Made by Volumetric Batching and Continuous Mixing (C 685). Two of the four trenches were filled with Mix 2. The trenches were excavated with a



rubber-tired backhoe and had approximate plan dimensions of 6 by 12 ft (1.83 by 3.66 m) and depths of approximately 6 fi (1.83 m).

Upon placement of the mixtures, penetration resistance and subsidence of the mixtures in the trenches were monitored with similar procedures used during our laboratory placements. During placement of the mixtures, 3- by 6-in. (76- by 152-mm) cylinders were cast, and the temperature, air content, unit weight, and flow consistence of the mixtures was obtained following similar procedures used in the laboratory. Unconfined compressive strength tests were performed on cylinders through 365 days of age.

The subgrade strength of the flowable fill in the trenches was measured by performing field California Beating Ratio (CBR) tests in accordance with the ASTM Test Method for CBR (California Beating Ratio) of Soils in Place (D 4429), and nonrepetitive static field load tests in accordance with the ASTM Test Methods for Nom'epetitive Static Plate Load Tests of Soils and Flexible Pavement Components, for Use in Evaluation and Design of Airport and Highway Pavements (D 1196). These tests were performed at intervals that ranged from 6 h to 45 days from placement offlowable fills. The CBR values obtained are reported as percentages of the strength of a properly compacted crushed aggregate base (CBR = 100); whereas the modiflus of subgrade reaction, k, values derived from the nonrepetitive static field plate load test are reported as load per inch of test deflection (psi/inch). A loaded tandem axle dump truck was used for the resistance weight. The plate load tests were performed at approximately the same location in the trenches as the CBR tests for each porticular time period.

Field Die,ability Assessment

The diggability of the CLSM was field demonstrated by excavating into each of the four experimental field trenches. It is not uncommon for CLSM, which have been placed in municipal utility or street cut/repair projects, to be excavated in subsequent street cut/repair or infrastructure rehabilitation projects. Reportedly, about 80 % of the current market for CLSM carries with it the expectation ofdiggability [2]. The purpose of this demonstration was to determine if the different types of hardened CLSM could be excavated with excavation equipment typically used by City of Tulsa Public Works Department. For this demonstration, a John Deere 310C rubber-tired backhoe was used.

The degree of excavation difficulty (diggability) was then quantified by the length of continuous time required to excavate each trench, by the backhoe operator's comments, and by the observed "rippability" of the material when excavated. The diggability was documented with photographs and a video camera.

Economic Analysis

The many advantages offlowable fill and how its utilization has resulted in lower in-place costs is discussed by Adaska and Hook [3], while detailed cost comparisons between flowable fill and conventional backfill methods have been developed in Canada



[4,5]. For this study, a cost analysis was prepared using conventional local backfill materials such as Oklahoma Department of Transportation (ODOT) Type "A" aggregate base (granular backfill) and compared to quick-setting flowable fill (Mixes 2 and 4) and regular flowable fill (Mix 1). The unit rates used in this analysis are based on set rates established for the approximately $2 000 000, 1995-1996 contract for street cut/repair for the City of Tulsa. Two cases were evaluated (see Fig. 1):

1. Case I is a 10-ft (3-m) long street cut for a 12-in. (305-ram) diameter pipe installed with 3 ft, 4 in. (1.02 m) of fill cover.

2. Case II is a 10-fi (3-m) long street cut for a 36-in. (915-ram) diameter pipe installed with 3 fi, 4 in. (1.02 m) of cover.

These two cases were selected since they are typical for utility cut/repair applications. Factors considered in the cost analysis included cost of excavation and waste disposal; in-place backfill material costs, pavement demolition and construction costs, and traffic control costs, such as safety/warning barricades and signs; and quality assurance (QA) testing and inspection costs. Our analysis was based on City of Tulsa specifications and traffic engineering control models for a typical four lane street with one lane closed [6,7].

TEST RESULTS AND OBSERVATIONS

Laboratory Mock-Up Trench Placements

At mortar penetrometer penetration resistance values of 400 psi (2.76 MPa), the CLSM appeared to be hard and stable. Corresponding tests of the material indicate a correlating unconfined compressive strength of approximately 6 psi (0.041 MPa). Mix 1 realized penetrometer resistance values of approximately 400 psi (2.76 MPa) at about 15 days. Mixes 2, 3, and 4 realized penetrometer values of 400 psi (2.76 MPa) at ages of 6, 1/3, and 5 2/3 h, respectively.

Approximately 1 1/4 in. (32 ram) of total subsidence was measured for Mix 1 within 1 1/2 h of placement. The total subsidence of Mixes 2, 3, and 4 was less than 1/10 in. (2.5 ram) of total subsidence for the 3-fi (914-ram) deep box. Mix I produced bleed water at the surface of the in-place material in the box, whereas Mixes 2, 3, and 4 did not produce bleed water at the surface.

Figures 2, 3 and 4 provide graphical representation of penetration and subsidence test results t~om the laboratory placement tests.

The physical test results and the unconfined compressive strength test results for this work are summarized in Tables 2 and 3. Graphical presentation of unconfined compressive strength testing through 365 days of age is included as Figures 5 and 6.



Typ

CASE I

"A" Aggregate B a s e B e f o r e Backf i l l

CASE I

Regu lar & Q u i k - S e t F lowable Fill

_ 1 l,-rp" I _ / r OOOT Type "B" I _ _ i - I ~,~1 - / asphalt ic concrete I - - 4 '

~ ' J / / / / / / / / / ~ / I "(tyP" throughout) ..... -I v / . / ! / / / !d / /~ - - - - - �9 .,." .~o : , . ~ ; . , . . . . ~ ",.:.- - ~...

.... -X-----I --':~: .... ..'-~ ~ .... ~"" .... ' ..... -I-, ..... ,-: ..... :-'I- ....

E x i s t l n - - a v e m e n t " " " " ~ T Port land cement concrete ~ l tvD I-~.'.-. '- g P "r / (typ. throughout) ' ' " " /

(typ. throughout) , ~ ' - 4 ~ 3 ' - 4 "

' I no.ou~ ~,, ..~.z'..o:D.. Type "A" o o o r / , ~ . - Aggregate Base* L ~ {

,J = 3 ' =

'-4"

t 1 ' - r

* Compacted to g57. Standard Density AASHTO T 199 8" max imum lifts

CASE II

Type "A" Aggregate Base Backfill

CASE II

R e g u l a r & Q u J k - S e t

Flowable Fill

12" I -- / 4" ODOT Type "13" I = 5 ' = I l t y p l . / a s p h a l t i c concrete I I

- - - - - - I / / / / / / / / / / / / / / / / / / / / / / / ~ / I - - ( t y P - throughout) - - '~- / / / / / / / / / / / I " - - - -

~ " ! : ~. ~.-2. ~ ~': -," ,~':, .:':-W'~"~':"~- ".l "L.L " -2~:,~ .~1-- . . . . . . - I ~ , : ." .. "-, - ~.." "~'~. "'.4' .". " . ~ - - ~ I

r G" e,,l.t,~ ~r -t t.e-t,~,~ .t.r,~-i

I - 6 ' - - 6 " =

~ 12- Ii&.')i'))."i'-)."i-i'.")-).").i')'). I" / t yp ".".'."-'.".'.".."-'. '. ' . ' . ' . ' . ' .

8" high early strength ....'.'.-.'--.-'.'.......'.-'.'...'.'. Port land cement concrete .'...'-.'.'-.'.'..".'.'..'.".'.". (typ. throughout) .- .".'- . 3"6d" 0 ~ ? ~ ".

\Type "A" OOOT :i'i'[ § ~'i'.: Aggregate Base * '.-.. ".'..

4 " - - ' ~ - - = 4 ' =

t 3 ' - r

3 ' - r

* Compacted to 95~ Standard Density AASHTO T 199 8" max imum lifts

FIG. 1 - T rench m o d e l s u s e d in cos t analysis. (1' = 30.48 cm, 1" = 2.54 cm)



800 -

700

~8oo

e"500

..~

~ 400

r ~.~300

~ 2 0 0

100

J

/

f J 5 10 15 20 25 30 35 40 45 50

( a ) T i m e , H o u r s

- - ~ Mix 1 L a b

--o- Mix 1 Field

800 ......

�9 ~ooo I - - / - I / - . - M~x 2i

�9 - Mix 2 Field ~,oo i - 1 - j ~ - - -

~ool-lj t - - +~,X~a Field ~.o. I - ) W - - -

100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

0 5 10 15 20 25 30 35 40 45 50

( b ) T i m e , H o u r s

FIG. 2 - Field and laboratory penetration resistance versus time: (a) Mix 1 - regular CLSM, (b) Mix 2 - quick-set CLSM. (1 psi = 5.8948 kPa)



800 -

700

e-,

tOO

o ~ ~eoo

e-, 500

..~

~ 400

�9 ~ 300

L -

Ir 2O0 ~J

O l 0 5 10 15 20 25 30 35 40 45 50

T i m e , t l o u r s

FIG. 3 - Field and l abora to ry pene t ra t ion res i s tance versus t ime.

Mix 3 - qu ick - se t C L S M . (I psi = 6.8948 kPa)

- -~ M i x 3 Lab

Lab

M i x 4 Field

0.5

._.4 r

r4~

10"0.5

L

-1

-1.5

0,5 1 1.5 2 2,5 3

Time, Hours 3.5

FIG. 4 - L a b o r a t o r y subs idence ve r sus t ime. (l in. : 2.54 cm)

~ M i x ! Rr

-II--Mix 2 Quick-Set

�9 - o - M ix 3 Quick-Sct

--lIP- M ix 4 Quick-Sct



T A B L E 2 - - P h y s i c a l p r o p e r t y s u m m a r y o f

l a b o r a t o r y p l a c e m e n t s and field t r e n c h e s .

DescripUon Cast Date Flow, m. ~

Mix 1 - Lab Box 1/25/95 9.5

Mix 2 - Lab Box 1/27/95 5

Mix 3 - Lab Box 1/27/95 3

Mix 4 - Lab Box 2/16/95 5

Mix 1 - Field Trench 4/4/95 8.5 - 9.5

Mix 2 - Field Trench 4/4/95 3 - 4.5

Mix 2A - Field Trench 4/4/95 3.5

Mix 4 - Field Trench 4/5/95 4.25 a I in. = 2.54 cm. b 1 pcf= 16.02 kg/m 3.

~ = 9/5(~ C) + 32.

Air, %

2.7

6.0

6.5

8.3

2.3

2.5

3.2

6.0

Mix/Air Unit Weight, Temperature,

p c f b ~ o

131.9 69/75

127.9 84/68

125.2 86/69

123.8 50/46

134.0 92/70

126.9 94/62

130.6 84/70

129.3 70/60

T A B L E 3 - - S u m m a r y o f m l c o n f i n e d c o m p r e s s i v e s t r e n g t h resul t s .

Description Avg. 6-8 Hrs. Comp.

Strength, psi a

Mix 1- Lab Mix 2 - Lab Mix 3 - Lab 2 Mix 4 - Lab 2 Mix 1 - Field Mix 2 - 2 Field Mix 2A- Field Mix 4 - 19 Field " 1 psi = 6.8948 kPa. b Sample tested at 119 days.

Core re-test at 164 days. d Core re-test at 180 days.

Avg. 1 Day

Comp. Strength,

psi

Avg.7-8 Day

Comp. Strength,

psi

Avg. 28 Day

Comp Strength,

psi

28

Avg. 90 Day

Comp. Strength,

psi

4 390 5 27 55 65 12 29 38 43 8 13 36 50

2 26 34and 970 (c)

8 25 52 57

9 41 67 76

25 34 42 48

Avg. 180 Avg. 365 Day Day

Comp. Comp. Strength, Strength,

psi psi

510 615 80 98 55 64

40 (b) 56 54 and 890 (d)

42 56

67 86

77 108



i _

7 0 0 -

..~oo

~4oo

" ~ 200

~ 1 0 0

0 50 100 150 200 250 300 350

( a ) Days 400

---- Mix 1 Lab

- o - M i x I Field

700

.m

~.~oo

. ~ 4 0 0

L

~00 0

~ 2 0 0

0 r.~100 e..

50 1 O0 150

( b )

2OO

Days

250 300 350 400

Mix 2 Lab

--o-. Mix 2A Field

--~Mix 2 Field

FIG. 5 - Unconfined compressive strength versus time: (a) Mix 1 - regular CLSM, (b) Mix 2 - quick-set CLSM. (1 psi = 6.8948 kPa)



700

o~ ra~ ,_~oo

~r L-

.~400

t__ ~oo

~200

~ 1 0 0

- J l 8

0 50 100 150 200 250 300 350

D a y s

400

--,- Mix 3

Lab

- o - - M i x 4

Lab

-,,- Mix 4 Field

FIG. 6 - Unconfined compressive strength versus time. Mix 3 - quick-set CLSM. (1 psi = 6.8948 kPa)

Unconfined compressive strength values obtained from the laboratory boxes for quick-setting CLSM ranged t~om 36 to 55 psi (0.248 to 0.379 MPa) at 28 days, from 43 to 65 psi (0.297 to 0.449 MPa) at 90 days, 40 to 80 psi (0.276 to 0.552 MPa) at 180 days, and 56 to 98 psi (0.386 to 0.676 MPa) at 365 days. The unconfined compressive strength for Mix 1 (Regular CLSM) was 28 psi (0.193 MPa) at 28 days, 390 psi (2.691 MPa) at 90 days, 510 psi (3.519 MPa) at 180 days, and 615 psi (4.244 MPa) at 365 days.

Flow values for Mixes 2, 3, and 4 ranged from 3 to 5 in. (76 to 127 mm). The current City o f Tulsa Specification for Quick-Setting CLSM requires a minimum flow value of 4 1/2 in. ( 114 mm). The flow value for the regular mixture was 9 1/2 in. (241 ram). City of Tulsa Specifications for Regular CLSM require a minimum flow of 8 in. r ~um).

The quick-setting mixtures were diggable with a hand-held spade. The regular CLSM mixture was hard and was not penetrable with the spade.



Field Trench Placements and Bearin~ Strength Tests

The physical test results and the unconfined compressive strength test results for the flowable fill placed in the field trenches are summarized in Tables 2 and 3. Figures 2 and 3 are graphical representations of penetration test results from the field placements.

The mortar penetrometer resistance values from the field trenches followed the same trend as experienced in the laboratory boxes. Mix 1 required approximately three weeks to reach values of at least 400 psi (2.76 MPa). Mixes 2, 2A, and 4 realized values of at least 400 psi at 6, 3 1/2, and 1 3/4 h, respectively.

Evidence of subsidence was observed for Mix 1, including surface drying cracks, but no measurable evidence of subsidence was discerned. Mixes 2 and 4 exhibited no visual or measurable evidence of subsidence. As with the laboratory boxes, Mix 1 produced bleed water at the surface, whereas Mixes 2 and 4 did not.

For Mixes 2 and 4, unconfined compressive strength values ranged from 42 to 67 psi (0.290 to 0.462 MPa) at 28 days, 48 to 76 psi (0.331 to 0.524 MPa) at 90 days, 42 to 77 psi (0.290 to 0.531 MPa) at 180 days, and 56 to 108 psi (0.386 to 0.745 MPa) at 365 days. The unconfined compressive strength for Mix 1 was 26 psi (0.179 MPa) at 28 days and 34 psi (0.235 MPa) at 90 days. The 90- and 180-day unconfined compressive strengths for Mix 1 appear to be erroneous data points based on the 90-day strength realized in the laboratory placements and on experience with regular CLSM. Tests of cores obtained from the trench on 15 Sept., 1995 resulted in an average unconfined compressive strength of 970 psi (6.693 MPa) at 164 days and 890 psi (6.141 MPa) at 180 days. This discrepancy in values for Mix 1 probably originates from the relative difficulty in obtaining homogeneous field cylinder samples from a very fluid mixture.

Flow values for Mixes 2 and 4 ranged from 3 to 4 1/2 in. (76 to 114 mm). The flow value for the regular mixture was 8 1/2 to 9 1/2 in. (216 to 241 mm).

Tables 4 and 5 present field CBR and plate load test data. Because of the softness of the material, CBR tests on the regular CLSM mixture were not performed until it was six days old.

TABLE 4 - - Field CBR and plate load bearing test results.

Mix Date CBR at 6 Placed Hrs.

Mix 1 4/4/95 Mix 2 4/4/95 25 Mix 2A 4/4/95 Mix 4 4/5/95 65

CBR at 24 CBR at 48 Hrs. Hrs.

40 70

65 40

CBR at 72 CBR at 6 CBR at 45 Hrs. Days Days

5 20

35



Anomalies in the data, such as the reductions in CBR and k values with age, are the result of normal field test variance. Overall, the data collected appear to be relatively uniform and within the range of anticipated values.

TABLE 5 - - Field plate load bearing test results,

Mix Date Placed

Mix 2 Mix 2A Mix 4 (a) fb)

k(.) at 6 Hrs. psi/in. (b~

at 24 Hrs. psi/in. (b)

at 48 Hrs. psi/in. (b)

k (a) at 72 Hrs. psi/in. (b)

k(.) at 45 Days psi/in. (b)

4/4/95 185 4/4/95 215 315 4/4/95 415

240 305 4/5/95 Modulus of subgrade reaction 1 psi/in. = 2.71 kPa/cm

370

Field Di~eability Assessment

The diggability demonstration was performed on 18 Aug., 1995, when the flowable fill materials had been in place for 135 to 136 days.

Mix 1--This mix was excavated to a depth of approximately 6 fi (1.83 m) below grade within 91 continuous minutes. The operator commented that the material was as hard as local shale, and that this is the flowable fill that he remembered having trouble excavating, often having to use jackhammers to remove. This material was not "excavated," but rather scraped, chipped, and hammered loose with the backhoe bucket.

Cores obtained from the trench on 15 Sept., 1995, resulted in an average unconfined compressive strength o f 970 and 890 psi (6.693 and 6.141 MPa) at 164 and 180 days, respectively. Mix 1 was placed with a flow of 8 1/2 to 9 1/2 in. (216 to 241 mm).

Mix 2 -This mix was excavated to a total depth of approximately 6 ft (1.83 m). Time o f excavation was 18 continuous minutes. The material was diggable and was described by the operator as the "second best" trench. The material was mostly rippable, with 10 to 30 % of the material excavated as cohesive blocks. The average unconfined compressive strength was 57 and 42 psi (0.393 and 0.290 MPa) at 90 and 180 days, respectively, and 56 psi (0.3864 MPa) at 365 days. Mix 2 was placed at a flow of 3 to 4 !/2 in. (76 to 114 mm).

Mix 2A--This mix was excavated to a depth of approximately 6 1/2 fi (1.98 m). Time o f excavation was 15 continuous minutes. The material was diggable and described by the City of Tulsa operator as the "third best" trench. The material was mostly rippable, with 10 to 30 % of the material excavated as cohesive blocks. The average unconfined



compressive strength was 76 and 67 psi (0.524 and 0.462 MPa) at 90 and 180 days, respectively, and 86 psi (0.593 MPa) at 365 days. Mix 2A was placed at a flow of 3 1/2 in. (89 mm).

Mix 4 -This mixture was excavated to a depth of approximately 5 1/2 tt (1.68 m) below grade within 15 continuous minutes. This material was described by the backhoe operator as "the most diggable" of all of the material excavated. The material was also the most rippable, with less than 10 % of the material excavated as cohesive blocks. The average unconfined compressive strength was 48 and 77 psi (0.331 and 0.531 MPa) at 90 and 180 days, respectively, and 108 psi (0.745 MPa) at 365 days. Mix 4 was placed at a flow of 4 1/4 in. (108 ram).

Economic Analysis

Results of our analysis are presented in '1"able 6 in 1995-1996 U.S. dollars and are based on the City of Tulsa contract unit rates for street cut/repair. Our analysis found that quick-setting CLSM resulted in lower costs than the corresponding regular CLSM or aggregate base backftUing options.

SUMMARY AND CONCLUSIONS

Unconfined Compressive Strength

For some of the unconfined compressive strengths, the data show a reduction of strength with age. This reduction is the result of normal test variance for this somewhat nonuniform material and should not be interpreted as a loss of strength with age for this material.

It is recommended that specifications for all CLSM types require a minimum unconfined compressive strength of 25 psi (0.173 MPa) at 28 days and a maximum unconfined compressive strength o f 100 psi (1.034 MPa) at 60 days. The minimum specified strength is intended to provide sufficient support for construction and vehicular loads, whereas the maximum specified strength assures that the material will be diggable, if necessary, at a later date.

Penetration Resistance and Time to Harden

At mortar penetrometer penetration resistance values of 400 psi (2.76 MPa), corresponding tests offlowable fill indicate a correlating unconfined compressive strength of approximately 6 psi (0.041 MPa).

Regular CLSM appears to be too soft at 24 h to support construction traffic loads. Based on the penetration resistance values from the laboratory placements and field tests, it appears that the regular flowable fill requires two to three weeks, as a minimum, to



realize sufficient strength to support pavement. It is recommended that placement of pavement over regular CLSM be permitted by construction specifications only upon achieving a penetration resistance of 400 psi (2.76 MPa) as measured with a Soiltest mortar penetrometer CT-42 IA, or equivalent. Material specifications should require that regular CLSM be designed to achieve a penetration resistance of 400 psi (2.76 MPa) within 14 days of placement.

Mix 1 - Regular CLSM requires three weeks to realize a penetration resistance value of 400 psi (2.76 MPa), yet develops very high long-term strengths in comparison with Mixes 2, 3, and 4. At such strengths, Mix I has exhibited very poor diggability characteristics. These characteristics do not appear to make Mix 1 compatible with typical street cut/repair and infrastructure rehabilitation projects that require little down time, minimal settlement of overlying pavements, and may be subjected to future excavations or repairs. In addition, the City of Tulsa has observed that pavements constructed over regular CLSM have experienced measurable subsidence, while those constructed over quick-setting CLSM have not.

The time required for the quick-setting CLSM tested to achieve penetration values of at least 400 psi (2.76 MPa) ranged from 1/3 to 6 h. It is recommended that placement of pavement over quick-setting CLSM be permitted by construction specifications only upon achieving a penetration resistance of 400 psi (2.76 MPa). Materials specifications should require that quick-setting CLSM be designed to achieve a penetration resistance of 400 psi (2.76 MPa) within 6 h of placement.

Bearing Strength Desisn

Table 6 contains recommended CBR and modulus of subgrade reaction, k, design values for the flowable fill mixes tested and also includes typical Type A aggregate base values for comparison purposes. CBR and k values are based on field testing. From CBR and modulus of subgrade reaction values, other pavement design parameters such as Soil Support Values (S) and resilient modulus (MR) can be correlated [8].

The recommended design values for the regular CLSM are based on a hardened undisturbed CLSM that is at least 45 days old. Based on the tmconfined compressive strength curve, penetration resistance, and diggability study for Mix 1, it follows that the long-term beating strength of Mix 1 will greatly exceed the 45-day test values. For this reason, the recommended design CBR and k values for Mix 1 (see Table 6) are equal to 100% of the field test values obtained (see Table 4) for Mix 1 at 45 days without reduction or "safety factor."

The field CBR value obtained in the regular CLSM after 6 days is comparable to a CBR value typical of a pavement subgrade considered poor. However, the field CBR and k values obtained for the regular CLSM at approximately 45 days fi'om placement is comparable to compacted ODOT Type A aggregate base material. As previously indicated, the relatively slow setting time but long-term strenmh inrroa~o for the regular


PONS ET AL./ENGINEERING PROPERTIES

CLSM explains a poor subgrade performance after 6 days o f placement, but the good pavement support characteristics after 45 days from placement.

83

TABLE 6 ~ S u m m a r y of f lowable fill properties,

Placeability Penetrometer Early Penetration Resistance Subsidence

Diggability

Recommended Pavement Design Values CBR, % Modulus of Subgrade ReacUon, k, psi/in

Quick-Setting CLSM Regular CLSM Type A Aggregate Base co)

excellent excellent 400 psi ob ta ined in 1/3

to 6 hours (~

negligible

diggable at UCS (~) of up to 60 psi

40 to 45 @ 24 hrs. 250 to 300 @ 24 hrs.

Relative In-place Cost Case 1 (12-inch pipe) $922.45 Case 11 (36-inch pipe) $1,279.45

400 psi obtained in 14 days

up to 4% subsidence depending on trench

soils difficult to excavate due to UCS (a) of up to 500

psi

20 @ 45 days 185 @ 45 days

$1,597.00 $1,864.00

requires compaction not applicable

may consolidate if improperly compacted

diggable

not tested (typ 80 - 90) not tested (typ. 700)

$1,373,75 $1,818.50

(a) (b)

(c~

Unconfined compressive strength. Compacted to at least 95% of modified Proctor maximum dry density (AASHTO T-180) within - 2% to + 1% of optimum moisture For Mixes 2 and 4, the minunum time in which 400 psi (2758 kPa) was achieved was 1 3/4 h.

The recommended design value for the quick-setting CLSM (which is derived from a combination o f results from Mixes 2 and 4) is based on hardened, undisturbed CLSM that is at least 24 h o f age. Based on unconfined compressive strength, penetration, and diggability data for Mixes 2 and 4. the 24-h field C B R and k tests may be more representative o f the long-term beating strengths o f Mixes 2 and 4. For this reason,

the recommended design CBR and k values for Mixes 2 and 4 were taken as the lower 20th to 33rd percentile o f the range o f field data (see Table 4).

Also, the field plate load tests, compared to the field CBR test, indicated more similar soil bearing strengths for Mixes 2 and 4. The plate load test uses a 30-in. (762- mm) diameter loading plate compared to the 2-in. (5 l-ram) diameter piston used in the CBR and is therefore less susceptible to localized material variances as a result o f nonuniform fill materials. For this reason, the recommended CBR design values for Mixes 2 and 4 are more similar than the corresponding field CBR test values.



The field CBR and k values obtained for Mixes 2 and 4 would generally be comparable to CBR and k values obtained from primarily sandy or gravely soils or both which generally constitute good subgrade materials for pavements.

Die,ability

Unconfined compressive strength was found to be a good measure of diggability. To facilitate future excavation requirements, a maximum 28-day unconfined compressive strength of 100 psi (1.034 MPa) should be used. The City of Tulsa Street Cut/Repair Specifications specify that 60 psi (0.414 MPa) should be the maximum 28-day unconfined compressive strength. Note that the long-term (>28 days) unconfined compressive strength of regular CLSM exceeds the recommended value of 60 psi (0.414 MPa). Regular CLSM is not recommended if future diggability is required.

Flow tests of the quick-setting CLSM at the time of placement in the field trenches ranged fyom 3 to 4-1/2 in. (76 to 114 mm). Based on further field observations and experience, a specified minimum flow of 7 in. (177 ram) is recommended to achieve a more self-leveling material. Material mixed and tested at such flows has resulted in similar unconfined compressive strengths and penetration resistance values, Flow tests of the regular CLSM at the time of placement in the field trench was 8 1/2 to 9 1/2 in. (216 to 241 mm). Based on the field observations and experience, a specified minimum flow of 8 in. (203 mm) is recommended.

Based on the times required to excavate each field trench, our engineering observations, and the backhoe operator's comments, it appears that Mix 4 is the most diggable of the CLSM at the time of excavation. It took only 15 min to excavate this trench, and the backhoe operator commented that this material was the easiest to excavate. Mixes 2 and 2A were the next easiest to excavate.

The most difficult mix to excavate was Mix 1. The backhoe operator commented that this material was comparable to digging local shale. It also exhibited the highest unconfined compressive strength.

The quantified diggability of each type of CLSM correlated to the known unconfined compressive strength of the material in each trench and provided an easily measurable benchmark for the design and acceptance testing of future CLSM.

Subsidence

Because of the rate of hydration in regular CLSM, it appears that Mix 1 is susceptible to bleeding at the time of placement and ~ settle similar to a supersaturated soil when provided with a drainage path at the open top of the trench or with low permeability trench walls.



From the test data, it appears that the majority of subsidence occurs in regular CLSM within the first 2 h of placement which is consistent with the typical time of initial set for Type I cement. Hence, regular tlowable fill depends solely on interparticle friction to resist subsidence. Conversely, the rapid hardening of the quick-setting mixtures provides added resistance to subsidence.

The classification of trench side wall soils does not significantly affect the subsidence and hardening of quick-setting CLSM. However, for regular CLSM, the surrounding soils may retain or absorb the bleed water, depending on the classification of the surrounding soils. The retention of bleed water in the CLSM mix will in turn, decrease the rate of hardening and may reduce subsidence.

Economic Analysis

Regardless of the tangible lower in-place cost for quick-setting CLSM, other intangible cost advantages make quick-setting CLSM an attractive backfill material fi~om an engineering, safety, and economic standpoint. The primary intangible advantage is lower liability exposure of worker excavation safety, as well as safety of the public exposed to open or fluid excavation pits.

The findings of this paper are summarized in Table 6.



REFERENCES

[1] Law Engineering, Inc., 1995, "Interim Report No. 3, Regular and Quick-Set Flowable Fill Testing Program," Project No. 392-50237-01, Tulsa, Oklahoma.

[2] Baas, W., Concrete Products Magazine, Nov. 1994.

[3] Adaska, W. S. and Hook, W., Supplementary Seminar Reading, Aberdeen's World of Concrete Seminar 06-28 Flowable Fill, Jan., 1994.

[4] "Utility Cut Restoration," Metropolitan Toronto Roads and Traffic Department Ready Mixed Concrete Association of Ontario, April 1985~

[5] Emery, J. and Johnson, T., ''Unshrinkable Fill for Utility Cut Restorations," American Concrete Institute, Special Publication 93-10, 1986, pp. 187-211.

[6] 'q'ypical Applications of Traffic Control Devices," City of Tulsa, Oklahoma, Public Works Department, Traffic Engineering Department, 1991.

[7] "Standard Concrete and Asphalt Pavement Cut and Repair Specifications," City of Tulsa, Oklahoma, Public Works Department, 1991.

[8] VanTil, et al., "Evaluation of AASHO Interim Guides for Design of Pavement Structures," NCHRP 128, Highway Research Board, 1972.


Robert J. Hoopes I

ENGINEERING PROPERTIES OF AIR-MODIFIED CONTROLLED LOW-STRENGTH MATERIAL

REFERENCE: Hoopes, R. J., "Engineering Properties of Air-Modified Controlled Low Strength Material," The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: The engineering and material properties of controlled low-strength material (CLSM) can be altered through the use of air-modifying additives, thereby broadening potential end-uses for CLSM. Air-modified low-water content CLSM retains the compressibility, shear, load-bearing, and flowability characteristics of non-air- modified CLSM, while improving permeability, subsidence, bleeding, and freeze-thaw properties. This paper details test procedures and results of several soil and other applicable backfill tests including compressive strength, direct shear, California bearing ratio (CBR), modified (cyclic loading) CBR, triaxial shear, incremental consolidation, thermal conductivity, water permeability, air permeability, freeze-thaw, and bleeding.

KEYWORDS: controlled low-strength material (CLSM), soil, compacted fill, air- modified, shear, triaxial, compression, bearing, permeability, conductivity

Controlled low-strength material (CLSM) is comprised of varying proportions of cement, water, fine aggregate, fly ash, coarse aggregate, and more recently, liquid air- entraining or air-modifying additives (Smith 1991). The inclusion of air-modifying additives into CLSM mixes allows for the design and engineering of fill materials throughout a diverse range of properties and broad spectrum of end-uses.

Marketing Technical Services Engineer, Grace Construction Products, 62 Whittemore Ave., Cambridge MA 02140.

87



Air-modified CLSM typically contains 15 to 35% air by volume, thereby allowing for significant reductions in water contents. Because of the lower water contents, air- modified CLSM maintains a homogenous matrix during placement and setting, with minimal segregation and bleeding (Gianetti et al. 1993).

The excellent flowability, placeability, and encapsulation properties of CLSM, when compared to compacted fills, is achieved with air-modified CLSM via millions of tiny air voids, in lieu of using high water contents. Unit weights of air-modified CLSM range from 1400 to 1900 kg/m 3 (90 to 120 lb/ft3), lighter than non-air-modified CLSM, thereby helping to assure ultimate strength cap specifications can be met.

This paper details several test procedures typically used for quantifying and categorizing the engineering properties of fill materials, along with results of extensive testing conducted on both air-modified and non-air-modified CLSM mixes. Comparisons of test results to typical compacted fill materials are also included. Specific tests include compressive strength, direct shear, California bearing ratio (CBR), modified (cyclic loading) CBR, triaxial shear, incremental consolidation, thermal conductivity, water permeability, air permeability, freeze-thaw and bleeding.

ASTM TEST METHOD FOR PREPARATION AND TESTING OF CONTROLLED LOW STRENGTH MATERIAL (CLSM) TEST CYLINDERS (D 4832)

ASTM Test Method D 4832 provides valuable quality control information on fill materials, yet is relatively simplistic and inexpensive to perform, compared to most soil test procedures. Specifications often require field compressive strength data to assure CLSM mixes do not exceed maximum strength caps, thereby allowing future excavation. CLSM compressive strength data also provides a general indication of the material's expected performance in other relevant soils tests.

Tables 1 and 2 depict compressive strength results for several air-modified and non-air-modified CLSM mixes at various ages. 28-day compressive strengths ranged from 0.23 to 0.95 Mpa (33.9 to 138 psi), with strength most significantly impacted by cementitous, air, and water contents. An ACI 229 R-94 Report entitled "Controlled Low Strength Materials (CLSM)" states compressive strengths of 0.33 to 0.66 MPa (50 to 100 psi) can be easily excavated with conventional digging equipment, yet are strong enough for most backfilling needs (ACI Committee 229 1994).

ASTM TEST METHOD FOR DIRECT SHEAR TEST OF SOILS UNDER CONSOLIDATED DRAINED CONDITIONS (D 3080)

Massive uncontrollable movements such as landslides initiate when shear stresses exceed maximum shear strengths of fill materials. ASTM Test Method D 3080 is a commonly used test to measure shear properties of fill materials and was used to


HOOPES/AIR-MODIFIED CLSM 89





determine shear properties of three air-modified and one non-air-modified CLSM mix at 3,7, and 56 days (Sowers 1979).

Referring to the middle column of Table 1, 56-day direct shear data reveals the two higher cementitous factor air-modified mixes had minimum direct shear values of 2.92 kg/cm 2 (2.92 tons/ft2). These values far exceed typical compacted fill direct shear strengths. The 59-kg/m 3 (100-1b/yd 3) cement factor air-modified mix had direct shear properties equivalent to typical compacted fill at 56 days,

At 3 and 7 days, all air and non-air-modified CLSM mixes performed at least equal to typical compacted soils. The later age shear properties of air-modified CLSM were obtained through the excellent cohesive properties of the cementitious constituents in the mix.

ASTM TEST METHOD FOR CBR (CALIFORNIA BEARING RATIO) OF LABORATORY-COMPACTED SOILS (D 1883)

Load-bearing capacity defines a fiN's ability to support foundations, pavements, and other structures without failing or suffering detrimental long-term settlement. A common test for determining a materials load-bearing ratio is the California bearing ratio or CBR test. CBR testing is widely utilized for qualifying materials for use as subbase and subgrade under pavements.

ASTM Test Method D 1883 includes measuring the force required to penetrate a surface with a 1936-mm 2 (3-in. 2) piston measured at 2.5-mm (0.1-in.) depth increments up to 12.7 mm (0.5-in.). Resulting load-deflection curces are compared relative to a reference, typically standard crushed rock. CBR indexes are correlated to soil's utilizing classification systems recognized by AASHTO and USCS (Nelson and Weber 1994).

Referring to Table 1 and Figs. 1 and 2, CBR testing was conducted on air- modified and non-air-modified CLSM mixes at 3,7, and 56 days. Figure 1 reveals the three air-modified CLSM mixes achieved minimum very good submade category (CBR of 20 to 30%) at 3 days and a ~ood base category (CBR of 30 to 80%) or better at 56 days.

Figure 2 plots CBR indexes for air-modified CLSM mixes on the X axis, with respective 56-day compressive strengths plotted on the Y axis. This figure shows a fairly linear relationship between CBR indexes and compressive strength. Table 3 depicts 56- day air-modified CLSM and typical compacted fill CBR indexes.



TABLE 3--CBR Indexes (%)

Soil Description CBR Index (%)

56 day air-modified CLSM Base rock, well graded Gravel, poorly graded

Gravel, uniformly graded Silty gravel

Clayey gravel Silty, sandy silts, gravely silts

Lean clays, sandy clays, gravely clays

Organic silts, lean organic clays Micaceous clays, diatomaceous soils

Fat clays, organic clays

50-130 60-80 35-60 25-50 40-80 20-40 5-15 5-15

4-8 3-5 3-5

CBR Rgure 1 (%) California Bearing Ratio (ASTM D 1883) 1 4 0

120 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

119 kg/m 3 cement, :L5.t% a i r ~ / 5 9 kg/meceme

4 0 . "" fins cement ,my ga~l

- ~148 kg/m s t lyash . . mJbgnm

@ I

3" 7" U

S p e c i m a n A g e ( d a y s ) i



II Figure 2 Califomia Bearing Ratio (%) versus

56 Day Compressive Strength

1 I ~ 0.9 o,~

~ 0.6- g o . s -

0 . 4 0.3-

o. 0.2- ~ 0 . t - (,,1

0 0

o

A A jL" . o

, . ~ ~

. o �9 "A~

I I i t I 20 40 60 80 100

California Bearing Ratio (%)

I 120 140

MODIFIED (CYCLIC LOADING) CBR (NOT AN ASTM PROCEDURE)

The California beating ratio test was modified to measure cyclic loading properties of air-modified CLSM. The modified test procedure cyclically loaded the specimen surfaces 30 times from 0.007 to 0.17 MPa (1 to 25 psi). The data was further extrapolated to 100 cycles. NOTE: 0.007 MPa (1 psi) simulates pavement weight and 0.17 MPa (25 psi) simulates approximate stress exerted on base coarse by a large commercial truck wheel.

Recoverable elastic and nonrecoverable plastic deformation strain components occur during each cycle. Plastic deformation, or cumulative strain, increases with each cycle, but at a decreasing rate. Modified (cyclic loading) CBR testing measures this cumulative strain component, thereby quantifying the deformation characteristics of fill materials.

Table 1 and Fig. 3 show results of modified CBR testing conducted on two air- modified and one non-air-modified CLSM mixes and a typical compacted granular soil (dense glacial till). Results show both air-modified CLSM mix designs had lower strain components when compared to dense glacial till and the non-air-modified CLSM mix.


9 4 CONTROLLED LOW-STRENGTH MATERIALS

Figure 3 Modified (Cyclic Loading) Califomia Bearing Ratio

56 Day Test-run to 30 cycles/extrapolated to 100 cycles sma. (%) 0.3

0.25 . . . . 30 kg/m = (50 Ib/yd =) cement . . . . . . . . . . . .

0 . , . . . . . . . . . . . . . . . . . . . . .

0.15 . . . . . . . . . . . . 119 kg/m = (200 Ib/yd )1 cement, . ~ ' - - " . . . - ~ 35.1% AIR

0.1

0 I

10 100

Number of Cycles

T R I A X I A L S H E A R - C O N S O L I D A T E D DRAINED (USACE E M 1110-2-1906)

A common test for predicting overall strength and rigidity properties of fill materials is the triaxial shear test. Testing is conducted in a drained or undrained mode, depending on material permeability properties. Since air-modified CLSM has relatively high permeability properties, testing was conducted in a drained mode.

Shear strength properties of granular materials will typically increase linearly as the critical effective conHning stresses are increased. This linear relationship is further defined by the Mohr-Coulomb failure law depicted below:

v~ c § (1) where

"t'ff = peak shear stress on failure plane at failure, that is, the shear strength;

r = effective normal stress on failure plane at failure; C = cohesion, or shear strength at zero confining stress; g) = friction angle; and

tan @, = coefficient of fi-iction of the material, or slope of the linear relationship between effective normal stress at failure and the shear strength,



Cohesion and friction angle characteristics for granular materials are best measured by testing specimens over a range of effective confining stresses and measuring the peak shear stress, then best fitting a straight line to the data. The intercept of this straight line with the shear stress axis equals the cohesion of the material. The slope of the straight line (change in shear strength/change in normal stress) equals tan ~.2

Triaxial shear testing was conducted on two air-modified CLSM mixes and one non-air-modified CLSM mix at 16 h, 7 days, and 28 days. Referring to Table 2, air- modified CLSM mixes achieve minimum 38 ~ friction angles at 16 h, while typical well compacted fill achieve ultimate friction angles in the mid 30s or higher.

Cohesion values of 16 h are negligible for the air-modified CLSM mixes, but most compacted granular fills also have negligible cohesion properties at all ages. From 16 h to 28 days, the excellent cohesive properties of the cementitous constituents begin to develop. For example, cohesion values for the 59-kg/m 3 (100-1b/yd 3) air-modified CLSM mix increased from 0.0014 to 0.043 MPa (0.2 to 6.3 psi).

In summary, triaxial shear testing results show air-modified CLSM mixes tested equal to or superior to typical compacted fill at 16 h, with further gains after 16 h as the cohesive properties developed.

ASTM TEST METHOD FOR ONE-DIMENSIONAL CONSOLIDATION PROPERTIES OF SOILS (D 2435)

ASTM Test Method D 2435 test data assist with estimating a fill material's expected rate and total amount of differential and total settlement. Consolidation data is also used to derive bedding factors and soil stiffiaess values needed for pipe bedding design.

A relationship exists between vertical strain and the change in vertical stress applied in a one-dimensional consolidation test for granular materials. This relationship is used to compute material vertical strain and settlement resulting from a load increment as further detailed by Eq 2 and 3 below:

Strain = m~ (Ar (2)

Settlement = Strain (D) (3)

where m~ = coefficient of volume compressibility of material measured in consolidation tests,

Ar v = change in vertical stress from loading, and

D = thickness of compressible layer. The right side column of Table 2 shows coefficient of volume compressibility of

material values (my) at 16 h, 7 days, and 28 days for air-modified CLSM and non-air-

2 T. McGrath, personal communication, Simpson, Gumpertz & Heger, Inc., Arlington, MA, 1995.



modified CLSM mixes. Mv values were calculated at crv loads of 1.0 and 4.0 kg/cm 2 (1 and 4 tons/ft2). M, properties of the air-modified CLSM mixes are not well developed at 16 h (firm clay to dense silty category), but improve significantly as the cohesive properties develop. At 28 days, m, values for the two air-modified CLSM mixes range in the dense gravel to dense sand categories.

This data depicts mv values decreasing as vertical stress increases. For backfill design, my values should be selected based on an average vertical stress acting at the middle of the flowable fill. Typical my values for several fill categories are shown in Table 4 below.

TABLE 4 - Coefficient of Volmne Compressibility (My) Typical values for compacted fills A

Fill Type My (W/ton equals cmZ/kg)

Dense gravel 0.0005-0.00 I0 Dense sand 0.001-0.002 Dense silt 0.002-0.004 Firm clay 0.0 I-0.03 Soft clay 0.03-0.15

Peat >0.15 See foomote 2.

ASTM TEST METHOD FOR MEASUREMENT OF HYDRAULIC CONDUCTIVITY OF SATURATED POROUS MATERIALS USING A FLEXIBLE WALL PERMEAMETER (D 5084)

The coefficient of permeability, K, expresses the rate or velocity that water flows through a material. Referring to the bottom of Table 5, typical fill materials have a very wide range of water permeability properties (greater than lx l0 "l to less than lxl0 "7 cm/s) 3. Particulate material grain size, shape, gradation, and void ratio, coupled with saturation level, are the major factors influencing water permeability properties.

Triaxial water permeability tests were conducted on two air-modified CLSM and one non-air-modified CLSM mix. Table 5 and Fig. 4 shows the 30 and 21% air- modified CLSM mixes having permeability values of 1.7 x 10 .2 and 1.2 x 10 "3 cm/s, respectively. These values fall into the sand/f'me sand "medium" permeability category. The non-air-modified CLSM mix had a lower permeability value of 1.8 x 10 "4 cm/s, which falls into the silty sand/dirty sand "low" permeability category. In summary, water permeability test data indicate that water will permeate faster through air-modified CLSM when compared to similarly designed non-air-modified CLSM.

3 A. Mart, personal communication, Geotcsting Express, Concord, MA, 1995.



TABLE 5--Water Permeabi l i ty (ASTM D 5084) Air /Gas Permeabi l i ty (ASTM D 4525)

Fill Type Water Permeability Permeability K, (em/sec) Rating

Coefficient of Air/Gas

Permeability

3 0 % A i r - m o d i f i e d C L S M 30 kg/m 3 (50 lb/yd 3) Cement

148 kg/m 33(250 lb/yd 3) Fly Ash 1333 kg/m (2246 lb/yd 3) Sand 123 kg/m 3 (207 lb/yd 3) water

2 1 % A i r - m o d i f i e d C L S M 59 kg/m 3 ~100 lb/yd 3) cement

1556 kg/m (2623 lb/yd a) Sand 176 kg/m 3 (297 lb/yd 3) water

1.4% air C L S M 30 kg/m 3 (50 lb/yd 3) Cement,

148 kg/rn 3 (250 lb/yd 3) Fly Ash 1619 kg/rn 3 (2728 lb/yd 3) Sand 298 kg/m 3 (502 lb/yd 3) water

Coarse gravel, rock Sand, fine sand

Sil ty sand, dirty sand Silt, Sandstone

1.7 x 10 "2 Med ium 18.20 m 2

1.2 x 10 -3 Med ium 1.3 m 2

1.8 x 10 .4 Low

greater 1.0 x 10 "t High 1 x l 0 "t to 1 x 10 "3 Med ium 1 x 10 "3 to 1 x 10 "s Low 1 x 10 "s to 1 x 10 -7 Very 10w

0.0016 m 2

~, 0.018

Figure 4 Water Permeability (ASTM D 5084)

0.016

u E 0.014 ,.,,,

,~ 0.012

.~ 0.01

0.008 Q

o.ooe I o.oo4 ~ 0.002

0 30% Alr- modlfled

Sand, llne sand

lx10-3 - - - to l x l 0 "6"

21'& Air- mocUfled

n ~ . stay modinml

ninV



ASTM TEST METHOD FOR PERMEABILITY OF ROCKS BY FLOWING AIR (D 4525)

The ASTM Test Method D 4525 measures the coefficient of specific permeability o f air, which can be used to predict expected flow rates of gas through fill materials. Permeability properties of fill used to encapsulate gas lines can be a critical material property from a safety point of view (Boston Gas Company 1996).

The right hand column of Table 5 depicts air/gas permeability test results conducted on two air-modified CLSM and one non-air-modified CLSM mix. The 30 and 21% air-modified CLSM mixes had coefficient of air permeability values of 18.2 and 1.3 m 2, respectively. The 30% air-modified CLSM mix had a magnitude five times faster air flow rate when compared to non-air-modified CLSM mix. (K = 18.2 m 2 versus 0.0016 m2). These test data confirm the material property versatility obtainable via the use of air-modified CLSM.

ASTM TEST METHOD FOR STEADY-STATE HEAT FLUX MEASUREMENTS AND THERMAL TRANSMISSION PROPERTIES BY MEANS OF THE HEAT F L O W M E T E R APPARATUS (C 518)

The thermal conductivity of a material is defined as the amount of heat that will flow through an medium when a temperature difference exits across the medium. Materials with low thermal conductivity values allow small amounts of heat flow and are called thermal insulators. Materials with large thermal conductivity values allow more heat to flow through the material under identical temperature gradients.

Table 6 depicts results of ASTM Test Method C 518 testing conducted on three 59-kg/m 3 (100-1b/yd 3) cement factor air-modified CLSM mixes. The mixes were tested under oven dry (0% relative humidity), saturated surface dry (SSD), and immersed in water conditions (Holometrix, Inc, 1993).

Results showed that under dry and SSD conditions, thermal conductivity properties for air-modified CLSM mixes were similar (0.42 to 0.48 W-m/K [2.9 to 3.4 Btu-irdhr-F-ft2]) and (0.51 to 0.53 W-m/K [3.5 to 3.7 Btu-in/hr-F-ft2]). However, when immersed in water, the thermal conductivity properties increased (1.1 to 1.7 W-m/K [7.8 to 11.9 Btu-in/hr-F-ft2]). Referring to the bottom of Table 6, thermal conductivity values for typical fill materials indicates that moisture content and material composition significantly impact thermal conductivity properties (Kersten 1992).

In summary, air-modified CLSM have good thermal insulation properties compared to typical fill materials. However, for both CLSM and typical fills, insulation properties tend to decrease as moisture contents increase.



TABLE 6--Thermal Conductivity (ASTM C 518) W/m-K (Btu-in./hr-F-ft 2)

0% Relative Saturated Immersed Air-modified CLSM Humidity- Surface Dry in water

Dry Condition (SSD)

37% Air-modified CLSM 0.43 (3.0) n/a 1.3 (9.1) 59 kg/m 3 (100 lb/yd 3) cement,

24.6% Air-modified CLSM 0.42 (2.9) 0.53 (3.7) 1.7 (11.9) 59 kg/m 3 (100 lb/yd 3) cement,

12.3% Air-modified CLSM 0.48 (3.4) 0.51 (3.5) 1.1 (7.8) 59 kg/m 3 (1 O0 lb/yd 3) cement,

Soil Type 2% Moisture 20% Moisture 80% Moisture

silts, clays 0.007 (0.05) 0.97 (6.87) 1.5 (10.71) sands 1.1 (7.69) 2.3 (16.5) .... gravel 1.4 (9.68) 2.9 (20.77) ....

ASTM TEST METHODS FOR FREEZING AND T H A W I N G COMPACTED SOIL-CEMENT MIXTURES (D 560)

ASTM Test Methods D 560 measure a fill material's ability to resist freeze-thaw cycling. The test procedure is relatively mild (12 freeze-thaw cycles), when compared to ASTM Test Method for Resistance of Concrete to Rapid Freezing and Thawing (C 666) which consists of 300 cycles. This is because relative to air-entrained 27.6-Mpa (4000- psi) concrete, both CLSM and typical fill materials will have minimal durability when exposed to surface freeze-thaw cycling (Gress 1996).

Referring to Table 7, testing was conducted on two air-modified CLSM mixes and one non-air-modified CLSM mix. Test results reveal the 21 and 30% air-modified CLSM mixes, while having significant volume loss at test completion, were significantly more durable than the non-air-modified CLSM mix. The non-air-modified CLSM mix (containing 1.4% entrapped air) suffered rapid freeze-thaw deterioration after only three cycles (1/3 of the sample broke off), and testing had to be discontinued after five cycles as a result of complete deterioration of the test sample.



TABLE 7--Freeze-Thaw (ASTM D 560) and Bleed (ASTM C 940)

Freeze-Thaw Fill Type Sample Volume Bleed

Loss (%) (%)

30% Air-modified CLSM 30 kg/m 3 (50 lb/yd 3) Cement,

148 kg/m 3 (250 lb/yd 3) Fly Ash 1333 kg/m 3 (2246 lb/yd 3) Sand 123 kg/m 3 (207 lb/yd 3) water

21% Air-modif ied CLSM 59 kg/m 3 (100 lb/yd 3) cement, 1556 kg/m 3 (2623 lb/yd 3) Sand 176 kg/m 3 (297 lb/yd 3) water

1.4% air CLSM 30 kg/m 3 (50 lb/yd 3) Cement,

148 kg/m 3 (250 lb/yd 3) Fly Ash 1619 kg/m 3 (2728 lb/yd 3) Sand 298 kg/m 3 (502 lb/yd 3) water

3 cycles-13% 5 cycles-27% 12 cycles-81%

3 cycles-8% 5 cycles-20% 12 cycles-82%

3 cycles-43% 5 cycles-47% 12 cycles-N/A

0%

N/A

2.4%

ASTM TEST METHOD FOR EXPANSION AND BLEEDING OF FRESHLY MIXED GROUTS FOR PRE-PLACED AGGREGATE CONCRETE IN THE LABORATORY (C 940)

Bleeding, or de-watering, can potentially occur concurrently with subsidence and segregation as the heavier constituents of the CLSM fall to the bottom of the fill. Excessive bleeding and subsidence may cause volume loss which may necessitate pouring a second lift or "topping out" with CLSM. This "falling out" of cementitous materials, can also result in a non homogenous in-place material. Air-modified CLSM mixes does not segregate, settle or bleed, resulting in a homogenous, cohesive CLSM which can be placed in one pass.

The right hand column of Table 7 depicts bleed testing per ASTM Test Method C 940 conducted on one 30% air-modified and one non-air-modified CLSM mix. The 30% air-modified mix had 0% bleed water, while the non-air-modified CLSM mix measured 2.4% bleed water at the top of the sample. Many CLSM specifications are now requiring 2.0% or less bleeding, which is equivalent to 20 mm per meter of depth (0.25 in. per foot o f depth).



REFERENCES

ACI Committee 229, "Controlled Low Strength Material (CLSM)," ACI 229R-94 Report, American Concrete Institute, Detroit, MI, July 1994.

"Controlled Density Fill (Flowable Fill) Position Report," Boston Gas Company, Maintenance Planning & Records Group, Boston, MA, Jan., 1996.

Gianetti, F., Rear, K., and Callander, I., "Non-Shrink Flowable Fill: A Revolutionary Cementitous Backfill Mixture Manufactured by Ready Mixed Concrete Producers," Presented at the 1 lth European Ready Mixed Concrete Congress, 21- 23 June, Istanbul, Turkey, Grace Construction Products, Cambridge, MA 02140.

Gress, D., "The Effect of Freeze-thaw and Frost Heave on Flowable Fill," Prepared for the New Hampshire DOT in cooperation with the US DOT and FHWA, Department of Civil Engineering, University of New Hampshire, Oct.1996.

Kersten, M. S., "Thermal Properties of Soils," University of Minnesota Institute of Technology Bulletin. No. 28, Minneapolis, MN.

Nelson, K. and Weber, R., "DaraFill Flowable FiI1-A Primer for Flowable Fill-Benefits of Flowable Fill," Grace Construction Products, Cambridge, MA, 1994, pp. 6-7.

"Report on the Apparent Thermal Conductivity and Thermal Resistance of Concrete," Report WRG-115, Testing Services Division of Holometrix, Inc., Oct. 1993.

Smith, A., "Controlled Low Strength Material," Concrete Construction. Vol. 36, No. 5, 1991, pp. 389-398.

Sowers, G., Introductory. Soil Mechanics and Foundations: Geotechnical Engineering. Macmillan Publishing Co., 1979, pp. 193-194.


Jon I. Mullarky, P. E]

LONG TERM STRENGTH GAIN OF CONTROLLED LOW-STRENGTH MATERIALS

REFERENCE: Mullarky, J. I., "Long Term Strength Gain of Controlled Low-Strength Materials," The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: Controlled low-strength material (CLSM) is commonly used as a backfill in utility trenches and other applications. The fill must gain sufficient strength to allow for early repaving and support traffic loads. However, the ultimate strength of the fill material must not exceed 50 to 200 psi (0.344 to 1.38 MPa) to allow for re-excavation of the trench should repairs be necessary. Concern over the long term strength gain of CLSM has prompted the National Ready Mixed Concrete Association to initiate a 2 year cooperative study that will investigate mix parameters that control long term strength. Comparisons of standard strength tests with removeability of the in-place fill will be made. The study will also evaluate ASTM provisional test methods for CLSM. Preliminary results are reported in this paper.

KEYWORDS: Controlled low-strength materials, flowable fill, strength gain, test methods

INTRODUCTION

CLSM, or flowable fill as it is commonly called, is a self-compacting, cementitious material used as backfill and other construction applications in place of compacted earth. According to ACI's definition, the material has a strength of 1,200 psi (8.27 MPa) or less. Typically in backfill applications where there is a possibility of re-excavation, strengths should be limited to a range of 50 to 200 psi (0.344 to 1.38 MPa). Other applications of the material include structural fills, insulating or isolation fills, pavement bases, conduit bedding, erosion control, void filling and bridge replacement. Projects in

~Vice President of Engineering, National Ready Mixed Concrete Association, 900 Spring Street, Silver Spring, MD 20910.

102


MULLARKY/LONG-TERM STRENGTH GAIN 103

each category are documented in the technical literature of American Concrete Institute, National Ready Mixed Concrete Association, Transportation Research Board and other organizations.

CLSM mixtures are manufactured using Portland or blended cement, fly ash, fine aggregate, water and admixtures. In many cases waste material such as foundry sand, slag, and non-standard aggregates are often used for CLSM mixtures.

The material must be flowable, gain some level of initial strength in the time dictated by the application, and achieve some required strength to carry service loads. Many applications require the fill to be easily removable, should the trench have to be reopened for utility repair. Often mixes that were thought to be easily removable have required the use of jack hammers and heavy duty excavating machines to remove the CLSM. Excessive strength gains can be caused by improper mix proportioning, long term pozzolanic reactions, or extra Portland cement being introduced in the batching process. Regardless of the cause, excessive strength gain can be an expensive problem for contractors and producers.

This paper reports the interim results of an investigation into the factors that influence the long term strength gain properties of CLSM. The study is being coordinated by the Engineering Division of the National Ready Mixed Concrete Association to develop more information about the properties of CLSM and the tests used to measure its physical properties. Test sites are being constructed at the Association's A. H. Smith Joint Research Laboratory (JRL) and more than 10 other sites at ready mixed concrete plants around the country. The study is scheduled to run for two years. Strength and removeability will be evaluated at 7, 28, and 90 days as well as one and two years after placement.

Research Objective

The objective of the cooperative research project is to investigate the long term strength gaining properties, and removeability of CLSM at later ages. The program is also designed to develop data to verify the applicability of proposed ASTM test procedures used to evaluate the flowability and early setting characteristics of CLSM.

Summary of Procedures

On September 6, 1996, despite heavy rains from Hurricane Fran, NRMCA Engineering Staff members and industry volunteers from five NRMCA member companies placed CLSM in two trenches at the Association laboratory site in Branchville, MD ~. Two mixtures were used. The first mix utilized a moist, high carbon fly ash and is marketed in the Washington DC area. The ash has a carbon content between 6 and 20 percent and is delivered to the batch plant with a moisture content of about 15 percent. The second trench was filled with a more typical CLSM formulation manufactured with cement, Class F fly ash and concrete sand. Table 1 shows the mix proportions for mixes used at the NRMCA site and at a producer site in the Atlanta area.

t Each trench was approximately 4 feet deep, 3 feet wide and 9 feet (1.9 by 0.9 by 2.7 meters) long and contained about 3 cubic yards (2.3 cu meters) of material.



Table 1. Mix Proportions for CLSM Placed at Two Test Sites

JRL T Materials East West North South Cement, lb./cu yd 50 48 75 50 (kg/m 3) (29.6) (28.5) (44.5) (29.6) Fly Ash, lb./cu yd 2370 305 100 500 (kg/m 3) (1,406) (180.9) (59.3) (296.6) Fine Aggregate, lb./cu yd 2375 1728 2113 (kg/m 3) (1,409) (1,025) (1,254) Water, gal./cu yd 59 54.5 45 55 (liters/m 3) (292) (270) (223) (272) Design Air Content 1% 8% 35% l 2%

The flowing material was batched into truck mixers at a ready mixed concrete plant, mixed, and delivered to the project site. At the site samples of the material was composited in accordance with ASTM PS 30-95, as the trucks discharged the CLSM into the previously excavated trenches. The following test were conducted on each sample:

ASTM PS 28-95 Flow Consistency

ASTM C 143 Slump

ASTM PS 29-95 Unit Weight

ASTM C 231 Air Content by the Pressure Method

ASTM C 1064 Temperature of Fresh Concrete

ASTM D 4832 Preparation of Cylinders

ASTM PS 31-95 Test Method for Ball Drop on Controlled Low-strength

Material

ASTM C 403 Time of Setting of Concrete Mixtures by Penetration Resistance

Both 4 by 8 in. (100 by 200 mm) and 6 by 12 in. (150 by 300 mm) cylinders were molded in plastic molds. The specimens were cured at the place where they were molded for the first 24 hours, then placed in the laboratory moist room for the balance of the curing period. Attempts will be made to recover and test cores from each trench at one and two years of age.



Tests of Fresh CLSM

The following comments are offered on the testing procedures:

Flow Consistency

The Provisional Standard Test Method for Flow Consistency of Controlled Low-strength Material (ASTM PS 28-95) utilizes a 3 by 6 in.(75 by 150 mm)cylindrical mold that is filled. After strike offthe mold is raised and the spread of the CLSM is measured. The test procedure requires the technician to obtain and carry special equipment into the field. Our experience indicates that 3-in. (75 mm) inside diameter cylindrical material is difficult to find. NRMCA used 3 in. (75 mm) steel cylinder molds, but not every lab has them available. Round scoops are more effective than fiat scoops in filling the mold. We found that the ASTM PS 28-95 test procedure was not as sensitive to consistency as the conventional slump test. Water and fine material ran out of the cylinder, leaving a sand cylinder standing. When the slump cone was used, the sand mix tended to flow with the water and fines.

Ball Drop Test

The Provisional Standard for Ball Drop On Controlled Low-strength Material to Determine Suitability for Load Application uses a modified "Kelly Ball" apparatus to test the early strength of the fill material. Test results are used to determine the readiness of the fill to accept loads. The procedure required special equipment (Kelly Ball) which is seldom used by most testing organizations. The equipment must also be modified to meet the requirements of the test. The test method should specify how far to lift the ball before it is dropped. Bleed water on the surface tended to splash on the operator when the ball impacted the surface. For this reason the test method should contain safety cautions requiring the use of eye protection when doing the test. In our opinion the Proctor penetration test (ASTM C 43) is as effective as the ball test in determining set, and correlates more directly with the strength of the material.

Unit We ight and Air Content

Unit weight of the CLSM samples was obtained using the procedures in ASTM PS 29- 95. The procedure worked well, however we would recommend that the container be tapped with a rubber mallet to aid in consolidation.

Preparation and Testing of Cylinders

Procedures detailed in Standard Test Method for Preparation and Testing of Soil-Cement Slurry Test Cylinders was used to mold and test CLSM specimens. Our experience indicates that tapping the cylinders aids in consolidation of the fresh CLSM.

Cylinders are extremely fragile, and must be handled very carefully, particularly those tested at 7 days. National Ready Mixed Concrete Association technicians used a table saw to cut through the sides and notch the bottoms of the plastic cylinder molds. This procedure allowed the molds to be peeled away with out damage to the specimen. The cylinders were capped with high strength gypsum plaster which worked well in our tests.



Our experience indicates that both 6 by 12 in. (150 by 300ram) and 4 by 8 in. (100 by 200 mm) cylinder molds can be used with no significant difference in indicated strength.

The test results for the mixtures placed in the four trenches are given in Table 2.

Table 2. Test Results for CLSM Placed at Two Test Sites

Trench Code NE NW TN TS

Flow in 6.25 5.75 8.25 12.5 (ASTMPS 28) (mm) (156) (144) (204) (316) Slump in 8.75 9 9.5 I 1.5 (ASTM C 143) (mm) (216) (228) (240) (288)

Spread in 16.13 20.25 NA NA (mm) (402) (504)

Unit Weight lb/cu ft 97.99 128.96 98.8 115.6 (kg/m 3) (1570) (2066) (1583) (1852)

Air % 1.1 0.2 29 6.4 ~ 84 78 65 66 Temperature (~ (29) (26) (18) (19)

Cylinder Strength (6x 12 in) (150x300 mm)

7 Day psi 30 23 NA NA (MPa) (0.21) (0.16)

14 Day psi NA NA 12 19 (MPa) (0.08) (0.13)

28 Day psi 50 46 16 20 (MPa) (0.34) (0.32) (0.11) (0.14)

90 Day psi (MPa)

59 (0.41)

114 (0.79)

37 (0.26)

22 (0.15)

Strength Gain

At this writing little of the strength gain data is available. Results up to 90 days from two sites are shown in Fig 1. Material NW has shown a significant strength gain between 28 and 90 days. Materials NE and TS have shown relatively little long term gain. The CLSM placed in trench NW is a conventional mix with 40 pounds (18.14 kg) of Portland cement, 305 pounds (1.588 kg) of Class F Fly Ash and 2,375 pounds (1077 kg) of concrete sand. Material NE contains 50 pounds (22.7 kg) of Portland cement and 2,370 pounds (1075 kg) of conditioned fly ash per cubic yard. Material TS has a high air content (12%) and a high (500 lb/cu yd or 297 kg/m 3) fly ash content. Examination of these early results seems to indicate that air and fly ash content are significant factors in controlling long term strength gain of CLSM.



150

~. 100

50

C L S M Strength Gain JRL Series 227

, NW

�9 Ts :

I I I I

7 14 28 90 Age, Days

0.8

0.6 ~

0.4 r~

0.2

Fig. 1 Strength Gain of CLSM

All four trenches were easily excavated with a small (90 horsepower) backhoe and hand shovels. Future work with data from one and two year tests will attempt to correlate removeability, and penetration with strength and mix properties.

CONCLUSIONS

The study reported in this paper is still on going. Only preliminary conclusions, based on experiences at two test sites can be drawn. The project demonstrated conclusively that CLSM materials can be placed successfully under hurricane conditions. Several improvements in the Provisional Test Procedures were noted. Preliminary strength data indicates that air content and fly ash content are significant factors in the control of long term strength gain.


H. Kent Hepworth, 1 J. Soni Davidson, 2 and Jennifer L. Hooyman 3

ADMIXTURE ENHANCED CONTROLLED LOW-STRENGTH MATERIAL FOR DIRECT UNDERWATER INJECTION WITH MINIMAL CROSS- CONTAMINATION

REFERENCE: Hepworth, H. K., Davidson, J. S., and Hooyman, J. L., "Admixture Enhanced Controlled Low-Strength Material for Direct Underwater Injection with Minimal Cross-Contamination," The Design and Application of Controlled Low- Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: Commercially available admixtures have been developed for placing traditional concrete products under water. This paper evaluates adapting anti-washout admixture (AWA) and high-range water-reducing admixture (HRWRA) products to enhance Controlled Low-Strength Materials (CLSMs) for underwater placement. A simple experimental scale model (based on dynamic and geometric similitude) of typical grout pump emplacement equipment has been developed to determine the percentage of cementing material washed out. The objective of this study was to identify proportions of admixtures and underwater CLSM emplacement procedures that would minimize the cross-contamination of the displaced water while maintaining the advantages of CLSM. Since the displaced water from radioactively contaminated systems must be subsequently treated before release to the environment, the amount of cross-contamination is important for cases in which cementing material could form hard sludges in a water treatment facility and contaminate the in-place CLSM stabilization medium.

KEYWORDS: tank stabilization, controlled density fill, Controlled Low-Strength Material, admixture, anti-washout admixture, water reducing admixture, flowable mortar, low density material, unshrinkable fill, void filling

1 Emeritus Professor of Mechanical Engineering, Northern Arizona University; permanent address: 206 Dusty Lane, Powell, TN 37849.

2 Senior Mechanical Engineer, Science Applications International Corporation, 301 Laboratory Road, Oak Ridge, TN, 37830.

3 Student, Marquette University, Milwaukee, WI (Oak Ridge National Laboratory summer intern); permanent address: 34 Rivers Run Way, Oak Ridge, TN 37830.

108


HEPWORTH ET AL./DIRECT UNDERWATER INJECTION 109

This paper addresses development of a suitable stabilizing packing material for interim in-situ remediation of tanks, vaults, and other underground structures with partial to wholly flooded void spaces. To satisfy regulatory requirements, all subterranean void spaces would need to be filled with a stabilizing material. Since waste management and environmental restoration interim remediation work often involves stabilizing contaminated structures, the filling medium of choice should possess characteristics that (1) minimally interfere with future dismantlement of a treated facility, (2) exhibit reasonable structural stability, (3) contribute to the well-being of the environment, and (4) cost less than other viable alternatives.

This study investigated commercially available admixtures to enhance a locally available fly-ash-based Controlled Low-Strength Material (CLSM) grout mixture and an injection procedure to allow placement of this material underwater. (Note: the acronym CLSM is a generic term referring to a wide variety of cementitious-based materials; however, this paper generally refers to CLSM formulated principally of sand, fly ash, cement, and water.) During the injection process, CLSM should accomplish the following: (1) displace the water, causing it and accumulated soft sludges (sp gr < 1.5) to float at the liquid grout interface, (2) maintain its self-leveling characteristic (that is, fill voids below the interface), and (3) hydrate to its designed low strength and low permeability. Operationally, the displaced solution and sludges are to be simultaneously removed as they are displaced and moved closer to the tank's access port. This admixture will assist in the interim remediation of liquid low-level (radioactive) waste inactive tanks and underground storage tanks containing difficult-to-remove aqueous-based inventories.

This study evaluated and selected admixtures for optimizing underwater injection of CLSM. Candidates tested are anti-washout admixtures, water-reducing admixtures, and pump-assisting admixtures. The objective is to prevent or mitigate cross contamination by investigating types and proportions of admixtures and underwater CLSM emplacement procedure.

Background

The U.S, Army Corps of Engineers has sponsored programs to develop a way for underwater (ocean, brackish, or freshwater) emplacement of high-strength concrete materials. The strength of the concrete must be maintained while ensuring water and concrete contamination control. These programs have produced additives that are adequate to allow the emplacement of concrete under tidewater conditions and to line or repair locks, dams, or canals without curtailing boat traffic or draining the facility.

CLSM is a cementitious material recognized by the American Concrete Institute (ACI), with oversight responsibility assigned to Committee 229. CLSM is defined by Cement and Concrete Terminology (ACI 116R) as material that exhibits "an unconfined ultimate compressive strength of 1,200 pounds per square inch (psi) [8.3 MPa] or less." In fact, most current CLSM applications specify compressive strengths of 2 MPa (300 psi) or less. This lower strength specification is to allow for future excavation of the material. CLSM is a member of the grout class of materials, is self-compacting, and was developed to replace compacted soil as a backfill medium. Traditional compaction of soil is labor intensive and presents difficulty with maintaining adequate quality control,



whereas CLSM achieves its properties through the design and control of its constituent mix and hydration process. Its composition uses traditional concrete grout constituents: portland cement, sand, and water, with fly ash an added ingredient. This CLSM formulation benefits the environment since it makes use of a previously wasted by- product from coal-fired electric utility power plants. CLSM has been demonstrated to be very geologically stable (does not swell or contract like bentonite clays), is reversible (can be removed by traditional excavation methods), and maintains a low permeability to groundwater intrusion.

CLSM has been successfully used at the Oak Ridge National Laboratory (ORNL) in the interim remediation of several tanks requiring governmental regulatory approved processes. Empty tanks with cut and capped pipelines were filled to capacity with CLSM. I f a tank had been removed from an underground vault, then vault space was satiated with CLSM. Based on certified testing laboratory sample results and the authors' experience with the ORNL fly-ash-based CLSM formulation, there are many advantages of CLSM materials for environmental restoration stabilization applications:

1. It is economical and readily available. 2. It is easy to install and self-leveling and fills all void spaces (flows or pumps

or both with ease). 3. It does not settle after hydration (during placement and hydration process,

CLSM settlement is approximately 1 cm per vertical meter [1/s in. per vertical foot]).

4. The hydrated material is nonhazardous to the environment. 5. It possesses low permeability of 1.5 x 10 .5 cm/s (9.84 • 1 0 -6 in/s). 6. It is easily remediated in the future (excavatable with conventional digging

equipment).

Hence, CLSM is useful for interim remediation or stabilization by entombing contaminated or radioactive facilities and equipment or both.

Stabilization o f water-shielded or -inundated structures--In many instances during restoration of nuclear facilities, water is used to shield a radioactive hazard. To protect workers and delicate equipment from radioactive components, water is frequently used as a radiation shield or barrier. Shielding examples are (I) reactor pools and canals used to transport or store spent nuclear fuel elements, irradiated and activated materials, and experimental apparatus, and (2) canals used to transport contaminated filters removed from facility ventilation systems. (Note: with age, facility surfaces become contaminated [for example, dissolved contaminants diffuse into a pool's concrete walls].)

I r a structure is inundated, it may be impractical or costly to remove water before installing CLSM as a stabilizing agent. It is impractical and potentially hazardous to the environment to isolate breached underground tanks located below the groundwater table. Groundwater will replenish water pumped from the tank, or artificial lowering of the water table will permit tankage water and accumulated sludge to migrate, further polluting the environment.



An alternative to removing water or tankage solution is to place simultaneously CLSM at the bottom of the confined space and pump or bleed off displaced water and accumulated sludges. However, in its uncured or plastic state, traditional CLSM components are quite susceptible to suspension in water, so its injection under water allows a cross-contamination via water migrating into and cementing products washing out of the CLSM. During material injection, turbulence or mixing is an aggravating influence for this undesirable interchange and should be minimized.

Program Objectives

Eliminate or minimize cross-contamination of tankage water with emplaced CLSM. This is important since cementing materials carried with displaced contaminated water solution to storage tanks or the treatment facility could result in formation of a hard sludge deposit. Furthermore, contamination of emplaced CLSM stabilization material would leave a legacy remnant, and if remediated by excavation in the future, the CLSM would be treated as a higher level radioactive solid waste.

2. Maintain the following advantages of the commercially available ORNL formulated fly-ash-based CLSM:

�9 Low permeability (< 1.5 • 10 .5 cm/s) with a specific gravity o f - 2.1 �9 Future remediation by excavation using standard digging implements �9 Void filling and ease of placement in cramped, contaminated, or hard-to-access

facilities (that is, tanks) �9 Low cost and availability of emplacement technologies and equipment

Definitions

�9 Anti-washout Admixture (A WA) [1]--A water-soluble polymer that physically binds the mixing water with the cementitious materials. AWAs are principally designed to enhance the stability of concrete used in underwater applications.

�9 Bleeding [2]--The separation of liquid constituents from the concrete product while it is in a plastic state (1. external bleeding - separation of liquids from the concrete interface, 2. internal bleeding - collection of liquids in channels or around embedments).

�9 Consistency [3]--A measure of the flowability of a cement product while in its fluid state. This study used the modified flow consistency test procedure (per the ASTM Standard Test Method for Flow Consistency of Controlled Low Strength Material [D 6103-97]).

�9 High Range Water Reducing Admixture (HRWRA) [ / ] - -An additive designed for concrete products to maintain high fluidity without impairing strength or durability.

�9 Permeability (per the ASTM Standard Test Method for Measurement of Hydraulic Conductivity of Saturated Porous Material Using a Flexible Wall Permeameter [D 5084-90] and the Corps of Engineers Test Method for Permeability of Concrete Using Triaxial Cell [CRD-C 163-92])---A material coefficient, k, relating the flow of a



fluid through a porous medium.

where: k Q A - dh

de

Permeability is defined as follows:

k - Q A dh

de

permeability coefficient (cm/s) volume flux (cm3/s) normal cross-sectional flow area (cm 2)

fluid piezometric gradient (h- piezometric head [cm], and Q - direction of flow spatial coordinate [cm])

�9 Pump Assisting Admixtures [3]--A polymeric viscosity regulator additive for grout types of concrete products to enhance their transportability through pumps.

�9 Washout--As used in the paper, the mass of the filterable solid fines (cementitious and sand) components flushed out and suspended in the surrounding water medium when a cement product is injected underwater.

Spec i f i ca t ions , T h e o r y , A n d P r o c e d u r e s

Admixtures

This study evaluates commercially available AWA, HRWRA, and pump-assisting admixtures applied to very flowable CLSM. Khayat [4] cautions industrial users of AWA and HRWRA products to ensure chemical compatibility when used in combination. The products of two suppliers 4 were chosen for this investigation:

Master Builders, Inc. 23700 Chagrin Blvd. Cleveland, OH 44122 (216) 831-5500

AWA - Rheomac | UW 450 (chemical family: modified cellulose ether)

HRWRA - Rheobuild | 2000B (chemical family: melamine polymer)

Sika Corporation 201 Polito Ave. Lyndhurst, NJ 07071 (201) 933-8800

AWA - Sikament | 100 SC (chemical family: sulfonated naphthalene and melamine polymer)

4 Reference to any specific commercial product, process, or service by trade name, trademark, manufacture, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the U.S. Government or agency thereof.

| Rheomac and Rheobuild are registered trademarks of SKW-MBT.

| Sikament is registered trademark of Sika Corporation,


HEPWORTH ET AL./DIRECT UNDERWATER INJECTION 1 13

HRWRA - Sikament | 10 ESL (chemical family: sulfonated vinyl copolymer, sodium salt)

Pump - Sika Pump VP (chemical characterization: water-based polymer for viscosity regulation)

Obtaining a National Environmental Policy Act - Categorical exclusion approval substantially reduced the time authorized for the experimental portion of the program. Hence, to complete the program on schedule and to ensure compatibility, manufacturers' products were not intermingled.

Test Procedures, Equipment, and Apparatus

Two tests were conducted for each CLSM test mixture: a consistency test and a washout test.

Modified Flow Consistency Test [3, ASTM D 6103-97]--Place an open-ended cylinder (7.62 cm [3 in.] in diameter by 15.24 cm [6 in.] long) vertically on a smooth level surface. Fill the cylinder flush to its top with CLSM. Lift the cylinder vertically, allowing CLSM to flow onto the level surface. Good flowability is achieved if there is no noticeable segregation and if the material spreads at least 20 cm (8 in.) in diameter.

Washout Test - -There is a standardized washout test for relatively high-strength stiff (low-slump) concrete (Army Corps of Engineers Test Method for Determining the Resistance of Freshly Mixed Concrete to Washing Out in Water, CRD C 61 [5, 6]). This test consists of filling a perforated steel basket with a 2-kg (4.4-1b) sample of fresh concrete, then allowing the basket to free-fall through a test column filled with 1.7 m (5.6 ft) of water. After three drop tests, the loss of mass is measured. This washout test is not an adequate model for the free-flowing CLSM required to fill tanks, vaults, and canals.

The consistency test diameter is suggested to be 30 cm (12 in.) or above to ensure adequate flow in filling inundated tanks and voids during injecting underwater. All constituent CLSM materials used in these tests are sifted through an ASTM number 16 Sieve (with a 6-per-cm [16-per-in.] mesh). A test rig that models the salient aspects of the pumping and injection process for CLSM into a tank with a quiescent water inventory was developed. The test fixture devised uses geometric and dynamic simulation to model a realistic, but severe, injection process.

Design for CLSM Anti-Washout Test Rig

The test rig is approximately 1/8 scale. Commercial grout pumps typically use a 6.35-cm (2.5-in.) internal diameter hose to deliver approximately 95 L/min (25 gal/min) of grout (that is, 8 min to pump 0.75 m 3 [one cubic yard] of grout). Note that 95 L/min

was baselined since water removal is to occur simultaneously with CLSM injection, and



most ORNL liquid transfer lines are designed as gravity drains constructed of 5-cm [2-in.] schedule 40 pipe. Grout pumps are of positive displacement design, resulting in a pulsating flow with operating frequency dependent on drive engine speed. To simulate this pulsating action, a positive displacement peristaltic pump was used. The peristaltic pump selected is a Watson Marlow PumpPro model DPM, operating with an 8.0-mm (0.315-in.) internal diameter tube.

The Watson Marlow PumpPro DPM peristaltic pump operating speed range is user programmable to operate from 3 to 300 r/rain and when equipped with the 8-ram bore Marprene tube, it provides from 30 mL/min to 3.0 L/min. Marprene tubing was selected for use with this pump because of its elasticity. Considering the flowability range of the CLSM to be tested, the operation of the pump was programmed at a speed of 200 r/min, and the quantity pumped was 2 L. These settings provided a pump volume flow rate of approximately 2 L/min.

Geometric Similarity---Speed of 94.6 L/min (25 gal/min) of CLSM through a 6.35-cm (2.5-in.) internal diameter grout pump transport tube is:

(94.6 L/min) (103 cm3/L) 191o = = 49.7cm/s (1.63ft/s)

(60 s/min)( ~ (6"35)z c m 2 / 4

The speed of 2 L/min (0.528 gal/min) of CLSM through an 8-mm (0.3125-in.) internal diameter peristaltic pump Marprene tube is:

IV[p = 66.3 crrds (2.18 fi/s)

Geometric Similarity = - - 191o 49.7 = - 0.75 [PIp 66.3

Dynamic Similitude--Based on the Reynolds Number of CLSM flowing through a transport tube:

Inertial Forces Reynolds Number (NRc) = Viscous Forces

_ V D _ 4Q v ~ D v

where: V - fluid speed, Q - fluid volume flux, D - tube internal diameter, and v fluid kinematic viscosity.

Reynolds Number (NRe)O Dynamic Similitude =

Reynolds Number (NRo)p


HEPWORTH ET AL./DIRECT UNDERWATER INJECTION 1 15

4 Qo

Do VCLSM Qo De 4Qp QpD o

Op VCLSM

- 5.95

Both the geometric similarity and dynamic similitude scale factors are within one order of magnitude, indicating that the peristaltic pump apparatus should adequately model a grout pump.

Washout Experimental Apparatus

Figure 1 illustrates the model flow apparatus to measure quantitatively and observe qualitatively washout during an injection process. The flow apparatus has been constructed to simulate a proposed tank remediation fill process. The model is designed to inject CLSM continuously at the rate of 2 L/min through an 8-ram tube. The model simulates an injection process as modeling (1) the start of an underwater injection process by allowing a 2.5-cm (1-in.) free-fall of the trial mix jet stream and (2) the free flow of the CLSM as it spreads by causing the trial mix stream to flow down a 30.5-cm (12-in.) slide inclined at 40 ~ The slide teen terminates into a landing region designed to accumulate 2 L. The injection process provides a flow speed of 0.66 m/s for a 1-min period. This design exposes an approximate trial mix surface area of 0.5 m 2 to the water in the test tank during the trial mix's free-fall and slide. The landing area's configuration allows determination of the equilibrium slope of the test mixture's free surface. This measurement provides a quantitative comparison of the flowability of the test mixtures underwater. To determine the mass fraction of trial mix washed out, the experimental apparatus is equipped with a sampling tube which is elevated 2.5 cm (1 in.) above the slide. The sample tube draws fluid through two orifices drilled in the tube. These ports are located 25 cm (10 in.) down the incline from the injection port. The sampling tube is connected to a siphon leading to a 2-L sample collection beaker.

Results

Mass Washout Percent Determination and Explanation

During a washout test, a cloud (more aptly termed a fog or smog layer) is formed by the particulate matter and the AWA and HRWRA compounds in the CLSM. The cloud is apparently of higher specific gravity than the surrounding water since it forms a definite and clearly visible interface.

The density of the cloud layer varies slightly from bottom to top; however, for analytical purposes the cloud was assumed to be represented by the integrated sample drawn from the sample tube during the washout test. (Note: the tank has been very carefully calibrated in volume percent, 0% at the bottom to 100% at the fill level.) The



eed Hopper)

I I Pump I

/ Ple~glas Tank

Wate~vel~

L~ CLSM Free r ~ Fall Glass Slide

wash ,e.

AR~rattm~ ~ - - ~ /A~tmln~nt Leveling Adjustn~nt ~ /Mechanism Mechan'sm\ /~ \ \ /

~4o ~ I ~ l l l l l l l l l l l l l l l l l l l l l l l l l l l l l J Ulllll l l l l l l

FIG. 1--Washout experimental test apparatus.

incompressible continuity equation was applied to account for the small variability in quantity of CLSM pumped from test to test. This variability is explained by the CLSM's apparent viscosity variation and the pump's reliance on tubing elasticity to draw CLSM into the tube volume from the supply hopper during a pumping cycle (intake time < 0.15 s per occluding stroke).



A comparative washout mass is determined by the following volume balance:

Washout Mass Fraction (%) = Projected CLSM Mass Washout CLSM Mass Injected

(Filtered Washout) (Tank Clouding) (Tank Volume [Vol.]) (Vol. Siphoned)(CLSM Density)[Vol. Siphoned - (A Tank Level)(Tank Area)]

(Filtered Washout) (Tank Clouding) (0.0067)

2 - (A Tank Level) (1.226)

where: filtered washout is in grams, tank clouding is in percent, and tank level is in centimeters.

The washout mass was collected and filtered to determine the mass of washout collected. Filters were thoroughly dried and weighed before and after each test.

Determination of the Relative Free Surface Slope

The relative slope of the free surface was measured after each test as water was siphoned from the tank. An indicator mark was located on the tank 7.6 cm (3 in.) from its right end. As the water was slowly siphoned from the tank, its level was measured as the CLSM free surface was exposed at the indicator mark and again as the surface was exposed at the tank's right end.

The measured difference is the CLSM rise, which is divided by a run of 7.6 cm (3 in.). The appearance of the surface was noted to ensure minimal segregation and uniformity of the exposed surface, with any anomalies noted on the data sheet.

Trial Mix Design

This study focuses on the consistency and washout behavior of CLSM. The test sequence was as follows: (1) measure and blend the trial mix constituents, (2) perform the consistency evaluation, and (3) execute the washout trial. The CLSM formulation used for these tests was chosen to provide similar compressive stress strength (o = 690 kPa [100 psi]) and permeability (k = 1.5 x 104 cm/s [9.84 x 10 .6 in/s]), which is typical of the commercial product used to remediate empty tanks and vaults at ORNL. Typically, the CLSM constituents' blend, per 0.75 m 3 (cubic yard), is 22.7 kg (50 lb) of portland cement, 272.4 kg (600 lb) of Type F fly ash, and 1089.6 kg (2400 lb) of dry sand. Masonry sand was substituted for the coarse concrete sand because of the small size of the peristaltic pump transfer tube. Water and admixtures were varied to determine the effects on consistency and washout. Typically, these mixtures consist of the following per cubic yard: 22.7 -* 45.4 kg (50 -~ 100 lb) portland cement, around 272 kg (600 lb) of Type F fly ash, 1090 ~ 1270 kg (2,400 ~ 2,800 lb) of cement sand, and 170 ~ 227 L (45 -* 60 gal) of water.



To minimize waste, the quantity of each test mixture was designed to produce 3 L. This quantity was sufficient to perform all required tests, with enough residual to ensure that some spillage could be tolerated. This test eliminated the following variables by fixing them as constant throughout the test matrix:

Constituent Portland cement (Type I, II) Fly ash Dry masonry sand

Mass Quantity 0.0708 kg 0.8544 kg 3.1250 kg

Note: The fly ash used is Type F obtained from the Tennessee Valley Authority John Sevier Power Plant. Each constituent was oven dried (12 h at 120~ [250~ and thoroughly sifted through an ASTM No. 16 Sieve before being added to test mixture, according to the procedure prescribed in the test plan. Water, HRWRA, and AWA were carefully measured and added to produce the quality control required for the test.

CLSM Test Results'

The results are arranged in Tables 1 through 4 by similar modified flow consistency test diameters (nominal diameter 4- 3 cm or 1 in.).

TABLE 1 - -Tes t results with nominal 25-cm (lO-in.) consistency flow diameter.

Consistency Tank Washout Diameter AWA HRWRA

Mixture Water Clouding Fraction # (cm) (in.) (mL) Type Mass (g) Type Mass (g) (%) (%)

4 25.4 10 1,000 . . . . . . . . . . . . 50 0.809

10 25.4 10 700 UW450 14.6 2000-B 18.65 33 0.013

16 27.9 11 1,000 UW450 14.6 2000-B 7.6 20 0.021

19 27.9 11 1,100 UW450 14.6 . . . . . . 20 0.013

22 22.9 9 800 100 SC 14.0 10 ESL 7.4 60 0.830

30 27.9 11 900 100 SC 18.0 10 ESL 3.6 70 1.616

TABLE 2 - -Tes t results with nominal 30-cm (12oin.) consistency flow diameter.


Water Clouding Fraction (cm) (in.) (mL) Type Mass (g) Type Mass (g) (%) (%)

Mixture #

3 30.5 12 1,050 . . . . . . . . . . . . 50 1.190

7 30.5 12 815 UW450 14.6 2000-B 18.65 50 0.020

15 33.0 13 1,100 UW450 14.6 2000-B 7.6 25 0.042

21 30.5 12 1,100 UW450 14.6 . . . . . . 20 0.214

33 30.5 12 1,000 100 SC 22.0 . . . . . . 35 0.318

36 33.0 13 950 100 SC 22.0 10 ESL 7.4 25 0.042



TABLE 3~Test results with nominal 35-cm (14-in.) consistency flow diameter,

Mixture #

Consistency Diameter

(cm) (in.)

AWA HRWRA Tank Washout Water Clouding Fraction (mL) Type Mass (g) Type Mass (g) (%) (%)

2 38.0 15 1,200 . . . . . . . . . . . . 75 4.772

6 35.6 14 900 UW 450 14.6 2000-B 18.65 25 0.114

18 35.6 14 1,200 UW450 14.6 . . . . . . 40 0.200

26 35.6 14 1,000 100 SC 14.0 10 ESL 7.4 50 0.917

27 35.6 14 1,000 100 SC 18.0 10 ESL 7.4 20 0.011

29 35.6 14 1,100 100 SC 18.0 . . . . . . 30 0.073

TABLE 4--Test results with nominal 40-cm (16-in.) or greater consistency flow diameter.

Consistency Diameter AWA HRWRA Tank Washout

Water Clouding Fraction (cm) (in.) (mL) Type Mass (g) Type Mass (9) (%) (%)

Mixture #

1 45.7 18 1,300 . . . . . . . . . . . . 75 6.082

5 40.6 16 1,100 UW450 14.6 2000-B 18.65 25 0.152

17 38.0 15 1,300 UW 450 14.6 . . . . . . 50 0.616

25 38.0 15 1,100 100 SC 14.0 10 ESL 3.7 40 0.124

One test was conducted using an admixture "under development" by the manufacturer to enhance pumpability to determine its effect on washout. The results of the test using the same test mixture as #27 with the addition of the Sika Pump are shown in Table 5.

TABLE 5~Tes t results using pump enhancement mixture.

Consistency Sika Tank Washout Mixture Diameter Water AWA HRWRA Pump Clouding Fraction

# (cm) (in.) (mL) Type Mass (g) Type Mass (g) Mass (g) (%) (%)

35 35.6 14 1,000 100 SC 18.0 10 ESL 7.4 3.6 55 0.712

Washout tests were also conducted using the test rig to simulate a proposed direct CLSM injection technique for remediation of an inundated vault. These tests were executed to determine the washout resulting from placing the fill tube near a comer of the vault. The process is as follows: ( l ) start the injection process to build a mound of admixture enhanced CLSM, (2) allow the injecting material to embed the fill tube within the mound and, (3) continue the fill process until the prescribed quantity of material has been pumped. These tests were conducted using optimized anti-washout admixtures from each of the two suppliers' products (Mixtures 7 and 27) and are shown in Table 6.


1 2 0 CONTROLLED LOW-STRENGTH MATERIALS

TABLE 6 - - T e s t results with direct injection.


Mixture Water Clouding Fraction # (cm) (in.) (mL) Type Mass (g) Type Mass (g) (%) (%)

39 33.0 13 815 UW 450 14.6 2000-B 18.65 30 0.043

40 35.6 14 1,000 100 SC 18.0 . 10 ESL 7.4 1 0.000

Discussion of Results

The tests indicate that the admixtures enhance the resistance of CLSM to washout. However, the quantity and ratio of AWA to HRWRA are relatively sensitive. The filling of a tank, vault, or canal to a satiated condition requires a very flowable material. When the structure to be remediated is equipped with internal appurtenances and is also inundated, the property of flowability is of paramount importance. The specific gravity of the CLSM is approximately 2.1, and when immersed in water (sp gr = 1.0), the forces of gravity that drive self-leveling are reduced to approximately half that o f an air environment. An admixture-enhanced CLSM mixture with a modified flow consistency diameter of 30 to 35 cm (12 to 14 in.) should allow an inundated tank, vault, or canal to be filled to satiation (without requiring the labor intensive task of continually moving the injection tube to reach and fill all "nooks and crannies" within the structure). As the washout data indicates, the admixtures will reduce washout by a factor of approximately 50 and can be essentially eliminated by direct injection (or an equally careful placement technique).

Observation of the CLSM during the mixing process and the execution of the consistency tests indicated that admixtures favorably affect the flowability of the enhanced material. During mixing, even a very small quantity of HRWRA immediately and abruptly causes the material to behave much more "liquid." However, the addition of the AWA somewhat reverses this effect. During the consistency portion of all the baseline tests, the CLSM would quickly "plop" to its equilibrium diameter. However, the admixture-enhanced CLSM would flow smoothly and deliberately toward the equilibrium diameter, sometimes requiring 20 s to reach its final "ceasing of creep" diameter. The admixtures from both suppliers exhibited this behavior in all admixture-enhanced tests (with or without HRWRA).

An interesting phenomenon occurred during all the washout tests. As pointed out, the test tank was filled and allowed to settle to a quiescent state before the injection process was initiated. During the injection phase of the test, a cloud (or fog) raised from the injected material and spread evenly throughout the tank, causing a stratification of adulterated water from the clear water. A distinct interface was observed which separated the two regions. It appeared that the adulterated water was of slightly higher specific gravity, although tests were not conducted to verify this. The color of the adulterated water varied depending on the quantity of washed-out material (from very dark gray to a light white/gray coloration). The same color intensity remained until the test was terminated, allowing approximately 15 min of observation. It appeared that the heavier



solid suspended materials rapidly settled, but the lighter materials seemed to hang in equilibrium. A sample from Mixture 7 was collected in a bottle and observed for several days. During this period some settlement occurred, but the white/gray fog remained. No confirmation was conducted, but it is surmised that this white/gray cloud resulted from admixture washout (the admixtures all have a sp gr > 1.0). During direct injection test 40, very little clouding occurred. Study of the Material Safety Data Sheet indicates that the constituents of the admixtures present little hazard to the environment or human safety, particularly in the concentrations present in the fog layer. Verification may require a separate evaluation.

Conclusions

Fly-ash-based CLSM is used routinely at ORNL with its placement, formulation, and material properties specified and controlled for each application. Anti-washout and high- range water-reducing admixtures have been designed, developed, and used to control washout and to improve the water-to-cement ratio with high-strength concrete materials. However, little investigation has occurred for using these admixtures in a low cementitious content fly-ash-based CLSM to minimize washout. The test rig developed for this study optimizes the important parameters affecting washout of cementitious materials from CLSM during its injection into an inundated tank, vault, or canal. The model was designed and built to simulate the procedures proposed to remediate inundated tanks, vaults, and canals at ORNL. Particular attention was focused on the compatibility of geometric and dynamic similitude of the model, with available commercial equipment proposed for the injection process of admixture-enhanced CLSM.

Test results indicate that washout contamination of the inundated tank fluid and cross-contamination of the CLSM with tankage inventory will be minimized by using admixture-enhanced CLSM. A ground rule for this program is that the CLSM developed must maintain a free-flowing characteristic. This allows the material to satiate the structure's volume by filling all voids and appurtenances and by effectively sealing all entrances and exits. An admixture-enhanced CLSM with a modified flow consistency test diameter of 30 to 35 cm (12 to 14 in.) should meet this stipulation for current tank, vault, and canal remediation applications. Trial mixtures 7 and 27 proved to be reproducible and resulted in minimized washout. Table 7 provides an extrapolation of each of these tests' constituents to a cubic yard commercial batch.

In specifying a commercially supplied admixture-enhanced CLSM, it is recommended that the quantities of cement, fly ash, dry sand, AWA, and HRWRA be specified by weight or volume and that the desired modified flow consistency test diameter be specified. The commercial supplier of the admixture-enhanced CLSM determines the quantity of water to be used. To control all parameters during this program, all the trial mix tests used very dry constituents. Each of the dry constituents was carefully sifted through a sieve before being weighed and mixed. The commercial supplier will use raw materials as they exist at the batch plant, which implies that they will contain an appreciable amount of water (for example, concrete sand normally contains about 2% water by weight).



Table 7--Extrapolation of test results to commercial batch parameters.

Constituent #7 Test #27 Test

Modified Flow Consistency Test 12 in. 14 in.

Portland Cement (Type I, or II) 55 Ib 55 Ib

Fly Ash (Type F) 650 Ib

Dry Concrete Sand 2400 Ib (manufactured or river run)

Water 625 Ib (75.0 gal)

Water/(Cementitious Materials) 0.88

Admixtures Commercial Supplier Master Builder, Inc.

650 Ib

2400 Ib

765 Ib (91.7 gal)

"[ .09

Sika Corporation

Anti-washout Admixture Rheomac UW 450 Sikament 100 SC 11.18 Ib (1.1 gal) 10.7 Ib (1 gal)

High Range Water Reducing Rheobuild 2000-B Sikament 10 ESL Admixture 14.3 Ib (1.36 gal) 5.67 Ib (0.61 gal)

An important parameter controlling the washout is the ratio of the quantity of AWA to HRWRA and the total mass ratio of admixtures (AWA plus HRWRA) to the cementitious materials (cement plus fly ash):

MAWA + MHRWe'A : Admixture Mass Ratio Mcement + MFIy Ash

Therefore, if it is deemed necessary to change the strength of an admixture-enhanced CLSM by adding or reducing the cement or fly ash, then holding this mass ratio constant should provide similar washout characteristics to the original mix.

Acknowledgments

This work was performed at the Oak Ridge National Laboratory, Oak Ridge, Tennessee and was supported by the U. S. Department of Energy under Contract DE-AC05-84OR21400. Neither the U. S. Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. The views and opinions of the authors expressed herein do not necessarily state or reflect those of the U. S. Government or any agency thereof.

The authors acknowledge the assistance provided by Pam Groves, Larry Hawk, Peter Souza, and Jasminn Pricer, all of the Oak Ridge National Laboratory, for their assistance in the testing. The authors also acknowledge Master Builders, Inc. and Sika Corporation for providing comments on the use of their products and for participating in the washout and consistency testing of their products.



References

[1] Khayat, K. H. and W. T. Hester, "Evaluation of Concrete Mixtures for Underwater Pile Repairs," Cement, Concrete, and Aggregates, Vol. 13, No. 1, Summer 1991, p. 32.

[2] Khayat, K. H. and Z. Guizani, "Use of Viscosity-Modifying Admixture to Enhance Stability of Fluid Concrete," to be published in ACIMaterials Journal, July-August 1997.

[3] "Controlled Low Strength Materials (CLSM)," ACI Report 229R-94, ACI Concrete International, July 1994, p. 55.

[4] Khayat, K. H., "Effects of Antiwashout Admixtures on Fresh Concrete Properties," ACI Materials Journal, March-April 1995, p. 164.

[5] Handbook for Concrete, U.S. Army Waterways Experiment Station, Vicksburg, MS, 1949.

[6] "Washing Out Test," Technical Report No. 3, Hydro-Beton, Belgium, 1982.


Angel Abelleira l, Neal S. Berke ~, and David G. Pickering ~

CORROSION ACTIVITY OF STEEL IN CEMENTITIOUS CONTROLLED LOW-STRENGTH MATERIALS VS. THAT IN SOIL

REFERENCE: Abelleira, A., Berke, N. S., and Picketing, D. G., "Corrosion Activity of Steel in Cementitious Controlled Low-Strength Materials vs. That in Soil," The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: Controlled Low-Strength Materials (CLSM) are high performance fills produced and delivered by ready mix suppliers. CLSM places faster than conventional compacted fill, requires less jobsite equipment, increases jobsite safety, and minimizes future settlement problems. Consequently, the use of CLSM as backfill material is a very attractive option. However, there are numerous factors that influence soil corrosion on buried structures, such as the electrical resistivity of the backfill material along with its pH and drainage characteristics. Corrosion experiments in which steel coupons were placed in simulated soil or covered with cement-based CLSM then placed in simulated soil are discussed.

KEYWORDS: CLSM, corrosion, air entrained, cementitious soil, soil resistivity, soil pH

Earthwork specifications are usually written requiring that some minimum degree of compaction be attained. The specific percent compaction is often related to the proposed use of the compacted soil. Compaction is used in construction practice to stabilize the material so that it can support foundations, pavements or other structures.

~Manager, Manager, and Research Engineering Associate, respectively, W. R. Grace & Co. - Conn., 62 Whittemore Avenue, Cambridge, MA 02140.

124


ABELLEIRA ET AL./CORROSION ACTIVITY 125

The compaction of soil increases its density, which produces three important effects: an increase in the shear strength of the soil, a decrease in future potential settlement, and a decrease in the permeability of the soil.

Controlled Low Strength Materials (CLSM) offer a number of advantages over compacted soils. Among these are ease and speed of placement, reduced equipment needs, no storage requirements, little subsidence, all-weather construction, and perhaps most importantly, improved worker safety. The in-place performance has made CLSM a true breakthrough in backfilling utility trenches and other cuts and holes in roads.

The use of CLSM in pipe bedding and backfill eases the placement of the pipe. Excavation only needs to be large enough for the material to flow easily under the pipe. No compaction has to be performed at the bottom of the trench, making pipe alignment easier, with less chance for settlement. High air entrainment of the CLSM leads to densities in the 1400 to 1900 kg/m 3 range, thus minimizing the need to anchor down the pipe to prevent floating. Consequently, the use of CLSM as pipe backfill is a very attractive option, and considerable work is being done to develop appropriate design parameters.

A major concern of those involved with the sub-grade placement of metal structures (pipe, piling, etc.) is the potential for corrosion. There are numerous factors that influence soil corrosion on buried structures. The potential for compacted fill to initiate corrosion of embedded metal is related to the electrical resistivity of the backfill material along with its pH and drainage characteristics, stray currents, reactive chemicals and bacterial (aerobic or anaerobic) action.

In this paper corrosion experiments in which 1018 steel was placed in simulated soil or covered with cement-based CLSM then placed in simulated soil are discussed. Corrosive water was applied periodically to have wetting and drying cycles and panels were removed at various times to determine corrosion as a function of time, thus representing severe exposure conditions. Resistivity and pH of the simulated soils and CLSM were determined and the contributions of each to corrosion were investigated.

Experimental

CLSM Mix Proportions

The CLSM used in this paper was a free flowing, stable-air modified, cementitious flowable fill produced using DaraFill* 2 for air entrainment. The CLSM (Table 1) was made with an Essick laboratory mixer with a six minute mix cycle. A

2Trademark ofW. R. Grace & Co.-Conn, 62 Whittemore Ave, Cambridge, MA 02140



typical concrete sand meeting ASTM Standard Specification for Concrete Aggregate (C 33), having a fineness modulus of 2.7 was used as the aggregate filler. Type I cement meeting ASTM Standard Specification for Portland Cement (C 150) (Table 2) was used as the binder.

TABLE 1--CLSM mix design

Material Content cement, (kg/m 3) 89 sand, (kg/m 3) 1400 water, (kg/m 3) 185 Air, (%) 25 DaraFill | (L/m 3) 0.116

TABLE 2--Partial chemical analysis of cement

Analyte Weight % SiO2 21.23 A1203 4.85 Fe203 1.43 CaO 64.57 MgO 3.33 SO3 2.83 Na20 0.08 K20 0.04 LOI 1.27 Free CaO 0.82

Preparation of Corrosive Water

Corrosive water containing 100 ppm each of sulfate, chloride and bicarbonate ions as the sodium salts was prepared in accordance with ASTM Test Method for Simulated Service Corrosion Testing of Engine Coolants (D 2570). This would be typical for exposure in marine environments.

Specimen Cleaning

Metal corrosion specimens were cleaned in accordance with ASTM Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens (G 1). A solution of 1:1 hydrochloric acid and water with 3.5 g/L hexametbylene tetramine added was used to remove the corrosion products.



P h y s i c a l Tes t ing o f C L S M

F l o w - The flow of the CLSM was measured in accordance with ASTM Test Method for Flow Consistency of Controlled Low Strength Material (D 6103).

Triaxial wa ter p e r m e a b i l i t y -- The triaxial permeability o f the CLSM was measured in acc6rdance with ASTM Test Method for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter (D 5084). The test specimens used were 101.6 x 203.2 mm cylinders that had been cured for 28 days, and then cut in half to produce 101.6 x 101.6 mm cylinders.

A i r p e r m e a b i l i t y -- The air permeability of the CLSM was measured in accordance with ASTM Test Method for Permeability of Rocks by Flowing Air (D 4525). The test specimens used were 101.6 x 203.2 mm cylinders that had been cured for 28 days, and then cut in half to produce 101.6 x 101.6 mm cylinders.

Compress i ve s t rength -- The compressive strength o f the CLSM was measured in accordance with ASTM Test Method for Preparation and Testing of Soil-Cement Slurry Test Cylinders (D 4832). Plastic cylinder molds 101.6 x 203.2 mm were used.

Cal i forn ia B e a r i n g Rat io -- The California Bearing Ratio testing of the CLSM was conducted in accordance with ASTM Test Method for CBR (California Bearing Ratio) o f Laboratory-Compacted Soils (D 1883).

Direc t Shear -- Direct shear measurements on the CLSM were conducted in accordance with ASTM Test Method for Direct Shear Test o f Soil Under Consolidated Drained Conditions (D 3080).

Incremen ta l Conso l ida t ion -- The incremental consolidation measurements were conducted in accordance with ASTM Test Method for One-Dimensional Consolidation Properties of Soils (D 2435). The load stress used was 4 kg/m 2.

Corros ion Test ing

Sample p repara t ion -- Sample coupons of 1018 steel (26 mm L x 13 mm W x 3 mm H, with a 6 mm diameter hole) with a surface area o f 910 mm 2 were washed in hexane, dried, and weighed to four decimal places. The coupons were then suspended in pairs inside of 101.6 x 203.2 mm plastic cylinder molds, approximately 25 mm apart, and 100 mm from the top of the cylinder (Figure 1).



f

f

FIG. 1--Schematic o f coupon suspended in cylinder mold

A batch of CLSM was prepared and carefully poured into the molds, and consolidated. The cylinders were allowed to cure in the molds for 3 days prior to stripping.

After stripping, the cylinders were placed in buckets (approximately 11 liters in volume) which had been filled to within 25 mm of the top with the same concrete sand used to prepare the CLSM. Each o f the CLSM cylinders containing the steel coupons were buried in the sand, one per bucket, such that the top o f the cylinders were just below the surface of the sand.

Additional metal coupons were cleaned and weighed and then embedded in other buckets of sand at a depth of approximately 100 mm and were positioned so that the coupons were separated from any other coupon by at least 25 mm.

Corrosive water was then added to the buckets until the water level was approximately 10 mm above the surface of the sand. These bucket were stored at a temperature of 38 ~ C to accelerate the test. The water in the buckets was allowed to evaporate until the water level fell below the buried coupons. At this point, additional tap water was added to bring the water level back up above the sand. This cycle was repeated for the duration of the test, at intervals of one week.

At appropriate intervals, one o f the CLSM cylinders (containing two coupons) and two additional coupons were removed from the sand. The cylinder was broken open, and the coupons removed. The coupons were cleaned and weighed according to ASTM G 1, and the mass loss determined.

Resistivity measurements -- The resistivity of the compacted sand and CLSM were measured in accordance with ASTM Test Method for Field Measurement of Solid resistivity Using the Wenner Four-Electrode Method (G 57). The sand was tested both as is, and when saturated with corrosive water. The resistivity of the CLSM samples was measured freshly prepared, after one day of curing, and saturated with corrosive water after curing.



p H measurements -- The pH of the compacted sand and CLSM were measured in accordance with ASTM Test Method for Measuring pH of Soil for Use in Corrosion Testing (G 51). The sand was tested both as is, and when saturated with corrosive water. The resistivity of the CLSM samples was measured freshly prepared, after one day of curing, and saturated with corrosive water after curing.

Results

Physical Testing

The physical properties of the CLSM being investigated are detailed in Table 3.

TABLE 3--CLSM physical properties

Test Parameter Measurement Result Comments

Flow, (mm) ASTM (D 6103)

Triaxial water permeability, (cm/sec) ASTM (D 5084)

Air permeability, (m 2) ASTM (D 4525)

Compressive Strength, (MPa): ASTM (D 4832) 3 days

7 days 28 days 90 days

1 year

California Bearing Ratio, (%): ASTM (D 1883) 3 days

7 days 28 days

Direct Shear, (kg/cm 2, to angle): ASTM (D 3080) 3 days

7 days 56 days

Incremental Consolidation, (cm2/kg): ASTM (D 2435) 16 hours

7 days 28 days

190

1.2 x 10 -3

1.20

10 "1 - 10 .3 sand 10 .3 - 10 5 silty sand

0.12 "Hand excavatable" 0.14 "Hand excavatable" 0.23 "Hand excavatable" 0.24 "Hand excavatable" 0.26 "Hand excavatable"

22.9 25 - 40 clayey soil 28.9 25 - 50 uniformly 52.3 graded gravel

0.07, to = 27.9 ~ 0.34, to = 26.6 ~ 0.84, t o = 22.5 ~

0.0090 0.0070 0.0006

2-4 x 10 .3 dense silt 1-2 x 10 .3 dense sand 0.5-1 x 10 "3 dense gravel



Corrosion Testing

The average corrosion rates for the metal coupons (~trn/yr) were calculated using the following formula:

Corrosion Rate = (K x W)/(A x T x D) (1)

Where: K = a constant (8.76 x 107), W = mass loss in grams, and A = area in cm 2,

T = time of exposure in hours, D = density in g/cm 3 (7.86)

The cumulative corrosion after 99 days of testing was almost three orders of magnitude higher for the samples stored in the sand than for those cast in CLSM (Figure 2). "The samples cast in the CLSM exhibited up to two orders of magnitude lower corrosion rates than those tested in sand alone (Table 4).

C u m u l a t i v e C o r r o s i o n v s T i m e

100

90

E 80

," 70 0

~, 6o

o 50

._~ 4O

~ 30 E

20

10

0,~,

0

l + Sand �9 DaraFill Treated CLSM

I v I V l I W l

10 20 30 40 50 60 70 80 90 100

Time (days)

FIG. 2 -- Graph of Cumulative Corrosion vs Time



T A B L E 4--Corrosion rates

C o r r o s i o n Ra te (p .m/yr)

T i m e (days ) S a n d C L S M

13 377.2 1.6 I

27 412.8 0.0

48 426 .4 0.2

71 349.2 0.7

99 349.7 0.0

1During the specimen removal process, it was noted that one of the coupons in the CLSM removed after 13 days had migrated to the edge of the cylinder such that a small portion of the coupon was exposed. After cleaning, this coupon had a single spot of pitting that corresponded to the position that had been exposed at the edge of the cylinder. The corrosion rate for this coupon was more than an order of magnitude greater than for its companion sample. Based on the results of the later samples, this result was not included in the data, and the corrosion rate determined at 13 days was calculated using only a single coupon.

U p o n r emova l f r o m the sand , t he c o u p o n s w e r e h e a v i l y enc rus ted wi th sand and

c o r r o s i o n produc ts . A f t e r c l ean ing , t he c o u p o n s s h o w e d s e v e r e surface pi t t ing (F igure 3).

The s a m p l e s cast in C L S M had a v e r y th in coa t o f C L S M af te r r emova l f rom the

cy l inde r s , and af ter c l e an ing s h o w e d v i r tua l ly no s igns o f c o r r o s i o n (Figure 4).

FIG. 3-- Photomicrographs o f test samples embedded in sand after 71 days of exposure to corrosive water.



FIG. 4-- Photomicrographs of test samples embedded CLSM after 71 days of exposure to corrosive water.

Resistivity and pH Measurements

Results from the resistivity and pH measurements (Table 5) show that the CLSM has a lower resistivity than the sand but a higher pH.

TABLE 5--Resistivity and pH results

Sample Sand Sand and corrosive water

Fresh CLSM CLSM cured for 1 day CLSM cured for 1 day, and corrosive water

Resistivity (f].cm) pH 1.3 x 10 6 6.5 5.5 x 10 3 6.6

1.2 x 10 3 11.9

2.0 x 10 4 11.4 1.7 x 10 3 11.2

D i s c u s s i o n

The results of the physical testing show the CLSM to have desirable characteristics compared to a conventional compacted soil. The water permeability value is in the range normally associated with sandy soils, leading to good drainage. The air permeability is on the high side, and has been found to increase with increasing air content. This level of air permeability could be advantageous when backfilling natural gas lines, as it would allow gas leaks to be readily located.



The incremental consolidation values at later ages, which can be used to derive bedding factors and soil stiffness values for pipe bedding designs, are similar to those of dense gravel. The compressibility properties are not that well developed after 16 hours, but do improve significantly as the cement hydrates. The direct shear testing showed that the CLSM performed like a typical compacted granular soil, while the compressive strengths of less than 1 MPa indicate a material would be excavatable; very desirable properties for a utility pipe backfill material.

The load bearing capacity of soil and CLSM is directly related to its ability to support foundations, pavements and other structures without failing or experiencing long- term settlement. The California Bearing Ratio (CBR) of this CLSM was determined at 3, 7 and 56 days, and rated a "very good subgrade" at the early ages, and a "good base" at 56 days. This gives a material that is very stable and resistant to deformation while remaining easy to excavate when needed.

The corrosion data clearly shows that the CLSM significantly improves corrosion resistance. Comparison to other corrosion data in soils indicates that the control specimens in sand had corrosion rates 3 to 10 times higher than typically found in corrosive soils (Escalante 1992, Coburn 1978). This was probably due to the high testing temperature of 38 ~ and a higher oxygen content due to the low depths of the buckets versus actual burial depths in soil.

Though pitting depths were not directly measured, Figure 3 shows that there were deep pits on the control specimens. This is in agreement with field data where a significant amount of pitting occurs on buried steel (Coburn 1978). No pitting was observed for the CLSM specimens.

Several authors note that as soil resistivity increases, corrosivity drops (Escalante 1992, Cobum 1978, Palmer 1990, Chaker 1990). However, even though the CLSM had a resistivity about one third of the sand value when saturated with the corrosive water, corrosion was essentially nil. This indicates that resistivity measurements are not necessarily a good indicator of performance for the CLSM material.

The CLSM material will have reduced resistivity due to the ionic components in the cement, which include sodium, potassium, calcium and hydroxide. These hydroxides raise the pH as noted in Table 5 to above 11. The thin layer of CLSM adhering to the steel specimens indicates that a cement-type environment was created next to the steel, and this would passivate the steel resulting in a significant reduction in the corrosion rate as noted in this study.



Conclusions

The following conclusions can be drawn from this study:

�9 CLSM can be produced with mechanical properties similar to that of compacted soils.

�9 Corrosion rates of carbon steel were significantly reduced with the specific CLSM mixture used relative to a good quality sand.

�9 The pH of the CLSM is over 11 providing a passivating environment for embedded steel.

�9 Resistivity measurements are not a good indicator of CLSM performance.

�9 The test method employed was able to differentiate performance differences between the specimens.

Given the acceleration of the test procedure and over two orders of magnitude improvement, the CLSM used in this study should significantly improve the corrosion performance of carbon steel in underground applications.

References

Chaker, V., 1990, "Corrosion Testing in Soils--Past, Present and Future," Corrosion Testing and Evaluation: Silver Anniversary Volume, ASTM STP 1000, R. Baboian and S. W. Dean, Eds., American Society for Testing and Materials, Philadelphia, pp. 95-111

Coburn, S. K., 1978, "Soil Corrosion," Metals Handbook Ninth Addition, Volume 1 Properties and Selection: Irons and Steels, Bruce P. Bardes, Ed., ASM International, Metals Park, OH, pp. 725-731

Escalante, E., 1992, "Measuring the Corrosion of Steel Piling at Turcott Yard, Montreal, Canada - A 14 year study," Corrosion Forms and Control for Infrastructure, ASTM STP 1137, Victor Chaker, Ed., American Society for Testing and Materials, Philadelphia, pp. 339-355

Palmer, J. D., 1990, "Field Soil Corrosivity Testing--Engineering Considerations," Corrosion Testing and Evaluation: Silver Anniversary Volume, ASTM STP 1000, R. Baboian and S. W. Dean, Eds., American Society for Testing and Materials, Philadelphia, pp. 125-138


Case Histories


William Hook 1 and Don A. Clem 2

INNOVATIVE USES OF CONTROLLED LOW STRENGTH MATERIAL (CLSM) IN COLORADO

REFERENCE: Hook, W. and Clem, D. A., "Innovative Uses of Controlled Low Strength Material (CLSM) in Colorado", The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: The use of controlled low strength material (CLSM), also known as flowable fill, has dramatically increased throughout the State of Colorado over the last eight years. This paper will outline the various uses of CLSM, mix designs, construction procedures, and problems encountered. Some specific uses that will be included are the filling below abandoned bridges in-place, filling an abandoned pipeline under Interstate Highway 70, backfill against a foundation of a large commercial warehouse, and other interesting uses.

KEYWORDS: controlled low-strength material (CLSM) flowable fill, controlled density fill, flowable mortar, unshrinkable fill, lean concrete backfill.

HISTORY

In 1988, the Colorado Department of Transportation (CDOT) and the City of Fort Collins began to allow controlled low-strength material (CLSM) as an alternate to structural backfill for the majority of their construction projects (Clem and Hook 1991). Since the adoption of that alternate specification by CDOT, over ten cities have allowed or specified or both, CLSM for backfilling pipelines. U.S West and Public Service Company of Colorado, a local gas supplier, have also accepted CLSM for backfill.

1Market Manager, Holnam, Inc., 3609 S. Wadsworth Blvd., #200, Lakewood CO 80235.

2Marketing Engineer, Colorado Ready Mixed Concrete Association, 6880 S. Yosemite Ct., #150, Englewood CO 80112.

137



Since 1988, the use of CLSM has expanded to include such applications as bridge abandonment, pipeline abandonment, foundation backfill, pipeline bedding, bridge abutment backfill, and backfill for tilt-up buildings. The future of flowable fill is only limited by the imagination of the design engineers.

MIX DESIGN

There are a number of different mix designs that are commonly used for CLSM. The most frequently used specification is the Colorado Department of Transportation's, which is shown in Table 1 (CDOT 1995). This mix design has proven to be a very economical, available, and dependable.

TABLE 1. Colorado Department of Transportation CLSM Specification.

MateriaE Ihs./(yd~)

Cement 50 Coarse Aggregate (AASHTO No. 57 or 67) 1700 Fine Aggregate (AASHTO M6) 1845 Water (39 gallons) (147 L) 325 (or as needed)

( 30 Kg/m 3) (1009 Kg/m 3) (1095 Kg/m 3) ( 193 Kg/m 3)

NOTES

1. Water shall be such that the structural backfill (flow-fill) flows into place properly without excessive segregation.

2. Contractor may substitute an aggregate that meets the following gradation specification if the cement is increased to 100 lbs/yd 3 (60 kg/m3):

Sieve Size %LPassing

1 inch (25.0mm) 100 No. 200 0-10

3. 30 lbs./yd 3 (18 kg/m 3) of cement and 30 lbs./yd 3 (18 kg/m 3) of fly ash (Class C or F)may be substituted for 50 lbs./yd 3 (30 kg/m 3) of cement.


HOOK AND CLEM/INNOVATIVE USES OF CLSM 139

4. 60 lbs./yd 3 (36 kg/m s) of cement and 60 lbs./yd s (36 kg/m 3) of fly ash (Class C or F) may be substituted for 100 lbs./yd s (60 kg/m s) of cement.

5. Recycled, broken glass (glass cutlet) is acceptable as part or all of the coarse aggregate.

Note that the CDOT CLSM standard now includes a provision which allows the use of recycled glass for a portion of the coarse aggregate. Mix designs associated with innovative applications will be discussed in later sections of this paper.

BRIDGE ABANDONMENT

Since 1990, CLSM has been used by the Colorado Department of Transportation for backfilling around pipes or box culverts under existing substandard bridges to convert the structure from a bridge to an on-grade roadway (Clem et al. 1995). The Colorado Department of Transportation (CDOT) first used CLSM in 1991 on two projects located approximately 10 miles (16 km) southeast of Hugo on Colorado Highway 40/287. In 1993, the Colorado Department of Transportation completed two additional Colorado bridge conversion projects using CLSM. One of these projects was located on Colorado Highway 385 ten miles (16 km) south of Burlington, Colorado, and the other on Colorado Highway 83, 1A mile (0.8 km) north of Franktown, Colorado. These bridges were all located on two- lane highways.

The use of CLSM to modify existing bridges to on-grade roadways has resulted in substantial savings for the Colorado Department of Transportation. In 1991, CLSM was used on a project to modify an existing steel I-beam and concrete deck structure with three 54-in. (1.37 m) corrugated metal culverts. The total project cost was approximately $170,000. In the same year, on a nearby project, a similar structure was removed and replaced with a concrete box culvert. The total cost for this reconstruction project was approximately $400,000. By using CLSM, CDOT saved more than 50% of the cost of total bridge replacement. In 1993, CLSM was used on a project to replace an existing treated timber structure with four 72-in. (1.83 m) corrugated metal pipes at a cost of approximately $93,000.

For an existing bridge to be convened to a culvert crossing using CLSM, two conditions must be met: (1) the new culvert(s) must have the appropriate hydraulic capacity (typically the 100-year discharge) and (2) the new culvert(s) must fit within the limits of the existing bridge structure and flow line of the channel. If either of these conditions is not met, the bridge must be reconsmacted using conventional methods.

If a bridge requires reconstruction under current CDOT standards, additional right-of- way (ROW) must be acquired because the existing ROW width is normally insufficient for construction of necessary detours around the ex!sting structure. The ROW cost ranges from



$100 per acre in eastern Colorado to as much as $500,000 per acre in the Denver metropolitan area, and can take up to three years to purchase. The use of CLSM virtually eliminates all costs associated with ROW purchase. Generally, a temporary easement is all that is required.

The most important property of CLSM for bridge rehabilitation is its flowability. A maximum compressive strength, which is normally required for CLSM placed over pipelines, is not critical in this application as it is highly unlikely that the placement will ever be excavated.

Normally, two different mix designs are necessary:

(1)

(2)

mix design for placement in critical locations such as between beams of the existing bridge and mix design for placemem in noncritical locations such as backfilling for open trenches and placement below the bridge under existing beams.

The required fluidity specification of the CLSM [as measured by ASTM Standard Test Method for Flow of Grout for Preplaced-Aggregate Concrete (Flow-Cone Method) (C939)] is 10 to 26 S for noncritical placements (Stages 1 and 2) and 10 to 16 S for critical placements (Stage 3). The higher fluidity of the CLSM for critical locations is necessary to ensure that the voids in those areas are completely filled.

The mix designs for CLSM used on Colorado Project CX 47-0083-28 completed in Franktown, Colorado in the summer of 1993 are shown in Tables 2 and 3.

T A B L E 2 - C L a M M i x D e s i t m F o r N o - " "

0Project C X 4 7 - 0 0 8 3 - 2 8 L

]Vlat~Hal II~./~d~

Cement 100 ( 59 kg/m 3) Fly ash (Class C) 300 ( 178 kg/m ~) Fine aggregate 2600 (1543 kg/m a) Water (60 Gal.) (227 1) 500 ( 297 kg/m 3)

Flowability required = 10 to 26 S.



TABLE 3 - CI.qlVl Mix i ~ i ~ n For Crltlenl Pinemn~nt~

1Ml~m'ial Ihg.llvd~

Cement Fly ash (Class C) Fine aggregate Water (60 Gal.) (227 1)

100 ( 59 kg/m 3) 400 ( 237 kg/m ~)

2400 (1424 kg/m 3) 500 ( 297 kg/m ~)

Flowability required = 10 to 16 S.

In the consU'uction phase, it is recommended that the CLSM be placed in three stages with a minimum set time of 48 h betwcen stages. Stage 1 is placed up to the spring line of the pipe. To keep the pipe from floating, bracing of the pipe is recommended for the fwst stage. The second slage is placed from the spring line of the pipe to within 1 f (0.3m) of the bottom of the girders or su'ingers (see FIG. 1).

FIG. 1 - CLSM (Stage 2) being placed on Franktown Bridge Project.

The third stage is the critical stage in which CLSM is placed in the remaining cavity beneath the bridge. This placement is made f ~ t from the sides and then from on top of the bridge through holes drilled in the deck using a funnel or pump to develop pressure. The



Colorado Department of Transportation recommends that the core holes drilled through the deck be 4 in. (102 mm) in diameter. The 4 in. (102 mm) diameter holes are large enough to allow proper placement of CLSM by pumping or by a funnel system and are small enough so that traffic can safely pass over them.

Quality control for CLSM includes two major components. First, the selected contractor must submit mix designs for approval by the Colorado Department of Transportation (CDOT) District Materials Engineer before incorporation into the work. The CLSM is also tested on-site for fluidity before placement. The fluidity of the CLSM material is measured according to the requirements of ASTM Test Method C939.

PIPELINE BEDDING AT DENVER INTERNATIONAL AIRPORT (DIA)

The City of Denver constructed a new international airport located northeast of Denver in 1991-1993. The project covered 53 square miles (137 km 2) and was constructed at a cost of over $3 billion dollars. To ensure proper drainage, an extensive system of concrete conduits was located beneath the concrete paved aprons and taxiways (Clem et al. 1992). As a part of the drainage design, 105,000 lineal feet (32,000 mm) of reinforced concrete pipe ranging in diameter from 15 inches to 96 inches (.40-2.44 m) was installed. CLSM was specified as a bedding material for this critical drainage system.

The flowable backfill was designed to completely surround the pipe and extend a minimum of 6" (152 mm) above the top of the pipe as shown in FIG. 2. In addition to providing positive bedding for the drainage pipe, flowable backfill was specified as a bedding for several other reasons. The use of flowable fill allowed the contractor to minimize the excavation required for the pipeline because workmen did not have to enter the trench to compact the bedding material in lifts. The flowable fill bedding is also expected to eliminate any settlement of the trench, which would present a serious problem beneath an operating aircraft apron or taxiway.

CLASS " B " BEDDING & F L O W F I I J . TYPICAl .

FI,OWFIIJ, dl = 6" CI,AN,q "J~" BEDDING

<24" dl=6" > =24" dl=12"

. d

~ ~6"MIN.

6"MIN.~ r. ~ ~--6"MIN. Be=PIPE O.D.

FIG. 2 - Typical bedding detail, 1 in. = 2.54 cin.



The original bid documents specified an earlier version of the CDOT mix design presented in Table 1. After investigating the on-site sandy materials, the City allowed a change order to use these materials in place of imported concrete aggregate and sand. This reduced the amount of construction traffic required at an already congested construction site.

A typical gradation of the on-site material is shown in Table 4.

T A B L E 4 - Typical t, radat ion of on~ i t e material_

Siev~Siz~e, No. Percent Passing

4 100 10 100 16 96 30 72 50 45

100 28 200 18

Table 5 shows the mix design that was finally approved for the project. The slump of this mix design ranged from 4-6 inches (102-152 mm), which was less than the original specification limits of 7-9 inches (178-229 mm). The lower slump was allowed because the flowable fill easily flowed beneath the pipe, and achieved an average strength at 28 days of 88 psi (.6 MPa). The lower slump also reduced the amount of bleed water, which lowered the amount of time required for the material to reach sufficient strength for start of earth backfilling operations.

TABLE 5 - E i n a l / l a w a h l e _ b e d f l h l g ~

Matea'i~ Ih~./~d~

Cement (Type V) 153 ( 91 Kg/m 3) Total water 600 ( 356 Kg/m 3) On-site sand (SSD) 2,600 (1543 Kg/m 3) Unit weight 124.3 pcf (1991 Kg/m 3)

Because the plant was located on the airport site, the hauling time from the plant to the pipeline placing location never exceeded 15 min. The flowable backfill material was usually



placed directly along the side of the pipe using the chute on the ready mix truck. At times, the flowable fill was placed along the center line of the pipe using a backhoe bucket. The flowable fill easily flowed under the concrete pipe, which was supported by 6 in. (152 mm) thick masonry blocks intermittently spaced.

By using flowable fill for the bedding material, the contractor was able to excavate a very narrow trench only 6 in. (152 mm) on each side of the pipe. A trench shield was used to protect workmen as they joined sections of concrete pipe. The use of elaborate sheeting and shoring for the pipeline bedding operation was not necessary because workers did not have to enter the trench to compact the bedding material in lifts.

The quality control program required the following tests every 150 yd 3 (115 m3):

Slump (ASTM Test Method C143) Temperature (ASTM Test Method C1064)

Unit Weight (ASTM Test Method C138) Compressive Strength Cylinders

(ASTM Test Method D4832)

Before testing the cylinders, the plastic molds were removed using compressed air and the cylinders were allowed to dry for 5 to 6 hours. The ends were then leveled and capped with a neoprene cap. Breaks were performed at 7 and 28 days, and two cylinders were held for future breaks if necessary. The average 7-day and 28-day breaks were 58 psi (.4 MPa) and 88 psi (.6 MPa) respectively.

To determine compressive strength, the cylinders were placed in a compressive machine with the load slowly applied by a hand crank. It was observed that the use of the normal method for concrete cylinder breaking did not always give reliable results for flowable fill as a result of the low range of strengths being measured, typically less then 100 psi (.7 MPa).

ABANDONMENT OF A PIPELINE

CLSM was the material of choice for the abandonment of a pipeline beneath a critical segment of Interstate 70 near Officers Gulch, immediately east of Copper Mountain, Colorado.

The 60-in. (1.52 m) corrugated metal pipe (crop) was to be replaced by a larger pipe to handle the drainage basin above the interstate. Complicating matters was the fact that the existing culvert had approximately 12 to 18 in. (305-457 ram) of water constantly running through it. The original mix design specified by the Colorado Department of Transportation was similar to the CLSM mix design for noncritical placements for bridge abandonments as shown in Table 2. Because access to the uphill opening of the pipe required pumping a distance of 200 f (61 m), this mix was not used. The pumping contractor had indicated that it would not be pumpable under the difficult conditions of this placement.



A second mix (see Table 6) was submitted to CDOT and tried in the field. About 40 yd 3 (31 m 3) of this CLSM was pumped and placed. Note that the flowability was lost very rapidly as a result of a flash set of the mix because of the amount of Class C ash, 350 lbs. (159 Kg).

T A B L E 6 - Tr ia l m i x t w n . TABLE 7 - l~almixJ.ime~

blaterial __ lh~/yd~ Material ___ Ih~./yd 3

Ceraent (Type I) 50 ( 30 Kg/n~) Cen~ent (Type I) 100 ( 59 Kg/m 3) Fly ash (Class C) 350 ( 208 Kg/m 3) Fly ash (Class C) 100 ( 59 Kg/m 3) Class 6 aggregate base course 3126 (1855Kg/m 3) Class Vl aggregate base course 3364 (1985Kg/m 3) Water (22 gallons) (831) 183 ( 109Kg/m 3) Water (34 gallons) (1291) 283 ( 167Kg/m 3) High air entraining agent High air e:tm'a~ng agent

A third mix was submitted and approved by CDOT as shown in Table 7. About 40 yd 3 (31 m 3) of this material was pumped into the pipe before it was determined that the CLSM was segregating.

A fourth field mix was then proposed and accepted by CDOT for a trial. This mix, as shown in Table 8, included an anti-wash admixture (used in underwater placements) which helped keep the mix from segregating as the CLSM displaced the water in the pipeline. This final liaix performed extremely well and was used for the balance of the project. The project required a total of 480 yd 3 (367 m 3) of CLSM.

TABLE 8 - ~f lakmixZol~

Material I I ~ . / f v t i ~

Cement (Type V) 350 ( 208 Kg/m 3) Fly ash (Class F) 395 ( 234 Kg/m 3) Fine aggregate 2004 (1189 Kg/m 3) Coarse aggregate (#8) 708 ( 420 Kg/m 3) Water (35 gal.) (132 1) 292 ( 173 Kg/m 3)

Following the successful filling of the old 60-in. (1.52 m) cmp, a new culvert was placed beneath the highway.



BRIDGE ABUTMENT

The Colorado Department of Transportation currently allows the use of CLSM to backfill the area adjacent to bridge abutments. The use of CLSM appears to have eliminated the unpleasant bump that is often experienced by motorists Iransitioning from the roadway to the bridge or concrete box culvert.

Not only does the use of CI.,SM eliminate the rough transition from pavement to bridge, it also reduced the conslruction time for backfill. CDOT allows the contractor to place the material in lifts of up 4 f (1.2 m) thick to ensure that there will not be too much fluid pressure' exerted by the CLSM on the abutment. The typical placement only requires one man in addition to the ready mixed concrete truck driver.

In July 1995, a contractor placed over 400 yd 3 (306 m 3) of CI_~M for backfdl of the abumaents of a bridge located along Colorado State Highway 135 near Crested Butte, Colorado (see FIG. 3). The conlractor made the placement in two lifts, a 125 yd 3 (96 m 3) lift followed by a275 yd? (210 m 3) lift. The Colorado Department of Transportation standard mix (50 lb. [23 Kg] of cement, see Table 1) was specified.

FIG. 3 - Placement o f CLSM for bridge abutment backrdl.

TII,T-UP CONSTRUCTION

Several innovative building contractors in the Denver area have used CLSM to speed up the consliuction sequence for tilt-up concrete buildings (Colorado Ready Mixed Concrete Association 1995). The conventional sequence for the concrete floor construction of a tilt-up



building has been to form and construct the floor to a point approximately 4 f(1.2 m) inside the exterior wall line. Once the tilt-up concrete panels are tilted into place on the foundation, the excavated area must be backfilled and compacted by hand. A 4 f (1.2 m) strip of concrete must then be constmeted between the newly placed wall panel and the existing concrete floor. The process of placing the concrete floor in two separate operations is very inefficient and costly.

The use of CLSM has provided a very efficient way to eliminate the two separate placements, allowing the construction of the concrete floor in one placement. Following the construction of the foundation, the contractor sets a form above the foundation to a line just inside the exterior wall line. Flowable fill is then placed between the existing subgrade and the form, filling the void created by the foundation excavation (see FIG. 4). The flowable fill is screened offto a finished grade which matches the elevation of the floor subgrade. Then, using the same exterior form, the entire concrete floor is placed. After the floor placement is completed, the contractor strips the form, tilts the concrete wall into place (see FIG. 5), and, finally, caulks the small gap, usually 0.50 to 0.75 inch (13-19 mm), between the edge of the floor and the wall panel.

FIG. 4 Placement of flowable fill in foundation construction cavity.

FIG. 5 Concrete panel tilted adjacent to existing concrete floor.

On one project constructed in Denver, it is estimated that approximately two days of construction time were saved by the use of this CLSM method of floor construction. The mix design used this particular project is shown in Table 9.



T A B L E 9 - Concrete Floor Igaekfill.

M~tprial Ihc-Hvd31 Cement 50 ( 30 Kg/m 3) Fly ash (Class C) 150 ( 89 Kg/m 3) Road base (3/4 in. [20 mini top s~e) 2900 ( 1721 Kg/m 3) Water (55 gal) (208 1) 458 ( 272 Kg/m 3)

F O U N D A T I O N B A C K F I I J .

In the summer of 1991, a large commercial distribution center was constructed in Lo.veland, Colorado. The contractor for this project elected to use CLSM in lieu of conventional granular backfill material to backfill the entire exterior foundation wall to save time on an very tight comtmction schedule.

By using CLSM, the contractor was able to shave about two weeks off of the construction schedule. The contractor was not only pleased with the savings of comtruction time, but also felt that the owner of the building would benefit by a very stable hackrfill which will be less likely to settle in the future.

Approximately 4000 yd 3 (3058 m 3) of CLSM was used on the project for foundation wall backfill (see FIG. 6). The average backf'dl cavity adjacent to the foundation wall was 5 f (1.52 m) deep and 18 to 24 in. (457-610 mm) wide. The contractor elected to place the CI_SM in two lifts to ensure that the foundation would not be damaged by fluid pressure from the placement.

FIG. 6 - CLSM being placed against foundation wall.



The contractor used the Colorado Department of Transportation CLSM mix as shown in Table 1. The backfill operation required only one person to guide the chute of the ready mixed truck. A typical placement ranged from 200 to 450 yd 3 (153-344 m 3) per day. Discharge time ranged from 5 rain. total in shallow placement areas to under 1 min. in deep placement areas.

Foundation backfdl was not the only innovative use of flowable fill on the project. The contractor also used CLSM for subgrade for a ramp, backfill over underground storage tanks, and sewer and water lines. They even used a low slump CLSM to fill in an area as a false form for elevated steps and landings (see FIG. 7).

FIG. 7 - Use of CLSM as a false form for step construction.

In Colorado, contractors and owners have found many innovative uses for controlled low-strength material (CLSM) beyond simply the backfilling of pipelines. Innovative uses such as bridge abandonment, pipeline bedding, abandonment of a pipeline, bridge abutment backfill, tilt-up construction, and foundation backfill are becoming more common in Colorado. The overall market for CLSM continues to expand rapidly as designers specify it to solve tough backfill situations.



Clem, Don A., Goldbaum, Jay and Hook, William, November 1995, "Controlled Low Strength Material (CLSM) for Abandonment of Substandard Bridges", American Concrete Institute Fall Convention, Montreal, Canada

Clem, Don A., Hansen, K.D. and Kowalsky, James B., March 1992, "Flowable Backfill for Pipeline Bedding at the New Denver Airport", 1992 American Concrete Institute Spring Convention, Washington, DC

Clem, Don A., and Hook, William, March 1991, "Flowable Fill - A Solution To Backfilling Problems", ASCE Pipeline Specialty Conference, Denver, Colorado

Colorado Department of Transportation, August 3, 1995, "Revision of Section 206, Structural Backfill", "Flow - Fill", Denver, Colorado

Colorado Ready Mixed Concrete Association, 1995, "On the Job" Report No. 20 "Flowable Fill - It's Not Just For Trenches Anymore", Denver, Colorado


Brian H. Green,: Kimberlie Staheli, 2 David Bennett, 3 and Donald M. Walley ~

FLY-ASH-BASED CONTROLLED LOW-STRENGTHMATERIAL (CLSM) USED FOR CRITICAL

MICROTUNNELING APPLICATIONS

REFERENCE: Green, B. H., Staheli, K., Bennett, D., and Walley, D. M., ' ' F l y - A s h B a s e d C o n t r o l l e d Low S t r e n g t h M a t e r i a l (CLSM) U s e d f o r C r i t i c a l MicrotunnelingApplications,'' ''The Design and Application of Controlled Low-Strength Materials (Flowable Fill), '' ASTMSTP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: A controlled low-strength material (CLSM) has been successfully used in two microtunneling applications. This CLSM, developed at the U.S. Army Engineer Waterways Experiment Station (WES), is a mixture of ASTM Class C fly ash, ASTM Type I portland cement, bentonite, and water.

The CLSM was first used during the microtunneling field trials at WES to stabilize a tunnel excavation while retracting the microtunneling machine through unstable, flooded, running sand. The void left by the retracted tunnel machine was filled with the CLSM to provide continuous support to the excavation and avoid settlement of the ground surface.

Based on the success of the WES tests, the CLSM was used on a second microtunneling project in Newark, California. The CLSM was used to stabilize the soil surrounding the sheet-piled shaft that would be used to launch a microtunnel boring machine. The use of this fly-ash- based CLSM greatly improved the stability of the soils and safety of the shaft during the launch. The use of the CLSM also provided cost savings in excess of $100,000 on the Newark project.

KEYWOBDS: CLSM, fly ash, microtunneling, shaft stabilization

Coal-fired electric generating plants produce large amounts of fly

iGeologist, Engineering Mechanics Branch, Concrete and Materials Division, Structures Laboratory, U.S. Army Engineer Waterways Experiment Station, CEWES-SC-C, 3909 Halls Ferry Rd~ Vicksburg, MS 39180.

2Research Civil Engineer, Soils Research and Testing Center, Geotechnical Laboratory, U.S. Army Engineer Waterways Experiment Station, CEWES-GS-GC, 3909 Halls Ferry Rd., Vicksburg, MS 39180.

3Chief, Soils Research and Testing Center, Geotechnical Laboratory, U.S. Army Engineer Waterways Experiment Station, CEWES-GS-G, 3909 Halls Ferry Rd., Vicksburg, MS 39180.

4Geologist, Engineering Mechanics Branch, Concrete and Materials Division, Structures Laboratory, U.S. Army Engineer Waterways Experiment Station, CEWES-SC-C, 3909 Halls Ferry Rd., Vicksburg, MS 39180 (deceased).

151

C o p y r i g h t �9 1998 by ASTH I n t e r n a t i o n a l w w w . a s t m . o r g Copyr igh t by ASTM In t ' l ( a l l r igh t s r e se rved) ; Thu Feb 7 18 :46 :02 EST 2013Downloaded /p r in ted byKar ina Agama (Freyss ine t+Tie r ra+Armada+Peru+S .A.C. ) pur suan t to L icense Agreement . No fu r the r r ep roduc t ions au thor i zed .


ash as a by-product of the coal-combustion process. This fly ash is routinely used as a constituent material in the production of concretes and grouts by producers across the United States.

Fly ash is also used as a constituent material in the production of controlled low-strength materials (CLSMs). CLSMs can be used to replace soil as fill or backfill material on construction projects and for other purposes. Unlike conventional backfilling with soil or other fill material, CLSMs require very little labor and require no compaction.

In support of a microtunneling research program, the U.S. Army Engineer Waterways Experiment Station (WES) proportioned a CLSM incorporating a large amount of ASTM Class C fly ash. This CLSM was successfully used to prevent overburden settlement of a 2-ft (0.6 m) diameter horizontal microtunnel bore through flooded, running sand, which had been created and abandoned by a microtunneling machine. The void left by the microtunneling machine was filled with the CLSM as the machine was retracted. Subsequent reentry of the microtunneling machine through the hardened CLSM 36 h later was also successful.

The second use of this CLSM mixture was on a field job in Newark, California, in support of the Newark Subbasin Lower Relief Sewer Project. The CLSM mixture was used to stabilize the poorly graded, wet sands surrounding tunnel shafts and ensured the safety of the work crew during the launching of a microtunneling machine.

CONTROLLED-LOW STRENGTH MATERIALS

The American Concrete Institute defines CLSMs as materials that result in unconfined compressive strengths of 1,200 psi (8 MPa) or less (American Concrete Institute (ACI) 1990). It is important that CLSMs be considered as a type of structural backfill rather than a type of low- strength concrete. CLSMs are also known as flowable fill, controlled- density fill, unshrinkable fill, flowable fly ash, flowable mortar, fly ash slurry, soil-cement slurry, and various other names (ACI 1994). The primary application of a CLSM is as a structural backfill or backfill in lieu of compacted soil. Because a CLSM needs no compaction and can be designed to be very fluid, it is ideal for use in restricted access areas where placing and compacting fill is difficult. If future excavation is anticipated, the maximum long-term compressive strength should generally not exceed 300 psi (2.1 MPa) (ACI 1994).

It is typical for the long-term unconfined compressive strengths of a CLSM to range between 50 and 300 psi (0.3 and 2.1 MPa), which represent very low strengths when compared to conventional concrete (ACI 1994). However, in terms of allowable bearing pressure, which is a common criterion for measuring the capacity of a soil to support a load, a CLSM of 50 to I00 psi (0.3 to 0.7 MPa) unconfined compressive strength provides bearing capacity equivalent to a hard clay or well-compacted fill (ACI 1994). CLSMs are very fluid while they are mixed and placed and have a consistency of a lean cement slurry or grout. However, several hours after placement, the material hardens enough to support loads without settling.

Although CLSMs generally cost more per cubic yard than most soil backfill materials, the material offers many advantages that often result in lower in-place costs. In fact, for some applications, CLSMs may be the only reasonable backfill method available (ACI 1994).


GREEN ET AL./MICROTUNNELING APPLICATIONS 153

COMPONENTS OF CLSMS

CLSM mixtures can be produced from some or all of the following components: portland cement, fly ash, natural pozzolans, ground granulated blast-furnace slag, coarse or fine aggregates, and water. Materials used to make CLSM may meet ASTM or other standards; however, it is not always necessary that the materials meet conventional standards. Selection of materials should be based on availability, cost, specific application, and the necessary characteristics of the mixture such as flowability, strength, excavatability, and density (ACI 1994).

For a Construction Productivity Advancement Research (CPAR) Program microtunneling application (described later), the WES CLSM was proportioned with a large amount of ASTM Class C fly-ash and water. These two constituent materials made up 95% of a given volume of the CLSM mixture, with portland cement and bentonite comprising the remaining 5%. A set retarder, citric acid, was used to extend the set time or setting of the CLSM.

A fly-ash-based CLSM was used for several reasons. A maximum unconfined compressive strength criterion, at 24 h age, of I00 psi (0.7 MPa) or less was set. Generally speaking, a fly-ash-based CLSM would inherently be weaker than a portland-cement-based CLSM at this early age. Also, ASTM Class C fly ash was readily available from the local ready-mix concrete producer who would also supply the fly ash for the experimental microtunneling application. The CLSM mixture cost would be lower since the costs for fly ash and water are lower than portland cement.

No fine or coarse aggregates were used in the WES CLSM. The void that was filled was of a size that did not require the use of filler particles, such as aggregates, to fill up a large volume. Also, it was easier to pump a fly-ash based CLSM without aggregate with the slurry pump on the microtunneling machine.

The U.S. Army Corps of Engineers supports the use of fly ash in all instances in which it is technically feasible. On 1 May 1995, as a follow-up to its 1983 regulation, the Environmental Protection Agency (EPA) issued additional regulations in the Federal Register (pp. 21390-21392), expanding its approved list of recovered products (Concrete Products 1995). The regulations state, "EPA recommends that procuring agencies specifically include provisions in all construction contracts to allow for the use, as optional or alternate materials, of cement or concrete which contain coal fly ash or ground granulated blast-furnace slag, where appropriate" (Concrete Products 1995).

COAL AND FLY ASH

Coal has been used as a power source for many years in the United States. The United States has approximately 22% of the world's coal resources (Johnson 1995). This ample supply of an energy source and the energy crisis of the 1970s led to the use of coal as the major raw material in the generation of electricity across the United States. According to preliminary reports, the United States' coal production reached a record 1.04 billion short tons (0.9 billion metric tons) in 1994 (Johnson 1995). This growth in production was in response to an increase in demand for coal for use in electric power production. The combustion of this coal, in turn, led to an increase in the amount of fly ash generated by the utilities. Effective use or disposal of this ash has been a problem for years.



The utility companies have struggled with the problem of what to do with the tremendous amount of coal combustion by-products produced annually in the electrical generation process. In 1994, approximately 89 million short tons (80.7 million metric tons) of coal combustion by-products (CCBs) were produced (Fly Ash Resource Center 1996). Approximately 55 million tons (49.9 million metric tons) of this amount, or 62%, is fly ash. To help decrease the amount of fly ash being dumped in landfills, researchers are continually developing new ways to use coal ash as filler in everything from tennis rackets to high-rise construction projects. Coal fly ash has been used as structural fill in roads, as a road subbase, and as a replacement for part of the cement content in concrete, concrete products, and grouting applications (Mininu Enaineerina 1994).

There are three primary forms of coal ash: (a) fly ash, (b) bottom ash, and (c) boiler slag. Of the three, fly ash is the best known and most widely used as a marketable product. About 10% of the fly ash produced in the United States is used in concrete.

R. E. Davis et al. (Davis et al. 1937) at the University of California published the results of research on concrete containing fly ash. This work served as a foundation for early specifications, methods of testing, and uses of fly ash. Fly ash is used in concrete for various reasons including cost savings, reduction of temperature rise, increased workability of fresh concrete, and improved durability and strength. Concrete containing fly ash is produced everyday across the United States for many different applications. The Federal Highway Administration, U.S. Army Corps of Engineers, and the EPA have allowed fly ash to be used in concrete where it is technically and economically feasible; indeed, the EPA has required the use of fly ash unless it can be shown that its use would be detrimental. No instance of such demonstration is known to the authors.

Fly ash can also function as a fill material by converting poor load-bearing soils and uneven terrain into usable land. Today, large structures and even entire housing developments have been built on fly ash fills. The mining industry can use fly ash to combat subsidence in abandoned underground mines. In underground coal mines, when the remaining roof pillars deteriorate, the roof collapses. This results in the subsidence of the ground above. But this can be prevented or controlled by creating column supports using grouts made primarily from fly ash (Minina Enaineerina 1994). Fly ash grouts can also be used to make low-cost plugs or to fill completely abandoned mine drifts to prevent entrance by unauthorized personnel. This plug material could be easily mined out in the future if necessary.

A new application for fly ash is for the production of controlled low-strength materials (CLSM). CLSM is a cementitious material that requires no compaction and is used primarily as a structural backfill material instead of conventional compacted-soil fill.

PROPERTIES OF FLY ASH

Fly ash is a by-product of the burning of pulverized coal or lignite or both in electric-power-generating plants. During combustion of powdered coal, ~he coal passes through the high-temperature zone in the furnace, and the carbon is burned off. The mineral impurities, such as clay, quartz, and feldspar, melt at the high temperature. The liquid matter is quickly transported to lower temperature zones, where it solidifies as spherical particles of glass. Some of this material agglomerates and forms bottom ash, but most of it is transported out with the flue gas stream and is called fly ash. The fly ash is



collected in electrostatic precipitators or by mechanical collectors as fine particles.

The ASTM Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Concrete (C 618) divides coal fly ashes into two categories based on differences in chemical and physical composition. The two categories are Class F and Class C. Class F must contain at least 70% combined silicon dioxide (SiOz), aluminum oxide (A1203) , and iron oxide (Fe203) , calculated from chemical analysis; Class C must have at least 50% of these compounds. Most Class C ashes cannot comply with the requirement for Class F because of their high CaO content. Class F fly ashes are usually derived from the burning of anthracite or bituminous coals. They generally contain less than 10% CaO. Class C fly ashes are usually derived from the burning of lignite or subbituminous coals and generally contain 15 to 35% CaO. Fly ashes are complex in their range of chemical and phase compositions. They consist of heterogeneous combinations of glassy and crystalline phases.

Class C fly ashes are in general more reactive than the Class F fly ashes because they contain most of their calcium in the form of reactive crystalline phases. There is also evidence that the principal constituent, the noncrystalline phase, contains enough calcium ions to enhance the reactivity of the aluminosilicate glass (Mehta 1986). Because of this high reactivity, Class C fly ashes often react directly with water to form cementitious phases (Mehta 1986).

The shape, fineness, size distribution, density, and composition of fly ash particles influence the properties of freshly mixed, unhardened concrete and grout, Fly ash primarily occurs as spheres of glass that are predominantly solid, but sometimes a small number of hollow spheres called cenospheres (completely empty) and plerospheres (packed with numerous small spheres) may be present. Particle size distributions show that the particles vary from <i to i00 pm in diameter, with more than 50% under 20 ~m.

The preceding section has provided background on the production of fly ash, chemical constituents and characteristics, and some of the more traditional applications. The remainder of this paper focuses on two innovative applications of CLSM to microtunneling.

WES CLSM / CPAR RESEARCH

A major concern to municipal officials and engineers contemplating the use of microtunneling for construction of gravity sewer pipelines in congested urban areas is the impact of underground obstructions that can halt the advance of the machine, often leading to claims that cause delays in projects and increased costs. In microtunneling, the common obstructions include rock or boulders, building debris, and mislocated or unmarked utilities (active or abandoned). In addition, machines are occasionally unable to proceed because of mechanical failures or incompatibility of the machine and ground.

Even the most thorough geotechnical investigation cannot be expected to always give a complete picture when tunneling in complex subsurface conditions. Once an obstruction is encountered, the list of remedial measures available to the contractor is brief, usually requiring retrieval of the machine or access to the face.

McLaughlin Manufacturing Company, Greenville, South Carolina, and Markham and Company Ltd., Chesterfield, England, have teamed up to address this potential problem by marketing an innovative retrievable microtunneling system first developed in Japan by Okamura (Thomas 1993). This system uses temporary, bolt-together, steel pipes for the



microtunneling operation (Fig. i). The bolted column of temporary pipes allows the system to be put into reverse at will from the control station to enable slight pulling back to relieve thrust or torque buildup. The system can be fully retracted should a drive have to be aborted for any reason. During this latter process, grout can be injected through the slurry lines to refill the void created by the retraction of the machine. The weak grout can be injected through the slurry system of the machine such that it gives full support to the ground but also allows reexcavation later. With this option available, the manufacturer claims high-risk jobs can be confidently undertaken. The option of retrievability offers some intriguing possibilities with regard to critical applications: where rescue shafts cannot be sunk for environmental remediation such as horizontal barriers beneath existing waste sites and construction of presupported grout-filled arches for larger excavations such as subway stations.

FIG. 1--Retrievable microtunneling system.

The overall objective of this component of the research project was to demonstrate, evaluate, and promote commercial acceptance of the retrievable microtunneling system through impartial documentation of performance. The specific primary objectives were to test the manufacturer's claims of retrievability while avoiding settlement and evaluate performance of the system under challenging ground conditions.

During the first portion of the WES test, the McLaughlin/Markham machine, with its temporary pipe system, was driven 12 m (40 ft) through flooded, running sands with groundwater levels approximately 1 m (3 ft) above the pipe crown. The machine was then retracted by reversing the jacking force and removing the temporary pipes through the launch shaft. A specially designed CLSM containing ASTM Class C fly ash, bentonite (smectite clay), ASTM Type I portland cement, citric acid, and water was pumped through the slurry inlet line to the face of the machine. The unconfined compressive strength of the CLSM was 70 psi (0.5 MPa) at 28 days. The mixture proportions of the CLSM are given in Table i. The fly ash used in this CLSM is a Class C fly ash used by the local ready- mixed concrete producer, Mississippi Materials Company (MMC). Fly Ash Products of Redfield, Arkansas, is the fly ash supplier to MMC. This mixture also contains a small amount of portland cement and bentonite. Bentonite is a smectite clay that is mined in Wyoming or South Dakota.



Bentonite is used in the oil- and water-drilling industry as drilling mud and is readily available across the country. It imparts viscosity and thixotropic properties to fresh water by swelling to about ten times its original volume (Smith 1990). Bentonite was used in the CLSM mixture to control bleeding and act as a pumping aid.

TABLE 1--Mixture proportions of the CLSM.

Batch Weights for One Cubic Meter

Materials Kg

ASTM Type I Cement 81

ASTM Class C Fly Ash 601

Bentonite 61

Citric Acid 1

Water 724

Final set achieved at approximately 24 h age.

Water to cementitious ratio is 1.06.

The mixture also contained citric acid to retard or slow the hydration of the mixture. This was necessary since this job required the CLSM to remain fluid for an extended period of time. Walley and Green discovered in early laboratory testing that a mixture of the Class C fly ash and water would reach final set in 20 min. At 24-h age, the unconfined compressive strength of this fly ash and water mixture was 900 psi (6.2 MPa).

The proportioning of this and any other CLSMs begins in the laboratory. A candidate CLSM is proportioned using a mixture proportioning data sheet and then batched and mixed in the laboratory. Each potential CLSM was mixed in a 0.10-ft 3 (0.28-m 3) batch using a planetary mixer which complied with ASTM Practice for Mechanical Mixing of Hydraulic Cement Pastes and Mortars of Plastic Consistency (C 305). A flat-paddle was used to mix the CLSM to simulate the type of action the CLSM would see in a truck mixer in a field placement. All laboratory grout mixtures are usually mixed and tested for flow at 5, 15, 30, 60, 90, and 120 min per ASTM Test Method for Flow of Grout for Preplaced-Aggregate Concrete (Flow Cone Method) (C 939). The CLSM required a 4-h placement time so the flow of the CLSM was monitored for an additional 2 h. At 4-h age, the flow of the grout was 10.2 s. Physical inspection for segregation of the constituent materials was performed after each flow test. After being mixed and tested for 4 h, the grouts were cast into 3-in. by 6-in. (76- by 152-mm) plastic cylinder molds, capped, and sealed with tape to prevent moisture loss. At 28 days age, these cylinders were tested and the average unconfined compressive strength was 70 psi (0.5 MPa).

Time-of-setting specimens were cast to determine the CLSM initial and final time of setting. A Ferioli time of setting apparatus was used to measure automatically this property. Unfortunately, the CLSM was so weak when it initially set up that it was below the threshold of the Ferioli's ability to detect. The time of setting was determined by manually monitoring the test specimens in this case.

After the laboratory work was accomplished and a mixture was proportioned that met all the requirements, actual field placement took place. Field mixing of this CLSM was accomplished using a truck mixer from MMC. The CLSM was batched in the following batching sequence to obtain an optimum mixture.



i. 80% of mixing water measured into the truck mixer.

2. Citric acid added to the mixing water in the mixer.

3. Cement and fly ash added to the water in the mixer.

4. Bentonite added to the mixer.

5. Final 20% of mixing water added to the mixer.

The mixer was then operated at high speed for 5 min before it left the batch plant. The mixing drum was continuously agitated on the way to the job site. After arrival at the job site, the CLSM was discharged from the truck into a progressive cavity pump and pumped to the holding tank for the microtunneling machine. The CLSM was pumped into the void area created by the retreating microtunneling machine and was held under pressure until it set. The grout pressure was carefully monitored at the operator's control console to balance grout-injection pressures with earth and groundwater pressures. A specially designed double-entry ring seal, with a guillotine closure between the seals and a grout-injection nipple (shown in Fig. 2), was fabricated to ensure that grout pressures could be maintained as the machine was fully retracted.

Ground movements measured during this phase of the test are shown in Fig. 3. The maximum settlement of 9 mm (0.35 in.) occurred near the drive shaft and was partly caused by loss of soil into the shaft through the sheet-pile walls. Settlements were less than 6 mm (0.25 in.) elsewhere, or well within typical specification tolerances.

This phase of the test was an unqualified success (3taheli and Bennett 1996). The ability of the McLaughlin/Markham machine to maintain stability of the excavation and avoid settlements was conclusively demonstrated under very challenging ground conditions. The double-entry ring seal with the guillotine closure was critical to this success of the retraction and could be used with different machines if retraction through unstable soils were a potential necessity. The CLSM was critical to the success of the operation and has many applications in microtunneling including shaft stabilization. This retraction and grouting capability could have significant potential applicatiors in environmental remediation, for example, in constructing horizontal barriers to contaminant migration beneath waste sites. Another potential application is the construction of grout-filled interlinked microtunnels to form arches to support the overburden loads during excavation of the interior for large tunnels.

NEWARK SUBBASIN

Shortly after the WES field trials were completed in December 1994, the Newark Subbasin Lower Relief Sewer Project was constructed in Newark, California. This project included the installation of approximately 7,800 lineal ft (2,377 m) of 36- and 24-in. (914 and 610 mm) sanitary sewer using microtunneling techniques. The tunneling machine was to be launched from shafts that were constructed with driven sheet piles. The tunnel alignment was approximately 15 ft (4.6 m) below the ground surface, and shaft stabilization problems were expected as a result of the soil conditions and shaft construction methods.

Boring logs taken at the launch shaft locations indicated the soil at the elevation of the pipeline was classified as a poorly graded sand (SP), using the Unified Soil Classification System (USCS). The field description of the soil was "SAND, light gray-brown, saturated, medium dense, fine to medium grained sand, below 14 ft (4.3 m): medium to coarse-grained sand, trace fine gravel" (Brown and Caldwell 1994).



FIG. 2--Specially designed double-entry ring seal.

0 . 2 0 �84

0.10

o 4130

-0.40

Ground IVbvaxz~s 2 Feet Above Crown After Retraction

1

/ \ 10 20 30 40 50 60 70 80

~stance From L a x ~ Shaft (feet)

FIG. 3--Measured ground movements. 1 in. = 25.4 mm and 1 ft = 0.3048 m.



Standard penetration tests in the vicinity of the tunnel alignment indicated a range of 8 to 24 blows per foot (0.3 m) using a 2.5-in. (64 mm) inside diameter split-spoon sampler. The water table was approximately 2.5 ft (0.8 m) below the ground surface, indicating 12.5 ft (3.8 m) of static head on the crown of the tunnel.

On any microtunneling project, it is necessary to cut a hole in the sheet piles or other shaft wall materials through which the machine is launched and retrieved. Because of the high groundwater head, the nearby source of recharge, and the sandy soils encountered on this project, ground stabilization techniques were clearly required around the shaft to avoid excessive soil and groundwater inflows into the shaft when the sheet piles were cut away. Dewatering wells had been installed along the launch face of the shaft to lower the groundwater and reduce the potential for soil inflows. However, because of the close proximity of the Oakland Bay, an infinite source of recharge, and the relatively high permeability of the sands, the wells were unable to lower the water table below the elevation of the tunnel machine. At other shaft locations in similar soils, the contractor attempted to use a chemical grout stabilization to aid in shaft construction; however, this technique proved to be ineffective as a result of the high groundwater level.

Based on the complete success of the CLSM during the retraction of the microtunneling machine on the CPAR project, the favorable progression rates of the retunneling through the CLSM, and the similarities of the soil conditions on the Newark Subbasin and CPAR projects, a decision was made to use the CLSM designed at WES as a stabilization material to stabilize the ground around the tunnel shafts, allowing launch of the tunnel machine. Although the CLSM would be used with a different objective in a slightly different application than on the microtunneling research experiments, it was believed that the material would behave similarly and provide a stable face through which to launch the microtunneling machine.

The CLSM was a combination of fly ash, bentonite, cement, and water and was mixed in a grout plant on the ground surface. ASTM Class C fly ash was used in the mixture, eliminating the need to add lime to the mixture. The self-cementing fly ash provided a very cost-effective stabilization agent for a wide range of applications. At the time the stabilization method was used, it was uncertain how long the material would have to gain strength before the launch of the machine could take place (time estimates ranged from 3 to 15 days after the stabilizing material was injected). Because it was not possible to allow the stabilization mixture to set for a long period of time, cement content was increased from 5 to 7 lbs (2.3 to 3.2 kg) per batch to obtain early strength. The early strength allowed the machine to be launched four days after the CLSM was injected. Bentonite was used in the fly ash CLSM to control bleeding and aid pumping. The bentonite also reduced the strength of the CLSM to ensure that tunneling through the material was possible.

In addition, it was not necessary to add the citric acid for the Newark project as this admixture was used to retard the set of the CLSM, a feature that was desirable on the CPAR project (to avoid grouting the machine in the ground during the retraction) but was not needed or desirable for the Newark application.

A stabilization method and injection pattern were developed to apply the fly ash CLSM to the face of the tunnel shaft. Six 2-in. (51 mm) nipples were welded to the inside of the sheet piles, and ball valves were installed at each of the six locations, as detailed on Fig. 4. The fly ash CLSM was mixed on the ground surface in a paddle mixer normally used to mix lubrication drilling fluids which are



FIG. 4-Stabilization method and injection pattern.



standard for microtunneling operations. The fly ash CLSM was then injected through each of the nipples using a 10-ft (3 m) packer that provided back pressure or confinement for the stabilization mixture. The injected material created a stabilized bulb of material that would stand when the sheet piles were removed from the face. The fly ash CLSM was pumped through the packers at a pressure of 25 to 50 psi (0.17 to 0.34 MPa), starting with the packer completely buried i0 ft (3 m) into the soil. The packer was slowly retracted while continuing to pump the CLSM mixture, until there was observable fly ash CLSM return through the seams in the sheet piles. When return was observed, the packer was removed through the nipple on the face, and the ball valve was closed. This procedure was repeated at each of the six locations. Angles of the grouting pattern are indicated in Fig. 4.

After the fly ash CLSM was injected and the ball valves were closed, the mixture was allowed to cure for 24 h, at which time the ball valves were opened. When the valves were opened, it was observed that the nipples were filled with a putty-like material created from the mixture of the pumpable fly ash CLSM and the sand. This observation was encouraging as some had feared that the stabilized material would not eliminate groundwater inflows into the shaft. The mixture was then allowed to cure for an additional 4 days to increase further stability of the face before the sheet piles were cut to provide an opening for launch of the machine.

The fly ash CLSM proved to be an effective means of stabilizing the ground surface as the tunnel face did not collapse when the sheet- pile wall opening was made. The machine was launched in slightly under 4 h with no measurable ground losses into the shaft. In addition, this soft ground mixture could be excavated with the microtunneling machine, and tunnel progression rates through the stabilized plug were comparable to the rates through the native sand material on this project and on the WES research. This is especially significant as many contractors in the United States have attempted to stabilize shafts with high-strength cement grouts which gained significant strength in a short time. The high-strength cementing grout damaged the cutter bits on the rnicrotunneling machine upon launch and, in extreme cases, made completion of the tunnel drive impossible.

In addition to providing the stabilization required to launch the tunneling machine, the cost benefits of using the fly ash CLSM were substantial. Actual material costs for the fly ash CLSM at the first shaft location was $54.80. Labor costs for the application of the CLSM were approximately $700. Chemical grouting operations (which may have had only marginal effectiveness) were quoted at $17,000, representing over $16,000 of cost savings for the use of CLSM on the first shaft location. This stabilization technique was used at several additional shaft locations, representing a saving of approximately $100,000 on the project. These cost savings, as a result of the use of the fly ash CLSM, represent 40% of the total projected profit margin for the project at the time the bid was prepared.

Although fly ash has been used for soil improvement for many years, its range of application continues to increase. Along with the advent of new mixtures, such as the CLSM developed at WES, new construction techniques offer new applications for the material. The Newark project was the first of its kind to use a CLSM for shaft stabilization.

The successful use of CLSM on the WES research for maintaining stability of the microtunnel bore during retraction through highly unstable soils should provide incentives for pioneering applications in waste site remediation and other critical projects where retrievability could be a distinct advantage. Because of the success on these



projects, the use of fly ash stabilization is sure to increase in microtunneling and other underground applications.

The development of this CLSM and the collaboration between the Corps of Engineers and industry that led to these highly successful demonstrations on critical microtunneling applications clearly show the benefits that can be derived by both government and industry where resources are focused on common problems.

ACKNOWLEDGMENTS

Presentation of this information was made possible by the U.S. Army Engineer Waterways Experiment Station. Some of the information provided in this text was based on experiences gained on microtunneling projects. This included projects constructed by Constructors Pamco of Seattle, Washington. Additional information was gathered on the Corps of Engineers' microtunneling research projects conducted under the CPAR project in Vicksburg, Mississippi. Permission to publish the results related to the Corps' CPAR program was granted by the Chief of Engineers.

We appreciate the cooperation of the authorities at the U.S. Army Engineer Waterways Experiment Station, Constructors Pamco, and the Headquarters, U.S. Army Corps of Engineers, that permitted us to prepare and present this paper for publication.

REFERENCES

American Concrete Institute, 1990, "Cement and Concrete Terminology," ACI 116-90, Publication SP-19, Detroit, MI.

American Concrete Institute, 1994, "Controlled Low Strength Materials (CLSM)," ACI 229 R-94, ACI Committee 229, Detroit MI.

Brown and Caldwell, Sept. 1994, "Union Sanitary District Newark Subbasin Lower Relief Sewer, Reference Materials," Project 50-61.

r Products, Aug. 1995, "Feds Potentially Increase Fly Ash Usage," pp. ii.

Davis, R. E., Carlson, R. W., Kelly, J. W. and Davis, H. E., May-June 1937, ~Properties of Cement and Concretes Containing Fly Ash," ACI Journal Proceedinqs, Vol. 33, No. 5, pp. 577-612.

Fly Ash Resource Center, 20 Dec. 1996, "Coal Combustion By-Products," information gathered from the Internet, URL address: http://www2.interaccess.com/flyash/index.html.

Johnson, T. B., Ed., 1995, Facts about Coal, National Mining Association, Washington, DC.

Mehta, P. K., 1986, Concrete Structures. Properties and Materials, Prentice-Hall Inc., Englewood Cliffs, NJ, pp. 269-270.



Minina Enqineerinq, 1994, "Once Only Waste, Coal Ash Now Finding Many Uses," Vol. 46, No. 8, p. 934.

Smith, D. K., 1990, Cementing, Revised Ed., Society of Petroleum Engineers, Inc., New York, p. 21.

Staheli, K. and Bennett, D., April 1996, ~Results of Controlled Field Tests of a Retrievable Microtunneling System with Reaming Capabilities," in Proceedinas of the International NO-DIG '96, pp. 183-202.

Thomson, J. C., 1993, PiDeJackina and Microtunneling, Blackie Academic & Professional Press, Glasgow, U.K.


Donald R. Snethen 1 and John M. Benson 2

C O N S T R U C T I O N OF CLSM A P P R O A C H E M B A N K M E N T TO MINIMIZE THE BUMP AT THE END OF THE BRIDGE

REFERENCE: Snethen, D. R. and Benson, J. M., "Construction of CLSM Approach Embankment to Minimize the Bump at the End of the Bridge," The Design and Application of Controlled Low-Strength Materials ( Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: The Oklahoma Department of Transportation and Oklahoma State University School of Civil and Environmental Engineering are currently conducting a research program to evaluate options to minimize approach embankment settlement. The research program involves construction of three new bridges on U.S. 177 north of Stillwater, Oklahoma. Five of the six approach embankments/abutment backfills were constructed using different construction materials and methods. The constructed approach embankments include: unclassified borrow (control section), geotextile reinforced wall, controlled low strength material, dynamically compacted granular backfill, and flooded/ vibrated granular backfill. The approach embankments/abutment backfills have been instrumented to measure earth pressure on the abutment walls, settlement and lateral movement of the approach embankments, and groundwater conditions. The paper documents the design and construction of the CLSM approach embankment and reviews the instrumentation data collected to date.

KEY WORDS: controlled low strength material, flowable fill, approach embankments, settlement, differential settlement, bridge construction

Background

Differential settlement at bridge abutments is a persistent problem for transportation agencies. Relatively small differential movements produce the "bump at the end of the

1professor, School of Civil and Environmental Engineering, Oklahoma State University, Stillwater, OK 74078.

2Civil Engineer, USAE, Kansas City District, Kansas City, MO 64106.

165



bridge," which results in ride discomfort and a potential hazard for motorists. Heavy vehicle traffic may accelerate the damage to approach slabs and bridge decks because of dynamic forces. Additional maintenance may be required to prevent deterioration of the approach fill and abutment system.

Differential settlement problems are usually attributed to excessive consolidation of the embankment and foundation soils or inadequate compaction of the approach embankment or both. Other factors that may influence the problem include soil erosion from improper surface or subsurface drainage, frost heave, or swelling soils. The Colorado Department of Highways studied 20 sites within their state and concluded that the primary causes of bridge approach settlement are one or more of the following:

�9 Time-dependent consolidation of embankment foundation. �9 Time-dependent consolidation of approach embankment. �9 Poor compaction of abutment backfill caused by restricted

access of compaction equipment. �9 Erosion of soil at the abutment face. �9 Poor drainage of embankment and abutment backfill.

The approach slab design and type of abutment and foundation may also affect performance.

In Oklahoma, the Oklahoma Department of Transportation (ODOT) sponsored research surveyed 52 state and federal transportation agencies that have had problems with bridge approach s~ttlement, and the survey results were similar to the conclusions from the Colorado Department of Highways study. Of the causes listed in the study, consolidation of the embankment or foundation materials was considered the most significant.

Most bridge approach embankments are constructed using conventional soil compaction methods. Soils from roadway excavations or borrow pits are commonly used. A major problem develops with approach embankment construction when conventional compaction equipment tries to compact the soil near the abutment wall and wing walls. The result is a nonuniformly compacted material that is more susceptible to differential settlement. The alternative to using conventional compaction methods is "hand" compaction using small scale vibratory or impact compaction machines. This becomes labor intensive and requires additional care to ensure uniformity and level of compaction.

In an effort to address the bump at the end of the bridge problem, ODOT has undertaken an experimental construction research project to evaluate five different approach embankment construction methods. The research is being conducted at a relocation project in which three new bridges are being constructed to relocate a two-mile section of U.S. 177 north of Stillwater, Oklahoma. Five of the six approach embankments are approximately the same height and the foundation soils are relatively uniform, consisting of fine to medium dense sands. The topography in the alluvial valley is level with no significantly varying geologic features. The relatively uniform conditions provide an excellent opportunity to evaluate approach embankment material and construction methods.

Materials and construction methods used for the five approach embankments in the study include:

�9 Unclassified borrow placed by contractor's discretion (i.e., equipment) at 95% Standard Proctor density. This serves as the control for the research study.

�9 Geotextile reinforced approach embankment using a nonwoven geotextile and granular backfill (i.e., concrete sand).

�9 Controlled low strength material. �9 Dynamically compacted granular backfill. �9 Flooded and vibrated granular backfill.


SNETHEN AND BENSON/APPROACH EMBANKMENT 167

During and following construction, all five approach embankments and bridge abutments were instrumented to evaluate the performance of the approach embankments and interaction with the abutment walls. Specific instruments and the parameters they monitored included:

�9 Total pressure cells on the back of the abutment walls at the pavement centerline to monitor lateral earth pressures caused by the approach embankments.

~ Amplified liquid settlement gages manufactured by SINCO beneath the approach embankments at the pavement centerline and offset 10 ft (3 m) to monitor settlement.

�9 Inclinometer casings with telescoping couplings to monitor lateral displacement and settlement by mechanical hook within the approach embankment and foundation materials.

�9 Piezometers (open-tube type) to monitor pore water pressures. �9 Surface survey points to monitor total surface movement.

The instruments were monitored during construction and for approximately 18 months since completion of the approach embankment construction, including approximately 9 months under traffic loading.

The major emphasis of this paper is the description of the construction, monitoring, and general performance of the controlled low strength material (CLSM) approach embankment.

General Construction Considerations

The CLSM approach embankment was constructed at the north end of Bridge 2 which is one of two overflow structures in the relocation project. The bridge consists of a cast-in-place reinforced concrete deck resting on precast concrete beams. A cast-in-place concrete pier cap rests on reinforced concrete columns attached to drilled shafts founded in the local shale, which underlies the alluvial sands. The foundation conditions at Bridge 2 are shown in Fig. 1. Essentially the foundation profile consists of approximately 32 ft (9.8 m) of poorly graded, fine-medium sands and silty sands in a generally medium to dense state. The shale is a hard dry claystone with intermittent layers of hard limestone.

The earth embankment just beyond the approach embankment to Bridge 2 is approximately 14 ft (4.3 m) high. The embankment construction sequence involved building the embankment to its full height, then excavating for construction of the abutment and wing walls and placement of the CLSM approach embankment. The approach embankment extended horizontally 16 ft (4.9 m) from the abutment wall at the base of the wall and approximately 24 ft (7.3 m) at the top of subgrade, as shown in Fig. 2. The abutment and wing walls are cast-in-place reinforced concrete founded on H-piles (vertical and battered) driven to the top of shale. Photographs in Fig. 3 show the major steps in the approach embankment construction from earth embankment construction through paving.

C L S M Construction Considerations

CLSM was selected as an option for approach embankment research because of its simplicity of construction and strength for performance under traffic loads (i.e., past experience with utility backfills). Essentially the CLSM approach embankment is a large mass of CLSM placed behind the abutment wall, confined on the sides by the wing walls and the back by the earth embankment. The total thickness is approximately 8 ft (2.8 m) and the top surface serves as the top of subgrade adjacent to the bridge. The pavement over



N SCALE

0 FEET 5

~ 'CONTROLLED LOW-

STRENGTH BACKFILL

5 UNCLASSIFIED

BORROW

SILTY SANDS/ SANDY SILTS

POORLY-GRADED SANDS

SANDY CLAYS/ CLAYEY SANDS

POORLY-GRADED SANDS

SHALE

PAVEMENT SURFACE_ TOP OF WALL.

TOP OF SUBGRADE" NORMAL COUPLING -~'

TOP TPC-

BRIDGE SEAT. MIDDLE TPC"

BOTTOM OF BEAM,

- - B O T T O M OF LOW BOTTOM TPC. STRENGTH P,LL

TELESCOPING COUPL I~1(~ ALSG"

BOTTOM OF FILL

TELESCOPING C OU PLIN~G "

TELESCOPING COUPLING-

BOTTOM OF SANDY SILTS/- SILTY SANDS

NORMAL COUPLING-

BOTTOM OF POORLY- GRADED SANDS

NORMAL COUPLING BOTTOM OF SANDY CLAYS

& CLAYEY SANDS

TOP OF SHALE/BOTTOM OF, POORLY-GRADED SANDS

1" GAPPED COUPLING-

BASE OF INCLINOMETER CASING-

,923.01 _922.10 -921.68 -920 .88 (-0.8' BELOW -920.13 SUBGRADE)

-917.63 -917.13

-915.13

-914.13 913.68 (-8') -913,13 -912.28 ( -9.4') -911.13

__9.~07 907.68 (-14') .28 (-14.4')

-902.18 (-19.5')

-893.78 (-27.9 ' )

-892.08 ( -29.6 ' )

-889.68 ( -32 ' )

-882.08 ( -39.6 ' )

-880,68 ( - 4 f )

875.18 ( -46.5 ' )

871.98 ( -49.7 ' )

869.68 ( -52 ' )

FIG. 1--Centerline cross section and subsurface profile for north abutment wall, Bridge 2.



STA. 168+69.37 [ELEV.= 921.73

r I . . . . ~ TOP OF SUBGRADE

E

TOP OF SUBGRADE THIS AREA IS TO BE EXCAVATED I-- L / B--T'-'BRI~ -~ON-TRA'-C-TOR-----'--"'-.~ I-] 11 ~ I q-

STA, 168+54.33 ,_,j,,,.r,,~, I 11--

EXIST. GROUND LINE

FORM ALONG OUTSIDE OF WING TO CONTAIN LOW STRENGTH BACKFILL MATERIAL

TOP OF SUBGRADE OW STRENGTH BACKFILL MATERIAL / I /

.,, ' ~

.... EXIST. GROUND LINE/ DETAIL

F I G . 2--Excavation, preparation, and construction sequence for CLSM approach embankment.



FIG. 3a--Earth embankment construction (i.e., over-build) for CLSM approach embankment.

FIG. 3b--Excavation for abutment wall construction at CLSM approach embankment.



FIG. 3c--Completed abutment wall and wing walls with steel at CLSM approach embankment.

FIG. 3d--Excavation o f backfill area at CLSM approach embankment.



FIG. 3e Prepared bac~ill area at CLSM approach embankment.

FIG. 3f--CLSM placement during approach embankment construction.



FIG. 3g--Finishing of CLSM a)%r placement.

FIG. 3h--Cured CLSM approach embankment with inclinometer casings (2) and piezometer riser prior to placing base course and paving.



the approach embankment consists of approximately 6 in. (15 cm) of select aggregate base course and 10 in. (25 cm) of full depth asphalt concrete.

The CLSM mix consisted of granular material cement, fly ash, and water in the following proportions per cubic yard:

2680 lbs granular material 50 lbs cement (Type I)

250 lbs fly ash (Class F) 500 lbs water

The mix was selected to obtain a compressive strength of 300 psi at 28 days. Quality control for the CLSM placement involved a flow test. Each ready-mix truck load was tested and the final water content adjusted to meet the slump requirement.

Construction of the CLSM approach embankment started with the excavation of earth embankment material from behind the abutment wall and between the wing walls. The earth embankment was shaped on a near IV-IH slope up to within approximately 2 ft (0.6 m) of the top of subgrade, which was protected with a wooden form. A small trench was excavated at each end of the backfill area to strengthen the edges and comers behind the wing walls. Additional cover sand was placed over the drain system behind the abutment wall to protect the drain material from contamination from the CLSM. The total pressure cells on the back of the abutment wall were covered with plastic to prevent the CLSM from bonding to the cells. A total of 8 man-hours was required to prepare the backfill area.

The CLSM was delivered in ready-mix tracks, with two typically dumping at the same time. A total of 23 ready-mix truck loads of 9 cubic yards each were dumped for a total volume of 207 yard 3 (158 m 3) in 4.5 hours. The comers between the abutment wall and wing walls were vibrated to assure that no voids resulted and the surface was finished with a large float. The total cost for the CLSM and its placement, which included preparation of the backfill area and finishing the CLSM, was $14,560. A general comparison of the equipment, construction time, and cost of the five approach embankments studied in the project is presented in Table 1.

TABLE l --Cost and time of construction summary

Approach Estimated Construction Embankment Quantities Cost Days

Unclassified Borrow 300 yd 3 $1500 4 (Control)

Geotextile 375 yd 3 fill $25000 5 Reinforced 2230 yd 2 textile Wall

CLSM 207 yd 3 $14560 2

Dynamically 306 yd 3 $15000 5 Compacted Granular Fill

Flooded and 306 yd 3 $16000 2 Vibrated Granular Fill

Equipment

Loader, walk-behind pad vibrator

Loader, walk-behind pad vibrator, concrete spreaders, water truck

Concrete trucks, concrete vibrator

Crane, concrete block, walk-behind pad vibrator, water truck

Water truck, concrete vibrator

i yd 3 =0 .765m 3



Performance Monitoring

The total pressure cells and amplified liquid settlement gages were installed prior to construction of the CLSM approachment. The inclinometers and piezometer were installed approximately two weeks after the CLSM was placed. The surface survey monitoring points were installed after the pavement was completed. Total pressure and settlement were monitored during construction and 5- to 6-week intervals since completion of construction. The total pressure measured on the back of the wall plotted with time is shown in Fig. 4. The upper two total pressure cells show very small pressures (i.e., less than 1 psi (6.9 kN/m2)). The lower cell is only slightly higher at about 1 psi (6.9 kN/m2). The slightly higher pressure on the lower cell is most likely due to the extra drain cover material which extended above the lower cell.

The amplified liquid settlement gages indicate a total settlement of the embankment material beneath the CLSM and settlement of foundation soils to be 0.13 ft (0.3 cm) and 0.34 ft (0.9 cm) for the offset and centerline instruments, respectively (Fig. 5). The most likely explanation for the increased settlement at a position 10 ft (3.0 m) from the centerline would be the influence of the spur dike construction adjacent to the abutment and wing wall to control flow toward the bridge. The total settlement of 0.13 ft (0.3 cm) has not shown up as any deformation of the pavement surface, probably because most of that settlement occurred prior to paving.

The limited surface survey data confirm that there has been no development of the bump at the end of the bridge. The inclinometer data show no significant lateral movement in or beneath the CLSM (Fig. 6). The telescoping couplings on the inclinometer casings have shown no significant movement in the embankment or foundation materials. In fact, they show less settlement than the amplified liquid settlement gages.

Summary

The use of CLSM as an approach embankment construction material appears to be a simple and reasonably cost effective method to reduce the potential for developing the bump at the end of the bridge. The construction procedure requires a bit more preparation time once the abutment and wing walls are completed; however, that is easily compensated for by the significantly reduced construction time and the associated need for quality control testing such as that required for earth approach embankments. The lateral earth pressure and settlement of the approach embankment are generally less than the other construction options study, so the overall performance is also favorable.



v

C L

2.0

1.0

3.0

L J

4-I 1-95 10-28-95

3.0 M I D D L E CELL

2.0

1.0

0 .0

5 -15-96 12-1-96

Date

4 -11-95

2.5

2.0

1.0

0.0

10-28-95 5-15-96 12 -1 -96

Date

4 -11-95 10-28-95 5-15-96 12-1-96

Date

FIG. 4--Total pressure on back of abutment wall at CLSM approach embankment.



o 350

o 300

o 250

o 200

o 15o

o l o o

o o50

o ooo

4,11/95

CENTERLINE

7/20/95 10/28/95 215/96 5/15/96 8t23/96 12/1196 3/11/97

Date

v

cO

o IBO

0 I ~ o

i , ' ~ 0

,, nc, n

,, 0 4 ' ~

o 02o

O F F S E T

7/20L95 I 0/28/95 215/96 5 l l 5/96 8123/96 1211/~$

Date

FIG. 5--Total settlement from amplified liquid settlement gages at CLSM approach embankment.



FIG. 6--1nclinometer data.for CLSM approach embankment.



Bibliography

Ardani, A., "Bridge Approach Settlement," Report No. CDOH-DTP-R-87-06, Colorado Department of Highways, 1987.

TRB, NCHRP Synthesis of Highway Practice 159, "Design and Construction of Bridge Approaches," Transportation Research Board, National Research Council, Washington, DC, 1990.

TRB, NCHRP Synthesis of Highway Practice 2, "Bridge Approach Design and Construction Practices," Transportation Research Board, National Research Council, Washington, DC, 1990.

Laguros, J. and Zaman, M., "Evaluation of Causes of Excessive Settlements of Pavements Behind Bridge Abutments and Their Remedies--Phase III," Study 2163, ORA 157-293, Oklahoma Department of Transportation, Oklahoma City, OK, 1990.

Laguros, J., Zaman, M., and Mahmood, I., "Evaluation of Causes of Excessive Settlements of Pavements Behind Bridge Abutments and Their Remedies--Phase II," Study 86-04-2, ORA 159-293, Oklahoma Department of Transportation, Oklahoma City, OK, 1990.

Laguros, J., Boyd, D., Zaman, M., and Mahmood, I., "Evaluation of Causes of Excessive Settlements of Pavements Behind Bridge Abutments and Their Remedies--Phase I," Study 84-12-2, Oklahoma Department of Transportation, Oklahoma City, OK, 1986.

Schwidder, A., "Estimation of Stress and Deformation Parameter at Salt Fork Bridges on U.S. 177," M.S. thesis, Oklahoma State University, Stillwater, OK, 1993.

Benson, J., "Construction of Experimental Approach Embankments at Salt Fork River Bridges on U.S. 177 and Their Initial Performance," M.S. thesis, Oklahoma State University, Stillwater, OK, 1996.


Donald D. Gray, l Thirupathi P. Reddy, 2 D. Courtney Black) and Paul F. Ziemkiewicz 4

FILLING ABANDONED MINES WITH FLUIDIZED BED COMBUSTION ASH GROUT

REFERENCE: Gray, D. D., Reddy, T. R, Black, D. C., and Ziemkiewicz, R F., "Filling Abandoned Mines with Fluidized Bed Combustion Ash Grout," The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: The hydraulic backfilling of abandoned room and pillar coal mines with ash-based grout holds promise as an environmentally beneficial method of ash disposal, capable of preventing acid mine drainage and subsidence. For this scheme to be economically viable, the grout must be sufficiently flowable so that mines can be filled from a small number ofboreholes. This paper describes the development andtesting of a water-ash-bentonite grout using ash from a coal and gob burning atmospheric pressure fluidized bed combustor. Bentonite was needed to prevent settling which would limit the ability of the grout to spread. Laboratory techniques were devised to measure the rheological parameters of the grout. A static model was developed to predict the maximum distance of spread due to gravity. A field injection of 765 m 3 of grout into an inactive mine panel showed that the grout flows well enough to make hydraulic backfilling feasible.

KEYWORDS." hydraulic backfilling, fluidized bed ash, grout, slurry, acid mine drainage, subsidence, yield stress fluid, flowable fill, CLSM

~Associate Professor, Department of Civil and Environmental Engineering, West Virginia University, Morgantown, WV 26506-6103.

2Graduate Research Assistant, Department of Civil and Environmental Engineering, West Virginia University, Morgantown, WV 26506-6103.

3Senior Project Coordinator, National Mine Land Reclamation Center, West Virginia University, Morgantown, WV 26506-6064.

4Director, National Mine Land Reclamation Center, West Virginia University, Morgantown, WV 26506-6064.

180


GRAY ET AL./ABANDONED MINES 181

This paper reports on the development of a method of remedying several environmental problems caused by the mining and burning of coal. For many years, the predominant technique for mining coal in Appalachia was the room and pillar method in which coal is removed to form a grid of intersecting passageways, and a checkerboard of rectangular coal pillars is left to support the roof. When these mines are abandoned, acid forms as air and groundwater come into contact with exposed pyrite. The resulting acid mine drainage (AMD) is a major cause of water pollution, often requiring expensive treatment for many years. Over time, the mined passages tend to collapse, which may result in subsidence at the surface, damaging roads and buildings. Power plant owners face the problem of disposing of the ash they produce. Although ash can be used beneficially, the supply often exceeds the market demand; and the ash is placed in increasingly expensive landfills. In the hydraulic backfilling method under investigation, abandoned mines are filled with an ash slurry which hardens in place, preventing acid formation and subsidence, and returning the ash to its place of origin, a space that has no other use.

Two factors are particularly important in determining whether hydraulic backfilling is economically competitive with existing practices. The slurry must be sufficiently fluid to fill the mine passages when injected through a small number of boreholes drilled from the surface, and the slurry must be able to harden with enough strength to support the roof. These properties must be achievable without using undue quantities of costly additives.

Ash Properties

The source of the ash used in this project is the Morgantown Energy Associates- Beechurst Avenue Power Plant in Morgantown, West Virginia. This plant burns a mixture of coal, gob (coal refuse), and limestone in an atmospheric pressure fluidized bed combustor (AFBC). The percentage of gob burned is varied depending on power requirements. The percentage of limestone is likewise varied to control sulfur emissions. The resulting powdery fly ash consists of irregular, popcorn-shaped particles which range in size from about 5 to 100 pm. The gravel-like bottom ash particles range from about 75 to 10 000 lam (1 cm). Primarily because of the limestone, the ash has cementitious properties. Finite element calculations indicated that a compressive strength of about 3.4 MPa was needed to prevent subsidence at the mine used for the field test described below. The ash-bentonite-water slurries reported in this paper self-hardened to strengths in excess of 6.8 MPa (Head et al. 1996). The time required for the slurry to harden is long enough that the change in properties during injection can be neglected. Ash samples from the plant have widely variable properties as a result of the changes in the fuel mixture and the manner in which the ash is collected and stored. Trucks that transport the ash from the plant to the disposal site contain randomly differing proportions of fly and bottom ash.

Grout Rheology

As a concentrated suspension of compact rigid particles, it was expected that an



ash-water grout would behave as a yield stress fluid of the Herschel-Bulkley (HB) or Bingham type (Gupta 1993). For an HB fluid, the constitutive equation for parallel shear flow is

where z is the shear stress, zy is the yield stress, r is the consistency index, y is the rate of strain, and s is the flow index. A Bingham fluid obeys a special form of Eq. 1 in which the flow index s is unity and the consistency index r is called the plastic viscosity. Although the grout was originally assumed to be an HB fluid, tests showed that the Bingham model was quite sufficient.

This rheology is dependent on the avoidance of direct particle to particle contact such as might occur as a result of settling. I f such contact occurs, an additional Coulomb friction term proportional to pressure must be added to the constitutive equation. For parallel shear flow of a Bingham fluid with Coulomb friction, this relation is

= zy + r y + ~tP (2)

where P is the pressure and ~t is the Coulomb friction coefficient. The Coulomb friction term dramatically reduces the distance a yield stress fluid

flows in response to gravity or pressure forces. This reduction could require an excessive number of injection boreholes to fill a mine, rendering hydraulic backfilling impractical. Consequently, it is important to devise a recipe for a grout that does not settle.

During the preliminary testing of fly ash and water mixes (without bentonite), settling was observed. When measurements of the pressure drop in a tube were attempted, the grout locked up, and there was no flow. An attempt to perform tests with a parallel rotating disk rheometer also failed because of settling.

The majority of the tests were performed using a commercial rotational viscometer in which a T-bar spindle is rotated at constant angular speed and the required torque is measured. The T-bar spindle consists of a shaft with a single perpendicular crossbar. The rotating crossbar tends to cut a path through the grout, so that the torque falls if the path is retraced. This was overcome by using a device that periodically translates the viscometer up and down parallel to the spindle axis so that the crossbar follows a helical path through previously uncut grout. The pitch of the helix has to be greater than twice the diameter of the crossbar to ensure that neither half-length of the crossbar passes through previously cut grout. Because the speed of translation is constant, a limit on the pitch imposes a limit on the angular speed of the spindle. A maximum angular speed producing a pitch twice the minimum was used.

When this device was used to test an ash and water grout, it was expected that the torque would vary periodically because the length of spindle shaft submerged in the grout varies periodically. However, the amplitude of the torque variation increased with time until the torque sensor reached full scale. This was evidence that settling of the particles caused the lower layers of the sample to become more concentrated than the upper layers, producing Coulomb friction and limiting the ability of the grout to flow.


G R A Y E T A L . / A B A N D O N E D MINES 183

G r o u t S t a b i l i t y

By definition, an unstable mix bleeds more than 5% of its water during a 2-h period of standing. Bleed tests were performed on various grouts, using procedures similar to ASTM Test Methods for Bleeding of Concrete (C 232). Freshly prepared samples were placed in cylindrical containers and covered to prevent evaporation. After 2-h, any clear water that bled to the surface was pipetted out and weighed. Mixes of fly ash and water only were unstable. To prevent the settling of the solid particles and thus make the grout stable, various weight fractions of WYO-BEN 250-mesh bentonite were mixed with the ash before the addition of water. A plot of these observations in Fig. 1 shows that the percent bleed increases almost linearly with an increase in the water fraction (of the total mass) and decreases with an increase in the bentonite fraction (of the solids mass).

16

14

12

10

8

6 Unstable grout

4 Stable grout 2

0 t _- 30 32

�9 0% bent

�9 �9 �9 3% bent. �9 �9 5 % b e n t .

_- �9 �9 �9 A

| �9 �9 I |

: & I ~ l I I

34 36 38 40 42 4 4

W a t e r F r a c t i o n ( % )

FIG. 1-- Results of bleed tests on mixes containing equal portions of fly ash and

bottom ash.

Further rotational viscometer tests were carried out with fly ash-water-bentonite grouts with various bentonite fractions. A special technique was devised to quantify the degree of settling. The T-bar spindle in the rotational viscometer was moved vertically downward at a constant rate from the top of the grout sample while rotating at a constant angular velocity. This was done twice for each sample, once immediately after stirring the mix to uniformity and again after waiting for a certain time. The torque increased as the spindle moved downwards in both cases, but the increase was greater in the second case. Assuming that no settling had occurred in the freshly stirred grout, the increase in the torque in this case can be attributed solely to the increase in the submerged length of the spindle. The differences between the torques in the freshly stirred grout profile and the torques at the corresponding points in the second profile show the effect of settling. The rate of increase of these residuals with depth is indicative of the degree of settling. Figure 2 shows a straight line fit for the torque difference versus a measure of depth for 48% water fraction grouts with 0% and 7% bentonite. There was very little settling in the



7% bentonite case, so this recipe was selected for rheological testing.

~=

O [-,

3.0

25

2.0

15

1.0

05

0

- - 7~ benr177 ...... no be.nconice

. i � 9

~

~

o

o . - ' ' " _ _ _ . ~ _ _ - - J - - ~ ---'- -

I I I I I L P ! !

2 3 4 5 6 7 8 9 10

Depth Measure

FIG. 2-- Effect of addition of bentonite on settling.

Theory of Rheological Testing

The mixer viscometer method introduced by Metzner and Otto (1957) and adapted to fresh concrete by Tattersall and Bloomer (1979) was extended to determine the rheological properties of stable grouts under the assumption that they were HB fluids�9 The mixer viscometer method uses the slope and intercept of the torque versus angular speed plot (either on linear-linear or log-log paper) along with two instrument constants to obtain parameters for Newtonian, power-law, Bingham, and HB fluid models. The instrument constants are found by testing materials with known properties.

The basic principle of this method is that the torque T needed to maintain a constant rotational speed N is equal to N multiplied by the apparent viscosity (rl) of the substance at the corresponding rate of strain and G, which is an instrument constant.

T = G 1] N (3)

For an HB fluid, the constitutive equation for parallel shear flow is given by Eq. 1. Solving Eq. 1 for the apparent viscosity gives

r I = ~ + r y,-1 Y

(4)

Further simplification requires that the rate of strain be related to the rotational speed�9



The simple assumption y = K N , where K is another instrument constant, has been verified for numerous non-Newtonian fluids (Skelland, 1983). Substituting into Eq. 3 yields

G ' ~ T - Y + G r K " - I N s (5)

K

To use T versus N data to determine r and s in the HB model, it is necessary to have an independent measurement ofzy. This was obtained using the vane method of Nguyen and Boger (1992) in which a four-bladed vane is immersed in the sample, and the torque is increased until the vane begins to rotate. The critical torque is related to the yield stress by assuming that the yield stress occurs uniformly on a cylindrical surface which circumscribes the vane. Data were collected using a Stormer viscometer fitted with a custom-made vane. Substituting the resulting yield stress into the Eq. 5, moving the yield stress term to the left side, and taking logarithms gives

G "c In ( T Y ) = In (G r K s-l) + s In (N) (6)

K

In this equation, G, Zy, and K are known constants. Plotting the left-hand side versus In(N) gives a straight line with a slope ofs and an intercept ofln(G r K~-/). Thus, all the parameters of the constitutive equation for the HB fluid are determined.

Rheological Test Procedure

The rheological parameters of fly ash-water-bentonite grouts were measured using a commercial rotational viscometer fitted with a T-bar spindle and a mount which translates the device up and down parallel to the spindle axis. The angular speed was increased in steps of 1 r/min starting with 1 r/min. An automatic setting on the viscometer allowed all torque readings to be taken at the same depth. This was done to counter the effect of increase in the submerged length of the spindle because of its vertical motion. The grout was stirred thoroughly between each reading to minimize any settling. A freshly mixed grout sample using ash from the same lot was used for each set of readings.

These tests showed that for the strain rates that were achievable, the 48% water fraction and 7% bentonite fraction grout was very close to a Bingham fluid. As shown in Fig. 3, the stress-strain plot is a straight line with a y-intercept value equal to its yield stress. The independent measurement of the yield stress was a confirmation of the extrapolation of the straight line to get the y-intercept.

Based on this plot the rheological parameters for the 48% water fraction and 7% bentonite fraction grout are:

plastic viscosity r = 0.0128 • 0.0006 Pa s yield stress zy = 55.38 • 3.54 Pa (from extrapolation)



yield stress Zy = 54.8 + 0.3 Pa (from independent measurement).

58 ~

57

56

E 5 5 f

) 54 <

53

For the Bingham Model Fit:

Plastic Viscosity = 0.0128N.S/m 2 = 0.766 N .m in/m:

Yield Stress = 55.38 Pa

Yield Stress Extrapolated = 55.38 Pa

Yield Stress Ind. Measurement = 54.80 Pa

520 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Average Strain Rate (per minute)

FIG. 3-- Stress-strain rate p l< for 48% water fraction and 7% bentonite.

Maximum Spread Model

One goal of this project was to predict the flow of grout into a mine by solving the partial differential equations of mass and momentum conservation for an HB or Bingham fluid using the numerical techniques of computational fluid dynamics. Although partial simulations were obtained, this problem turned out to be too ambitious for the present generation of personal computers. This motivated the formulation of a simplified model to predict the maximum distance of spread using algebraic formulas.

The basis of this model is the concept that grout ceases to flow when the driving force is balanced by the shear force transmitted through the flow boundaries. In the case



of a stable yield stress fluid, the maximum possible shear stress at a wall when the fluid stops is the yield stress. For an unstable fluid, Coulomb friction can generate much larger shear stresses. As the grout spreads, the area of contact with the bounding surfaces increases continually so that the resisting force also grows.

When grout is first injected through the mine roof, it piles up on the floor and spreads radially by gravity. When the leading edge reaches the walls, the grout begins to flow primarily along the axis of the mine passage(s). Until the grout reaches the ceiling, gravity is the driving force, even i f the floor is horizontal. I f the free surface rises to the ceiling, the pressure generated by the injection pump must also be considered. Because the pressure generated by a pump is always finite, a flow of yield stress fluid driven solely by pressure always has a finite maximum spread. This case was first considered by Lombardi (1985), whose results were corrected during this project. But in the present application, a gravity flow model is more appropriate as a result of the low yield stress and stability of the grout.

Consider first the radial (axisymmetric) spread of a stable yield stress fluid on a horizontal floor. When the fluid comes to rest it forms an axisymmetric mound with a maximum thickness t,,~ at radius r = 0, decreasing to 0 at r,,o~. On a free body consisting of the fluid contained in a 180 o arc between r and r+dr , the only horizontal forces are the resultants of the nearly hydrostatic pressure distributions on the vertical surfaces and the yield stress on the bottom. Summing these forces to zero in some horizontal direction gives this differential equation for t.

d t 2 2 ~ _ y ( 7 )

d r w

Here w is the specific weight of the grout. This equation can be solved to give the thickness as a function of radius. The maximum radius of spread is

2 W tma x

r m a x - 2 1 :

Y

(8)

Substituting the values appropriate to the Fairfax mine test described below (w = 12 350 N/m3~ Zy = 55.4 Pa, tmo ~ = 1.5 m ) gives r,,~ = 250 m. This indicates that gravity spreading will certainly enable the grout to reach the passage walls and begin to flow along the passages. This calculation conservatively ignores the effect of the sloping mine floor at Fairfax.

As the grout enters a passage, its flow becomes similar to that of water in a rectangular canal. Assume that the passage is straight with a bottom slope of 0 with the horizontal and a constant width o f b. Choose as a free body the fluid contained between cross sections at axial coordinates x and x + dx, measured along the sloping floor. When the fluid comes to rest, the forces parallel to the channel axis are the resultants of the nearly hydrostatic pressures on the cross sections, the shear stresses on the sides and



floor, and the component of weight along the passage. Summing and equating to zero leads to the following differential equation.

d t _ t a n ( O ) - ( 2 t + b )

d x b t w cos(O) (9)

For the special case of a horizontal passage (0 = O) the solution is

t I 2 2z x = tma x Y W

(10)

and the maximum distance of spread Xmo~ is

2

W tma x X

max 2 (11)

For sloping passages, the condition for a finite distance of spread is d t / d x < O. This requires that

b t z > w sin(O) (12) Y (2 t + b)

For slopes for which this condition is violated, the spread is theoretically unlimited, although the hardening of the grout would impose a practical limitation. For the Fairfax mine test, b = 5.5 m and 0 = 0.57 ~ (1%). Assuming t,,,~ = 1 m gives a right-hand side of 90.6 Pa, violating the criterion for finite spread. This indicates that the grout should be able to spread indefinitely in the Fairfax mine.

The solution for the finite spread case is

X - w b co, o, [ tmax_ t , c + b,c In I ct b' l c . . . . . 'max'- b (13)

c = 2 ~y- w b s in(0) (14)



The maximum distance of spread is found by substituting t = O.

Spread Test

The variability of the ash requires that the grout recipe be varied in the field to maintain consistent flowability. A spread test was adopted as a field test to assess grout flowability. The spread test uses a cylinder 3 in.(7.62 cm) in diameter by 6 in.(15.24 cm) in height, open at both ends. The cylinder is placed vertically on a horizontal surface and filled with grout. The cylinder is slowly lifted, the grout is allowed to spread radially, the distance of spread is measured in two perpendicular directions, and these distances are averaged. This procedure was adopted from Bhat et al. 1995. It was later learned that it also described in the Provisional Standard Test Method for Flow Consistency of CLSM (ASTM PS-28).

Spread tests were done with varying amounts of bentonite and water. Figure 4 shows that increasing the water fraction increases the spread and that increasing the bentonite fraction reduces the spread of the grout somewhat.

During the test injection at the Fairfax mine, the problem of ash variability was handled by adding enough bentonite to obtain the same spread as was measured in the lab for the 48% water, 7% bentonite grout. For the test injection a 48% water, 5% bentonite mix was adopted.

200

,80 t ,,.., 160 t E 140 E

-~ 12o

1oo

~o 80

> 60 < 40

20

o 3

- - I l l

= 46% Water

Fraction

& 48% Waker

Fraction

50% Water

Fraction

I

5

Percent of Bentonite

---t

7

FIG. 4-- Spread versus bentonite percentage for fly ash-water-bentonite samples at varying water fractions.



Field Injection

A small-scale field injection of about 765 m 3 of grout was completed at the Fairfax mine in Preston County, West Virginia, to verify the practicality of the hydraulic backfilling concept and the adequacy of the grout recipe and maximum spread model. The Fairfax mine is a partially abandoned room and pillar mine. The coal seam has a thickness of about 1.5 m and lies about 70 m below the ground surface.

Injection began at 9:35 a.m., 21 May 1996. Johnnie Nichols, Mine Superintendent, and Paul Ziemkiewicz were in the mine, 25 m from the injection borehole when injection began. AFBC ash slurry was injected in batch mode from two alternating concrete trucks on the surface. Each pour comprised about 7 to 7.5 m 3 of slurry. Each pour lasted about 20 min, and the interval between pours was 5 to 10 rain.

Pour 1 flowed 23 m from the borehole. At the downstream end of the ash lobe its depth was about 2.5 cm. At the borehole the depth was about 5 cm. The ash front continued to advance until injection stopped. The slurry was very fluid, finding and progressively filling low spots. It formed a leveled channel between 30 to 60 cm wide with the narrower widths associated with higher flow rates over constrictions and overfalls. In incompletely filled headings, slurry flowed down the center line of a channel which was semicircular in cross section, about 1.2 m wide and 7.5 cm deep at the center line. When these channels eventually became occluded, side channels would break out and initiate a new lobe.

Pour 2 advanced a further 23 m. Upon the subsequent pours, the slurry front remobilized with roughly a minute lag time, initiated by a roughly 1.2-cm wave which propagated along the axis of advance. The wave was parabolic with its apex at the downstream end. The second pour did not ride over the first pour. Rather, it displaced the first pour from the upstream end, pushing the entire mass forward. Shale rocks (10 to 15 cm long, 5 cm square) were carried along with the slurry. The slurry velocity was 0.3 m/s at overfalls and more typically 0.15 m/s on the level floor.

Pour 3 advanced only about another 0.3 m, but it spread out to fill two headings from pillar to pillar (5.5-m heading width). At the end of Pour 3, the thickness at the downstream end was 5 cm. A zone of bleed water about 1.2 cm wide was observed at the downstream end of the slurry. Between pours, when the slurry advance stopped, a thin (1 to 2-ram) layer of bleed water could be seen moving slowly along the top of the slurry. At the end of Pour 3, slurry depths were 5 cm at the downstream end, 15 cm in a low spot at the first spad (center of intersection), and 10 cm at the borehole. There appeared to be some particle size segregation with higher sand contents at the borehole and in the main channels with more fines at the downstream end and in the side channels and bays.

The slurry flowed down the 1 to 2% slope of the mine floor. It would dam behind roof falls and floor irregularities, then flow over or around. Pouring continued until 5:30 p.m. About 95 m 3 of slurry was injected on the first day. The slurry was warm to the touch but not uncomfortable (like bath water). It generated a good deal of vapor. Also, since AMD treatment water was used to make up the slurry, and the AMD was treated with ammonia (NH3), contact with the lime caused deprotonation of the ammonium ion and release of more than perceptible amounts of NH 3.

m of mine floor were covered by the end of the first day to an average About 500 2



depth of about 20 cm. While the floor elevation varied in the order of 30 to 60 cm from roof falls, the slurry had the effect of level ingto an almost planar surface. From an almost watery consistency the first day the slurry had set up slightly to a Jell-O consistency. At the end of Day 1, the injection crew ran about 3 m 3 of water down the line to clean out the pump. This flushed out the slurry channels leaving them free for the next day 's slurry.

Day 2 of injection began at 7:30 a.m. While deforming the Day 1 slurry in the immediate vicinity of the injection borehole, the new slurry flowed on top of the old slurry. It did not remobilize the old slurry to any significant extent. Since the AFBC ash had been allowed to sit out overnight in a thunderstorm, it had developed a crust. This broke into 5- to 8-cm diameter chunks which were seen floating by in the slurry channel.

With well-developed channels, the flow proceeded in surges, particularly at constrictions and overfalls. The velocity would decelerate over a period of minutes, stop for a second or so, then release in a surge. The flow would then spread out evenly behind a small (2.5-cm) wave below the overfall. Injection proceeded to 24 May 1996 until about 765 m 3 of grout were placed in the mine.

One week after injection the grout had solidified to the extent that samples had to be chopped out with an entrenching tool. In spots of more than 15 cm of slurry, it was still moist 7.5 cm from the top. The slurry had developed cracks which penetrated about 10 cm. These tended to run normal to the direction of ash flow. As Fig. 5 shows, the ash had flowed about 170 m from the injection borehole and surrounded four pillars. Headings were filled pillar to pillar and some rooms were filled with 0.6 m of slurry (the roof was 1.2 m high). At the injection borehole the slurry had coned but was still about 25 cm from the roof. These results tend to confirm the prediction of unlimited spread by the maximum spread model.

Conclusions

Methods have been developed to stabilize a grout made from AFBC ash, to measure its rheological properties, to calculate its maximum spread, and to adjust the grout recipe in the field. A small field injection supports the results of the lab and analytical studies. It suggests that the hydraulic backfilling method is a practical solution to ash disposal with collateral benefits in preventing AMD and subsidence. A full-scale test is planned to verify this conclusion.

Acknowledgments

This work was prepared with the support of the U.S. Department of Energy (DOE) Cooperative Agreement DE-FC21-94MC29244. The contents of this paper do not necessarily reflect the views of the U.S. DOE.



box

; Grout

FIG. 5-- Plan view of Fairfax mine showing area covered by grout.

References

Bhat, S. T., Lovell, C. W., Scholer, C. F., and Nantung, T. E., 1995. "Flowable Fill Using Waste Foundry Sand," in Proceedings of l lth International Symposium on Use and Management of Coal Combustion Byproducts, Vol. 2, pp. 39.1-39.14.

Gupta, R. K., 1993. "Particulate Suspensions," Flow and RheoIogy in Polymer Composite Manufacturing, S. G. Advani, Ed., Elsevier Science, Amsterdam.

Head, W. J., Ziemkiewicz, P. F., Gray, D. D., Sack, W. A., Siriwardane, H. J., Burnett, M., Hamric, R., and Black, D. C., 1996. "Disposal of Fluidized Bed Combustion Ash in an Underground Mine to Control Acid Mine Drainage and Subsidence," Topical Progress Report for Phase I, Submitted to U.S. Department of Energy.

Lombardi, G., 1985. "The Role of Cohesion in Cement Grouting of Rock," in 15th 1COLD, Lausanne, Q58, R13, pp. 235-261.

Metzner, A. B. and Otto, R. E., 1957. "Agitation of Non-Newtonian Fluids," A. I. Ch. E. Journal, 3, p. 3-10.

Nguyen, Q. D.,and Boger, D.V., 1992. "Measuring the Flow Properties of Yield Stress Fluids," Ann. Rev. Fluid Mech., pp. 47-88.



Skelland, A. H. P., 1983. "Mixing and Agitation of Non-Newtonian Fluids," in Handbook of Fluids in Motion, N. P. Cheremisinoffand R. Gupta, Eds., Ann Arbor Science, Michigan, pp. 185.

Tattersall, G. H. and Bloomer, S. J., 1979. "Further Development of the Two-Point Test for Workability and Extension of its Range," Magazine of Concrete Research, Vol. 31, No. 109, pp. 202-210.


Michael R. Gardner 1

DEVELOPING C O N T R O L L E D LOW-STRENGTH MATERIALS TO MEET INDUSTRY AND CONSTRUCTION NEEDS

REFERENCE: Gardner, M. R., "Developillg Controlled Low Strength Materials to Meet Industry and Construction Needs," The Design and Application of Controlled Low- Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: A ready mix supplier in the Seattle marketplace took the initiative to develop and market controlled low strength material (CLSM). Seven CLSM projects over the past eight years are reviewed showing several examples o f how the owner and contractor saved money by reducing both time and risk to employees. Aggregate options other than those used in conventional fill or concrete production were used.

Quality control o f CLSM began with the ready-mix supplier providing all of the testing, and using the information internally. Testing laboratories are now testing CLSM and evaluating it as if it were concrete, this has driven the need for new ASTM standards specifically for CLSM.

KEYWORDS: unit weight, backfill, trenches, safety, environmental, native soils, CLSM, flowable fill.

Stoneway Concrete has been involved in the development and marketing of controlled low-strength materials (CLSM) for over eight years. During this time span, we have learned many lessons, both from our customers and our own research, on how to design CLSM for many applications. Seven of our projects will be reviewed that start with our first to our most recent job and encompass very simple ideas to the most challenging applications.

1 Technical Service Manager, Stoneway Concrete, 1915 Maple Valley Hwy, Renton, WA 98055.

194

Copyright�9 by ASTM lntcrnational www.astm.org Copyright by ASTM Int'l (all rights reserved); Thu Feb 7 18:46:02 EST 2013Downloaded/printed byKarina Agama (Freyssinet+Tierra+Armada+Peru+S.A.C.) pursuant to License Agreement. No further reproductions authorized.

GARDNER/INDUSTRY AND CONSTRUCTION NEEDS 195

Our company was one of the first ready mix suppliers in the Seattle area to promote CLSM. Because of this, we developed some of our own testing and definitions o f CLSM before ASTM and ACI had an opportunity to address CLSM. To us, and our customers, CLSM is a material that replaces conventional backfill and still needs to be hand or machine excavated (machines such as backhoes, trackhoes, and so forth not by jackhammer).

PROJECTS

Project 1-To fdl in from the top of the arch o f an underground bus tunnel to the subgrade just below paving level was our first CLSM project. The challenges o f this project were: �9 depth of placement varied from 4.6 to 9.1 m, �9 unit weight o f mix had to fall below 1842 kg/m 3, �9 many utilities varying from water and sewer to fiber optic cables, and �9 downtown Seattle on a busy arterial.

Our company developed a mix consisting of 13.6 kg of cement, 136.1 kg of flyash, 1111 kg of sand, 136 kg of water and 18 to 20% air entrainment. The unit weight was less than 1842 kg/na 3 which enabled us to transport 0.76 m or more additional per truck. The strength of the mix measured by our company's Technical Service Department was 0.1 to 0.6 MPa depending on how wet the mix was placed.

The contractor initially was not planning to use CLSM on this project, however; when the backfilling began, it was realized that if conventional backfill was to be used, 80% would have to be done by hand tools. It was then decided to try CLSM, the mix was successfully developed and over 38 000 m 3 were used on this project.

The contractor would remove a street panel to provide access to the roof of the tunnel. The CLSM was placed at the consistency of pancake batter and flowed over a city block without aid of vibration or pumping. The CLSM was placed from the truck chute and unloaded 9.18 m 3 in 45 s in situations where fast production was necessary.

During this project, Stoneway Concrete undertook a yearlong marketing effort to promote CLSM to various cities, engineers, and contractors. The promotion included presentations, slide shows, and field demonstrations. The marketing that was done has laid a solid foundation for a healthy CLSM market for all o f Seattle's producers and has continued to grow since the iniIial push seven years ago.

Project 2-A cast-in-place hospital parking garage with a spread footing was just beginning construction when the contractor unexpectedly discovered a dumpsite in areas that were supposed to have bearing soils. This area o f garbage ran east to west on the south end o f the footing and was approximately 1.8 m deep before bearing soil, and at the north end of the building running south to north, the garbage varied 1.8 to 7.9 m in depth.



The contractor then had the choice o f using conventional backfill and over- excavating for safety reasons or using CLSM and digging a trench with ve~ical walls because they would not need to put any people or equipment in the excavation. The contractor estimated that using conventional fill materials would increase his costs of import and export o f material and take several weeks to complete. The engineer and contractor decided on CLSM.

The engineer required a maximum strength o f 0.83 MPa. Our Company provided a design with 40.8 kg of cement, 136.1 kg of Class F flyash, and 19 mm coarse aggregate. The majority o f the project was completed in two pours, with one placement exceeding 750 m 3. The only testing on the material was performed by our company's Technical Service Department.

Project 3-Manufacturing Plant 1 - This owner was updating one o f their plants and doing construction inside while continuing manufacturing in areas all around the perimeter. The owner had very tight security and very expensive and sensitive machinery still needed to be used in the construction area. Because o f this, the owner wanted to keep the construction traffic down and not be bothered by employees complaining of pollution from trucks. The concept of CLSM was very appealing to the owner.

Our company provided the identical mix that was used on the first project because o f its ability to flow and its unit weight. The mix was line pumped over 305 m on some placements and met all of the owners and contractors needs. No testing was done for strength on this project. The owner has now been specifying CLSM for over seven years on new construction and remodels.

Project 4-The water department needed to replace a very old 914-mm water main that went under numerous train tracks. The train tracks are in downtown Seattle and come in from the south from as far as California and go northward to Canada. This water main went east to west in the middle of this massive switching yard.

The water department decided to use CLSM because of its versatility and how well some CLSM mixtures self compact around pipes and prevent the pipes from settling. Two CLSM mixes were used for the project, both had quick setting characteristics to speed up the project. Strengths o f the mixes varied from 0.34 to 0.83 MPa but were not tested on site.

A higher strength mix was used just in the areas that needed asphalt; the contractor would pour in the afternoon and pave over the CLSM the next morning. A second mix was used where the pipe intersected the train tracks. The contractor tunneled under the train tracks and did not need to provide support for the trench sides because they used CLSM in the excavation. Each set o f tracks had a time window to complete installation while the tracks were down; this time was very important to the water department because o f possible cost impacts from the railroads. The contractor would pour in the afternoon,



and the next morning the CLSM would be covered with railroad ballast and the track reopened.

Approximately 305 m of 914-mm water main was replaced. With successful mix proportioning, and placement technique, flotation of the pipe was not an issue. The project was completed in four days making this a very successful project for the water department.

Project 5-Sewage Treatment Plant - our company did not actually supply the job; however, we worked with the engineers before it went to bid, and we leamed quite a bit about using native soils in CLSM.

The project was situated next to a residential community and a large city park on Puget Sound. The owner wanted to limit the amount o f truck traffic into the project. The job required large quantities of backfill, and CLSM was already written into the specs. Our technical services department took samples of the soils from the site and ran many laboratory trials with the soils to develop a CLSM that could be made from the soils available on site and reduce cost of import and export o f material.

Because the soils varied from one part of the site to the other, our company developed several mixes for each soil condition. One of the soils was very fine, and a type A (ASTM C 494) water reducer was added to reduce water content and decrease set time. Other soils worked almost as well as typical concrete sand. When all of our testing was complete, we had two mixes of similar strength approximately. 0.5 to 0.7 MPa and a third mix that was approximately 1.4 to 2.1 MPa. Finally, we brought in a load of soils from the project and put on a demonstration for the engineers to see it actually batched and poured into place from our portable batch plant.

Project 6-Manufacturing Plant 2 - A new manufacturing plant was being built on property that was deemed a Superfimd cleanup site. The owner was given a choice of hauling the contaminated soil off site to a dump over 640 km away or finding a way to encapsulate it on site. It was decided that if we could develop a mix that used the contaminated soils and met the EPA requirements, that they would encapsulate it and monitor the material.

Stoneway Concrete worked with an environmental engineer to develop the mix design; however, information on the testing and mix design may not be published. The engineers came to our laboratory and performed tests on the material and took samples back to their laboratory to test for permeability and leachability. The concern of the EPA was water migrating through the CLSM and running offinto the lake nearby. Tests on the CLSM showed that it was capable of performing as the EPA required.

The mix design used water reducers and higher than normal flyash and cement contents. The mix tested at 0.4 to 1 MPa, however, strength was not specified. Once the job started, an environmental contractor was brought in to encapsulate what was



designated as "hot spots." Because of the sensitivity o f the project, our company leased the equipment to the contractor to batch and deliver on site. Stoneway Concrete also consulted with the contractor when the material characteristics changed and the mix needed to be adjusted.

Project 7-Street and Sewer Project - The contractor needed to install a 1.5-m- diameter pipe that was placed 1 m over a 762-mm water main. The pipes then would be backfilled and paved immediately after placement. CLSM was chosen for this project due to the ease o f placement and the speed at which the material could be put in place versus conventional backfill. Our company supplied a mix with 13.6 kg of cement, 113.4 kg of flyash, sand, and 19 mm coarse aggregate. This job was unique because CLSM was picked up by the contractor at our batch plants in dump trucks. The CLSM was batched at zero slump and frequently no water was added, just the moisture from the sand and coarse aggregate which resulted in a sufficient slump that worked well for placement.

The material was placed in two 2-m rifts in the trench and compacted by machinery around the first water pipe, and complete compaction was achieved immediately so that they could place the larger sewer pipe above and continue working. At one time during the project the contractor had extra material delivered to the job and stockpiled on Saturday that he did not use until Monday. The agency monitoring the project was concerned about the material still being usable, so they requested that Stoneway Concrete and Pozzolanic Northwest visit the site and investigate. Richard Halverson from Pozzolanic NW performed the ASTM Test Method for the Ball Drop on Controlled Low- Strength Material to Determine Suitability for Load Application (D 6024). Results of the test proved that the CLSM was suitable as no water pumped to the surface and the material held together upon impact. The owner agreed and the material was approved for u s e .

TESTING

When Stoneway Concrete first started supplying CLSM to projects, compressive strength was not tested by the laboratories. All of the testing was done by the supplier and that was just for our information. The concrete test methods did not work well for us with CLSM because the strength we did report did not appear to represent well what we saw in the field.

I began trying different ways o f handling the cylinders. I first left the cylinders out on the lab counter until test date; the cylinders dried out too much and crumbled. I then tried curing them in the lime-saturated water, but the cylinders became too saturated and fell apart. What we finally decided on was curing the cylinders in lime-saturated water and leaving the cylinders in their mold until test date. This method appears to best represent the material in place.

I have also seen the progression that commercial laboratories have made in testing CLSM. The material is much more likely to be tested today than it was five years ago. I



frequently witness cylinders handled too soon and test reports from commercial laboratories reporting much lower breaks than ours. It is not uncommon for an engineer in Seattle to specify 0.7 MPa maximum and a laboratory reporting that a 0.35 MPa test as being out o f compliance with specifications.

Testing o f CLSM needs improvement in the Seattle area. Testing should evolve with the publication o f new ASTM standards that address some of industries concern.

CONCLUSION

Stoneway Concrete has demonstrated that a ready mix supplier can develop CLSM mix designs that can save the contractor money and strengthen the reputation and demand for the CLSM product in the marketplace.

CLSM has made great strides in the Seattle area in the past eight years and will continue to do so with better testing standards becoming more available, and the engineers and contractors continuing to ask for more. Our company believes that CLSM mix designs are not one size fits all for our customers, we believe that we will design our customers any mix they need to ensure that it works well for their application.

Specifiers need to allow for materials other than those specified in the ASTM Specification for Concrete Aggregates (C 33). Stoneway Concrete has demonstrated quite successfully using native soils and alternate materials work well for CLSM and provid economic benefits. Specifications need to be performance driven not prescriptive.


Michael P. Walker ~ and James R. Ash 2

F L O W A B L E FILL B A C K F I L L FOR USE IN SEQUENTIAL EXCAVATIONS IN CONTAMINATED SOIL

REFERENCE: Walker, M. P. and Ash, J. R., "Flowable Fill Backfill for Use in Sequential Excavations in Contaminated Soil," The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: The use of controlled low-strength materials (CLSM) or flowable fill for backfill of pipelines and adjacent to structures has become common practice because of ease o f placement, lack of need for compaction, and relatively fast set time of the material. These properties are also ideal for backfill placed underwater or fill placed to allow sequential excavation.

CLSM was used to backfill excavations conducted to remove oil contaminated soil adjacent to foundations of existing structures and under standing water. The contaminated soil was sequentially excavated in narrow trenches and backfilled with CLSM, allowing excavation of subsequent adjacent trenches while minimizing soil movement into the open excavation. This sequential excavation would not have been possible with conventional compacted backfill. CLSM backfill was successfully placed underwater using tremie methods.

KEYWORDS: sequential excavation, tremie backfill, contaminated soil, groundwater control, flowable fill

P R O J E C T BACKGROUND

The project site was a former rope manufacturing facility that operated from 1824 until 1971 on Plymouth, Harbor in Plymouth, Massachusetts (Fig. 1). Steam power was

~Senior Structural Engineer, Design Division, GEI Consultants, Inc., 1021 Main St., Winchester, MA 01890.

2Project Manager, Environmental Division, GEI Consultants, Inc., 1021 Main St., Winchester, MA 01890.

200


WALKER AND ASH/CONTAMINATED SOIL 201

produced for the facility by burning coal and oil in the power plant in Building 4. Oil was stored in underground storage tanks (USTs) in a courtyard between Building 4 and Building 2, and in an oil cellar south of Building 2. The oil cellar was a subsurface brick and concrete structure that housed four 10,000-gal. (37 854-1) fuel oil USTs. The primary contaminant at the site was No. 6 fuel oil, which resulted from historical releases from the USTs. Free product characteristic of degraded No. 6 fuel oil was present in monitoring wells in both the oil cellar and the courtyard.

/ BUILDING No . 4

(2 STORY)-7 r (3 STORY) HA I; F COAL T POCKET / \ tr-% RBOR .-.-- / \ . = . - - . - - . . . .

o 2 . . . . . . . . . . . . \ _ o I I l - il o1$ Cnvl o ~ O I L C ~'/I XlR]..

'1 ; ~ " " B"RICK SMOKESTACK ~ / ' ' ' ' ' ' ' ~ - ~ / ~ " /C"'rH"&UR~Y'ARD ' ' ' ' ~ ] ~ / ' -~- " ! , [ ~ BUILD NG No. 2 ~1 Is l$

1 1 ~ (3 STORY) ~J[] I I //~1]~,~.,,. I \ I .~,

BOILO,,o ,o . , ~! I I / / 1 1 \ , . . . . . . . . . . . . . . . . . . . . . . . . . . . . i ' " . . . . . . . . . . . . . . . . . . . . . \

I IIi ' \ I _ _ : / ~ / I

1 IN. = APPROX. 150 IL--] -. (1 IN. = 2.54 CM ond 1 FT. = 0.3 M)

Fig. 1 - - S i t e Plon

The project was conducted to remove free product and soil with total petroleum hydrocarbon (TPH) concentrations greater than 500 parts per million (ppm) from the two areas at the site. The work was completed as a Release Abatement Measure to comply with Massachusetts environmental compliance regulations. No. 6 fuel oil is relatively immobile in the subsurface and, therefore, was not amenable to free product removal systems that depend on flow of the product to recovery wells or trenches. Also, since the contaminants were already relatively old and degraded because of the age of the release, significant additional remediation of the contamination by natural biodegradation was considered unlikely. These factors led to the selection of excavation and offsite disposal o f the material as the most feasible altemative.



SITE CONDITIONS

/

The courtyard was an area approximately 40 ft (12 m) wide by 80 ft (24 m) long, located between Buildings 2 and 4 (Fig. 2). An approximately 200-ft (61-m) tall brick smokestack with a 20-ft (6.1-m)diameter base was located at the midpoint of the courtyard, and a one-story brick pumphouse was attached to Building 4. The buildings surrounding the courtyard had slab-on-grade floors with no basements. Several tunnels, formerly used for transportation of coal to the power plant and as a cooling system for the factory, were located beneath the buildings.

-- BRICK STACK TYPICAL TRENCH (APPROXIMATE) BUILDING No. 4 SORIENTATION

/'//////////,////////////'//////////'/////////////,////////////, #

f ~ ( ( " / i " ' r ~ ~ i / i i i i i i I f r r i i i ~ [ i / i / [ f [ r r r ~

r f l 1 F 7 . . . . :, I .ous r .... ..7

i \ \ J - - - - 4 I- .... -L I " - , ~ . !l I! / i �9 , / !J ~! / i ~ 1 t _ _ _ I I t_ . . . . _ . r ? . ~ / . t . . _ . - -

, . . . . . . jt I LOCATION OF ~ ~ A H F . FORMER UST LOCATIONS I

CONCRETE SLAB II (APPROX. lOFT. BGS.) ~ " ~ 1 I I

. _ ~ _ _ - : p _ - - - ~ - - _ - 4 I 1 L ~ _ _ - - _ _ _ _ _ _ J /

APPROX. LIMIT -n BUILDING No. 2 ~--APPROXIMATE LIMIT OF EXCAVATION OF EXCAVATION

AT 12 FEET BGS 1 IN. = APPROX. 15 FT.

(1 IN. = 2.54- CM and 1 FT. = 0.5 M)

FIG. 2 - - C o u r t y a r d P l a n

Soils at the site generally consisted of up to 1 ft (0.3 m) of topsoil overlying 12 to 13 ft (3.7 to 4 m) of fill, overlying silty clay. The fill consisted of widely graded urban fill with brick and other debris and narrowly graded silty sands. Silty sand and clay beneath the fill corresponded to the original grade along the beach line. The urban fill and topsoil were placed after the construction of a sea wall and facility buildings along the beach in the late 1800s. Groundwater was present at depths of 9 to 11 ft (2.7 to 3.4 m) below grade and showed some fluctuation as a result of tides. In the courtyard, oil contamination was present primarily in the fill material from depths of approximately 8 ft (2.4 m) below grade to the clay layer at 12 to 13 ft (3.7 to 4 m) below grade.

Buildings 2 and 4 were constructed with load-bearing masonry walls with timber or steel framing. The exterior masonry walls were founded on a dressed, granite block



foundation. The foundation wall rested on a slightly wider granite block footing. The granite block footing rested on the silty sand and clay strata approximately 10 to 12 fi (3 to 3.7 m) below grade.

The oil cellar was approximately 65 ft (20 m) long, 30 ft (9 m) wide, and 12 ft (3.7 m) deep and constructed of concrete and brick walls on a brick base. The USTs formerly located in the oil cellar had been removed years earlier, and the structure was backfilled with soil and debris. Oil contamination was present in the fill material inside the structure and in native soil and fill outside the structure. The nearest building to the oil cellar excavation was approximately 40 ft (12 m) away. Hence, the limits of the excavation in the vicinity of the oil cellar were not controlled by adjacent buildings.

DESIGN CRITERIA

The goal of the project was to remove as much contaminated soil as feasible without threatening the stability of the adjacent structures. The design criteria were established based on geotechnical, structural, and environmental requirements as follows:

Geotechnical and Structural CJciteria

�9 Maintain global stability of the adjacent structure and minimize potential movements and differential settlement of the building foundations.

Maintain local stability of sections of the granite block foundation wall including potential failure of the wall resulting from lateral earth pressures or local undermining of the foundation.

Limit migration of fines during dewatering. The removal of fines from soil beneath the foundations may have resulted in undesired settling of the footings and foundations.

Environmental Criteria

�9 Minimize the handling and disposal of contaminated groundwater.

�9 Minimize the handling of contaminated soil.

�9 Minimize mixing of contaminated and uncontaminated soil during excavation.

�9 Remove as mucla contaminated soil as feasible while meeting geotechnical and structural criteria.



DESIGN SOLUTIONS

The criteria listed above were met by excavating the contaminated soil in narrow trenches perpendicular to the building foundations in the courtyard and backfilling the trenches beneath the groundwater surface with CLSM. Dewatering in the courtyard was limited to the removal of small quantities of free product and contaminated groundwater from the excavations. CLSM was used in the oil cellar excavation as backfill beneath the groundwater surface in limited areas to improve accessibility for excavation equipment and divide the excavation into cells that limited the dewatering requirements.

Preliminary limits of the excavation in both the courtyard and oil cellar areas were established based on a geotechnical evaluation of soil conditions at the site, adjacent building foundations, and estimated foundation loads from the buildings and the 200-ft (6 l-m) high brick chimney. The limits of excavation were adjusted in the field using an observational method that combined sequential excavation and backfill with geotechnical and structural instrumentation on the adjacent structures. Building settlements were monitored using optical surveying methods, and rotational movements of the masonry wall were monitored using tiltmeters. The field engineer was able to increase the limits of the excavation to remove additional contaminated soil based on the exposed soil conditions and the absence of observed movements of the adjacent structures.

In the courtyard, the excavation sequence was divided into two phases: general excavation and controlled excavation. The upper 7 ft (2 m) oftmcontaminated fill above the water table was excavated and stockpiled nearby during general excavation. The sequence of the general excavation was controlled by the contractor based on the limited accessibility to the excavations and the limits of the equipment. During controlled excavation, the remaining contaminated soil was sequentially excavated in 5- to 8-ft (1.5- to 2.4-m) wide trenches perpendicular to the building foundation. Multiple trenches were allowed if at least 10 ft (3 m) of fill or original soil Separated the walls of the trenches. A cross section showing the limits of general and controlled excavation along the building foundation in the courtyard is shown in Fig. 3. The trenches were filled at the end of each day with CLSM. The CLSM was delivered onsite by conventional concrete transport trucks and placed in the excavation using tremie methods. The material was placed using the truck chute and an 18-in (46-cm) diameter corrugated steel drainage pipe, approximately 10 ft (3 m) long. The pipe was held in a nearly vertical position using a chain attached to the arm of an excavator with the bottom of the pipe at the bottom of the trench. The CLSM was sluiced into the pipe and the flow controlled to maintain a continuous placement of the material. The pipe was slowly raised as the CLSM level in the trench rose.

RESULTS

The trenches in the courtyard were excavated with limited dewatering. In several cases, the entire trench was excavated with only a small amount of groundwater inflow, while in adjacent trenches, groundwater filled the trench and required excavation beneath



P.)

(20'-0" ]AVATION)

;TING GRADE

PRE! LIMIT

S OF GENERAL o ,AVATIO N AND I :ED ORDINARY FILL 7 7--.

1 LIMITS OF CONTROLLED

AND CDF FILL EXCAVATION 7

"r--

i

(1 IN. = 2.54 CM and 1 FT. = 0.3 M)

F ig . .3 - -Typ ica l Section At Building Foundation

the water table. The CLSM displaced loose soil and water during placement and appeared to result in a uniform material with no significant infiltration of water or soil. An additional unpredicted benefit of CLSM was the displacement of small quantities of free product that was not captured during the excavation. The free product collected on the surface of the CLSM and could be removed by hand using a shovel after the CLSM had cured.

The contractor excavated on either side of a CLSM trench after it had cured (usually the following day). The CLSM fill could be excavated to a near vertical face which minimized the amount of over excavation along the trench interfaces. Generally, the excavation equipment could operate and drive over the CLSM fill after one day of curing. This allowed the contractor access to the subsequent trench locations while maintaining the excavation sequence.



During the first CLSM placement, the contractor added extra water to the mix, thinking it would be needed to allow tremie placement of the material. As a result, it took two days for the material to cure adequately to support construction traffic, and the resulting material displayed less cementation than the undiluted mixes. Subsequent batches were prepared without additional water and were successfully placed using the tremie pipe.

Excavation in the oil cellar commenced following completion of the courtyard excavation. Soils in the oil cellar area were more widely graded and coarser which allowed rapid inflows of groundwater and resulted in poor side slope stability. As a result, the excavation sequence in the oil cellar was controlled by the reach of the excavator and the stability of the side slopes of the excavation. To improve the accessibility of the excavator to the contaminated soil, CLSM was used to backfill trenches (cells) dug along the edge of the excavation. The filled trenches were used as a working platform for the excavation of adjacent areas. Lower cost peastone fill was placed below the groundwater surface in trenches excavated between CLSM-filled trenches to reduce the overall project cost. The advantages of CLSM over peastone were: (1) the CLSM could be excavated at a near-vertical slope and (2) the CLSM reduced the flow of groundwater into the excavation.

On several occasions during the oil cellar excavation, it was necessary to dewater sections of the excavation that had accumulated surface water runoff. CLSM was used as backfill beneath the groundwater surface to partition a portion of the excavation, which was subsequently used as a recharge basin. Water was pumped from the excavation into a fractionation tank to separate free product and contaminated water, then discharged into the recharge basin. The CLSM partition limited the flow of water back into the excavation.

TESTING

The CLSM was specified as Type 1-E very flowable, excavatable controlled density fill, consistent with Massachusetts Highway Department (MHD) (formerly the Massachusetts Department of Public Works) Specification M 4.08 O (Commonwealth of Massachusetts, 1988). The MHD standard suggests material tests of the CLSM for cement by the ASTM Specification for Portland Cement (C 150) and for fly ash by ASTM Specification for Coal Fly Ash and Raw or Calcinated Natural Pozzolan for Use as a Mineral Admixture in Concrete (C 618). The MHD standard also suggests test requirements for slump and compressive strength, although no standard tests were listed. For this project, we used the recommendations for slump specified in the American Concrete Institute (ACD_Manual of Practice (ACI 1995), which consisted of the ASTM Test Method for Slump of Hydraulic Cement Concrete (C 143).

The MHD suggested mix design is listed in Table 1.


WALKER AND ASH/CONTAMINATED SOIL

TABLE 1 --MHD Suggested Mix Design

207

Material Quantity Test

Cement 50 lb (23 kg) ASTM C 150

Fly ash 250 lb (115 kg) ASTM C 618-Class F

Sand 2700 lb (1225 kg) MHDM4.02.02

Water 60 gal (225 1) ...

The performance requirements specified by MHD are as follows:

Compressive strength at 28 days Compressive strength at 90 days Slump

30 to 80 psi (210 to 550 Kpa) 100 psi (700 Kpa) (maximum) 10 to 12 in (250 to 300 mm)

The MHD Specification for CLSM requires testing for slump and compressive strength. However, the 28- and 90-day compressive strengths of the material were not critical for this application, because the primary use of the CLSM was as backfill that could be placed under water and provide lateral support to the surrounding soil. The CLSM fill also had to support construction equipment within one to two days after placement. Testing for compressive strength was not performed because the fill was covered with up to eight feet of backfill within several days after placement and before any compressive strength test results would be available. Therefore, testing of the CLSM for this project was limited to a performance-based evaluation. The CLSM was specified as excavatable for contractor convenience during construction. It is not anticipated that the CLSM or overlying fill will be removed in the foreseeable future.

The Commonwealth of Massachusetts requires all batch plants to have batch systems that provide truck tickets listing all relevant data (material weights, water, and so forth). Truck tickets listing material batch weights were checked in the field to verify that the material proportions were consistent with the submitted mix design. In addition, the wet unit weight of the CLSM was measured using a mud balance in accordance with ASTM Test Method for Density of Bentonite Slurries (D 4390), and samples were collected for dry unit weight testing. The wet unit weights exceeded 100 lb/ft 3 (1602 kg/m3), which was the maximum reading of the balance. Unit weights were not included in the specifications.

A hand auger was used to core through the CLSM mass at several locations following placement and curing of the material for several days. The CLSM mass was observed to be fairly uniform and showed no evidence of voids, discontinuities, debris, or contaminated soil. There was evidence of debris and some soil along the bottom of the CLSM mass at the CLSM/clay interface, likely a result of ravel from the sidewalls during placement.



The settlement and rotation instrumentation on the adjacent buildings was monitored at least twice a day (morning and evening) with additional readings taken during the day, as warranted. The instrumentation was left in place and monitored for approximately 30 days following completion of the excavation. Differential movements recorded by the instruments were within a range approximately equal to the accuracy of the instruments. There were no trends indicating movement of the structures.

CONCLUSIONS

The use of CLSM as a backfill material in sequential excavations was successful for this application. The use of CLSM as backfill allowed narrow, controlled excavations beneath the groundwater surface with limited dewatering and uniform placement of material in the excavated trenches. The cured CLSM supported excavation equipment within one day following placement, provided support to the sidewalls of the excavation, and limited the slumping of clean soil into the excavation. The contractor was able to excavate near vertical faces within the CLSM and along the contact of CLSM with unexcavated soil, limiting the size of the trenches and redundant excavation of soil.

The primary goal of the project was to remove as much contaminated soil as feasible without causing damage to adjacent building foundations or detrimental movements Of the adjacent structures. Our evaluation of the CLSM focused on the performance of the material during placement and during subsequent excavation in adjacent trenches following curing of the material for one to two days. Field testing of the CLSM was primarily limited to review of truck tickets, limited wet unit weight tests, slump tests, and visual observation of placement. The longer term evaluation of the performance of the CLSM was limited to monitoring the potential movements of the adjacent structures during and after construction.

The testing of CLSM on this project was constrained by the schedule and sequence of excavation and backfill. The wet unit weight testing was used as a screening technique to establish a minimum requirement since the apparatus can not measure more than 100 lb/ft 3 (1602 kglm3). Where unit weight of the fill is important, the use of preconstruction testing may be appropriate. The test should establish a correlation between the wet unit weight established using ASTM Test Method D 4380 and the cured unit weight using ASTM Test Method for Unit Weight, Yield, and Air Content (Gravimetric) of Concrete (C 138). Where strength parameters are important, ACI suggests the use of ASTM Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance (C 403) or the ASTM Test Method for Preparation and Testing of Soil-Cement Slurry Test Cylinders (D 4832). The use of compressive strength tests for field testing during this application was problematic because the CLSM was in place and covered by additional soil before the standard 28-day test period.



REFERENCES

Commonwealth of Massachusetts, 1988, Standard Specifications for Highway and Bridges, Massachusetts Department of Public Works, Boston.

American Concrete Institute (ACI), 1995, ACI Manual of Concrete Practice, Part 1, Cxmtrolled Low Strength M a t e ~ , ACI 229R-94, Detroit, MI.


Thomas F Mason I

USE OF CONTROLLED DENSITY FILL TO FILL UNDERSLAB VOID

REFERENCE: Mason, T. E, "Use of Controlled Density Fill to Fill Underslab Void", The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: During the removal of a portion of a warehouse slab for the United States Na~% a large void that was caused by water erosion was discovered. The void was created behind a concrete seawall by years of tidal and current action. Conventional granular backfill material was considered but was dismissed as being nearly impossible to install and compact. Controlled density fill (CDF) was proposed and accepted as an acceptable backfill method.

Access holes were drilled along the exterior of the warehouse to allow easy placement of the CDF. A bulkhead made from sandbags was installed in the void to prevent the CDF from flowing past the limit of approved work. The CDF was installed over a period of two days to lessen lateral pressure on the sand bag bulkhead and vertical pressure on the bottom of the void adjacent to the concrete seawall.

By using controlled density fill, the project was successfully completed quickly and at a fraction of the original estimated cost using conventional granular backfill materials and methods.

KEYWORDS: void, water erosion, controlled density fill, CDF, backfill, controlled low strength material, CLSM, flowable fill

The United States Navy has an installation at Rough & Ready Island, Stockton, California. The facility is bordered on the north side by the San Joaquin River. The river develops some current during the winter and spring runoffs. At all times of the year, the river level is affected by tidal fluctuations through San Francisco Bay. The San Joaquin River is large enough for inland ship traffic to the Port of Stockton. The ship traffic also

tAssistant Sales Manager, Lone Star Northwest, Inc., P.O. Box 1730, Seattle, WA.

210


MASON/CONTROLLED DENSITY FILL 211

contributes to local currents as water is displaced by the ship's hull. At Rough & Ready Island, the Navy has installed a number of wharfs along the San Joaquin River side of the island. These installations consist o f a concrete bulkhead next to the land that extends well below the water level. A series of warehouses runs parallel to the bulkhead along its entire length.

In one o f these warehouses, a contract was let to install some tenant improvements for the Navy. One portion of this work involved removing a section of the existing concrete floor near the water side of the warehouse and placing a concrete footing base for future machinery installation.

THE PROBLEM

A 1.2 m x 1.8 m section of the floor was sawcut full depth. When the sawed concrete section was removed, a large void under the slab was discovered. It was evident that ever since the building was completed, almost 50 years before, small amounts of backfill used to fill behind the concrete bulkhead and act as a base material for the warehouse slab had been gradually washed away from under the toe of the wal lby tidal and current forces of the river. This condition was consistent on this building along its entire 183 m length.

?



The initial reaction of the Navy and the contractor to correct the situation was to install and compact a granular backfill material. However, they could not figure out how to compact this material in the tight access areas. The contractor performing the tenant improvements had never used controlled density fill but was familiar with the product and concept of its use as a result o f a presentation that had been given to them. Upon arriving at the site, a ladder was lowered and seven people went down into the void.

THE SOLUTION

Upon inspection of the site, we concluded that controlled density fill would indeed provide an excellent way to backfill the void. It had a definite advantage over conventional granular backfill material because o f its ability to flow into the remote areas of the void. The Navy authorized the use of CDF for 36.5 m of the 183-m void. This represented the portion of the building corresponding to the scope of the tenant improvement work being performed by the general contractor. To prevent the CDF from flowing past the 36.5 m limit of the authorized work, the general contractor installed a bulkhead consisting of sand bags. It was decided that the CDF would be installed in two lifts on two consecutive days. This would lessen the lateral pressure on the sand bag bulkhead and provide a plug at the bottom of the void to prevent the vertical pressure of the CDF from pushing out into the river under the concrete bulkhead. Since the CDF would be installed in a confined space, no bonding of the two layers was deemed necessary. Holes were drilled along the exterior of the building on approximately 6 m centers to allow for convenient access points to deposit the CDF directly into the void from the ready mix trucks. At the most eastern end of the building where the void was shallow, a small concrete line pump was used to force the CDF under the slab. As the CDF was deposited into the void and neared the bottom of the concrete slab, material was deposited from one direction only along the access holes. Material was brought up to the bottom of the slab at the next hole "downstream" before the filling operation was moved to that next hole. A visual inspection of the in-place CDF the next morning showed the elevation of the material was still at the bottom of the existing concrete slab floor.

The controlled density fill mix design consisted of 13.5 kg of cement, 181 kg of Type "F" fly ash, 227 L of water and a 70% sand / 30% pea gravel aggregate mixture per m 3, Pea gravel was utilized in the mix to reduce the cost. The mix achieved a fluid consistency with this water content. The CDF was delivered in conventional rear discharge ready mix trucks. Approximately 46 m 3 of material was delivered on each day. No strength requirements were established for the mix. Batch weights were closely monitored.

CONCLUSION

Controlled density fill provided a low-cost, highly effective means to fill completely this underslab void. The total costs were less than 20% of the amount authorized by the owner for the placing and compaction of conventional granular backfill.


Timothy P. Dolen 1 and Abel A. Benavidez 2

PROPERTIES OF LOW-STRENGTH CONCRETE FOR MEEKS CABIN DAM MODIFICATION PROJECT, WYOMING

REFERENCE: Dolen, T. E and Benavidez, A. A., "Properties of Low-Strength Concrete for Meeks Cabin Dam Modification Project, Wyoming", The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: Low-strength, "plastic" concrete mixtures were proportioned to construct a cut-off wall through permeable features in the foundation of Meeks Cabin Dam, Wyoming. Low strength concrete was required to match the deformation properties of the concrete with the embankment materials in the dam. The mixtures were proportioned with zero (control mixture), 10, 15, and 20 % bentonite by mass of cement plus bentonite. The bentonite reduces compressive strength and elastic properties when compared to conventional concrete. Mixtures were proportioned to meet the desired fresh and hardened concrete properties. All mixtures met the 8 in. (200 mm) slump required for tremie placing. The design compressive strength is 200 lb/in. 2 (1,380 kPa) at 7 days and 400 lb/in. 2 (2,760 kPa) at 28 days. The 15 % bentonite mixture met the strength requirements and was chosen for more detailed testing. Additional tests evaluated the triaxial shear strength, flow-pump permeability, and erodibility of the low- strength, hardened concrete, and determined the effect of adding a retarding admixture on setting time and slump loss of fresh concrete.

KEYWORDS: Concrete Cutoff Walls, Controlled Low-Strength Materials, Plastic Concrete, Earth Dams, Rehabilitation.

Research Civil Engineer, U. S. Bureau of Reclamation, P.O. Box 25007, Attn: D-8180, Denver, CO 80225-0007.

Materials Engineering Technician (Retired), U.S. Bureau of Reclamation, 12057 W. New Mexico Ave., Lakewood, CO 80228.

213



This paper summarizes the effects of adding bentonite on the fresh and hardened properties of low-strength concrete for Meeks Cabin Dam Modification, Lyrnan Project, Wyoming. Meeks Cabin Dam is a zoned-earthfill dam, 180 ft (55 rn) high and 3200 ft (975 m) long. The dam is about 22 miles (35 kin) southwest of Ft. Bridger, Wyoming. A concrete cutoff wall was placed through the core of the dam into the foundation. The cutoff wall reduced foundation seepage flows in contact with the cutoff trench along an 825 ft (250 m) section of the left abutment of the dam. The cutoff wall was composed of low-strength, or "plastic" concrete to be compatible with the elastic properties of the soil during normal and earthquake loading conditions.

Low-strength, "plastic" concrete mixtures were proportioned with zero (control mixture), 10, 15, and 20 % bentonite (B) by mass of cement plus bentonite (C+B). The bentonite reduces compressive strength and elastic properties when compared to conventional concrete. The results of fresh and hardened concrete tests are summarized for the concrete mixtures. Mixtures were proportioned to meet the desired fresh and hardened concrete properties. All mixtures met the 8 in.(200 mm) slump required for trernie placing. The design compressive strength is 200 lb/in. 2 (1,380 kPa) at 7 days and 400 lb/in. 2 (2,760 kPa) at 28 days. The 15 % bentonite mixture met the strength requirements and was chosen for more detailed testing. Additional tests evaluated the triaxial shear strength, flow-pump permeability, and erodibility of the low-strength, hardened concrete, and determined the effect of adding a retarding admixture on setting time and slump loss of fresh concrete.

MATERIALS PROCESSING AND TEST METHODS

Cement, bentonite, and aggregates were obtained from potential suppliers of concrete materials located near the job site. Samples from potential aggregate sources were evaluated before testing. Aggregate sample No. M-8042 was selected due to proximity of the source to the site and potential concrete suppliers.

ASTM Specification for Concrete Aggregates (C 33) sand grading and coarse aggregate grading No. 57, 1 in. to No. 4 (25.0 to 4.75 mm), were specified for the mixture proportioning program. A larger sample of aggregates (sample No. M-8060) from the same source as M-8042 was crushed by a commercial producer for the program. The bulk sample had a 1 in. (25 rnm) nominal, maximum-size-aggregate (NMSA). The sample was washed and separated into minus No. 4 (4.75 mrn), No. 4 to 3/8 in. (4.75 to 9.5 mm), and 3/8 to 1 in. (9.5 to 25 mrn) aggregate sizes. After experiencing significant slump loss testing trial mixtures, the sand and coarse aggregates were examined petrographically and found contaminated by caliche. Caliche apparently was not removed from overburden and did not break down during initial washing and screening. However, the caliche did break down in the concrete mixer during initial trials. Caliche was subsequently removed from the sand and coarse aggregate by vigorous rewashing. The overburden from this source was stripped to remove caliche before processing aggregates for the dam construction. Additional sand was obtained from this source to complete


DOLEN AND BENAVIDEZ/MEEKS CABIN DAM 215

slump loss and time-of-set tests. This sample was designated M-8070. A third sample from an alternate aggregate source was investigated in the Phase II test program. Aggregate physical properties are given in Table 1.

Table 1--Meeks Cabin Dam Modification Project - Aggregate Physical Properties

Sample No. 4 to 3/8 in. 3/8 to 1 in. Number Sand (4.75 to 9.5 mm) (9.5 to 25 ram)

Specific Absorption Specific Absorption Specific Absorption Gravity Gravity Gravity

M-8060 2.57 1.6 2.57 2.1 2.6 1.2

M-8070 2.59 1.0

M-8078 2.6 1.0 2.61 1.1 2.61 0.8

Sand Grading - Cumulative Percent Passing Indicated Sieve

Sample No. 4 No. 8 No.16 No.30 No.50 No.100 No.200 Number 4.75 mm 2.36 mm 1.18 mm 0.6 mm 0.3 mm 0.15 mm 0.075 mm

M-8060 99 83 70 49 24 5 2

M-8070 100 98 88 46 14 3 3

M-8078 100 83 68 50 26 8

Bentonite met the quality requirements of American Petroleum Institute (API) Specification No. 13A (Wyoming Grade, 125 barrel/ton yield). Bentonite was obtained from a commercial supplier in Denver, Colorado. Slurry filtration characteristics of bentonite were determined by filter press test according to USBR Procedure No. 5893. The slurry mixture was prepared by adding 5 % bentonite to project drainage water. The results of the slurry filter press test are given in Table 2. The bentonite was premixed as a dry powder with the cement before batching the concrete mixtures.

Bureau of Reclamation laboratory standard cement was used for the concrete mixtures. This meets the ASTM Specification for Portland Cement (C 150) Specification for Type II, low alkali, Portland cement. It was obtained from a plant located in Devil's Slide, Utah and was also used for dam construction.



Table 2--Meeks Cabin Dam Modification Project - Bentonite Filter Press Test Results

Sample Number M-8062 ! / M-8063 2/

Bentonite Slurry Concentration - 5 %

Slurry Temperature - 86 ~ 30 ~

Initial Slurry Temperature - 74 ~ 23.3 ~

Filtrate Loss - 0.41 oz 12 ml

Thickness - 0.14 in 3.5 mm

Consistency - Firm

Final Slurry Temperature - 75.4 ~ 24.1 ~

1_/Water sample No. M-8062. 2/ Bentonite laboratory sample No. M-8063.

MIXTURE PROPORTIONS

Mixture proportions for low-strength concrete closely followed the recommendations of US Army Corps ofEngineers (USCOE) 1Report No. REMR-GT-15. Starting proportions were determined based on the following USCOE assumptions:

1. C+B (cement plus bentonite) Content: 300 lb/yd 3 (178 kg/m3). 2. Sand Content: 50 % by volume of total aggregate. 3. B (bentonite) Content: 0, 10, 15, and 20 % by mass of C+B. 4. Slump: 8 +/- 1 in. (200 +/- 25 mm) 45 minutes after mixing (required for tremie

placing). 5. Aggregate Grading: ASTM C 33 sand grading and ASTM No. 57, 1 in. to No. 4

(25.0 to 4.75 mm) coarse aggregate grading. 6. Air Content: 0 to 1%.

The water content for each mixture was adjusted to achieve a slump of about 8 in. (200 mm), 45 minutes after the C+B contacted the water. The 8 in. (200 mm) slump was selected for tremie placing workability. The 45 min delay for slump testing was selected to allow the bentonite to hydrate. The mixing procedure was according to ASTM Practice for Making and Curing Concrete Test Specimens in the Laboratory (C 192); 3 min mix, 3 min rest, and 2 min mix. Slump was tested according to ASTM Test Method for Slump of Hydraulic Cement Concrete (C 143) immediately after mixing (about 10 min) and 30 and 45 min after mixing to allow the bentonite to absorb water. The concrete was re-mixed for 1 min just before testing slump at 30 and 45 min. Forty-five minutes



after mixing, the density and pressure air tests were done, and strength test specimens made. These tests were performed according to ASTM Test Method for Unit Weight, Yield, and Air Content (Gravimetric) of Concrete (C 138) and (C 192), respectively. The inside of the cylinder molds was coated with a spray on lubricant and a 6 in. (150 mm) diameter piece of Whatman, Grade 113, filter paper was placed inside on the bottom of the molds in order to strip the plastic molds from the test specimens without damage.

Mixture proportions and the properties of fresh concrete are given in Tables 3 and 4, respectively. The water content required to produce a 8 in. (200 mm) slump after 45 min increased from 435 to 560 lb/yd 3 (260 to 330 kg/m 3) for the 0 to 20 % bentonite mixtures, respectively. This closely follows the USCOE published results for a 300 lb/yd 3 (178 kg/m 3) C+B content, low-strength concrete mixture.

PHASE I - EFFECT OF BENTONITE ON STRENGTH AND ELASTIC PROPERTIES

Phase I of the program included compressive strength, modulus of elasticity, and Poisson's ratio tests at 3, 7, 14, 28, and 90 day's age. Tests were performed according to ASTM Test Method for Compressive Strength of Cylindrical Concrete Specimens (C 39) and Test Method for Static Modulus of Elasticity and Poisson's Ratio of Concrete in Compression (C 469), except that the load rate was reduced for the low-strength concrete compression tests. A load rate of 4 to 8 lb/in. 2 (30 to 60 kPa) per second (about a 0.03 to 0.054 in./min (0.75 to 1.4 mm/min) rate of travel) was used to avoid shock loading the low-strength concrete. The strain at failure ranged from 2500 to 4500 x10 "6 in./in. (0.25 to 0.45 %). The chord modulus of elasticity and Poisson's ratio were determined with an extensometer-compressometer apparatus at 3 and 7 day's age, and with epoxied strain gauges at 14, 28, and 90 day's age. The modulus of elasticity and Poisson's ratio are determined from stress-strain values corresponding to an initial strain of 50 x 10 .6 in./in. and the strain at 40 % of the ultimate compressive strength.

Results of compressive strength and elastic properties tests are given in table 5. Results are consistent with the USCOE published literature. The 15 % bentonite mixture exceeds the required 7-day compressive strength by 40 lb/in. 2 (275 kPa) arid the required 28-day strength by 15 lb/in. 2 (100 kPa). The 28-day compressive strength of the 15 % bentonite mixture is about half the control mixture. Compressive strength increased about 29 % between 28 and 90 day's age for the control mixture and 43 % for the average of the three cement-bentonite mixtures.

The modulus of elasticity of the 15 % bentonite mixture is about 0.8 x 10 6 lb/in. 2 (5,520 Mpa) at 28 days. The modulus of elasticity increased with compressive strength as shown in table 5. Poisson's ratio increases with age until about 14 or 28 days, then decreases slightly between 28 and 90 days. The values of Poisson's ratio are similar to conventional concrete.


Tab

le 3

--M

eeks

Cab

in D

am M

odif

icat

ion

Pro

ject

- D

esig

n M

ixtu

re P

ropo

rtio

ns

~.

GO

Mix

A

ir

Num

ber

Con

tent

(%

)

MC

-O

1.0

MC

-IO

1.

0

MC

-15

0.5

MC

-20

0.5

Wat

er

Cem

ent

Ben

tonR

e Sa

nd

No.

4 to

3/8

in.

2/

3/

3/

(l

b/~d

3) (k

$/m

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Table 4--Meeks Cabin Dam Modification Project - Fresh Concrete Properties

Mix Number

MC-0

MC-10

MC-15

MC-20

MC-15 /

MC-15

Bentonite Temperature Slump 4/ Air Density Density Content (o F) (~ (in.) (mm) Content (lb/ft 3) (kg/m 3) (lb/yd3)(kg/m 3)

(%) (%)

0 64.4 18 8 203.2 0.4 139.31 2232 3761 2231

10 61.7 16.5 9 228.6 0.2 135.05 2164 3646 2163

15 69.8 21 8.25 209.6 0.3 133.76 2143 3612 2143

20 68.0 20 8.25 209.6 0.2 131.99 2114 3564 2115

15 71.6 22 8.0 203.2 0.3 131.9 2113 3561 2113

15 66.2 19 9.0 228.6 132.4 2121 3575 2121

1/ Mixture MC-0 to MC-20; aggregate source No. M-8060. 2/ Mixtures tested for triaxial shear strength, flow-pump permeability. 3/ Mixture MC-15 sand; aggregate source No. M-8078. 4/ Slump tested 45 minutes after mixing.

P H A S E I I - F I N A L D E S I G N M I X T U R E

Phase II of the mixture proportioning program began after examining the Phase I, 28-day compressive strength results. Mixture MC-15 with 15 % bentonite was selected for Phase II testing based on meeting the desired 28-day strength of 400 lb/in. 2 (2,760 kPa). Tests included:

1. Flow-pump permeability - 28 to 51 days 2. Erodibility - 28 days 3. Triaxial shear strength - 28 days 4. Slump loss of fresh concrete 5. Setting time of concrete by penetration resistance 6. Compressive strength at 7, 14, 28, and 90 days 7. Fresh concrete properties of mixture MC-15, with alternate aggregate source No.

M-8078 (Byrnes Pit) 8. Compressive strength of mixture MC-15, with alternate aggregate source No. M-

8078

The erodibility specimen cast from the first batch of specimens in Phase II, mixture MC- 15 had considerably lower compressive strengths at 7 and 28 day's age than the Phase I tests. The concrete had a 28-day compressive strength of 300 lb/in. 2 (2,070 kPa) versus 415 lb/in. 2 (2,860 kPa) for the MC-15 design mixture. Triaxial specimens were not tested from this batch. Triaxial shear strength and flow-pump permeability specimens were



made using the design mixture, MC-15, yielding compressive strengths at 7, 14, and 28 day's age similar to the Phase I tests. Mixture proportions and the results of fresh and hardened properties for Phase II mixture MC-15 are given in tables 3 through 5.

Table 5-- Meeks Cabin Dam Modification Project - Average Properties of Hardened Concrete

Mix Number

1/

MC-0

MC-10

MC-15

MC-20

Bentonke Age Compressive Strength Modulus of Elast~ity Poisson's r~io Content 4/

(%7 (days) (lb/in. 2) (kPa) (106 lb/in. 2) MPa

0 3 425 2930 0.76 5240 0.098

0 7 610 4206 1.04 7171 0.115

0 14 700 4827 1.14 7860 0.197

0 28 820 5654 1.26 8688 0.162

0 90 1060 7309 1.8 12411 0.168

10 3 235 1620 0.415 2861 0.07

10 7 305 2103 0.525 3620 0.145

10 14 370 2551 0.545 3758 0.206

10 28 465 3206 0.92 6343 0.172

10 90 645 4447 1.34 9239 0.164

15 3 180 1241 0.31 2137 0.122

15 7 240 1655 0.395 2724 0.127

15 14 320 2206 0.555 3827 0.154

15 28 415 2861 0.795 5482 0.200

15 90 610 4206 1.155 7964 0.177

20 3 130 896 0.22 1517 0.099

20 7 175 1207 0.295 2034 0.137

20 14 245 1689 0.36 2482 0.121

20 28 335 2310 0.625 4309 0.194

20 90 475 3275 0.79 5447 0.152



Table 5-- Meeks Cabin Dam Modification Project - Average Properties of Hardened Concrete

Mix Bentonite Age Number Content 4/

1/ (%) (days)

MC-15 15 7 2/

Compressive Strength Modulus of Elasticity

(lb/in. 2) (kPa) (106 lb/in, z) MPa

220 1517

15 14 320 2206

15 28 420 2896

15 90 590 4068

Poisson's ratio

MC-15 15 7 190 1310 3/

15 28 320 2206

_I/ Mixtures MC-0 to MC-20; Aggregate Source No. M-8060. 2/ Mixture tested for triaxial shear strength, flow-pump permeability. 3/ Mixture MC-15; Aggregate Source No. M-8078. 4/Bentonite Content - % by dry mass of cement plus bentonite_.

Flow-pump Permeability

The flow-pump permeability began at 28 days and was tested at 51 days according to ASTM Test Method for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter, Method D (D 5084), and ASCE (American Society of Civil Engineers) Special Publication No. 24, Vol. 1, Geotechnical Engineers Conference. The 6 in. (150 mm) diameter cylindrical specimen was 4 in. (100 mm) high. The 23 day delay between beginning the test and determining the permeability was the time required to reach a "B" value of 0.95, indicating saturation. After saturating the test specimen, the flow-pump permeability was determined using an effective confining pressure of 45 lb/in. 2 (310 kPa); back pressure of 65 lb/in? (450 kPa) and confining pressure of 110 lb/in. 2 (760 kPa). The coefficient of permeability was determined after 417 minutes when the specimen reached a steady-state flow condition. The coefficient o f permeability for the plastic concrete is about 240xl 0 -j~ cm/s. The coefficient of permeability of mixtures with 20 % bentonite tested by the USCOE ranged from about 210x10 1~ to 4x10 1~ cm/s. However, the tests are not directly comparable due to different test ages, applied pressure, and test procedures.



Erodibility

There is no standard procedure for testing erodibility of low-strength concrete. Erodibility was tested according to the guidelines of Corps of Engineers publication REMR-GT-15. Tap water is injected through a formed 1/8 in .(3.2 mm) diameter hole, lengthwise through the center of the cylindrical test sample. The water, at a pressure of about 40 lb/in. 2 (275 kPa), is injected continuously for 28 days and the total mass of eroded material is determined. The specimen had an erodability of about 0.03 % retained on the 75Um (No. 200) sieve after 28 days. The erodibility test result is likely conservative, since a higher strength mixture should have better resistance to erosion than the tested mixture. Since there is no standard for erodability of plastic concrete the results can only be compared to the USCOE publication. The results fall within the range of 0 to 0.05 % retained on the 75 Um sieve tested by the USCOE for mixtures with 0 to 60 percent bentonite, respectively.

Triaxial Shear Strength

Three triaxial shear specimens were tested according to USBR 5755 Performing Consolidated-Drained Triaxial Shear Strength of Soils at 28 day's age. Three lateral confining pressures were used in the tests, 45, 90, and 180 lb/in. 2 (310, 620, and 1,240 kPa). Triaxial test results are given in table 6. The angle of internal friction and cohesion at zero normal load were determined from a straight line fitted through a plot of the peak shear stress versus normal stress for the three test specimens.

Table 6-- Meeks Cabin Dam Modification Project- Consolidated-drained Triaxial Shear Strength - Mixture MC-15

Test Dry Density Water Volume Axial Normal Shear Stress Effective No. Content Change Strain Stress 1/ Confining

1/ 1/ Pressure

lb/ft 3 kg/m 3 % % % lb/in. 2 kPa lb/in. 2 kPa lb/in, z kPa

No.1 116 1858 15.7 0.1 1.83 175 1207 227 1565

No.2 117 1874 15.4 0.9 3.75 248 1710 276 1903

No.3 118 1890 14.7 1.5 8.94 379 2613 348 2399

Angle of Internal Friction (phi) = 30.5 degrees Cohesion (shear stress at 0 normal load intercept) = 127 lb/in, z (875 kPa)

1/ Values at peak shear stress.

Slumo Loss and Settim, Time

Mixture MC-15 was tested for slump-loss and time-of-set tests with an ASTM Specification for Chemical Admixtures (C 494), Type B (retarding) admixture and

45 310

90 620

180 1240



without the admixture (control). After mixing, the slump was tested every 30 minutes for 5 hours. The concrete was placed in a flat pan after 30 minutes and remixed with a shovel before each slump test. After about 2 to 3 hours, both mixtures began to stiffen with little or no apparent slump. The mixtures regained some fluidity after remixing. The stiffening may be the result of continued bentonite hydration or forming initial chemical bonds during cement hydration.

Time-of-set specimens were cast from the same mixture at about one hour. The time-of- set was determined according to ASTM Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance (C 403). For this test, initial and final set are defined as a penetration "resistance" of 500 and 4,000 lb/in. 2 (3.4 and 27.6 MPa), respectively. Penetration resistance should not be confused with compressive strength. Both mixtures reached initial set after about 13 hours and final set after about 2 days. The estimated compressive strength of the concrete at 2 day's age is about 100 lb/in. 2 (690 kPa). Slump- loss and time-of-set results are given in Tables 7 and 8, respectively.

Table 7-- Meeks Cabin Dam Modification Project - Phase H-Slump Loss o f Fresh Concrete - 1/

Elapsed Time

Mixture MC-15 (no retarder)

Slump Temperature

Mixture MC-15 (with retarder)

Slump Temperature

(hr:min) (in.) (mm) (~ (~ (in.) (mm) (o F) (~

0:30 8.75 222 10.00 254

0:45 8.50 216 9.25 235

1:00 . . . . 8.25 210 66 19

1:30 6.25 159 7.50 191 65 18

2:00 5.00 127 65 18 7.25 184 65 18

2:30 4.75 121 66 19 6.50 165

3:00 4.00 102 5.00 127

3:30 3.50 89 66 19 4.00 102 66 19

4:00 3.50 89 4.00 102

4:30 4.00 102 3.5 89

5:00 3.50 89 66 19 3.5 89 66 19



Table 8-- Meeks Cabin Dam Modification Project - Phase 11- Setting Time of Fresh Concrete

Mixture MC- 15 1/ (no retarder)

Elapsed Time (hr:min) [min]

(4:15) [255]

(5:15) [315]

(5:40) [340]

(6:30) [390]

(7:30) [450]

(8:30) [510]

(8:30) [510]

(9:30) [570]

(10:30) [630]

(11:30) [690]

(12:30) [750]

(22:00) [1320]

(22:00) [1320]

(24:00) [1440]

(26:00) [1560]

(28:00) [1680]

(30:00) [1800]

(47:20) [2840]

(48:00) [2880]

Mixture MC- 15 1/ (with retarder)

Penetration Penetration Resistance Resistance

(Ib/in. 2) (kPa) (lb/in. 2) (kPa)

4 28 (3:15) [195] 1 7

20 138 (4:15) [255] 8 55

32 221 (4:40) [280] 14 97

40 276 (5:30) [330] 22 152

60 414 (6:30) [390] 40 276

140 965 (7:30) [450] 65 448

130 896 (8:30) [510] 140 965

200 1379 (8:30) [510] 160 1103

260 1793 (9:30) [570] 180 1241

290 2000 (10:30) [630] 260 1793

440 3034 (11:30) [690] 320 2206

1200 8274 (21:00) [1260] 1200 8274

1300 8964 (21:00) [1260] 1250 8619

1700 1 1 7 2 2 (23:00) [1380] 1600 11032

2000 1 3 7 9 0 (25:00) [1500] 1800 12411

2200 1 5 1 6 9 (27:00) [1620] 2000 13790

2300 1 5 8 5 8 (29:00) [1740] 2400 16548

3600 24822 (46:20) [2780] 3200 22064

4000 27580 (47:00) [2820] 4000 27580

Elapsed Time (hr:min) [min]

1/ Mixture MC-15; coarse aggregate sample No. M-8060; fine aggregate sample No. M- 8070 (second fine aggregate sample obtained from the same source as M-8060).



Compressive Strength of Mixture MC-15 With Alternate Aggregate Source

Mixture MC-15 was retested using aggregate source M-8078. Aggregate physical properties test results are given in table 1. Mixture proportions and fresh and hardened concrete test results are given in tables 3 through 5. The slump after 45 minutes was higher and the compressive strength at 7 and 28 day's age was lower for this mixture than the slump and compressive strengths of same mixture using aggregate source M-8060, respectively. Aggregate sample M-8078 is more rounded than sample M-8060. Using rounded versus crushed aggregates in concrete normally lowers the design water content at similar slump. If the water content is reduced to lower the slump to the same value as the Phase I and II tests, the strength would likely increase to comparable values also.

Additional Recommendations and Future Research Needs

Develop procedures for batching bentonite in low-strength concrete mixtures-- Presently, low-strength, concrete mixtures can be batched with pre-hydrated bentonite slurry or dry bentonite powder mixed with cement. Both methods have advantages and disadvantages. There is no standardized test method for adding pre-hydrated bentonite to low-strengt h concrete. A pre-hydrated slurry has the advantage of reducing slump loss. A disadvantage is two separate batching operations must be monitored carefully to maintain batch-to-batch consistency. Conventional, batch-type mixing plants are not set up for batching slurry. These plants could be modified to add pre-hydrated slurry as either an admixture or possibly by using a water meter. The Corps of Engineers reported difficulty mixing low-strength concrete with pre-hydrated bentonite due to the fines "bailing up".

Dry-batching conforms better with standardized test methods and conventional concrete mixing plants. Most batch-type plants can add a second dry ingredient similar to pozzolan. The disadvantage is that the dry bentonite must have sufficient time ( 30 minutes to 1 hour) to hydrate before being tested or placed due to slump loss. This is not a major problem if the low-strength concrete is mixed off site and there is a 30 minute to 1 hour haul. I f mixed on site, the mixing trucks will have to be delayed to allow the bentonite to hydrate before placing.

Whether to pre-hydrate slurry or dry-batch may depend on the equipment available and the bentonite content. High bentonite content mixtures may require different batching methods than low bentonite mixtures. The two methods should be compared over a range of different bentonite replacement percentages and total cement plus bentonite contents.

Develop standardized test methods for low-strength, concrete--The properties of low- strength concrete fall between soil and concrete. The low-strength concrete may be either too stiffto test as a soil or too weak to test as a concrete. Standardized methods for making and testing either soil or concrete can be modified to accommodate low-strength concrete. Other methods may have to be developed and standardized. The precision of current methods should be investigated.



Investigate the long-term properties of low-strength concrete--The hardened properties of concrete change with age. Low-strength concrete mixtures should be tested for long- term strength and elastic properties. The long-term durability should also be investigated.

Conclusions

1. The compressive strength of low-strength concrete is reduced at all ages tested (3, 7, 14, 28, and 90 days) by adding 10, 15, and 20 % bentonite by mass of C+B (cement plus bentonite). The reduction in strength increases with increasing bentonite content.

2. The bentonite content required to meet a 400 lb/in. 2 (2,760 kPa) minimum compressive strength at 28 day's age is about 15 % by mass of C+B for the 300 lb/yd 3 (178 kg/m 3) C+B mixture.

3. The average compressive strength of the three bentonite mixtures tested increased with age. The average compressive strength was 43 % of the control (no bentonite) at 3 days and 58 % of the control at 90 days.

4. Adding bentonite reduced the modulus of elasticity of low-strength concrete.

5. The modulus of elasticity of both control and bentonite mixtures increases with increasing compressive strength and increases with age.

6. Long-term strength and elastic properties tests are recommended to determine whether adding bentonite to fresh concrete continues to affect the hardened properties of low-strength concrete proportionally with age.

7. As the bentonite content (B/(C+B)) increases, the design water content required to maintain a constant slump after 45 minutes increases. The design water content required to maintain a constant slump of 8 in. (200 mm) at 45 minutes increased from 435 lb/yd 3 (260 kg/m 3) for the control mixture to 520 lb/yd 3 (309 kg/m 3) for 10 % B, 535 lb/yd 3 (317 kg/m 3) for the 15 % B, and 560 lb/yd 3 (332 kg/m 3) for the 20 % B mixtures, respectively. This is similar to the results reported by the USCOE.

8. As the design water content increases (with increasing bentonite content), the density decreases proportionally. The density of fresh concrete decreased 3.1, 4.1, and 5.5 % when the bentonite content increased from 0 to 10, 15, and 20 %, respectively.

9. The density of fresh concrete tested about 1 to 2 % higher than the theoretical, air-free density based on design quantities. A possible explanation for the error may be the high moisture content of the sand and possibly the loss of paste from the fresh density sample during rodding.



Reference:

Kahl, et. al., Plastic Concrete Cutoff Walls for Earth Dams, US Army Corps of Engineers echnical Report No. REMR-GT-15, Waterways Experiment Station, Vicksburg, MS, p. 71, March, 991.


Case Histories--Pipelines


David Brinkley 1 and Paul E. Mueller 2

TEN-YEAR PERFORMANCE RECORD OF NON-SHRINK SLURRY BACKFILL

REFERENCE: Brinkley, D. and Mueller, R E., "Ten Year Performance Record of Non-Shrink Slurry Backfill", The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: Over ten years ago, the City of Prescott, Arizona, first installed a non- shrink slurry as a controlled low-strength trench backfill material. Since then, the process has become a standard for all utility trench installations. The non-shrink slurry backfill is a controlled low-strength portland cement concrete product with a compressive strength of 120 to 150 psi (827 to 1034 kPa) in 30 to 60 days and has a 0- inch slump. Prior use of aggregate backfills resulted in a thilure rate of greater than 80 %. The City has re-excavated numerous trenches filled with the slurry material and successfully removed the slurry from various pipe systems including water, sewer, natural gas, electric, telephone, cable, and fiber optic installations. The City of Prescott now requires this controlled low-strength slurry, in all trench restoration work. The failure rate over a ten-year period has been less than 1%.

KE~3k'ORDS: non-shrink slurry, CLSM, flowable fill, 0-inch slump, pedbrmance, re- excavation

During the past ten years, the City of Prescott has continued and expanded its use of non-shrink slurry backfill. The development of the backfill was the result of a building boom that stretched the City's staff beyond its ability to inspect every utility trench cut restoration. This lack of inspection of compacted soil-aggregate backfills resulted in unwanted depressions and potholes in more than 80 % of backfills and their road surfacings. Financial restraints prohibited the hiring of additional staff, and the local building boom continued to increase work loads. An alternative solution became necessary to remedy the ever-increasing problems.

1Chief inspector, Department of Public Works, PO Box 2059, Prescott, AZ 86302-2059. 2Consulting civil engineer, 4514 N. 82nd St, Scottsdale, AZ 85251-1702.

231



The City investigated the experiences of, the City of Toronto, Canada regarding utility cut restorations. That city's early use of a non-shrink slurry using fly ash as the binding agent was the motivation to Prescott's trials in this slurry backfill process.

Fly ash was not readily available in the Prescott area, and portland cement became the logical choice for the cementitious material. The other major ingredient was a small-sized aggregate, predominantly 3/8 inch (I0 mm) or smaller. This mix design has changed little over the past ten years and basically consists of:

Fine aggregate - 0.375 in. (10 mm) Concrete sand Portland cement Water

2,600 lbs ( 1179 kg) 800 lbs ( 363 kg)

94 Ibs ( 42.64 kg) 11 gals ( 42 1 )

Fine aggregate, such as pea gravel, is often not commercially available in the Prescott area and substitute sizes had to be used over the past decade. One such substitute, that can best be described as a flaked sand, is a by-product of a crushing operation. Although considerably finer in size, this man-made aggregate is often substituted directly for the 3/8 in. (10-mm) aggregate material, in the same quantities. The resulting strength characteristics are about equal. There is a change in the workability, however, when the flaked sand is used. The resulting mix tends to be a little sticky during placement and is more difficult to discharge from a ready-mix truck.

Over the years, 5% entrained air has been added in this standard mix in an attempt to increase flowability. There is a small benefit from using this additive, but the accompanying small increase in cost has negated its use. The result is that air-entrained slurry mixes are used in special situations, hut this is not common.

Another substitute tried during the past decade involves increasing the fine aggregate size to 3/4 in. (19-mm). Again, an equal weight of this larger aggregate was used in the generic mix design, and the strength results were equal, The contractors, however, found the flow characteristics were impeded, and they would rather use the smaller sizes when available.

The City is now considering using some recycled materials, including crushed glass, porcelain wastes or both. Slurry using these materials has not yet been placed, however.

In reviewing the successfhl use of the non-shrink slurry over the past ten years, the City and the authors believe that aggregate type and size are not critical in developing a workable mix design. The amount of portland cement and water are far more critical in terms of strength development and flow characteristics. Too little cement will result in poor flowability; too much will result in strengths too high to allow successful trench re- excavation. Water content is also critical. The City of Prescott's use of a mix design that results in a 0-inch slump differs from the high-slump designs used in much of Arizona


BRINKLEY AND MUELLER/NON-SHRINK SLURRY 233

and throughout the United States. This particular mix design, however, is also used as a standard in the nearby Town of Prescott Valley and in Yavapai County. With this mix~ we are primarily intent on coating all the aggregate particles with cement paste and not causing any cementitious material to be washed off or wasted in the process.

Prescott has benefited from the use of a non-shrink slurry material in situations other than trench restoration The material has been used as a cement-treated base for various asphalt surfacings and as a stabilizing product for pumping subgrades. It proves to be a fast and effective tool whenever time becomes critical on a construction project.

One example involved a sewer project that required a 17-fl (6.7-m) deep cut across a major arterial street. The area to be cut was in an unstable fill, and required extensive shoring for the sewer pipe placement. Standard backfilling and compaction of thin lifts would have required 24 to 48 h for completion. By using the non-shrink slurry, the pipe was placed, backfilled with slurry around the pipe and up to within 2 inches of the final surface. The slurry is self-compacting with little eftbrt during placement. The roadway opened to traffic within 7 hours, and results in savings in both time and money.

Another example involved a conduit bank that required backfilling and compacting to a 95% standard Proctor density. The large number of conduits in the bank, and their proximity to each other, made obtaining that required density extremely difficult. (Fig. 1)

FIG. 1 - Conduit placed and excess soil removed before slurry placement



Projects often require backfilling several layers ofconduits within atrench. In this case, slurry material is placed over the lower level conduit. (Fig. 2). The process continues with the middle level conduit being placed on top of the first slurry level, and the procedure repeated to allow a third and final level of conduit near the top. The operation is continuous, and 500 fl (152 m) of such slurry placement can be completed in less than 4 h..

FIG 2 - Slurry placed over lower conduit line. Second layer conduits placed directly

over this layer before the next level slurry placement.

One outstanding advantage to using non-shrink slurry in trench restoration is the stability afforded by the mass immediately after placement. This allows the contractor to place an asphalt surfacing directly over the freshly placed material as the final step in the restoration process. No waiting time is needed, and the impact to both vehicular traffic and other construction operations is minimized. Additionally, the savings in traffic control costs, although not quantified by any studies, appears to be considerable.


BRINKLEY AND MUELLER/NON-SHRINK SLURRY 235

When the City of Prescott first placed this type of slurry in utility trenches, and ultimately mandated its use for all utility underground construction within the City's jurisdiction, it was assumed that the resulting hardened material would have a low enough compressive strength that would allow the hardened slurry to be easily excavated during line repairs. In fact, the affected utility companies required that assurance. In the past few years, a large number of such trenches have been re-excavated, and the hardened slurry from around the pipe systems has been easily removed using standard equipment.

Most re-excavations begin with a backhoe breaking up the hardened material in the vicinity of the pipes. As the pipe system is exposed, laborers use shovels, bars and small hand-held lightweight chipping hammers in a cleaning-offprocess. The slurry tends to peel rapidly away from the pipe leaving it clean of any clinging soil. This has been found to be particularly valuable in waterworks construction.

The City of Prescott's experience with portland cement-based non-shrink slurry has been positive over the past decade. The performance of this material has exceeded all expectations, with a failure rate of less than 1%. Several issues, however, continue to concern us. The first involves the delivery of the material in standard, locally available, ready-mix trucks. When the City first started using this material, the transit mixers had a difficult time properly mixing the ingredients. Their ability to discharge the desired 0- inch slump mass was also a problem. Mixer truck manufacturers assisted in redesigning the mixer units, and the problem was overcome by increasing the height of the blades or fins within the mixing chamber. This redesign increased agitation and mixing efficiency and resulted in a more complete coating of cementitious material around aggregate particles. The change in blade dimensions also increased the drum's ability to discharge the 0-inch slump slurry from the unit, The t/me-related cycling of trucks to and from the jobsite increased substantially.

The second concern involves the portland cement-based material when it encases copper or brass pipes and fittings. The chemical makeup of portland cement paste creates corrosive forces that attack nonferrous metals. A number of options have been considered. The most cost-effective and easiest solution was to sleeve all brass and copper fittings and appurtenances with polyethylene sleeves, Residential and commercial construction has used such sleeving on nonferrous pipe materials, and it has been an easy transition. Since the sleeving was made part of ASTM standards several years ago, no instances of corrosion have been found.

A third concern is a result of the successful excavation of an old trench that was placed with the slurry material. While the slurry removal process has become a routine and somewhat easy procedure, this success is often offset by ever-decreasing locations where there is sufficient room to dispose of the excavated cementitious materials. This requires the use of haul trucks and adds an unexpected cost to the process.



In conclusion, the City. of Prescott's has successfully used non-shrink slurry backfill and the material has a performance record that indicates a failure rate of less than 1%. The use o f slurry in the years ahead is expected to increase as the area continues to grow.


Mark C. Webb, ~ Timothy J. McGrath, 2 Ernest T. Selig 3

FIELD TEST OF BURIED PIPE W I T H CLSM BACKFILL

REFERENCE: Webb, M. C., McGrath, T. J., and Selig, E. T., "Field Test of Buried Pipe with CLSM Backfill", The Design and Application of Controlled Low- Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: A buried pipe was installed using controlled low strength material (CLSM) as backfill as part of a study of installation procedures for buried pipe. A laboratory evaluation of mix designs was undertaken prior to the field test to determine the suitability of the component materials and establish a mix with acceptable flow characteristics and a 28 day compressive strength of less than 1000 kPa (145 psi). The mix selected developed an average compressive strength of 334 kPa (48 psi) at 7 days and 600 kPa (87 psi) at 28 days, and Young's moduli of 120 MPa (17 ksi) at 7 days and 190 MPa (28 ksi) at 28 days. The field installation was in a trench with a width equal to the pipe outside diameter plus 600 mm. One length each of 900 mm nominal inside diameter concrete, corrugated steel and corrugated HDPE pipe was elevated on bags of gravel to allow the CLSM to flow under the pipe. The plastic and metal pipes were weighted with bags of gravel to minimize flotation. The CLSM was placed to the springline in two lifts, two hours apart. The metal pipe floated slightly while the second lift was being placed. Backfilling above the CLSM with a native clay commenced about 16 hours after installation of the CLSM. The CLSM provided excellent support for the pipe in especially hard to reach areas underneath the pipe. Pipe deflections were small and similar to those for the same pipe and high quality crushed stone backfill carefully placed and well compacted. Re-excavation of the installation about three weeks later showed that the CLSM backfill provided excellent support; however, excavation was difficult, even at that early age. A lowering of the target strength for the CLSM mix design to between 200 kPa and 400 kPa (30 psi and 60 psi) at 28 days is recommended for providing more excavatable backfill.

~Senior Engineer, University of Massachusetts, Department of Civil and Environmental Engineering, Amherst, MA 01003 2principal, Simpson Gumpertz and Heger, Inc., 297 Broadway, Arlington, MA 02174- 5310 3Professor of Civil Engineering, University of Massachusetts, Department of Civil and Environmental Engineering, Amherst, MA 01003

237



KEYWORDS: CLSM, buried pipe, field installation, fly ash, compressive strength, Young's modulus, backfill, trench, flowable fill

INTRODUCTION

Controlled low strength material (CLSM) also known as flowable fill, controlled density fill, and flowable mortar, has been used as structural backfill for many years and for reasons that include: �9 ease of placement in hard to reach places (haunches) or in narrow trenches where

space is limited, �9 fast backfilling operations since CLSM is not compacted or tested for compaction

requirements, �9 readily available from most ready-mix suppliers, and �9 ability to be removed if correct mix design is used.

CLSM is generally made up of Portland cement, fine aggregate, fly ash and water. Sometimes high air content is used to create good flow characteristics with less fly ash. These constituents are mixed in different quantities to produce the required flow characteristics during placement and the required strength after placement. Compressive strengths varying between 345 and 1400 kPa (50 and 200 psi) at 28 days are typical. Although experience shows that CLSM with strengths in the higher end of this range are difficult to re-excavate.

A study was conducted at the University of Massachusetts in which different pipe installation and backfilling procedures were tested and evaluated. One full scale field test was conducted with CLSM as backfill material. Prior to the field test 9 CLSM mixes with different component quantities were evaluated in a laboratory study for flowability, segregation and compressive strengths at 7 and 28 days. The selected mix was used to backfill 900 mm (36 in.) inside diameter pipe in a trench 300 mm (12 in.) wider than the pipe on both sides. The pipe sections were elevated on bags of gravel about 150 mm (6 in.) above the trench bottom to facilitate material flow under the pipe. CLSM was placed in two lifts to the pipe springline. The three types of pipe used were reinforced concrete, corrugated metal, and corrugated high density polyethylene. The pipe performance was monitored during backfilling and the CLSM material was examined when the pipes were re-excavated about 3 weeks later.


WEBB ET AL./FIELD TEST OF BURIED PIPE 239

MIX DESIGN

The mix design study involved preparing a total of 9 trial batches with different component quantities and testing for flowability and compressive strength (Gagnon 1994). The components of the mix were sand, fly ash, cement and water. These materials were obtained from a nearby concrete batch plant. The sand serving as fine aggregate is classified as a poorly graded sand (SP) according to ASTM Standard Classification of Soils for Engineering Purposes (D 2487). The component quantities for the 9 trial mixtures are shown in Table la.

Specimen Preparation and Testing

Specimens were prepared in accordance with ASTM Standard Test Method for Preparation and Testing of Soil-Cement Slurry Test Cylinders (D 4832 - 88). The CLSM was mixed in a bowl with an egg beater type paddle for 2-3 minutes. Water was added to the mixer first, followed by sand, cement, and finally fly ash. The addition of fly ash to the mix resulted in an enormous increase in flowability.

Flowability tests were conducted on all trial batches by placing a freshly mixed sample of CLSM in a 75 mm diameter (3 in.) by 150 mm (6 in.) high open ended tube, and quickly lifting the tube vertically allowing the CLSM sample to slump into a circular mound. The circular sample spread was then measured. A minimum acceptable spread of 200 mm (8 inches) and no segregation of water were adopted acceptance criteria based on guide specifications of the Texas Aggregates and Concrete Association (TACA 1989). These criteria have been adopted by other agencies as well.

Strength tests were performed for each mix using the following procedures: 1. The fresh mix was poured into 3 or 4 cylindrical plastic molds 100 mm diameter

and 200 mm high (4 in. by 8 in.). 2. Specimens were allowed to set for about 10 to 15 minutes, after which additional

CLSM was added to displace bleed water, and a lid was placed loosely on the filled mold.

3. The total volume of CLSM produced in the batch was determined. 4. The specimens were allowed to cure overnight in the laboratory before moving

them to a moist room the next morning. 5. Seven days after the molds were filled, two specimens of each mix were removed

from the moist room and the plastic molds were stripped. The specimens were allowed to air dry for about 4 hours.

6. The specimens were then capped with sulfur on both ends to prepare for compression testing.

7. The cylinders were loaded to failure in a compression testing machine and the compression strength calculated as the failure load divided by the initial cross sectional area.

8. Steps 5, 6 and 7 were repeated after 28 days.



TABLE 1--Mix Component Quantities and Strength Results

a. Mix Constituents

Material Designation (kg)

Nom A B C D E F X Y

Cement 44 30 59 44 44 44 44 36 44

Fly Ash 296 148 296 222 296 296 296 148 148

Sand 1570 1570 1570 1570 1720 1570 1570 1570 1570

Water 296 296 296 296 296 237 355 296 296

w/c ratio I 6.7 9.9 5.0 6.7 6.7 5.4 8.1 8.2 6.7

w/(c+fa) 0.87 1.7 0.83 1.1 0.87 0.70 1.0 1.6 1.5 ratio I

b. Test Results

7 Day 1055 NT 2 1410 515 825 1435 515 Compr. (153) (205) (75) (120) (209) (75)

Strength, kPa (psi)

28 Day 1890 350 2710 16453 1295 2900 1115 Compr. (275) (51) (393) (239) (188) (421) (162)

Strength, kPa (psi)

Segre- None Yes Very Little Little Very Little gation little little

Spread, 380 No 250 280 220 No 315 mm 4 spread spread

205 (30)

54O (79)

Yes

NT 2

295 (43)

Yes

No spread

Notes: 1. 2.

c = cement, w = water, fa = fly ash Specimens A and Y were very fragile at 7 days and both fell apart during the removal of the plastic molds and/or during capping. NT = not tested.

3. Individual test results are widely separated (820 kPa and 2465 kPa) 4. ASTM Provisional Standard Test Method for Flow Consfstency of Controlled

Low Strength Material (PS 28 -95) 5. 6.89 kPa= 1 psi 6. 25.4 mm = 1 in.



Results

Compression and flowability test results are summarized in Table lb. These results indicate the following:

Water to cement plus fly ash ratios of greater than or equal to 1.5 resulted in very low compressive strengths. For example the 7 day strength was 205 kPa for Specimen X. Specimens Y and A could not be tested at 7 days since they fell apart upon removal of the plastic molds. An inability to conduct compression tests does not mean that the mix is not suitable, only that the compression testing may not be an appropriate method of quality control.

For the same amount of fly ash, sand and water in the mix a 33 % increase in cement content resulted in a 34 % increase in 7 day compressive strength (43 % at 28 days) (Specimens Nominal and B).

For the same amount of cement, sand and water in the mix a 25 % decrease in the amount of fly ash resulted in about a 50 % decrease in 7 day compressive strength (13 % at 28 days) (Specimens Nominal and C).

For the same amount of cement, fly ash and water in the mix a 10 % increase in the amount of fine aggregate in the mix resulted in a 22 % decrease in 7 day compressive strength (32 % at 28 days) (Specimens Nominal and D).

For the same amount of cement and fly ash in the mix a 20 % reduction in the amount of water resulted in a 36 % increase in 7 day compressive strength (53 % at 28 days) (w/(c+fa) ratio of 0.87 for Specimen Nominal and 0.70 for Specimen E). Conversely, a 20 % increase in the amount of water in the mix (w/(e+fa) ratio of 0.87 for Specimen Nominal and 1.0 for Specimen F.) resulted in about a 50 % decrease in 7 day compressive strength (41% at 28 days) when keeping the amount of cement and fly ash the same.

For the same amounts of cement and fly ash in the mix a 20 % increase in the amount of water and a 10 % decrease in the amount of sand resulted in a 38 % decrease in 7 day compressive strength (14 % at 28 days) (Specimen D and F).

Specimens with low amounts of fly ash in the mix had water segregating from the mix as indicated by Specimens X, Y, and A. Specimen F which had more water than the others showed little water segregating from the mix. The remaining specimens, all of which had w/(c+fa) ratios of less than about 1.0, showed little or no segregation.

Conversely, specimens with high amounts of fly ash (222 kg/m 3 and more) in the mix met minimum spread requirements of 200 mm except for Specimen E which fell over and had the least amount of water. Specimens Y, X and A having 148 kg/m 3 fly ash did not meet the 200 mm requirement.



Specimens which could be tested at 7 days increased in compressive strength by a factor of between 1.6 and 3.2 when tested at 28 days. The factor of 3.2 corresponds to Specimen C which had two widely different 28 day compressive strengths.

The importance of fly ash in improving flowability, controlling water segregating from the mix, and increasing the compressive strength, is clearly indicated by these test results. Even though class F fly ash has no cementitious properties, an increase in compressive strength for increasing amounts of fly ash due to the pozzolanic reaction is clearly evident. The w/(c+fa) ratio (including the amount of fly ash) is a good indicator of expected material strength. Based on the results of the mix design study the mix selected for the field installation study is shown in Table 2.

TABLE 2--Selected Mix for Field Installation Study

Material kg kg/m 3

Cement 45 46

Class F Fly Ash 244 247

Dry Concrete Sand 1,583 1,606

Water 270 274

w/(c+fa) ratio 1 0.93 0.93

Notes: 1. 2.

c = cement, w = water, fa = fly ash 1 lb/yd 3 = 1.69 kg/m 3

FIELD INSTALLATION

Detailed information about the field test program which included the CLSM installation is given in other references (Webb 1995, Webb et al. 1996). The CLSM test was conducted at a "clay" site where the natural soils consisted principally of a sedimentary varved clay deposit (CL) overlain by a clay fill (CL). The pipe was backfilled to the springline with CLSM. The backfill above the CLSM was the in situ clay material. The target strength for the CLSM mix was 690 kPa (100 psi) at 28 days. The material was delivered in two batches, with 28 day compressive strengths of 780 kPa (113 psi) and 430 kPa (62 psi), respectively. The corresponding modulus of elasticity values at 28 days were 234 MPa (34 000 psi) and 145 MPa (21 000 psi), respectively. The two batches were supposed to'be identical. Presumably the supplier made an error in one of the batches resulting in the difference in strength.

The plastic pipe had a bending stiffness (load in a parallel plate load test required to produce a unit deflection in a unit length of pipe) of 390 kN/m/m (56 lb/in./in.) and a hoop stiffness (uniformly applied radial pressure required to produce a unit


WEBB ET AL./FIELD TEST OF BURIED PIPE 2 4 3

circumferential strain) of 16xl 03 kN/m/m (2.4xl 03 lb/in./in.). The corresponding bending and hoop stiffnesses for the metal pipe were 430 kN/m/m (63 lb/in./in.) and 730x103 kN/m/m (110x 103 lb/in./in.), respectively.

Interface pressure cells were installed in the walls of the concrete pipe. Pipe deflections were measured in all 3 pipes with a rotating profilometer mounted on a three- legged support system. Details of the instrumentation are given elsewhere (Webb 1995).

Test Procedure

The CLSM test required some deviation from typical procedures followed for installing the pipe when using traditional backfill materials. The trench was excavated in the native clay material with a width 600 mm greater than the pipe outside diameter (Fig. 1). However, construction operations were hampered by heavy rains that caused portions of the lower trench wall to fail including one large section with approximate dimensions of 2.4 m (8 ft) long by 1.2 m (4 ft) high by 300 mm (1 ft) wide located in between the metal test piece and end section (Fig. 2). Water was pumped out of the trench and the softened in situ material was removed. This resulted in an uneven trench with portions wider than intended.

General steps for the CLSM test included:

1. Some seepage of water occurred into the trench from permeable seams in the trench walls. Thus approximately a 50-ram (2-in.) thick layer of stone was placed to cover the soft trench bottom and puddles of water. This stone was compacted with a vibratory plate compactor.

2. Plastic bags were filled with 23 kg (50 lb) of pea gravel. Two bags of pea gravel were placed near each end of each section of pipe to support the pipe about 150 mm (6 in.) above the trench bottom, allowing room for the CLSM to flow under the pipe. Initial instrumentation readings were taken.

. Twelve bags of pea gravel were then placed on top of the metal pipe and ten bags were placed on the plastic pipe (Fig. 2) to resist flotation. Instrumentation readings were again taken.

4. When the CLSM arrived at the site the water content was adjusted until a 230 mm (9 in.) spread diameter was achieved. The first layer of CLSM was placed to just above the pipe invert. The material flowed under the pipe without difficulty and flowed longitudinally about 2.4 m (8 ft) during placing. The discharge chute was moved along the length of the trench and alternated between the two sides. After this CLSM layer was placed instrumentation readings were taken.

5. Approximately 2 hours after the first placement, the CLSM was firm enough for placement of another layer. Again, water was added to the material as delivered in


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FIG. 2--Pipe backfilled with CLSM



order to achieve the required 230 mm (9 in.) flow diameter. The second layer of CLSM was placed to 600 mm (24 in.) above the pipe invert or to 150 mm (6 in.) above the springline. During this placement the metal pipe was pushed sideways approximately 75 mm (3 in.) and lifted approximately 50 mm (2 in.). The plastic pipe did not lift, even though it was lighter because the deep corrugations were held in place by the first batch. The concrete pipe also did not move. After the second lift was placed, instrumentation readings were taken and work was stopped for the day.

6. The next day readings were again taken to check for any change from the previous day without any further backfilling. The CLSM had hardened enough to walk on it. Some fine shrinkage cracks were noted in the CLSM.

7. The pea gravel filled bags were then removed from the top of the metal pipe (12 bags) and plastic pipe (10 bags). Instrumentation readings were then taken.

8. Nuclear density readings were taken on the surface of the CLSM sixteen hours after placement.

9. A layer of native clay was placed over the CLSM to 150 mm (6 in.) below the top of the pipe. This layer was compacted with two coverages using a rammer compactor. Readings were taken.

10 Another layer of native clay was placed to 150 mm (6 in.) loose thickness above the top of all pipes. This layer was compacted with the rammer (two coverages), except for the center strip, 460 mm (18 in.) wide, over the top of the pipes (Fig. 1).

11 Four layers of in situ material (Fig. 1) were placed and compacted to achieve a total cover thickness of 1.2 m (4 ft). Readings were taken after compaction of each layer.

12 The final readings were taken and the pipes were removed twenty-two days after the start of the CLSM test. However, excavation was difficult even when using a backhoe. The CLSM had to be broken away with the bucket of the backhoe and shovels were of little help. With most of the CLSM removed from around the pipe, the backhoe had to be used to rip the pipe out. The plastic pipe with the deep corrugations was especially difficult to remove. After the pipes were removed, the bedding (CLSM) was photographed and inspected. Excellent flowability of the CLSM was observed, filling all the voids below the pipe including those formed by the pipe corrugations (Figs. 3,4 and 5 for the concrete, plastic and metal pipes, respectively). The gravel bags used to support the pipe can also be seen in these figures. For the plastic pipe some of the corrugations shown in Fig. 4 had been damaged during excavation.


WEBB ET AL./FIELD TEST OF BURIED PIPE 2 4 7

FIG. 3--Photograph showing haunch region of concrete pipe

FIG. 4--Photograph showing haunch region of plastic pipe



FIG. 5--Photograph showing haunch region of metal pipe

Resul~

The measured deflections and concrete pipe interface pressures for the CLSM test are presented and the measured results are compared to those from tests where traditional backfill materials have been used. The results of all the tests are given in (Webb 1995, Webb et al. 1996).

Interface Pressures--Interface pressures in the CLSM test for the pipe invert, and for 30 ~ 60 ~ and 90 ~ from the invert are shown for the concrete pipe (Fig. 6). The interface pressure at each of these locations is the average pressure from two interface pressure cells. The backfill depth is normalized by the pipe outside diameter in Fig. 6. A normalized depth of-0.5 represents backfill at the springline, a depth of 0 represents backfill at the top of the pipe, and a depth of 1.1 represents the top of the backfill. The top of the first layer of CLSM corresponds to a depth of-0.64 and the top of the second layer corresponds to a depth of-0.36. Two sets of readings were taken at each depth of CLSM immediately after pouring and some time later to evaluate stiffening of the CLSM on interface pressures. The second set of readings taken for the last CLSM pour was done the following morning. The drop in pressures at a depth of 0.9 occurred overnight. It is interesting to note that the invert pressure did not drop while the pressures at 60 ~ and 90 ~ from the invert dropped significantly, more than that at 30 ~ from the invert. It is believed that shrinkage of the CLSM and/or the concrete pipe due to an overnight drop in temperature may have been a factor. The least drop in pressure is expected at or near the



invert since the pipe is still in contact with its support. The pressures increased with additional backfilling following the overnight drop.

The invert developed the lowest pressures compared to pressures measured farther away from the invert. The final CLSM invert pressure was signifcantly less than that in most other tests backfilled with traditional materials as indicated in Table 3. The invert pressures in Table 3 were all zeroed after the pipe was set in place to eliminate the effect of the weight of the concrete pipe. At 30 ~ away from the pipe invert the CLSM developed relatively high interface pressures indicating excellent support for the pipe and demonstrating the good flow characteristics of the CLSM. Most traditional backfill materials develop very little to essentially zero pipe support in the lower haunch because of the difficulty in placing and compacting the materials in this area (Table 3) as discussed by (Webb 1995, Webb et al. 1996).

561.o

40

30

2 0 -

10

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-1.0

It

-0.5 0.0 0.5 1.0

! 1

-: Top of pipe 30 ~ from invert ~ ~.~ 60 ~ from invert ~ _ ~ - . " ~ . ~ 9gv~176 invert / ~

[

, , I I I I I I -I , I r I I , I , I f

-0.5 0.0 0.5 1.0

Normalized backfill depth

FIG. 6--Concrete pipe interface pressures

5

4 o ~

2 m

0

At 60 ~ away from the pipe invert, the CLSM resulted in pipe support of similar quality compared to tests with haunching effort, backfilled with stone material, and compacted with a rammer (Tests 1, 3 and 9 in Table 3). Haunching was achieved by working the backfill material into the haunches using the ends of shovels or rods. Generally, tests with haunching effort and compacted with a rammer developed higher support pressures than tests without any haunching effort and either placed without compaction or compacted with a vibratory plate (Table 3). At 90 ~ away from the pipe invert, the CLSM produced interface pressures larger than those for most other tests backfilled with traditional materials (Table 3).



TABLE 3--Final Interface Pressures (kPa)

Test Haunch Comp. Backfill Location material 2

Inve~ 30 ~ 60 ~ 90 ~

CLSM NA I NA 1 CLSM 15 31 34 29

1 Yes Rammer Stone 219 3 29 18



6 Yes Rammer Silty sand 61 7 41 20

8 Yes Rammer Silty sand 7 8 13 34

4 No V. plate Stone 179 2 3 26

7 No V. plate Silty sand 170 2 5 13

2 No None Stone 238 2 4 11

5 No None Silty sand 241 2 2 6

Notes: 1. 2.

NA = Not applicable Stone = 19-ram (3/4-in.)-maximum-size, broadly graded crushed stone Silty sand = poorly graded silty sand The stone and silty sand were classified as SW and SM materials, respectively, according to ASTM Standard Classification of Soils for Engineering Purposes (Unified Soil Classification System)(D 2487 - 92)

The measured interface pressures indicate that CLSM provides very uniform and excellent support, especially in the areas where it is difficult to place and compact soil. Furthermore, pipe support provided by CLSM further away from the invert corresponds to installations where material has been worked into the haunches and adequately compacted.

Pipe Deflection--Vertical and horizontal diameter changes with backfill depth are shown in Fig. 7 for the plastic and metal pipes. The concrete pipe did not measurably deform. Each curve is the average of two profiles done at two pipe cross sections. The first set of profile readings was taken only after the second layer of CLSM was in place and had gained sufficient strength to support the pipe. Profile readings were not performed prior to this stage since the reading activities could move the pipes. Therefore, diameter changes indicated in Fig. 7 do not include pipe deformation resulting from pouring the first two layers of CLSM but represent diameter changes resulting from placing and compacting native clay material above the CLSM. Both plastic and metal pipes peaked upward during placement and compaction of material on the sides of the



pipe, after which the pipes were pushed downward during backfilling over the top of the pipes (Fig. 7).

1.0

~ 0.5

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-0.5

-1.0

-1.0 I I

' ' I . . . . I . . . . I . . . . I ' ' '

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I eadings ~ ~ _ ~ t _ ~ . . . . " k I(22 d ~ s after start of t e ~ -

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-0.5 0.0 0.5 1.0

Normalized backfill depth

i

1.0

0.5

0.0

-0.5

-1.0

I

1.5

FIG. 7--Plastic and metal pipe deflections

The peaking and downward deformation of the pipes are compared to those tests backfilled with traditional materials in Fig. 8. The plastic and metal pipe deformations for the CLSM were about the same as those tests backfilled with stone material and compacted with a rammer. However, the CLSM may have peaked slightly more than these tests (Tests 1, 3 and 9) when deformation due to the 2 layers of CLSM are considered. The plastic pipe installed in CLSM recovered all of its peaking deformation, whereas the metal pipe recovered very little of this deformation. This disparity is believed to be the result of circumferential shortening of the plastic pipe (Webb 1995, Webb et al. 1996). The significant peaking of tests backfilled with silty sand and compacted with a rammer (Tests 6 and 8) are clearly shown in Fig. 8. Tests with less stiff backfill material (Tests 7, 2 and 5) clearly indicate the larger change in pipe deformation during overfilling as indicated in Fig. 8. The significance of downward deformation of pipe lies in the fact that a stiff sidefill material will help carry the load placed above a pipe resulting in less downward deformation whereas, a compressible material will give little support to the pipe causing the pipe to deform under the load placed above the pipe.

CLSM Unit Weight--Two nuclear density and moisture tests were performed on the CLSM prior to covering it with native clay material (about 16 hours after finishing second pour). The wet unit weight of the CLSM was 20.9 kN/m 3 (133 pcf) with a moisture content of 19 %.



~ 0 o

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@

-_. Stone _. l_ Silty - R a m m e ~ - sand " 1 I I I I I

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Test No./Trench width, N-~aarrow, W=wide, I=intermediate

3

2

1

0

-1

-2

-3

FIG. 8--Summary of fieM test deflections



CONCLUSIONS

A laboratory CLSM mix design study was conducted to develop a suitable mix for a pipe field installation. Conclusions from the CLSM mix design are: �9 Fly ash significantly improved flowability, controlled water segregating from the mix,

and increased compressive strength. �9 A water to a total cementitious material ratio of about 1.0 and a fly ash content of

about 220 kg/m 3 produces good flow characteristics.

A field test installation of concrete, plastic and metal pipes backfilled with CLSM was conducted and measured results were compared to those tests backfilled with traditional materials. Conclusions from the field test include: �9 Of particular benefit was the good CLSM support for the pipe in especially the hard to

reach areas underneath the pipe. �9 The CLSM used in the test had good flow characteristics such that the delivery

vehicle only had to be positioned at 2 locations along the entire 8 m (26 fl) length of pipe backfilled with CLSM.

�9 Flotation caused by the fluid CLSM, however, needs to be considered during construction since this may lift and displace the pipe out of its intended position.

�9 Lower target strengths may be needed if ability to re-excavate the pipe is of importance. This requires controlling both the cement and the fly ash content. Compressive strengths of less than about 400 kPa (58 psi) at 28 days should be considered for this purpose.

�9 Flow test was useful as quality control in field with delivered batch before pouring into trench.

ACKNOWLEDGMENTS

The work reported in this paper was supported by funding from the National Science Foundation, the Federal Highway Administration, the states of California, Iowa, Kansas, Louisiana, Massachusetts, Minnesota, New York, Ohio, Oklahoma, Pennsylvania, and Wisconsin, and the Eastern Federal Lands Highway Division of the Federal Highway Administration. The pipes used in the tests were donated by Contech Construction Products, CSR/New England, Hancor Inc., and Plexco/Spirolite Inc. Steve Gagnon conducted the mix design study and Glen Zoladz provided substantial assistance with the field tests. The Massachusetts Highway Department provided a nuclear density gauge for use during the field tests.

REFERENCES

Gagnon, S., 1994, "Evaluation of Different Design Mixtures of Controlled Low Strength Material," A Senior Honors Activity Report, Department of Civil Engineering, University of Massachusetts, Amherst,/VIA



Texas Aggregates and Concrete Association (TACA), November 28, 1989, "Suggested Guide Specifications for Flowable Fill"

Webb, M. C., September 1995, "Field Studies of Buried Pipe Behavior During Backfilling," Geotechnical Report No. NSF95-431 P, Department of Civil and Environmental Engineering, University of Massachusetts at Amherst, MA

Webb, M, C., McGrath, T. J., and Selig. E. T., 1996, "Field Tests of Buried Pipe Installation Procedures," Transportation Research Record 1541, TRB, National Research Council, Washington, D.C., pp.97-106


James R. Hegarty I and Steven J. Eaton 2

FLOWABLE FILL PROMOTES TRENCH SAFETY AND SUPPORTS DRAINAGE PIPE BURIED 60 FT (18.3 M) UNDER NEW RUNWAY

REFERENCE: Hegarty, J. R. and Eaton, S. J., "Flowable Fill Promotes Trench Safety And Supports Drainage Pipe Buried 60 Ft (18.3 m) Under New Runway," The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: In 1995, Kent County International Airport began building a new crosswind runway. The new runway traversed a 66-ft (20. l-m) deep ravine and a stream. Designers chose to enclose the stream in a 60-in (1500-mm) inside diameter reinforced concrete pipe before building the runway embankment. To minimize earth loads on the rigid concrete pipe, a narrow 10-ft (3-m) trench was specified. Safety authorities demanded a wider trench, however, in spite of vertical clay trench walls. Because a wider trench would place unacceptable earth loads on the pipe, designers proposed a modified narrow trench and backfilling the pipe with flowable fill. Flowable fill was placed to the springline; then granular soil was compacted to 12 in (30 cm) above the crown of the pipe before a clay embankment was placed over it to the final grade. The culvert pipe has been inspected three times since installation and is performing well.

K E Y W O R D S : flowable fill, trench safety, concrete pipe, rigid pipe, deep fills, pipe design, SAMM, PIPECAR, trench design, buoyancy, airports, drainage

When Kent County International Airport in Grand Rapids, Michigan decided to build a new crosswind runway, the design team faced a number of challenges. One of those challenges was to enclose a stream crossing the proposed new runway and located in a ravine 66 ft (20.1 m) below the new runway's final elevation.

1 Civil Engineer, Prein & Newhof, Grand Rapids, MI 49505. 2project Manager and Director of Airport Services, Rust Environment & Infrastructure, Des Moiues, IA 50309.

255



The stream was enclosed in a new culvert (Fig. 1). To carry the flow of the stream and allow for future inspections, an inside diameter of 60 in (1500 ram) was selected for the new culvert. The culvert was placed in a trench roughly paralleling the path of the existing stream, requiring two horizontal bends. The trench was excavated partially from native clay soil and the remainder from compacted clay fill.

The design team selected reinforced concrete pipe for the culvert material after evaluating several other options including ductile iron, prestressed concrete, polyethylene, and metal. The most attractive attribute of concrete pipe was its proven durability. Because concrete pipe is a rigid material, it is subject to high loads under deep fills and must be designed to withstand these loads.

FIG. 1-Over 1700 fi (517.7 m) of 60 in (1500 mm) diameter reinforced concrete drainage pipe was installed to enclose a stream under the new runway.

TRENCH WIDTH/PIPE LOADS

For indirect concrete pipe design, the strength needed in the pipe material is a function of the loads placed on it reduced by the quality of the bedding and installation (American Concrete Pipe Association 1981, 1990). The concept can be expressed as:

Pipe Strength = Load On Pipe~Installation Quality (Eq. 1)

Figure 2 relates the effect of trench width upon earth loads for a pipe buried 60 ft (18.3 m), as measured from the final grade to the top of the pipe.


HEGARTY AND EATON/FLOWABLE FILL 257

70,000 -

60,000

50,000

40,000

30,000

20,000

10,000

i I I I I I

9 10 11 12 13 14 15

Trench Width (ft)

FIG. 2-Loads on buried concrete pipe as a function of trench width.

16

Earth loads shown in Fig. 2 were computed using the SAMM (Spangler And Marston Method) computerized design program (McTrans Institute et. al. 1989).

Input parameters used for all SAMM computations are as follows:

Diameter (in)/(mm) 60/(1500) Wall thickness (in)/(mm) 6.75/(17.1) Fill depth (fl)/(m) 60/(18.3) Soil density (lbs/ft3)/(kg/m 3) 135/(2163) Bedding class B Installation type Trench Soil lateral pressure (K mu') 0.1300 Positive projection ratio 1.00 Positive settlement ratio 0.50 Lateral soil pressure coefficient .33 Trench width Varies Safety factor, 0.01 in crack 1.00

There are two options to optimize the deep-burial design of concrete pipe. One is to install it in a narrow trench; the other is to design extra-thick pipe walls. It quickly becomes clear from Fig. 2 that controlling trench width reduces the loads on the pipe. A narrow trench, however, raises concerns for worker safety during pipe placement and backfilling.



PIPE DESIGN/LOAD-CARRYING CAPACITY

The ASTM Specification for Reinforced Concrete Culvert, Storm Drain, and Sewer Pipe, (C 76) includes five pipe strength classes. In ASTM specification C 76, design strength is measured as the pipe's ability to withstand externally applied loads in a three-edge bearing test apparatus before developing a 0.01-in (0.25-mm) crack at the invert and inside crown of the pipe. Ultimate strength is measured as the three-edge bearing load on the pipe when the steel reinforcing yields. Design and ultimate strengths are given in Table 1 for standard ASTM specification C 76 pipe classes.

TABLE 1-ASTM Specification C76 concrete pipe strength standards.

Pipe Class Design Strength Ultimate Strength lb./ft/ft, (kg/m/m) lb./ft/ft, (kg/m/m)

ASTM C 76 1 800,(3 906) 1200, (5 858) ASTM C 76 II 1000, (4 882) 1500, (7 323) ASTM C 76 III 1350, (6 591) 2000, (9 764) ASTM C 76 IV 2000, (9 764) 3000, (14 646) ASTM C 76 V 3000, (14 646) 3750, (18 307)

Using the earth loads from Fig. 2, and assuming a standard Class B soil bedding, pipe strength classes were calculated as a function of trench width for a 60-ft (18.3-m) burial depth. Figure 3 relates the outcome of these calculations using the SAMM design program.

6,000

5,000

4,ggg

-~ 3 ,000

2 .~ 2,000

1,000

ASTM C '76 Standard Pipe Designs O K

I : I

9 10 �9 11 12 13 14

Trench Width (ft)

FIG. 3- Required design strengths as a function of trench width.

After comparing the pipe strength needed from Fig. 3 with the standard available pipe strengths from Table 1, it becomes clear that a standard pipe with a design strength within the ordinary limits for ASTM specification C 76 concrete pipe is impossible unless the trench width is held to 8.5 ft (2.55 m) or less.



The ASTM Specification for Reinforced Concrete D- Load Culvert, Storm Drain and Sewer Pipe (C 655) allows custom pipe designs to meet specific strength criteria beyond those outlined in ASTM specification C 76. It was learned dttring the design process that concrete pipe with design strengths up to 5000 lb/ft/ft (24 410 kg/m/m) was available without using extra-heavy pipe walls, and at a reasonable cost compared to pipe manufactured in accordance with ASTM specification C 76, Class V.

A narrow 8.5-ft (2.55-m) trench width is easy to specify but difficult to control, and perhaps unrealistic, even in stiff soils.

For the KCIA project, Fig. 4-The pipe trench was cut through very stiffclay, therefore, it was decided to

select a pipe with a 0.01-in. (0.25-mm) crack strength of 5000-1b/ft/ft (24 410-kg/m/m) and to specify a maximum trench width of 10 ft (3 m) to deal conservatively and realistically with the loads expected on the pipe at the 60-ft (18.3-m) burial depth.

P1PECAR, another computerized design program, was used to custom design the concrete pipe for this 5000 lb/ft/ft (24 410 kg/m/m) application (McTrans Institute et. al. 1988). Fortunately, PIPECAR enabled pipe to be built using standard wall thicknesses by altering conventional steel-reinforcing areas and configurations. Thick-walled pipe is not only expensive to produce, it is heavy and may require heavier machinery to lift and place

it.



TRENCH CONFIGURATION/SAFETY

It was felt during design that stiffclay trench walls, 10 ft (3 m) wide, would be sufficiently stable to allow safe working conditions in the pipe trench. Michigan Occupational Safety and Health Administration (MIOSHA) officials responsible for trench safety argued otherwise. MIOSHA standards require no greater than a 5-ft (1.5-m) deep trench without shoring or other internal supports or a 'benched' excavation within a deeper trench to limit effectively any exposed trench face to the 5-ft (1.5-m) deep limit (MIOSHA 1993). MIOSHA trench regulations are presented in Fig.5.

E3fAMI~.E I 0 - - 5 " OEEP

a R O U N O LEVEL

A GROUND M A ~ ' R I A I .

E X C A VA TION B o r T o I ~

S I D E A

C U ~ N O ~ V ~ Z

E X C A V A n ~ BOTTOM

I F t :X ,~ , I INATION 0 t - THE CROUNO INOIC,~TE'O H A Z A R O ~ S ~ ~ O ~ E N T M A Y B E * 1 ~ H ~ T A L " I ~ R R C ~ EXPECTED. S I D E A SHALL B E C U T 1-0 T~Is A N ~ E OF:" R p ~ OR A ~ R N G S ~ M . ~ E R U ~ 9 4 4 ( 3 ) F ~ L O ~ ~ H E I ~ ~ A ~ ~ P R O H ~ D .

Open Trench Benched Trench

FIG. 5-MIOSHA trench regulations for excavations without shoring.

Fig. 6-Flowable fill was placed to the springline of the pipe.



If shoring were used, the thickness of the shoring material would widen the trench. This would produce excessive loads, while if conventional benching were employed it would have the same effect, or worse. In this 60-in. (1500-mm) diameter application, the trench depth from the top of the pipe to the bottom of the trench, including the 6 in. (15 cm) of bedding material, was 6.5 ft (1.98 m). Thus, it was impossible to provide an unbenched or unshored trench and still satisfy safety officials.

After working with the contractor and MIOSHA, the benched trench shown in Fig. 7 was approved. The trench width was 9 ft (2.7 m) at the top of the pipe, satisfying designers' concerns about loadings. It allowed room for 6 in. (15 cm) of loose granular pipe bedding material, but only about 18 in. (46 cm) between the outside of the pipe wall and the inside of the trench. This narrow width would not allow for effective compaction of granular fill, and since compaction in this area was critical for the pipe/soil structure, flowable fill was chosen.

FIG. 7-Pipe trench design.

Besides solving compaction concerns by placing flowable fill to the springline of the pipe, safety officials' worries were addressed as workers would never need to enter the narrow area between the pipe and the trench wall until flowable fill was poured to the pipe's springline. MIOSHA officials felt this design was safe enough to allow workers to enter the trench to place and join sections of pipe.



BUOYANCY

Until it reaches an initial set, flowable fill must be treated as a liquid (Garbini 1993, 1994). Even with heavy concrete pipe, buoyancy is a concern. The density of the specified flowable fill mix was 142 lb/ft 3 (2275 kg/m3). In this case, buoyant forces of 2091 lbs/ft (3111 kg/m) were expected from the flowable fill, while the concrete culvert weighed 1475 lbs/fl (2194 kg/m). Since the pipe would float if application of the flowable fill was uncontrolled, the flowable fill was placed in two lifts.

F L O W A B L E FILL DESIGN

The purpose of flowable fill in this application is to provide a structural Fig. 8-Granular fill was compacted to 12 in (30 cm) over the top substitute for compacted of the 60 in (1500 ram) pipe's crown. granular soil. As such, it needed sufficiently low strength to allow for future excavation while providing adequate support for the pipe (Garbini 1993, 1994; Brewer 1990). Discussions with producers of flowable fill and literature research yielded the flowable fill specification shown in Table 2 and the mix design in Table 3.

T A B L E 2-Flowable fill specifications.

Unit weight 142 lb/ft 3 (2275 kg/m 3)

Slump (max) 9 in. (22.8 cm)

Water/cement ratio 0.68

28-Day compressive strength (max) 100 lb/in 2 (70 310 kg/m 2)



TABLE 3-flowable fill mix design.

Cement ASTM C 150 50 lbs/yd 3 (29.66 kg/m 3)

Fly Ash, ASTM C 618 Class F 500 lbs/yd 3 (296.6 kg/m 3)

Aggregate, ASTM C 33 2887 lbs/yd 3 (1712.6 kg/m 3)

Water 376 lb /yd 3 (223 kg/m 3)

F O L L O W - U P INSPECTIONS

The drainage pipe was installed in July 1995, and three subsequent follow-up inspections have been conducted. The inspections were performed primarily to confirm the structural integrity of the pipe and to check for any settlement.

The first inspection was completed shortly after backfilling was begun on 25 July 1995. The second inspection was held on 9 Nov. 1995 after the backfill reached the final grade, and the final inspection was made on 21 Oct. 1996 after the final grade had been in place for nearly one year (Fig. 9).

The conservatism employed in the design of this pipeline was borne out in the inspections. To date, there have been no observations of any structural distress or even hairline cracking of the pipe, and none are expected in the future. Both fabricated bends are in excellent condition and show neither signs of cracking nor spalling. There are only slight grade variations in the pipe

Fig 9- The pipe has passed three separate inspections since being installed in July 1995.



invert, but they are well within normal variations for large-diameter pipe installations regardless of height of cover.

CONCLUSION

Flowable fill provides pipe designers with an excellent structural backfill material. Because it is fluid, it requires little or no compactive effort to place, even in the hard-to- reach and structurally critical pipe haunch area. It is particularly effective on projects in which the trench is cut from stiff materials.

Where a narrow trench is advantageous to reduce loads on pipes and therefore increase design safety factors for critical pipelines, flowable fill provides a safe, cost-effective backfill material. In this case, flowable fill provided an extra margin of design safety and worker safety.

Because it is fluid, its buoyant forces must be taken into account during design, and placement may need to be done in lifts to keep pipe material from floating.

REFERENCES

Brewer, W. E., "The Design And Construction Of Culverts Using Controlled Low Strength Material - Controlled Density Fill (CLSM-CDF) Backfill," Proceedings Of The First National Conference On Flexible Pipes, Ohio Department Of Transportation, Columbus, OH, 1990.

Concrete Pipe Design Manual (eighth printing), American Concrete Pipe Association, Vienna, VA, 1990.

Concrete pipe Handbook (second ed.), American Concrete Pipe Association, Vienna, VA, 1981.

Construction Safety Standards Commission Safety Standards, Michigan Department of Labor, Part 9, Excavation, Trenching & Shoring, Lansing, MI, 1993.

Garbini, R. A., "Backfilling Around Pipes And Culverts With Flowable Fill," Concrete Products, Dec. 1993.

Garbini, R. A., "Rights And Wrongs Of Flowable Fill," Concrete Products, March 1994.

PIPECAR Computer Program, McTrans Institute, University of Florida, Gainesville, FL; American Concrete Pipe Association, Vienna, VA; Federal Highway Administration, Washington, D.C., 1988.

SAMM Computer Program, McTrans Institute, University of Florida, Gainesville, FL; American Concrete Pipe Association, Vienna, VA; Federal Highway Administration, Washington, D.C., 1989.


Timothy J. McGrath I and Robert J. Hoopes 2

BEDDING FACTORS AND E' VALUES FOR BURIED PIPE INSTALLATIONS BACKFILLED WITH AIR-MODIFIED CLSM

REFERENCE: McGrath, T. J. and Hoopes, R. J., "Bedding Factors and E' Values for Buried Pipe Installations Backfilled with Air-Modified CLSM," The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: The use of controlled low strength material (CLSM) as a pipe bedding and backfill material requires characterization in terms of traditional design parameters such as bedding factors for rigid pipe and modulus of soil reaction, or E', values for flexible pipe. Triaxial compression and one-dimensional consolidation tests were conducted on two mixes of air-modified CLSM to establish parameters for use in finite element analyses of buried pipe installations. Both trial mixes contained 25 to 30% entrained air to provide flowability. The tests were conducted at ages of 16 hours, 7 days and 28 days to evaluate the change in strength and stiffness with time.

Results of the tests were analyzed to fit parameters to the Duncan hyperbolic soil model with the Selig bulk modulus model. These parameters were then used in analyses of flexible and rigid pipe installations, backfilled with CLSM, to determine traditional installation design parameters.

The finite element analyses indicate that bedding factors for rigid pipe installations range from 1.8, for trench installations backfilled at an age of 16 hours, to 2.5 for trench installations backfilled at an age of 28 days. Bedding factors for embankment installations of rigid pipe range from 2.5 to 4.8 for ages from 16 hours to 28 days, respectively. Values for the modulus of soil reaction (E') for installation of flexible pipe range from 7 MPa to 21 MPa (1,000 psi to 3,000 psi) for ages from 16 hours to 28 days respectively.

KEYWORDS: buried pipe, CLSM, flowable fill, backfill, modulus of soil reaction, bedding factor, triaxial testing, fly ash

I Principal, Simpson Gumpertz & Heger Inc., 297 Broadway, Arlington, MA 02174

2 Technical Services Engineer, Grace Construction Products, 62 Whittemore Avenue, Cambridge, MA 02140

265



When controlled low strength material (CLSM), also known as flowable fill, is used as a backfill material for buried pipe installations it is desirable to conduct the backfilling operations as soon as possible after the material is placed. This minimizes time for street closures and traffic control, which contributes to improved economy and public safety. Backfilling within a few hours of placing means that the material will not be cured and that the CLSM will develop its strength and stiffness from the packing of the individual constituents, as does a soil. Thus, traditional soil testing practices, rather than concrete testing practices should yield the most useful information about the behavior of the material during backfilling operations.

CLSM has desirable characteristics for use as a pipe backfill material. Most buried pipe, both rigid and flexible, depend in some way on the support of the surrounding embedment to safely carry the loads imposed by overburden and surface vehicles. The most important areas of support are the bedding, under the pipe, where vertical loads must be supported, and the sidefill, where a soil reaction develops to prevent a pipe from deflecting outward: These areas are shown in Fig. 1, which also defines the crown (top), springline (sides) and invert (bottom) of the pipe, as well as other areas of the backfill. An area of particular importance in the backfill is the haunch zone. Good soil support in this region is significant to pipe performance because it contributes both to carrying vertical load and resisting lateral deformations. With soil embedment, backfill must be worked into the haunch zone by hand and with care; an operation that is labor intensive and subject to high variability. CLSM is an excellent backfill material for pipe because it flows into place around the pipe and provides uniform and continuous support in the bedding, sidefill and haunch zones. With soil backfill, most current pipe design methods assume that support to the haunch region will be inconsistent.

Fig. 1--Terminology for pipe and soil zones.

This paper reports on tests conducted to determine buried pipe backfill design parameters for CLSM material mixed with DaraFill CLSM Performance Additive (air- modified CLSM), a concrete additive that creates a flowable material with 15 to 30%


MCGRATH AND HOOPES/BEDDING FACTORS 267

air. The high air content produces flowable characteristics with greatly reduced quantities of fly ash and serves to limit the long term strength gain and improve future excavatability. Other features of air-modified CLSM are presented in Hoopes (1997).

TEST P R O G R A M

The quality of support provided to a pipe by soil or CLSM is a function of both the strength and the stiffness of the material. As the CLSM cures the strength and stiffness change. The properties of air-modified CLSM were evaluated by triaxial compression and incremental consolidation tests. The test variables are listed in Table 1. Samples were prepared and tested by an outside geotechnical testing laboratory. Triaxial compression tests were conducted as consolidated drained tests. Test specimens were 75 mm (3 in.) in diameter by 150 mm (6 in.) high. Incremental consolidation tests were run in standard oedometer test apparatus. The specimens were approximately 150 mm (6 in.) in diameter and 50 mm (2 in.) high. The test program was limited in scope, thus only one data point was gathered for each set of test conditions.

Sample stress-strain curves for CLSM Mix 1, at ages of 16 hours, 7 days and 28 days, are shown in Fig. 2 for the triaxial and incremental consolidation tests. Data from Mix 2 shows similar trends.

63

s 63

0) E3

250

200

150

100

50

0 0

' " 1 ' ' " 1 ' " ' 1 ' ' " 1 ' ' " _

- 2/'8 d'~y"~s 20H;ra ~ ;s i ; ! - / \ -_

I[ / / 7 / d - d a y s ~ . _~

l/ 16 hours

1 2 3 4 5

40

30

20

10

0

1200 '~, g_

1000

~ 8oo "~ ~ 600 o -~ 63 o I ~ ~ 400

o > 200

0 0

200

/ . ~ 1 6 h o u r s _ 50

: . . . . I . . . . . . . l l l l ~ l l l l l 0 2 4 6 8 10

150 '~ I / l

. 0

I l l >

Strain, % Strain, %

a. Triaxial test results b. Incremental consolidation test results

Fig. 2--Sample stress-strain curves, mix 1, air-modified CLSM test.

TABLE l--Test program variables.

Parameter Conditions

CLSM Mix 1

CLSM Mix 2

Age at test

Triaxial confining stress

cement: 59 kg/m 3, Type 1; sand- 1413 kg/m3; air: 25-30 %

cement: 30 kg/m 3, Type 1; fly ash: 148 kg/m3; sand - 1608 kg/m3; air: 27 %

16 hotirs, 7 days, 28 days

20, 40, and 60 kPa (3, 6, and 9 psi)



The triaxial compression tests (Fig. 2a) produce stress-strain curves under conditions of constant lateral stress. The deviator stress is the vertical stress applied in excess of the confining stress and is twice the shear stress in the sample. Because the lateral stress is held constant, the slope of these curves is the Young's modulus (E~) of the soil for the given stress conditions. In the triaxial test the soil is able to strain laterally and becomes less stiff as the vertical stress is increased. At the peak vertical stress the modulus is, of course, zero. The figure shows that both the modulus and strength (peak deviator stress), increase with time.

The incremental consolidation tests produce stress-strain curves (Fig. 2b) under conditions of zero lateral strain. The slope of this curve is the constrained modulus, Ms, which is sometimes called the one-dimensional modulus because it represents the stiffness of soil that is straining in only one direction. In the incremental consolidation tests the soil is confined against lateral strain by the sample container, thus as the vertical stress is increased the soil becomes more stiff, as shown by the increasing slope of the curves under increasing vertical stress. The incremental consolidation stress-strain curves also show that the modulus of CLSM increases with time. Because of the confined conditions, no failure occurs in the incremental consolidation test.

PIPE BACKFILL DESIGN PARAMETERS

Parameters for use in engineering CLSM as pipe backfill can be determined from stress-strain data such as that in Fig. 2. Analysis of the data was undertaken in accordance with methods developed by Duncan (1980) and Selig (1988) to develop a nonlinear elasticity model of CLSM that could be used in finite element studies of pipe installations to evaluate CLSM performance and to develop traditional parameters for pipe backfill design. The complete soil model requires determination of eight parameters. The parameters and the methods used to determine them are discussed in Selig (1988). As noted, there was not a significant difference between Mix 1 and Mix 2, also, since the test program was limited in scope, there was limited data available to assess variability, thus only one set of parameters were derived for each age. The values are presented in Table 2.

TABLE 2--Hyperbolic soil model parameters for air-modified CLSM.

Parameter Symbol Value 16 hours 7 days 28 days

K 630 800 1000 n 0.8 0.75 0.65 Rf 0.86 0.6 0.55

C, kPa (psi) 0 (0) 28 (4) 42 (6) dO, deg 38 38 38

AdO, deg.(Note 1) 0 0 0 B/Pa 19 40 450

~ 0.17 0.15 0.09

Note 1. The term AdO accounts for the non-linear Mohr-Coulomb failure envelope observed in many soils. The scope of the testing program was not sufficient to determine the shape of the envelope for CLSM, thus it is assumed to be linear by setting AdO = 0.



B A C K F I L L D E S I G N P A R A M E T E R S F O R R I G I D P I P E - B E D D I N G F A C T O R S

The available load bearing capacity of rigid pipe is commonly determined in a three-edge bearing test (Fig. 3a). The resulting strength is expressed in kN/m (pounds per lineal foot) of pipe. A three-edge bearing test is a concentrated load condition and is more severe than actual in-ground loadings (Fig. 3b). Rigid pipe are designed based on moment capacity. The in-ground load, W E that will cause the design moment at the pipe invert is related to the three-edge bearing load, WTEB, that will produce the same moment in the three-edge bearing test is given by the bedding factor,Bf:

W E WTE B -- (1)

B f

Fig. 3--Design and in-ground loading conditions for rigid pipe.

The value of the bedding factor for any given installation is a function of the manner in which a pipe is installed, i.e., the density of the backfill and uniformity of support to the pipe. Bedding factors are discussed in more detail in ACPA (1988).

Finite element studies with the pipe-soil interaction program SPIDA (ACPA 1993) compared the performance of the CLSM backfill with soil sidefill. The soil installations were modeled after the SIDD (Standard Installation Direct Design) Installations recently adopted by ASCE (1994) and AASHTO (1996 and 1993). There are four SIDD installations, Type 1 being a carefully haunched and densely compacted backfill, Type 2 is a slightly lower quality installation, roughly equivalent to the traditional Class B Marston Spangler bedding, Type 3 is roughly equivalent to the traditional Class C Marston Spangler bedding and Type 4 is roughly equivalent to the



traditional Class D Marston Spangler bedding. For this study, installations with CLSM were compared to the SIDD Type 1 and Type 3 installations. The installation cross-section and the soil types used for each zone are shown in Fig. 4.

The benefits of CLSM backfill in providing support to the haunch zone are readily evident in Fig. 5 which shows the normal pressure around the pipe for soil compared to CLSM backfill at an age of 16 hours. Because the CLSM flows into the haunch it provides uniform support while the two soil installations show a drop in soil support at the haunch. This can have a significant effect on the bending moments in the pipe. CLSM backfill has no effect relative to soil backfill on the normal pressure above the springline. Although the SIDD Type 1 installation and the 16-hour CLSM installation appear to be comparable, the slightly lower pressure near the invert and the higher pressure from 40 to 60 degrees from the invert in the SIDD Type 1 installation produced substantially better performance. Analyses such as these lead to the recommendations in Table 3 for bedding factors relative to the traditional and SIDD bedding factors. The general conclusion is that air-modified CLSM provides an installation quality roughly similar to a Traditional Class B, or SIDD Type 2 bedding at an age of 16 hours, improving to about the quality of a SIDD Type 1 bedding at an age of 28 days.

Zone Backfill Type and Classification

Air-modified SIDD Type 1 SIDD Type 3 CLSM

1 CLSM SW85 ML85

2 CLSM SW95 ML90

3 CLSM SW95 ML90

Note: Soil backfill types are classified with 2 letters representing the soil classification per the USCS system and a number representing the soil density as a percentage of maximum standard Proctor.

FIG. 4--Soil zones used in FEM analysis of buried pipe installations.



13_

g co I1) {3.

E O

Z

8 0 0 ~ '

600

400 I 200

0 0

l I l l ~ I l ' ' I , , , I I h , l l , , i , , , i , , , i , ,

SIDD Type 3 Installation

120

~ SIDD Type 1 Installation <.... r CLSM

20 40 60

100

80

60

40

20

0 80 100 120 140 160 180

5

09

13_

O Z

Angle from Invert, Degrees

Fig. 5--Normal pressure distribution around rigid pipe.

One question is whether CLSM needs to be placed under the pipe, as assumed for this analysis or whether the pipe can be placed on soil bedding and the CLSM placed in the haunch and sidefill zones (Zone 3 in Fig. 4). The answer to this question will not always be the same. If the pipe is placed on soil bedding then that soil under the pipe should not be hard and the CLSM should be allowed to set to a stiffness at least equal to that of the bedding soil prior to additional backfilling. Thus, if the soil is in Zone 1 is kept at a low stiffness (density), and the soil in Zone 2 is compacted, then the CLSM could be used solely as haunching and sidefill.

Although not reported in this paper, tests with CLSM without air-modification show better performance at an early age (16 hours) than reported here for the air- modified CLSM because the material is less dependent on the cement reaction for strength and stiffness.

TABLE 3--Comparison of suggested bedding factors for air-modified CLSM .with bedding factors for soil backfill.

Age Backfill Condition

Air-modified Marston Spangler SIDD Type 1 and CLSM B, C, D Type 3

Trench Embank. Trench Embank. Trench Embank.

16 hrs 1.8 2.5 to 2.8 B: 1.9 B: 2.1 to 2.8 Type 1: Type 1: 2.3 3.6 to 4.4

7 days 2 3.0 to 3.4 C: 1.5 C: 1.8 to 2.3 Type 3: Type 3: 1.7 2.2 to 2.5

28 days 2.5 4.0 to 4.8 D: 1.1 D: 1.1 to 1.3



B A C K F I L L D E S I G N P A R A M E T E R S F O R F L E X I B L E P I P E - M O D U L U S O F SOIL R E A C T I O N

Flexible pipes rely on pipe backfill to resist deflection, defined here as a change in vertical diameter under load. The most common method used to calculate the deflection of pipe under load is the Iowa formula, developed by Spangler (1941):

where: A v

D l = K = W E = E = I =

r

E' =

D1KW E A v =

El - - + 0.061E' r 3

change in vertical pipe diameter, m, in. deflection lag factor bedding factor load on pipe, MN/m, lb/in. modulus of elasticity of pipe material, MPa, psi moment of inertia of pipe wall per unit length of pipe, m4/m, in.4/in. mean radius of pipe, m, in. modulus of soil reaction, MPa, psi

(2)

The deflection lag factor, D~, accounts for increases in deflection that occur with time after the completion of an installation. There is no data currently available to provide design values for the deflection lag factor when pipe are backfilled with CLSM. Engineers should probably not change their current practice in selecting values of the deflection lag factor until such data becomes available.

The bedding factor, K, accounts for the effects of varying uniformity of backfill support to the lower half of the pipe. A bedding factor of 0.110 represents a line support at the bottom of the pipe and a bedding factor of 0.083 represents full, uniform support to the entire lower half of the pipe. The use of CLSM as backfill should a full uniform support, allowing engineers to select values of the bedding factor that are at or near the minimum value of 0.083.

Current work indicates that the load on flexible pipe, WE, should be determined in the same manner as current practice.

The term EI/r 3 represents the pipe stiffness and is not affected by the use of CLSM as backfill.

The modulus of soil reaction, E' , represents the stiffness of soil support at the sides of the pipe. It is actually an empirical parameter, and not a true soil property. Finite element studies using the CLSM properties from Table 2 and assuming the entire pipe zone embedment (Fig. 1) was filled with air-modified CLSM were conducted. These analyses indicate that design values of the modulus of soil reaction presented in Table 4 can be used in Eq. 2 to estimate the deflection of pipe embedded in air-modified CLSM. For comparison, values of the modulus of soil reaction that are commonly used for installations backfilled with soil (Howard 1977) are presented in Table 5.



TABLE 4--Modulus of soil reaction values MPa (psi) for air-modified CLSM.

Mix Age

16 hours 7 days 28 days

Air-modified CLSM 7 (1,000) 14 (2,000) 21 (3,000)

TABLE 5--Modulus of soil reaction, MPa (psi) values for soil [10].

Sidefill Soil Type Compaction level (% of maximum standard Proctor density)

85% 90% 100%

Crushed stone

Coarse-grained with little or no fines

Coarse-grained with fines or fine-grained with low plasticity and greater than 25% coarse particles

Fine-grained with low plasticity and less than 25% coarse particles

21 (3,000) 21 (3,000) 21 (3,000)

7 (1,000) 14 (2,000) 21 (3,000)

3 (400) 7 (1,000) 14 (2,000)

3 (400) 3 (400) 7 (1,000)

CONCLUSIONS

Air-modified CLSM can be effectively used as a pipe backfill material. Although the strength and stiffness of air-modified CLSM increase with time, the standard backfill parameters developed as part of this paper indicate that good pipe support is provided at an age as early as 16 hours after placing the material.

ACKNOWLEDGMENTS

The work reported in this paper was conducted with funding from Grace Construction Products, Cambridge, MA. CLSM samples were prepared and tested by Geotesting Express, Acton, MA.

REFERENCES

American Association of State Highway and Transporations Officials (1993) AASHTO LRFD Bridge Design Specification.

American Association of State Highway and Transporations Officials (1996) Standard Soecification for Highway Bridges, 16th edition.



American Concrete Pipe Association (1988) Concrete Pipe Handbook, Dallas, TX.

American Concrete Pipe Association (1993) Concrete Pipe Technology Handbook, Dallas, TX.

American Society of Civil Engineers (1994) "Standard Practice for Direct Design of Buried Precast Concrete Pipe Using Standard Installations," ANSI/ASCE 15-93, New York, NY.

Duncan, J.M., Byrne, P., Wong, K.S., and Mabry, P. (1980) "Strength Stress-Strain and Bulk Modulus Parameters for Finite Element Analysis of Stresses and Movements in Soil Masses," Report No UCB/GT/80-81, Department of Civil Engineering, University of California, Berkeley, CA.

Hoopes, R.J. (1997) "Engineering Proper~ties of Air-Modified CLSM", "The Design and Application of Controlled Low Strength Materials (Flowable Fill)", ASTM STP 1331, A.K. Howard, and J.L. Hitch, Eds., American Society for Testing and Materials.

Howard, A.K. (1977) Modulus of Soil Reaction Values for Buried Flexible Pipe," ASCE Journal of the Geotechnical Engineering Division, Vol. 103, No. GT1, American Society of Civil Engineers, New York, NY.

Selig E.T. (1980) "Soil Parameters for Design of Buried Pipelines," Proceedings, Pipeline Infrastructure Conference, American Society of Civil Engineers, New York, NY, pp 99-116.

Spangler, M.G. (1941) "The Structural Design of Flexible Pipe Culverts," Iowa Engineering Experiment Station, Bulletin No. 153, Ames, IA.


T. Harry W. Baker'

FROST PENETRATION IN FLOWABLE FILL USED IN PIPE TRENCH BACKFILL

REFERENCE: Baker, T. H. W., "Frost Penetration in Flowable Fill Used In Pipe Trench Backfi l l", The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT" Flowable fill is being used in Canadian municipalities as a select trench backfill under urban streets subjected to heavy traffic loads. The flowable fill mixture being sold by the Canadian ready mixed concrete industry for backfilling utility trenches has been found to be a good structural fill in supporting the overlying pavement and, in some cases, has been used to physically support buried utilities. The high thermal conductivity of this material has been found by some municipalities to contribute to a deeper frost penetration when used as a trench backfill. This deeper frost penetration has caused hydrant laterals and water service lines to freeze as well as differential frost heave of the asphalt surface surrounding the trench. This paper discusses these problem, presents some results from a full-scale experiment in Edmonton, Alberta, and suggests some potential solutions.

KEYWORDS: frost action, frost depth, frost heave, thermal properties, backfill materials, trench reinstatement

Poor utility trench reinstatement has been implicated as a major contributor to the deterioration of urban roads in the United States and Canada [1,2]. Excessive settlement of the reinstated pavement as a result of poor compaction of the soil backfill is often the problem. Flowable fill has been investigated as a solution to this utility trench problem by several municipalities since the early work carried out by Metropolitan Toronto, in 1985 [3]. When properly formulated, flowable fill has been found to have many admirable

' Research Engineer, Urban Infrastructure Laboratory, Institute for Research in Construction, National Research Council of Canada, Ottawa, ON, Canada, K1A 0R6.

275



qualities including: ease of handling and placement, suitable for winter placement, provides a minimal delay before being able to support traffic loads, no settlement with time, stable under dynamic traffic loading, and is relatively easy to remove for future repairs [2].

The flowable fill currently being sold by the Canadian ready mixed concrete industry for backfilling utility trenches is typically a mixture of Portland cement, sand, water and admixtures (e.g. air entraining agents, chemical admixtures, and flyash) conforming to the requirements of the Canadian Standards Association. Typically the air content is around 5 + 1%, the slump is 100 + 25 mm, and the 28-day compressive strength is 0.2 to 0.4 MPa. This material has been found to be a good structural fill in supporting the overlying pavement and, in some cases, has been used to physically support buried utilities. This material will be refered to in this paper as the typical flowabte fill.

FROST PENETRATION PROBLEM

Two basic reasons why flowable fill is not being used more often in Canadian municipalities is the high price ($50 to $90/m 3) of the material and because the particular mixture being distributed has been found to contribute to a deeper frost penetration in the trench material. Water lines are buried at depths associated with "worst winter" frost penetration in the native soil subgrade without taking into consideration the thermal effects of the trench backfill material. Several western Canadian municipalities (personal communication) have told us that their use of flowable fill has contributed to the freezing of water service lines and fire hydrant laterals (Fig. 1). In these installations there were

\V// / / / / ,~/ ,,,,-: "l=low'ab'le i i / l " , : uones ive / , . . . , . , , , , , , , , , . , . , . , , , , , , , , , , , , , , , , , , soi, , , ' , ' , ' , , , ' , - , ' , - . ' , ' , ' , ' , ' , ' , ' , > / x / x / x /d ,

,,,-,-,.--= . . . . . . , , . .~ Hydrant lateral , u, uu~iv~ ...... Ji~,'.,'.,'.V////////.i

FIG. 1--Deeper frost penetration freezing water services and hydrant laterals.


BAKER/FROST PENETRATION 277

no design adjustments made for the thermal conditions associated with the use of the particular flowable fill. This led to programs to thaw the frozen pipes and to bleed water constantly to prevent the water service lines from refreezing during the rest of the winter. In these municipalities the use of flowable fill was stopped until a design incorporating insulation around the pipes was found.

Figure 2 shows the minimum water line burial depths, in cohesive soils, specified by several municipalities across Canada. Some municipalities have extensive gravely soils. In these municipalities separate burial depths are specified in areas where gravely soils make up the native soil. As colder winters are experienced (like the extremely cold winter of 1993-1994 in central Canada and USA) these depths may be modified by the municipality. No consideration is given for the type of trench backfill material used. It is usually assumed that the trench spoil material is used as the trench backfill. In Calgary, Alberta, the minimum water line burial depth in cohesive soils is 2.7 m and in gravely soils is 3.3 m.

COMPUTER SIMULATION

A two-dimensional finite element computer model was used by my colleagues at the National Research Council of Canada to simulate the effect of various trench backfill and native soil conditions on frost penetration, using a design winter freezing index 50% greater than average [4,5]. This model showed that the use of a full-depth flowable fill in Calgary would extend the frost depth to 3.8 m. Figure 3 shows calculated frost depths for other Canadian municipalities, based on a similar analysis and with flowable fill used as a full- depth backfill, in a cohesive native soil. It can be seen that some frost penetrations would be doubled with the use of flowable fill.

FIG. 2--Typical minimum water line burial depths, in cohesive soils, in Canada.



FIG. 3--Calculated frost depths when flowable fill backfill is used full-depth.

Another result of a deeper frost penetration is differential frost heave of the surface of the pavement on either side of the utility trench. This is a particular problem in asphalt surfaced roads associated with a frost-stable (no frost heave) trench backfill and frost-susceptible (frost heave) native soil. This frequently is the case when flowable fill or granular materials are used as trench backfill in cohesive native soil subgrades. Figure 4 shows the resulting surface heave where a bump is formed on either side of the trench during late winter. These bumps usually disappear during the spring thaw, but result in cracked

FIG. 4--Differential frost heave of pavement surface around a trench.



pavement on either side of the trench. We have observed other instances, after the spring thaw, where the mass of flowable fill has heaved up as a plug and a bump is left on the asphalt surface directly over the trench. These bumps are even more accentuated after the spring thaw.

TRENCH BACKFILL EXPERIMENTS

The above frost-related problems are associated with the thermal properties of the trench backfill material and the surrounding native soil. To determine the thermal influence of various backfill materials, the finite element analysis was followed up by establishing an instrumented full-scale test site in Edmonton, Alberta in October, 1993.

The locally distributed flowable fill was one of the backfill materials investigated at the Edmonton test site and compared with sand, clay, lightweight aggregate, and bottom ash fill materials. Details of the Edmonton trench backfill experiment and data analysis are presented in [Refs. 6 through _9].

The following is a summary of what we have learned about the properties of the backfill material in promoting deeper frost penetration:

1. Frost protection of buried water lines is affected not only by burial depth, but also by the thermal properties of the backfill and the surrounding native soil. The rate at which frost penetrates into the trench is directly proportional to the thermal conductivity of the backfill material.

2. Moist backfills will normally have their highest thermal conductivity when they are frozen. At the same time, however, latent heat must be removed to freeze the material, and, if there is a significant amount of water, this latent heat effect would prolong the time of freezing. At the depth of the pipe, this often occurs near the end of winter just before the time when the warmer spring weather causes the ground to thaw.

. In a homogeneous material, the rate of frost penetration is proportional to the ratio of frozen conductivity (kf) (measured in situ using thermal conductivity

probes) to the latent heat (L) (determined by the volumetric water content measured in situ using time-domain reflectometry probes).

Some typical ranges for the ratio kf/L for certain backfill materials, measured as part of a field study being carried out in Edmonton, are given in Table 1. The table shows that the highest kf/L values occurred for flowable fill, with sand not far behind, while clay was intermediate. The lowest ratio was found in the bottom ash material. The lightweight aggregate was dry and therefore did not have a latent heat component. Lightweight aggregate has been used in trenches around water lines as an effective insulation 1~_0_]. Figure


280 C O N T R O L L E D L O W - S T R E N G T H MATERIALS

5 shows the frost depths in these backfills recorded during the winter of 1994/1995. The order of frost depth corresponds to the order of frozen thermal conductivity and the ratio of kf/L presented in Table 1 with the exception of the lightweight aggregate.

TABLE 1-- Thermal properties of the backfill materials affecting frost penetration.

Backfill Materials Frozen Thermal Latent Ratio Conductivity (kf), Heat (L), (kf/L),

W/mK MJ/m 3 10-9m2/sK

Flowable fill 3.6 67 53 Sand 3.0 67 45 Clay 1.6 90 18 Bottom ash 0.4 67 6 Light weight aggregate 0.1

2.4

FIG. 5

2.1

1.8

E .d 1.5

13

s 1.2 1.1_

0.9

0.6

0.3

I I I I ,-- I Flowable fill

_ - . . . . . . . . Sand Clay / . " - - ' ~ ' ~ . ~

.................................. Bottom ash .--*

_ , : ~ . . I ~

'Sf~ I I I I -

~I ~'s .... "

Dec. 94 Jan Feb Mar Apr, 95

Time, month

Frost depths during the winter of 1994/1995 at the Edmonton test site (LWA = lightweight aggregate).



POTENTIALSOLUTIONS

To have a trench backfill with the same thermal properties as the surrounding native backfill would be ideal in preventing deeper frost penetration and differential frost heave of the pavement surface. For most situations, native material is unsuitable as a trench backfill as it is difficult to compact well enough to prevent trench settlement. It is for this reason flowable fill was developed.

To improve the thermal performance of flowable fill particularly around water lines it has been suggested that insulation be used to prevent water service lines and hydrant laterals from freezing [4,5,10]. Insulation configurations that have been studied include: horizontal board insulation placed in the trench just above the pipeline, inverted U-shaped insulation, and cylindrical insulation around the pipe, to insulating backfill materials such as: lightweight aggregates, bottom ash, [5, 6] and waste plastics [1_!1].

Other potential solutions that have not yet been studied include: the use of foaming agents to increase the thermal resistance of the flowable fill l[.t~], the addition of thermal insulating particles into the flowable fill, and the addition of latent heat materials.

CONCLUSIONS

The use of flowable fill in some Canadian municipalities has resulted in deeper frost penetration in the trench backfill and differential heave of the asphalt surface on either side of the trench. Deeper frost penetration puts water service lines and hydrant laterals at risk of freezing. Increasing the depth of burial of water lines is expensive. Differential surface heave causes bumps and cracks in the pavements.

Field experiments carried out by the National Research Council of Canada in Edmonton indicated that, under freezing conditions, flowable fill has a high thermal conductivity but a moderate moisture content and, for these reasons, would promote deeper frost penetration. As mentioned above, the addition of insulation can control the frost action in and around the trench.

REFERENCES

[1] Todres, H. A., "Utilities Conduct Research in Pavement Restoration," APWA Reporter, American Public Works Association, Nov. 1996, pp. 4- 19.

[_2_] Baker, T. H. W. and Goodrich, L. E., "Trench Backfill and Reinstatement," in Proceedings of the American Waterworks Association Distribution Systems Symposium, Nashville, TN, Session 9.4,1995, 9 pages.


282

[3]

[4]

[_5]

[_6]

[Z]

[8]

[9]

[10]

11!3.]

[1__2]

CONTROLLED LOW-STRENGTH MATERIALS

"Utility Cut Restoration: Problems and a New Policy," Metropolitan Toronto, 1985, 19 pages.

Goodrich, L. E. and Sepehr, K., "Frost Protection of Buried Water Lines: Results from a Finite Element Model Study," in Proceedings of the Canadian Society of Civil Engineering Annual Conference, Vol. 3, Fredericton, NB, 1993, pp. 21-30.

Sepehr, K. and Goodrich, L. E., "Frost Protection of Buried PVC Water Mains in Western Canada," Canadian Geotechnical Journal, Vol. 31, No. 4, 1994, pp. 491-501.

Zhan, C., Goodrich, L. E., and Rajani, B. B., "Thermal Performance of Trench Backfills for Buried Water Mains," in Proceedings of the 2nd International Conference on Advances in Underground Pipeline Engineering, American Society of Civil Engineering, 1995, pp. 650-661.

Rajani, B. B. and Kuraoka, S., "Field Performance of PVC Water Mains Buried in Different Backfills," in Proceedings of the 2nd International Conference on Advances in Underground Pipeline Engineering, American Society of Civil Engineering, 1995, pp. 138-149.

Rajani, B. B., Zhan, C., and Kuraoka, S., "Pipe-Soil Interaction Analysis of Jointed Water Mains," Canadian Geotechnical Journal, Vol. 33, No. 3, 1996. pp. 393-404.

Kuraoka, S., Rajani, B. B., and Zhan, C., "Pipe-Soil Interaction Analysis of Field Tests of Buried PVC Pipe," Journal of Infrastructure Systems, Vol. 2, No. 4, 1996, pp. 162-170.

Dilger, W. H., Goodrich, L. E., Pildysh, M., and Humber, C. A., "Insulation of Buried Water Lines in Cold Regions," in Proceedings of the 7th International Specialty Conference on Cold Regions Engineering, Edmonton, Alberta, American Society of Civil Engineering, 1994, pp. 481-497.

Crawford, J. R., Baker, T. H. W., and Felio, G.Y., "Waste Plastic to Stop City Water Lines from Freezing," in Proceedings of the 17th Canadian Waste Management Conference, Quebec City, 1995 pp. 1-9.

Adaska, W. S., "Controlled Low-Strength Materials," American Concrete Institute Special Publication, No. SP-150, 1994, 113 pages.


Specifications, Standards, and Testing


Amster Howard I

PROPOSED STANDARD PRACTICE FOR INSTALLING BURIED PIPE USING F L O W A B L E FILL

REFERENCE: Howard, A. K., "Proposed Standard Practice for Installing Buried Pipe Using Flowable Fill," The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 1331, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: This paper will present a proposed new ASTM standard "Standard Practice for Installing Buried Pipe Using Fiowable Fill" describing how to use "flowable fill" (CLSM, CDF, Soil-Cement Slurry) for installing buried pipe. There are six different ASTM Committees that prepare and oversee standards for pipe products and their installation. Rather than the six different committees developing separate flowable fill installation standards for their particular pipe, there should be only one standard for the engineering community to use. Contractors and specifiers should be more willing to use flowable fill if there is only one set of procedures and instructions. Familiarity with the material and its application may reduce the cost of installing pipe.

KEYWORDS: controlled low strength material, CLSM, flowable fill, pipe, underground installation, field tests, construction control, quality control, embedment, backfill, soil stabilization

INTRODUCTION

This paper will present a proposed new ASTM standard "Standard Practice for Installing Buried Pipe Using Flowable Fill" describing how to use "flowable fill" (CLSM, CDF, Soil-Cement Slurry) for installing buried pipe. ASTM Committee D-18 on "Soil and Rock", which currently has jurisdiction over five standards pertaining to flowable fill, will develop the standard.

Consulting Civil Engineer, 1562 S. Yank St., Lakewood CO 80228

285

Copyright�9 by ASTM lntcrnational www.astm.org Copyright by ASTM Int'l (all rights reserved); Thu Feb 7 18:46:02 EST 2013Downloaded/printed byKarina Agama (Freyssinet+Tierra+Armada+Peru+S.A.C.) pursuant to License Agreement. No further reproductions authorized.


on "Soil and Rock", which currently has jurisdiction over five standards pertaining to flowable fill, will develop the standard.

There are six different ASTM Committees that prepare and oversee standards for pipe products and their installation. Rather than the six different committees developing separate flowable fill installation standards for their particular pipe, there should be only one standard for the engineering community to use. ASTM Committee C 3 on Clay Pipe already has begun mentioning the use of flowable fill in their Standard C 12 that covers installation of clay pipe.

The advantages to having only one standard are:

Contractors will be more willing to use flowable fill if there is only one set of procedures and instructions. Familiarity with the material and its application may reduce the cost of installing pipe.

�9 Promotes the use of flowable fill for pipe installation which will lead to safer, more economical, longer lasting, and more efficient buried pipelines.

Each pipe manufacturer or trade association won't have to spend money to develop their own standard or set of guidelines. There will not be six separate ASTM committees developing and maintaining six basically parallel standards.

The effort to develop this standard is being funded by three pipe companies and two trade associations.

STANDARDS AND PRACTICES

While some municipalities, states, and federal agencies have standard specifications and standards for flowable fill use in pipe installation, national consensus standards such as American Society for Testing and Materials (ASTM) and American Water Works Association (AWWA) are lacking. At the end of 1995, only one pipe installation standard included flowable fill. ASTM C 12-95, "Standard Practice for Installing Vitrified Clay Pipe," was adopted January 15, 1995 and published in March 1995. The trench cross- section using CDF from ASTM Practice C 12 is shown in Fig. 1.

The pipe is laid on a bedding of 4.75 mm to 19.0 mrn (1/4 in to 3/4 in) crushed rock, and soil-cement slurry (CDF) is placed to the top of the pipe. The strength requirement for the CDF is 0.7 to 2.0 MPa (100-300 psi). The bedding thickness is either 1/8 of the outside pipe diameter or a minimum of 10 cm (4 in). Other suitable materials may be used in place of the crushed rock. The recent adoption of this installation method was based on field tests performed by the National Clay Pipe Institute (Sikora, et al, 1995).


HOWARD/PROPOSED STANDARD PRACTICE 287

Initial B a c k f i l l ~

oCo o �9 material

I 12 in. (300 ) min.

Bc

Be/8, 4 in (100 ram) rain.

F I G U R E 1 Use of CDFfor Clay Pipe (from ASTM C 12)

PROPOSED STANDARD

The proposed standard is presented here to generate comments and questions from the engineering community. Comments and suggestions can be addressed to the author at the address listed at the beginning of this paper.

More information on the "gap filler" method can be found in the references by Howard ( 1994, 1996).

"Standard Practice for Installing Buried Pipe Using Flowable Fill"

1. SCOPE

1.1 This practice describes installation procedures for buried pipe using flowable fill.

1.1.1 Flowable fill is also known as CLSM (controlled low strength material), CDF (controlled density fill), soil-cement slurry, unshrinkable fill, K-Krete, and other similar names.

1.1.2 For simplification, the term pipe will be used in this document to mean pipe

1.2 This practice does not cover underwater installations, pipe that needs to be supported on piling, or pipe or tubing that is used for land drainage.



1.3 Pipelines through areas described as "expansive soils," "collapsing soils," landfills or water-logged land such as swamps should be constructed using site-specific installation procedures and are not covered in this practice.

1.4 This practice is not intended to cover all situations. Specific pipe characteristics, fluid transported, local site conditions, environmental concerns, or manufacturer's recommendations may require different installation procedures.

1.5 The construction practices discussed may be affected by the installation requirements of owners, specifying organizations, or regulatory agencies for pipelines crossing roads and highways, other pipelines or cables, or waterways such as streams, drainage channels, or floodways.

1.6 The values stated in SI units are to t-e regarded as the standard. The inch-pound units in parentheses are given for information only.

2.

2.1

A674

C33

C 40

REFERENCED DOCUMENTS

ASTM Standards

Practice for Polyethylene Encasement of Ductile Iron in Water or Other Liquids 2

Specification for Concrete Aggregates 3

Test Method for Organic Impurities in Fine Aggregate for Concrete 3

C 150 Specification for Portland Cement 3

C 618 Specification for Fly Ash and Raw or Calcined Natural Pozzolean for Use as a Mineral Admixture in Portland Cement Concrete 3

D 653 Terminology Relating to Soil, Rock, and Contained Fluids 4

Classification of Soils for Engineering Purposes (Unified Soil Classification D 2487 System) 4

D 2488 Practice for Description and Identification of Soils (Visual-Manual Procedure) 4

D 5084 Test Method for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter 4

Annual Book of ASTM Standards, Vo101.02 3 AnnualBook ofASTMStandards, Vo104.02 4 Annual Book of ASTM Standards, Vo104. 08



D 6103 Test Method for Flow Consistency of Controlled Low Strength Material (CLSM) 4

D 6023 Test Method for Unit Weight, Yield, and Air Content (Gravimetric) of Controlled Low Strength Material (CLSM) 4

D 5971 Practice for Sampling Freshly Mixed Controlled Low Strength Material (CLSM) 4

D 6024 Test Method for the Ball Drop on Controlled Low Strength Material (CLSM) to Determine Suitability for Load Application 4

3. T E R M I N O L O G Y

3.1 Definitions are in accordance with Terminology D 653 unless otherwise indicated.

3.2 The definitions and descriptions of soil are in accordance with the Unified Soil Classification System as presented in Classification D 2487. Soils may be identified and described in the field using the procedures stated in Practice D 2488.

3.3 Descriptions of Terms Specific to This Standard:

3.3.1 Flowable Fill - a mixture typically composed of a cementitious material, filler materials, and water, that hardens into a material with a higher strength than the filler material. Admixtures may be used to change the properties of the mixture, such as flowability, strength, set time, etc. Flowable fill is used as a replacement for compacted backfill soil. The 28 day compressive strength of the hardened mixture is

typically 350 to 700 kPa (50 to 100 lb/in2) for most applications.

4. S IGNIFICANCE AND USE

4.1 This practice can be used as a reference of acceptance construction practices for the proper installation of buried pipe using flowable fill.

4.2 This practice should not be used to replace project specification requirements, manufacturer's recommendations, plumbing codes, building codes, or ASTM pipe installation standards.

5. USE OF F L O W A B L E FILL IN PIPELINE CONSTRUCTION

5.1 Embedment - Flowable fill can be used as embedment for pipeline construction in either one of two ways, as follows:



5.1.1 T r e n c h F i l l e r - Flowable fill is used as a replacement for compacted soil used for the pipe bedding and embedment, as shown in Fig. 2. The embedment area starts at the bottom of the pipe and extends up to a point that can range from 0.25 of the pipe outside diameter up to 30 cm 0 2 in) over the pipe, depending on the type of pipe and the specification requirements.

. , , . ,

F.~...A i Fill ~

Flowable

Used as Embedment

and Bedding

FIGURE 2 Flowable Fill Used as "Trench Filler"

5. 1.2 Gap F i l l e r - The flowable fill is used to fill a small space between the pipe and the excavated trench, as shown in Fig. 3. When used in this way, the hardened flowable fill transfers the load from the pipe to the in si tu material. Because of the thin layer of flowable fill used, the flowable fill cannot be considered as providing any side support for the pipe. The native soil must be able to provide all of the necessary support for the pipe.

5.1.2.1 The pipe is usually supported on two small soil pads, or sand bags, so that the flowable fill will easily flow all the way under and around the pipe. The soil pads also provide a simple way of maintaining grade for the pipe since the area to be raised or lowered is much smaller. Concrete blocks, or any other hard material,



must not be used to support the pipe. Any material contacting the pipe that is harder than the flowable fill may create a point load on the pipe.

5.2 Backfill - Flowable fill may be used as full or partial backfill over the pipe and embedment up the ground surface. I f the flowable fill is not being placed in lifts to prevent flotation (see Section 11), the flowable fill for the embedment and the backfill are usually placed at the same time, filling the trench from top to bottom.

_'_Ak_

t " ~ I . ~ . . ~ 7 I' o.25 o.o. fo,

Flowable Fill ~ rigidpipe

F I G U R E 3 Flowable Fill Used as " G a p Filler"

6. T R I A L BATCHES

6.1 For new mixes or for any change in materials for established mixes, trial batches should be designed and tested for conformance to specifications.

7. M A T E R I A L S

7.1 Flowable fill usually consists of a cementitious material, filler materials, water, and sometimes admixtures.

7.1.1 The materials used in flowable fill must all be environmentally safe.

7.1.2 A Material Safety Data Sheet (MSDS) must be available for each material used in the flowable fill mixture.



7.2 Cement i t ious Materials:

7.2.1 Portland Cement Any cement meeting the requirements of ASTM Specification C 150.

7.2.2 Class C Fly Ash - Any fly ash meeting the requirements of Class C fly ash as described in ASTM Specification C 618.

7.2.3 Any cementitious material that has been investigated and tested and found appropriate for the intended use of the flowable fill.

7.3 Fil ler Materials:

7.3.1 Concrete Aggregates - Any aggregate meeting the requirements of ASTM Specification C 33

7.3.2 Non-standard aggregates - Any aggregate that has been investigated and tested and found appropriate for the intended use of the flowable fill.

7.3.3 Soil - Silty sands (SM) and silty sands with gravel (SM) are generally acceptable soil types for use in flowable fills. The fines content should not exceed about 30 %. The fines should be nonplastic or have a low plasticity (plasticity index below 4). The soil used should not contain a quantity of organic impurities that would affect the time of set or the strength of the flowable fill. The presence of organic impurities should be checked in accordance with Test Method C 40. If the soil has not previously been accepted for use in flowable fill, trial mixes should be used to evaluate if the soil is appropriate for the intended use of the flowable fill.

7.3.4 Recycled materials - Materials such as crushed concrete, recycled glass, manufacturing waste or byproducts (such as foundry sand or slag), or fly ash not meeting the requirements of ASTM Specification C 618, may be used for flowable fill. For flowable fill mixes that require consistent properties, recycled materials may need to be thoroughly mixed before using since the sources of recycled materials may not be uniform. Trial mixes should be used to evaluate if the recycled material is appropriate for the intended use of the flowable fill. All recycled materials should be evaluated for hazardous contaminants.

7.3.5 Class F Fly Ash - Any fly ash meeting the requirements of Class F fly ash as described in ASTM S]aecification C 618.

7.4 Water - The water used in the flowable fill mixture should meet one of the following criteria:

7.4.1 Potable



7.4.2 Found suitable for use in concrete. Typically, the water should be free from oils, salts, acid, strong alkalis, vegetable matter, and other impurities that would adversely affect the set time, strength, or durability of the flowable fill.

7.4.3 Found acceptable by testing trial mixes. The results should be compared to mixes made with known acceptable water.

7.5 Admixtures:

7.5.1 Bentonite - Bentonite may be added to improve the flow characteristics of the material when pumped through delivery lines.

8. PROPERTIES OF MIXTURE

8.1 A minimum unconfined compressive strength value is usually specified so the hardened flowable fill has a strength higher than the compacted soil that it replaces. For placements that may need to be easily excavated in the future, a maximum compressive strength may be specified. Compressive strength tests should be made in accordance with Test Method D 4832.

8.1,1 To prevent long term strength gains, some mixtures may be restricted to certain ingredients, or admixtures may be specified.

8.1.2 For flowable fill that needs to be easily excavated, typical 28 day strength should be in the range of 280 to 560 kPa (40 to 80 psi) or 350 to 700 kPa (50 to 100 psi). Additional strength-time requirements may also be specified, such as 90 day strengths, to evaluate long term strength trends.

8.2 A requirement for the flowability of the flesh mixture may be specified to ensure that the material will flow readily into all voids. ASTM Test Method D 6103 describes a procedure for measuring flowability.

8.3 For ductile iron pipe, the corrosion potential of the hardened flowable fill should be determined in accordance with Practice A 674. For corrosion protection of the proposed, parallel, or crossing ductile iron pipeline, polyethylene encasement, conforming to the requirements of Practice A 674, should be required.

8.4 For odor migration to determine the location of possible gas leaks, the permeability of the hardened flowable fill material should be determined in accordance with Test Method D 5048.

8.5 When backfill or pavement needs to be placed over the flowable fill as soon as possible, admixtures can be added to the mixture to reduce the set time.



9. M I X I N G

9.1 Any method of batching and mixing the flowable fill can be used as long as the material has a uniform consistency and appearance just before placement. Known methods of mixing include ready-mix plants, transit-mixers, pug mills, and volumetric mixer trucks.

10. P L A C E M E N T

10.1 Flowable fill should not be placed against frozen ground.

10.2 The set time and hydration of flowable fill is affected by cold temperatures. In cold weather, additional time may be required before placement of backfill or pavement.

10.3 The flowable fill should not be poured from a height or placed in a manner that will displace the pipe. (also see Section 11 "Flotation")

11. F L O T A T I O N

11.1 Because fresh flowable fill has a fluid consistency when placed, pipe can float depending on the weight of the pipe and the height of the flowable fill beside the pipe. If the exact density of the flowable fill mixture to be used is not known, the flotation potential can be estimated using about 2 Mg/m 3 (130 lb/ft 3) Because of the variables associated with flotation, a test section at the beginning of the job could be useful to establish the specifics of any flotation prevention procedures and the spacing of weights or restraints.

11.2 I f the pipe might float, one (or a combination) of the following procedures could be used:

11.2.1 Place the flowable fill in lifts, with the first lift just below the point on the pipe where flotation has been calculated (or determined by a test section) to occur. After the initial set of the first lift, the remainder of the flowable fill can be placed because the adhesion between the pipe and the flowable fill will prevent flotation.

11.2.2 Place sand bags on top of the pipe.

11.2.3 Fill the pipe with water.

11.2.4 Use physical restraints such as (1) re-bars driven into the ground in an "X" over the pipe, tying the re-bars together where they cross; (2) horizontal bars, resting on the top of the pipe and then turned on a horizontal plane to wedge against the



trench walls, or (3) commercial tie downs and anchors made for pipe, If the uplift forces are significantly high, do not use a restraint system that may create excessive point loading on the pipe

12. CONSTRUCTION CONTROL

12.1 One or more of the following test methods may be specified and used as quality control measures during construction:

12.2 S a m p l i n g - Obtaining samples of the flowable fill for construction control tests shall be in accordance with Practice D 5971.

12.3 Uni t Weigh t , Yield, a n d A i r C o n t e n t - Determining the unit weight, yield, or air content of a flowable fill mixture shall be in accordance with Test Method D 6023

12.4 F l o w C o n s i s t e n c y - Measuring the flowability of the flowable fill mixture shall be in accordance with Test Method D 6103.

12.5 C o m p r e s s i v e S t r e n g t h - Preparing compressive strength cylinders and testing the hardened material for compressive strength shall be in accordance with Test Method D 4832. In addition to comparing to specification requirements, the compressive strength can provide an indication of the constancy of the mix ingredients and proportions,

12.6 L o a d A p p l i c a t i o n - Determining when the hardened mixture has become strong enough to support load, such as backfill or pavement, shall be done in accordance with Test Method D 6024

13. KEY W O R D S

13.1 pipe; underground installation; field tests; construction control; quality control; embedment; backfill; flowable fill; CLSM; controlled low strength material; soil stabilization

REFERENCES

Howard, A. K., "Soil-Cement Slurry Pipe Embedment," ACE SP-150 Controlled Low Strength Materials, American Concrete Institute, Detroit MI, 1994

Howard, Amster, Pipeline Installation, Relativity Publishing, Lakewood CO, 1996

Sikora, E. J., et. al., "CDF - A New Bedding System for Clay Pipe," Proceedings of the Second International Conference Advances in Underground Pipeline Engineering, American Society of Civil Engineers, Bellevue WA, 1995, TJ 930.A32 1995


Eugene H. Riggs' and Roy H. Keck 2

SPECIFICATIONS AND USE OF CONTROLLED LOW-STRENGTH MATERIAL BY STATE TRANSPORTATION AGENCIES

REFERENCE: Riggs, E. H. and Keck, R. H., "Specifications and Use of Controlled Low-Strength Materials by State Transportation Agencies," The Design and Application of Controlled Low-Strength Materials (Flowable Fill), A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998.

ABSTRACT: Controlled low strength material, CLSM, was not used by state transportation agencies until recently, although its use in general construction dates back to the early 1970's. The documentation of its present inclusion by many states is important in the progress of the technology of this relatively new material. States surveyed include Alabama, Florida, Georgia, North Carolina, South Carolina, and Virginia. The individual specifications are reviewed and compared. Testing methods are also discussed, along with representative data from laboratory and field test reports. Finally, a composite specification is suggested based on the consensus of the ones reviewed.

KEYWORDS: Flowable fill, flowable mortar, controlled low-strength material, backfill, fly ash

Controlled low-strength material (CLSM) has been used by the construction industry for over thirty years as a replacement for conventionally placed soil backfills. The advantages of CLSM are that it is placed from a ready-mix concrete truck similarly to flowing concrete and requires no additional compactive effort. This lends it to many unique applications that have been recognized by specifying agencies, and these specifications

Director of Technical Services, Monex Resources, Marietta,GA 2Director of Marketing, Blue Circle Williams, Marietta, GA

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RIGGS AND KECK/STATE TRANSPORTATION AGENCIES 297

and their use by state transportation departments in the southeastern United States will be the subject o f this report.

CLSM has been called by a variety of names, some of them as follows: controlled density fill, flowable fill, flowable fly ash, lean mix backfill, and flowable mortar. CLSM has a variety of applications, including backfilling, structural fills, insulating fills, pavement bases, conduit bedding, erosion control, and void filling.

CLSM MIXTURES CLSM mixtures generally consist of cement, pozzolan, water,and fine aggregate.

The simplicity of the mixtures make it possible for most ready-mix batching plants to produce this type o f grout. Because the quality o f the ingredient materials is often not critical, many aggregates not suitable for concrete can be used in CLSM. Ashes from power plants burning coal are quite often used in an on-site batching facility for construction at the power plant.

Admixtures may be used to modify the water requirement or to entrain air or both. Air-entraining agents that produce high air contents have the following effects:

(1) air volumes from 10 to 30 % lower the cost of CLSM usually making the application more cost -effective

(2) the air entrainment imparts extreme workability at a greatly reduced water content (as much as 50% lower) and aids in reducing plastic settlement and shrinkage of the CLSM.

(3) the density of the CLSM is reduced proportionately to the per cent of air entrained. This helps reduce the buoyant force on pipes being encased.

Because the strength requirements are usuallyvery low, from 50 to 1200 psi (345 to 8270 kPa), low cementitious contents are normally used. The strength must be limited to maintain excavatability at a later date, as is the case in utility construction. To insure future removability by backhoes or manual labor, strength is usually maintained at less than 300 (2068 kPa) psi.

The use of pozzolans is important to produce the best flowability with the least amount of cement. In many applications, the cost of the mix is critical to its selection and cement must be used sparingly. Additionally, CLSM is often placed by pump, and pozzolans are extremely beneficial as a lubricant which increases efficiency of the pump equipment.

ASTM TEST METHODS FOR CLSM In recent years, ASTM has adopted several test methods for evaluating the quality of

CLSM. Among those test methods that have been either adopted or pending are the following titles:

D #597t-96

D #4832-96

D #6023-97

D #6024-97

Practice for Sampling Freshly Mixed Controlled Low Strength Material Test Method for Preparation and Testing of Controlled Low Strength Material Test Cylinders Test Method for Unit Weight, Yield, and Air Content (Gravimetric) of Controlled Low Strength Material Test Method for Ball Penetration in Freshly Mixed



PS #28-95 Controlled Low Strength Material Provisional Test Method for Flow Consistency of Controlled Low Strength Material

The availability of these test methods is noted so that readers will be aware that in spite & t h e fact CLSM has been around for over 30 years, only recently has ASTM seen the need for standard methods. They are now available for inclusion in project specifications. Most of the state specifications we reviewed treated CLSM as concrete when testing for acceptance, and others improvised in the absence of available standards.

CLSM S P E C I F I C A T I O N S BY STATE DEPARTMENTS OF T R A N S P O R T A T I O N The states selected for survey of how CLSM is specified included six southeastern

states of the United States of America. These states are included in a network of marketing efforts by ash marketing companies and represent a reliable database. The states and specifications reviewed are listed in Table 1.

TABLE 1 - States surveyed and their ,specification

State Specification and Title of Section Issue Date

Alabama Florida Georgia

N. Carolina S. Carolina Virginia

Section 260 Low Strength Cement Mortar 1996 Section 121 Flowable Fill (rev 1996) 1997 Section 600 Controlled Low Strength 1995

Fiowable Fill Controlled Low Strength Material Specification 1996 Spec. 11 Specification for FIowable Fill 1992 Spl. Prov. for Fiowable Backfill 1991

It is readily apparent that all of these specifications were issued after 1990, and so the use o f CLSM is relatively new to standard transportation road construction. Following are comparisons of various requirements for similarities and differences.

The first criteria reviewed are compressive strength and age of evaluation. Table 2 gives a summary.



TABLE 2 -Specified acceptance strengths and ages

State Age, days Strength, psi (mPa)

Alabama 28 80 (0.55);200 (1.4); 1000 (6.9);1100 (7.6); 175 (1.2)

Florida 28 100 (0.7)(maximum); 12s ( 0.9);

Georgia 28 100 (0.7)(maximum); 12s (0.9)

N. Carolina 28;56 125 (0.9); 150 (1.0)(maximum)

S. Carolina 28;56 80 (0.55); 125 (0.86) Virginia 28 30 - 200 (0.2-1.4)

Note : Maximum strengths are resticted to enable excavation at later ages, i f desired or needed

The general acceptance age is 28 days with 2 states having 56-day requirements. Because of the high levels of pozzolans in many CLSM mixtures, there can be significant strength increases after 28 days. Several states have both excavatable and nonexcavatable mixtures. If the CLSM will be removed at a later date, its strength must be limited to less than 300 psi (2068 kPa), which can be assured only if later age strengths are evaluated.

MATERIALS Materials in many cases do not need to meet stricter concrete limits; however;

some states do require materials to meet their current standard specifications. Most CLSM is produced by ready-mix concrete plants using concrete materials, and, therefore, it is not a hardship when standard requirements are applied. Table 3 summarizes the materials generally permitted in CLSM mixtures.

TABLE 3 -Material requirements

State Cement Fine Agg. Water Pozzolans Air Entr.

Alabama type I (a) (a) F fly ash (a)(c) Florida type 1,11,II1 (b) (a) fly ash, slag (a)(c) Georgia I,II,III,IS,IP (b) (a) fly ash (a)(c) N. Carolina I,IP,IS (a)(d) (a) fly ash (a)(c) S. Carolina (1) (a) (a) fly ash (a)(c) Virginia (1) (a) (a) fly ash, slag (a)

(a) Standard specification material.



(b) Gradatton requirement is waived. (c 9 High air generators are permitted. (d) Power plant bottom ash is permitted.

Cement is generally assumed to be ASTM C #150 Type I in most of the states. IP and IS, blended cements using either slag or fly ash, are permitted in North Carolina. Three states have no restrictions on cement. Type III, high early cement, could be used if desired, but is not referenced by any of the states. Type 1II may be helpful in applications in which a quicker setting time may be desired.

Fine aggregate must be of concrete quality in three states. In North Carolina, bottom ash, produced at electric power plants, may be used. The gradation requirements are modified or waived in three states. Many suitable aggregates are commercially available and cannot be used for making structural concrete, but when evaluated in CLSM produce excellent results.

Water is required to be compliant with concrete quality standards, although this is another material that could vary and not significantly affect ultimate quality of the CLSM. Most batch plants have clean water from either wells or municipal sources, and so this is usually not an issue. It should be noted that the amount of water in the CLSM will have a pronounced effect on flowability and setting time. Typically, the extra water in the mixture will bleed rapidly and cause what is called "subsidence," or plastic settlement, resulting in the need to add more CLSM to maintain desired final elevations in a backfill.

Pozzolans are specified based on what is locally available in the states. Slag is directly referenced in the Virginia and Florida specifications. North Carolina permits slag or fly ash in blended cement owing to its commercial availability.

Fly ashes are required based on market availability. Alabama specifies a Class F fly ash, while all of the other states simply refer to fly ash without distinguishing which Class, either F or Co is intended.

Admixtures are permitted and must comply with the applicable slate standard requirements. The popularity of air entrainment is reflected in the inclusion of high air generators in all states but Virginia. Note, however, that the Virginia specification is the oldest and probably was written before these chemicals were widely marketed.

RECOMMENDED PROPORTIONS GIVEN IN STATE SPECIFICATIONS All but one of the states, Virginia, have recommended or suggested mixture

proportions. In any case, the contractor may submit his own mixture for review. Table 4 summarizes the mixtures for comparison.



TABLE 4 - Suggested mixture proportions, lbs per cu. yd. ( kg per cu. nt)

Cement Pozzolan Fine Agg. Water Air Range

Alabama 61 (36) 331 (196) 2859 (1696) 509 (302) not given 185 (110) 0 2673 (1586) 500 (297) " 195 (116) 572 (339) 2673 (1586) 488 (290) " 195 (116) 572 (339) 2673 (1586) 488 (290) " 517 (307) 0 413 (245) 341 (202) "

Florida 75-100 0 (a) (a)(b) 5-35 (44-89) 75-150 150-600 (a) (a)(b) 15-35 (44-89) (89-356)

Georgia 75-100 0 (a) (a)(b) 15-35 (44-89) 75-150 150-600 (a) (a)(b) 5-15 (44-89) (89-356)

N. Carolina 40-100 (a) (a) (a)(b) 0-35 (24-59) 100-150 (a) (a) (a)(b) 0-35 (59-89)

S. Carolina 50 (30) 600 (356) 2500 (1483) 458 (272) none (c) 50 (30) 600 (356) 2500 (1483) 541 (321) none (c)

Virginia contractor must submit his own mixture ("mix design")

(a) Proportion to yield one cu. yd. (cu. m.). (b) Proportion to produce proper consistency. (c) Air up to 30% may be used i f requested.

As can be seen, a wide variety of mixtures are given. In most cases, even though the proportions are written into the specifications, the contractor may elect to use a mixture that is specifically designed for the project. The inclusion of proportions is intended to give less familiar contractors a mixture to use immediately if needed, as is the case in smaller projects.

Air entrainment is used or allowed by all states, owing to the benefits discussed under the CLSM Mixture section. Admixture manufacturers are marketing what are called high air generators to facilitate air contents in excess of usual ranges found in ready-mixed concrete. Traditional chemicals used for entraining air usually produce less than 10% by volume, even at the high dosages. More effective agents, such as are used in masonry cement and for other products, have proven very effective at low dosages.

Pozzolans are used in all of the mix tables. The origins of CLSM go back to ash marketing efforts by power companies, and early uses were an effort to dispose of an abundant amount available which did not meet ASTM specifications. Note that several



mixtures allow up to 600 lbs (272 kg), and North Carolina leaves the quantity entirely up to the contractor.

MIXING PROCEDURES Mixing procedures are typically given as "similar" to or as required in the

standard specifications for producing and delivering ready-mixed concrete. Two states waive the need for mixer revolution counters. Alabama gives the exact batching sequence: sand, fly ash, cement, then water and admixtures, followed by 3 min. of mixing.

PLACING PROCEDURES Where placing of CLSM is discussed, it is presumed that the material will be

treated similarly to ready-mixed concrete and will be placed directly from the truck chutes in most cases. Florida and Alabama permit the use of chutes or pumps, and for the discharge of CLSM under water, Florida specifically states that a tremie must be used.

APPLICATIONS OF CLSM Table 5 gives the allowable uses for CLSM listed in the state specifications. In

general, it may be used in lieu of compacted soil, however, some of the states have expanded the list to include many applications.

Table 5 - Applications of CLSM

State Applications

Alabama Florida

Georgia

N. Carolina

S. Carolina

Virginia

Backfill for drainage structures and utility cuts Beddings; encasements; closures for tanks, pipes; trench backfill Beddings; encasements; closures for tanks, pipes; trench and abutment backfill Filling underground storage pipes and pipe culverts; backfilling culverts, bridges (where culverts or pipes are installed under a bridge), retaining walls, roadway trenches Backfilling under foundations, abandoned pipelines, culverts, tanks, utility trenches, catch basins, drop inlets, vertical taps, bridge abutments In lieu of compacted soil or aggregate backfill

W E A T H E R LIMITATIONS CLSM will be subject to much the same limitations as ready-mixed concrete and

is treated that way in general by the various states. Georgia and South Carolina state that



it must be subject to the same limits as concrete. Virginia simply says to deliver at a minimum of 50" F (10 ~ C) and protect from freezing. Alabama has a minimum allowable air temperature of35 ~ F ( 1.6 o C), or if 40" F (4.4~ and falling, air temperature may not fall below freezing within 24 hours of placing CLSM. Georgia also requires protection from freezing for the first 36 hours.

South Carolina permits the placing of CLSM in rain i fa less flowable mixture is used. This type mixture may also be placed in standing water, for example, when placed in a trench. It is presumed that the CLSM will displace any water. On the other hand, Florida does not permit placement during rain or if the temperature is below 35 ') F (1.6~

FLOATATION OF PIPES Several of the states warn that if CLSM is used to backfill around pipes, it is

possible that the pipes may "float" if not secured before beginning the backfilling. This is due to the fact that the liquid CLSM will exert buoyant tbrce on a hollow pipe, especially lightweight pipes. Virginia directs that pipes will be secured by some means, such as soil anchors to prevent misalignment.

SUBSIDENCE South Carolina discusses the natural tendency of CLSM to subside upon setting,

as a result of the mix water gravitationally separating while it is consolidating. Once the CLSM has hardened, there is no further change in the volume. The use of air entrainment is discussed in the section entitled "CLSM Mixtures," and has been found to mitigate subsidence problems.

CURING No special instructions regarding curing are given in any of the standards. The

water content is so high generally, and most CLSM is placed below grade, so curing does not seem to be a problem. In fact, the strength gain past 28 days should not be excessive, if the CLSM will likely be re-excavated at some later date for additional construction. Some of the states, such as Alabama, evaluate excavatable CLSM at 56 days age to check for the capability to remove it later. Excessively high strengths should therefore be avoided, and thus, the lack of attention to curing.

OPENING TO TRAFFIC The setting time of CLSM can be quite lengthy in some cases, because of the high

water content required to produce sufficient flowability. Alabama allows the use of accelerators to reduce the opening time to 12 h. Florida requires the field use of a soil penetrometer (refer to ASTM C #403, Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance) to measure setting time, and when 60 psi (414 kPa) penetration resistance is obtained, construction may proceed.

South Carolina gives wide ranges of setting times, from 8 to 20 h, and directs the contractor to use a steel plate over the CLSM if rutting is likely or if traffic will be reopened in less than 8 h. Three states, Georgia, Virginia, and North Carolina, do not discuss opening to traffic.



ACCEPTANCE TESTING Only one state, Alabama, requires actual test cylinders to be cast when placing

CLSM. All o f the other states rely on use of their the prescriptive mixes and the documentation at the project for each batch verifying the correct material weights were used. South Carolina allows the use of a "low density" mix, with proportions selected by the contractor, in which case the test results are submitted in advance of placement of the CLSM.

LABORATORY DATA FOR CLSM CLSM is a relatively new material to specifiers and is further different in that it is

treated like concrete in the batching, mixing, and delivering, but behaves as a soil in its function. Table 6 gives the results of compressive strength tests and the California Bearing Ratio. The data were developed by an ash marketer for the purpose of providing the specifier with this type of comparison. Specific materials for a given project should be tested if desired.

Table 6 - Mix proportions and data forflowable CLSM

Materials lbs. per cu. yd. (kg per cu. m.)

Cement 50 (29.7) 100 (59.3) 150 (92.6) FlyAsh 350(208) 300(178) 250(148) Sand 2677(1588) 2690(1596) 2706(1605) Water 470 (279) 520 (309) 520 (309)

Unit Weight, pcf 129.4 (58.7) 127.8 (69.7) Compressive Strength, psi (mPa)

14 Day 40 (0.28) 60 (0.41) 28 Day 40 (0.28) 60 (0.41) 90Day 50(0.34) 160(1.10)

California Bearing Ratio (CBR),% 0.1 in. 19.7 0.2 in. 23.7

127.8(69.7)

90(0.62) 130(0.90) 280(1.93)

CLOSURE This paper has been prepared to give users and specifiers the current requirements

of six transportation agencies, with the intention that general construction specifications can be modeled after the consensus of all of them. It is obvious that CLSM is in general use and the use of it will continue to expand as the economics o f its manufacture and placement are improved. Sample requirements are given as follows:

Controlled Low Strength Material (CLSM)- Standard Specification 1.0 Description: This work shall consist of furnishing and placing CLSM as an alternate to compacted soil, as approved by the Engineer.



2.0 CLSM : CLSM will be composed of cement, pozzolans, fine aggregate, water, and admixtures. CLSM will have a low cement content to reduce strength to allow for future removal if that becomes necessary. 3.0 Mix Proportions: The contractor will submit mix proportions for CLSM. If materials meet applicable ASTM standards, documentation of those test results shall be submitted. lfthe materials are nonstandard (not conforming to available standards), the trial batch results for the mix proportions shall be documented and submitted for acceptance. Submit test results for the proposed mixture set time and strength at 28 and 56 days age. 4.0 Manufacturing: CLSM will be produced in accordance with procedures in ASTM C #94, Specification for Ready-Mixed Concrete. Submit any proposed variances for review. 5.0 Acceptance : Contractor will provide documentation of batch weights to confirm proper mix proportions are used in construction. 6.0 Construction: After CLSM is placed, further construction proceeding upon it will be permitted after initial set is attained, as measured by ASTM C #403, Test Method for Time of Setting of Concrete Mixtures by Penetration Resistance. 7.0 Payment : Additional pay for CLSM will not be allowed unless so specified in contract documents.

BIBLIOGRAPHY a. Controlled Low Strength Materials (CLSM), ACI 229, American Concrete Institute, P. O. Box 19150, Detroit, Mi 48219. b. Fly Ash Facts fo r Highway Engineers, American Coal Ash Association, 2760 Eisenhower Avenue, Suite 304, Alexandria, VA. 22314, August 1995. c. Smith, A., "Controlled Low Strength Material," Concrete Const!'uction, May 1991. d. "What, Why, and How? FIowable Fill Materials," CIP 17, National Ready Mixed Concrete Association, 900 Spring Street, Silver Spring, MD 20910, 1989.


Robert Scavuzzo ~ and Betsy A. Kunzer 2

Heat of Neutralization Test to Determine Cement Content of Soi l -Cement or Roller- Compacted Concrete

REFERENCE: Scavuzzo, R. and Kunzer, B. A., "Heat of Neutralization Test to Determine Cement Content of Soil-Cement or Roller-Compacted Concrete," The Design and Application of Controlled Low-Strength Materials (Flowable Fill), ASTM STP 133l, A. K. Howard and J. L. Hitch, Eds., American Society for Testing and Materials, 1998. .~,BSTRACT: A construction control field test method for determining the cement content of freshly mixed soil-cement or roller-compacted concrete (RCC) is discussed. Typical Bureau of Reclamation practice is to establish the most economical mix design requiring the lowest possible cement content that meets both strength and durability specification criteria. Gradation characteristics of available borrow material can dictate mix designs having a significant percentage of plus 4.75-mm (No. 4) sieve-size particles. The ability to determine quickly and accurately the cement content of soil-cement or RCC as it is being placed is critical to help ensure that specification strength and durability requirements are being met. The heat of neutralization test method presented (as modified by the Bureau of Reclamation) has been found to be accurate to within _+ 1 % of actual cement content for mix designs having cement contents of 3 to 16 % and up to 50 % plus 4.75-mm (No. 4) sieve-size particles; does not require the separation of plus 4.75-mm (No. 4) sieve-size material; and cement content determinations can be made using durable field equipment within 15 to 20 min. Precision and bias statements have been established for the test method in accordance with the ASTM Practice for Conducting an Interlaboratory Test Program to Determine the Precision of Test Methods for Construction Materials (C 802) and the ASTM Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials (C 670) and are presented.

KEYWORDS: soil-cement, roller-compacted concrete (RCC), heat of neutralization, cement content, construction control, field test method

~Senior Engineer, CTC-Geotek, Inc., 155 S. Navajo St., Denver, CO, 80223. 2physical Scientist, U.S.B.R. D-8340, PO Box 25007, Denver, CO, 80225.

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SCAVUZZO AND KUNZER/CEMENT CONTENT 307

Essential characteristics of an effective construction control test method can be summarized as follows. The method (1) must possess an acceptable accuracy, (2) be easy to perform, (3) use durable test equipment, and (4) produce timely and repeatable results. Construction control test methods used for soil-cement or roller-compacted concrete (RCC) placements are traditionally titration methods for determining cement content and 7- and 28-day cylinder compressive strengths.

Titration methods typically require separating the plus 4,75-mm (No. 4) sieve-size material and include the time-consuming task of screening and washing the soil-cement or RCC mix to obtain test specimens of appropriate size and gradation characteristics. Additionally, titration tests are not easily performed and require careful handling of fragile glassware that may not be compatible with a construction environment.

Compressive strength testing of 7- and 28-day cylinders is considered a reliable method for determining the acceptability of a soil-cement or RCC placement. However, if compressive strengths are not up to project specification requirements, the time necessary to obtain the results may require material removal and replacement resulting in added rework costs.

A discussion of the ASTM Test Method for Determining Cement Content of Fresh Soil- Cement (Heat of Neutralizatiort Method) (D 5982) is presented. The purpose is to provide insight into the requirements of the standard with the goal of establishing a higher level of confidence in the test method by increasing the level of understanding of its development.

Heat of Neutralization

The heat of neutralization test method is based upon the reaction between an acidic buffer solution of glacial acetic acid (H(C2H302))and sodium acetate (Na(C2H302))having a pH of approximately 2 and the calcium hydroxide (Ca(OH)2) contained in a soil-cement test specimen. The equation for this reaction is:

2H(C2H302) + Ca(OH)2 - ~ Ca(C2H302)2 + 2H20 + Heat

Given the same soil and type of cement from the same supplier, the heat produced by this exothermic reaction is linearly proportional to the amount of cement present in the test specimen. Based upon this linearity, a calibration curve and corresponding line equation for a specific mix design can be established. Soil-cement or RCC test specimens of unknown cement contents can then be tested, the heat of neutralization obtained, and the cement content determined from the established calibration curve.

Heat of neutralization can be generally defined as the temperature increase resulting from



the exothermic reaction in the acidic buffer solution when mixed with a soil-cement or RCC test specimen. Specific to the test method, it is defined as the difference between the temperature of the soil-cement/buffer solution after mixing and the average of the buffer solution and soil-cement test specimen temperatures before mixing.

Background

Soil-cement placement for slope stabilization at Jackson Lake Dam, Wyoming in 1988 by the Bureau of Reclamation prompted the initiation of a program to develop a test method for determining the cement content of soil-cement or RCC during placement. The test method was to be capable of determining cement content for mix designs having 3 to 16% cement, not require separation of plus 4.75-mm (No. 4) sieve size material to obtain a test specimen, and have an accuracy o f + 1% of actual cement content in field applications.

An Australian Test Method Q 116B-1978, Cement Content of Cement Treated Materials (Heat of Neutralization) ['1], was reviewed and evaluated for possible use. This method specifies that a 5-kg soil-cement test specimen be mixed with a 1-L buffer solution consisting of sodium acetate, glacial acetic acid, and distilled water.

A calibration curve consisting of seven different percentages of cement contents that bracket the target mix design cement content is established. Duplicate heat of neutralization tests at each of the seven cement contents are performed. The temperature increase corresponding to each of the 14 tests is plotted versus cement content and a calibration line is calculated. Subsequent soil-cement test specimens of unknown cement contents can than be tested, the heat increase obtained, and the cement content determined using the calibration line established for mix.

Test Method Q 116B-1978 was originally developed for soil-cement mix designs having cement contents of 3.5 % or less. At cement contents greater than 3.5 %, the specified mixture of 1-L of buffer solution with a 5-kg test specimen was found to gel into a solid mass, preventing proper mixing.

Reclamation Procedural Changes

After an extensive testing program performed by the Bureau of Reclamation, revisions were made to the originhl Australian heat of neutralization test to accommodate the needs of soil-cement or RCC quality control. The changes were:

reduce the number of cement contents required for obtaining a calibration curve from seven to three; perform three heat of neutralization tests at each of the three cement content values selected to construct a calibration curve using nine data points reduced from fourteen; and



use 1.5-L of buffer solution mixed with a 1.5-kg soil-cement test specimen for mix designs consisting of up to 16 % cement and 50 % plus 4.75-mm (No.4) sieve size material.

ASTM Test Method D 5982

The ASTM Test Method D 5982 provides a method for determining the cement content of fresh soil-cement or RCC using the heat of neutralization procedure. The procedure can be used for determining the cement content of samples that contain 3 to 16 % cement and can be used for testing soil-cement or RCC samples that contain a significant percentage of plus 4.75-mm (No.4) sieve-size material. It provides a quality control method that reliably determines the cement content in approximately 15 to 20 min within +_1% of actual cement content, which is generally adequate for most construction control applications.

The test method can be summarized simply as follows: (1) a representative soil-cement test specimen is obtained; (2) the temperature of the soil-cement test specimen and a buffer solution are determined separately and recorded; (3) the buffer solution is added to the soil-cement test specimen and vigorously mixed; (4) after mixing, the temperature of the soil-cement/buffer solution is determined and recorded; and (5) the heat of neutralization is calculated and, from a previously established calibration curve, the cement content o f the test specimen is obtained.

Required Test Equipment

As previously discussed, the equipment used to perform the test must to be durable for field use. Provided below is a description of the required test equipment.

Balance or Scale - two required; one for obtaining the mass of a soil-cement test specimen readable to 0.01 kg (0.01 Ibm) and having a capacity of approximately 9.1 kg (20 Ibm); one for preparing the buffer solution readable to 0.1 g and having a capacity of approximately 3000 g. Digital thermometer - 0 to 100~ readable to 0.1 ~ and equipped with a thermocouple probe as short as possible not to exceed 1270 mm (5 in.) in length. Specimen container - minimum of three required; leakproof, widemouth plastic (Nalgene) container, 4-L (1-gal) capacity, with screw cap. One cap should be pierced in the center to allow insertion of the thermometer probe. Timing device - stopwatch readable to 1 s. Glass or plastic beaker - approximately 3000-mL capacity, graduated to show 1500 mL. Hand scoop - flatbottom scoop with approximate bowl dimensions of 890 by 1525 mm ( (3-V2 by 6 in.). Gloves - protective gloves to be worn whenever handling buffer solution and



cement. Specimen container holder - angle irons, woodblocks, or other suitable material capable of holding the specimen container securely in an inverted position. Buffer container - suitable container with pouring spout or spigot, preferably plastic, of sufficient capacity to hold a buffer solution supply for daily testing. Each test performed requires 1.5 L of buffer. Pail - plastic pail, minimum of 4-L (1-gal) capacity. Spoon - large metal spoon for mixing the soil-cement calibration test specimens. Mixing container - an 11- to 15-L (3- to 4-gal) container, preferably plastic, used for mixing the soil-cement calibration test specimens. Blender (optional) - electric blender with glass or plastic receptacle for quickly dissolving sodium acetate in distilled water. Funnel (optional) - funnel with stem having an inside diameter of at least 520 mm (2 in.) for quickly placing entire test specimen in specimen container.

Reagents

Reagents used in performing the heat of neutralization test are distilled water, technical grade or better sodium acetate in crystalline form, and technical grade or better glacial acetic acid in liquid form. A 1.5 L of buffer solution is used for each cement content determination and is prepared by dissolving 225 g of the sodium acetate in 500 mL of distilled water.

NOTE: sodium acetate tends to clump when added to room temperature distilled water. If electricity is available, a blender significantly reduces the time needed to get the sodium acetate into solution. When the sodium acetate is dissolved, the solution is poured into the beaker.

Then 360 g of glacial acetic acid is added to the sodium acetate/distilled water solution. Additional distilled water is then added to bring the final volume to 1.5 L and the buffer solution is mixed thoroughly. The strength of the buffer solution once prepared was found to deteriorate with time, and therefore, the buffer solution should be used within 24 h after it is mixed.

In addition, the chemicals used in the buffer solution have been found to be irritating to exposed skin. Therefore, it is recommended that rubber gloves, laboratory coat, and safety glasses or goggles be worn, and that the procedure be performed in an area with adequate ventilation and with rinse water available.

Test Specimens

Test specimens can be obtained during batch plant production process verification or during soil-cement placement at the time of construction. Batch plant samples should be taken immediately after the soil-cement is dumped from the hopper into the truck. Segregation of the gravel fraction may occur during dumping, therefore, visual



observation of the sample obtained should be made to insure that it is representative of the specified mix proportions. A minimum 2-kg (5-1bm) sample should be obtained and placed in an airtight bucket. During soil-cement placement at the site, a minimum 2-kg (5-Ibm) sample representative of the mix design proportional can be obtained from the material obtained for density or compressive strength testing or both.

Calibration Curve

One of the key components associated with the effectiveness of the heat of neutralization test method is obtaining a calibration curve that is representative of both mix proportions and borrow material. It is essential that calibration test specimens are prepared using material obtained from the borrow area to be used in construction because of the possible reaction of calcareous material inherent in the soil. If borrow material is not used, the heat rise obtained from construction control tests may not be solely representative of the calcium hydroxide in the cement resulting in an inaccurate cement content determination.

A calibration curve is to be established by determining the heat of neutralization of soil- cement test specimens prepared at known cement contents which bracket the value of percent cement to be used for construction. Nine 1.50-kg (3.30-Ibm) soil-cement test specimens are to be prepared using the percentages of gravel, minus 4.75-mm (No. 4) material, and water as specified by the mix design proportions. The amount of cement to be added to the calibration specimens is to be as follows: three calibration specimens should be 2 % less than that specified for construction, three specimens 2 % greater, and three specimens having the same percent cement as specified for construction.

The mass of the gravel, minus 4.75-mm (No.4) material, water and cement for one 1.50- kg (3.30-Ibm) soil-cement test specimen are determined to the nearest 0.01 kg or 0.01 Ibm and placed in four separate containers. The gravel and minus 4.75-mm (No. 4) material is combined with one-half the required amount of water in an 11- 15-L (3- to 4- gal) container and is mixed thoroughly using a large spoon or other suitable mixing device to ensure that the gravel is evenly wetted and that no dry clumps of minus 4.75- mm (No.4) material are present. The required amount of cement and the remainder of the water is added and mixed thoroughly to ensure that no cement clumps are present and that no cement is sticking to the sides of the container. The soil-cement calibration specimen is placed into the test specimen container using care to prevent portions from sticking to the sides of the funnel and ensuring that all of the calibration specimen is removed from the mixing container and placed into the test specimen container. Once the transfer is complete, the soil-cement test specimen container lid should be secured in place.

Heat Of Neutralization Determination

A thermocouple probe is submerged into 1.5- L of buffer solution and the temperature is



determined and recorded after 1 rain. The thermocouple probe and lid are thoroughly rinsed with fresh water and dried. The lid, which has been pierced by the thermometer probe, is secured on the soil-cement specimen container. The soil-cement specimen container is inverted onto a stand ensuring that the entire specimen is at the bottom and that the thermocouple probe is completely covered by the specimen. The temperature of the soil-cement specimen is determined and recorded after 2 min. The buffer solution is then added to the soil-cement specimen and the specimen container lid secured. The soil- cement/buffer solution mixture is vigorously mixed by hand for 4 rain. During this mixing process, the test specimen container is to be agitated thorough 180 ~ of rotation by inverting and uprighting the test specimen container to ensure an even and thorough mixing of the soil-cement and buffer solution. The lid pierced by the thermocouple probe is placed on the specimen container, the container inverted on a stand, and the temperature of the soil-cement/buffer solution mixture is determined and recorded after 1 rain.

The average of the buffer solution and soil-cement temperatures is calculated and recorded. The temperate difference between the soil-cement/buffer solution and the average temperature previously calculated is determined. The procedure outlined above is repeated eight additional times to obtain the nine heat of neutralization determines.

The average of the temperature difference values obtained for the three trials performed at each of the three cement contents is calculated. The range (difference between the highest and lowest) of the three individual temperatures at the same cement content should not exceed 3~ A plot of heat of neutralization (average temperature difference) versus cement content is prepared, and an equation of the established calibration line is determined by performing a linear regression analysis to obtain the best-fit line through the data points obtained.

During batch plant process verification or construction control, a 1.50-kg (3.30-Ibm) test specimen is obtained and the heat of neutralization is determined as described. Using either the calibration curve or equation, the cement content of the test specimen can be determined.

Technical/Safety Issues

A number of technical issues and safety precautions regarding the heat of neutralization test method are summarized below:

The calibration curve is specific to the mix design and materials used. If any part of the mix design is changed i.e., change in cement content, supplier, or cement type, or if a different borrow area is used, a new calibration curve must be developed. Soil-cement test specimens are to be tested within 30 min from the time they are prepared (calibration) or obtained (construction control). Soil-cement test samples must be protected from moisture loss before testing.



The temperature difference between the buffer solution and soil-cement test specimen should be less than 4~ If the temperature difference is equal to or greater than 4~ the buffer solution and soil-cement test specimen are to be placed in the same environment or the higher temperature mixture cooled until the temperatures are within 4~ Gelling or stiffening of the soil-cement/buffer solution mixture may occur when testing specimens having cement contents greater than 16 % or highly calcareous soils. If this occurs, the ratio of mass of buffer solution to mass of soil-cement test specimen (1.65 to 1.50 kg [3.64 to 3.30 Ibm]) should not be used, and a new mass ratio must be established. The buffer solution reacts with the calcium hydroxide in the cement and may react with calcareous material in the soil to produce heat. Because fly ash may not contain any calcium hydroxide for reaction, this test method is not feasible if there is less than 3 % cement in the mix and will not test for percentage of fly ash. The buffer solution used consists of glacial acetic acid, water, and sodium acetate. Glacial acetic acid is corrosive and ignitable and gives a distinct vinegar odor to the buffer mixture. Sodium acetate and calcium acetate (a reaction product) are not considered to be toxic or hazardous chemicals. The acidity of the buffer solution changes from pH 2 to pH 5.2 during testing and can be disposed of with cement waste. If, after testing, a higher pH value is desired or if there is unreacted buffer solution, additional cement or lime may be added to the mixture before disposal. The heat o f neutralization test should be performed in an area isolated from drafts and maintained at a constant temperature. It is recommended that the calibration and testing be performed at the same location.

Precision and Bias Statements

After these changes were incorporated into the Australian test method, an interlaboratory test program was performed in accordance with ASTM Practice for Conducting an Interlaboratory Test Program to Determine the Precision of Test Methods for Construction Materials (C 802). The test program was performed to validate the procedural changes outlined, solicit user comments on the revised heat o f neutralization test method, and provide reliable information from which precision statements of the type prescribed in ASTM Practice for Preparing Precision and Bias Statements for Test Methods for Construction Materials (C 670), could be developed.

The interlaboratory test program was performed on two soil-cement mix designs in two separate phases. Phase I consisted of testing soil-cement specimens of a fine-grained mix design and Phase II used a coarse-grained mix design. Fine- and coarse-grained mix designs were selected to determine if the changes made to the test method were effective both on a fine-grained mix and on one in which a significant percentage of plus 4.75-mm (No. 4) material was present.

Testing laboratories from the federal, state, and private sectors participated in the test



program. Ten testing laboratories participated in Phase I of the test program, and eight testing laboratories participated in Phase II. Participating laboratories were provided with a written procedure and individual test specimens of appropriate soil mass, each with a corresponding amount of cement. Each laboratory was required to mix thoroughly the soil, cement, and water, as specified, for each test specimen before performing the heat of neutralization test. A moisture content of 8 % was specified for each test specimen. A detailed discussion of the test program phases and results is provided in Reference (2),

Phase I

In Phase I, each participating laboratory performed a total of 15 cement content determinations on soil-cement test specimens. The specimens consisted of 5 % minus 9.5-ram (3/8-in.) and 95 % minus 4.75-mm (No. 4) material. Nine determinations were performed on test specimens of known cement contents: three at 5 %, three at 7 %, and three at 9 % cement to develop a calibration curve and determine a calibration line equation. The remaining six cement content determinations were performed on duplicate test specimens designated for each laboratory as Test Specimens A, B, and C, but of unknown cement content to the participating laboratories. Test Specimens A were prepared at 6 % cement, B at 7 % cement, and C at 8 % cement.

Phase II

Phase II of the test program consisted of the same number of test specimens at the same cement contents as in Phase I. The gradation of Phase II test specimens was as follows:

Material Size % Retained

19 to 37.5 mm (3/4 to 1-1/2 in.) 9.5 to 19 mm (3/8 to 3/4 in.) 4.75 to 9.5 mm (No. 4 to 3/8 in.) Minus 4.75 mm (No. 4)

14 20 16 50

lnterlaboratory Test Program Results

Statistical analysis performed on data obtained from the 90 Phase I calibration test specimen heat o f neutralization tests, 30 at each o f the three cement contents, resulted in a correlation coefficient 0.981 with a corresponding R 2 value of 96 %. Similarly, statistical analysis performed on data obtained from the 72 Phase II calibration test specimen heat of neutralization tests, 24 at each of the three cement contents, resulted in a correlation coefficient of 0.974 with a corresponding R: value of 95 %. The closer the correlation coefficient is to 1, the greater is the degree of linear statistical relation between cement



content and heat of neutralization.

Interlaboratory test program results for unknown cement content Test Specimens A, B, and C (Phase I) and Test Specimens D, E, and F are summarized in detail in Determining Cement Content of Soil-Cement by Heat of Neutralization [2].

The precision and bias statements developed from the interlaboratory test program are as follows:

Repeatability for Calibration Specimens - The single-operator standard deviation of a single test ~esult (a test result defined as the average of three separate measurements) was found to be 0.5 ~ Therefore, results of two properly conducted tests by the same operator (each consisting of the average o f three calibration specimens of the same cement content) should not be more than 1.5 ~

Repeatability for Test Specimens - The single-operator standard deviation of a single test result (a test result defined as the average of two separate measurements) was found to be 0.14 % of cement content. Therefore, results of two properly conducted tests by the same operator (each consisting of the average of two cement content determinations) should not exceed 0.40 % of cement content. The range (difference between the highest and the lowest) of the two individual cement content determinations used in calculating a test result should not exceed 0.55 % of cement content. Reproducibility for Calibration Specimens - The multilaboratory standard deviation of a single test result (a test result defined as the average of three separate measurements), was found to be 0.8~ Therefore, results of two properly conducted tests in differently laboratories on the same soil-cement mix should not differ by more than 2.3~ Reproducibility for Tests Specimens - The multilaboratory standard deviation of a single test result (a test result defined as the average of two separate measurements) was found to be 0.26 % of cement content. Therefore, results of two properly conducted tests in different laboratories on the same soil-cement mix should not differ by more than 0.74 % of cement content. Bias - When experimental results are compared with known values from accurately compounded specimens, the bias of the test method is found with 95% confidence to lie between + 0.55 % of actual cement content.

Conclusions

Based upon both field experience to date and the results of the interlaboratory test program, the changes made to Test Method Q116B-78 by the Bureau of Reclamation produce results that are well within acceptable construction control limits. The revised heat of neutralization test method can accurately and quickly determine the cement content of freshly mixed soil-cement or RCC containing from 3 to 16 % cement and up to 50 % plus 4.75-mm (No. 4) material. The test is easily performed by field personnel, does



not require separation of plus 4.75-mm (No. 4) material to obtain a test specimen, and, in field applications performed to date, the method is accurate to within +_ 1% of actual cement content.

References

[1]

[2]

Cement Content of Cement Treated Materials (Heat of Neutralization). Test Method Q 116B-1978, Main Roads Department, Queensland, Brisbane, Australia, 1978. Scavuzzo, R., Determining Cement Content of Soil-Cement by Heat of Neutralization, Transportation Research Record 1295, Soil Stabilization, Transportation Research Board, National Research Council, Washington, DC, 1991.


Appendix CLSM Standards


( ~ ) Designation: D 4832 - 95 el AMERICAN SOCIETy FOR TESTING AND MATERIALS 100 ~ Harbor Dr, W ~ t Consho~xx~en PA 19428

Repnnted Ifom the AnnUal ~ook of ASTM Standards Copyright ASTM If ~ot hsted m the curre+l! comt~ned trxlex, w41 appear in the ~ x t edit o~

Standard Test Method for Preparation and Testing of Controlled Low Strength Material ( C L S M ) T e s t C y l i n d e r s 1

This standard is i~uad under the fixed designation D 4832; the number immediately following the desisnation indicates the year of original adoption or, in the case of revision, the year of last revlsion. A number in parentheses indicates the year of last re.approval. A supa~cdpt r (e) indicates an editorial change since the last rev,sion or reapproval.

et Hor~--Editorial changes were made in January 1997.

1. Scope*

1.1 This test method covers procedures for the preparation, curing, transporting and testing of cylindrlcal test specimens of controlled low strength material (CLSM) for the determination of compressive strength.

1.2 This test method also may be used to prepare and test specimens of other mixtures of soil and cementitious materials, such as self-cementing fly ashes.

1.3 CLSM is also known as tlowable fill, controlled density fill, soil-cement slurry, soil-cement grout, unshrinkable fill, K-Krete, and other similar names.

1.4 The values stated in SI units are to be regarded as the standard. The inch-pound equivalents are shown for information only.

1.5 This standard does not purport to address all o f the safety concerns, i f any, associated with its use. It is the responsibility o f the user o f this standard to establish appropriate safety and health practices and determine the applicability o f regulatory limitations prior to use. See Section 7.

2. Referenced Documents

2.1 A S T M Standards: C 31 Method of Making and Curing Concrete Test Spec-

imens in the Field 2 C 39 Test Method for Compressive Strength of Cylin-

drical Concrete Specimens 2 C 172 Method of Sampling Freshly Mixed Concrete 2 C 192 Method of Making and Curing Concrete Test

Specimens in the Laboratory 2 C 470 Specification for Molds for Forming Concrete Test

Cylinders Vertically z C 617 Practice for Capping Cylindrical Concrete Speci-

mens 2 C 1231 Practice for Use of Unbonded Caps in Determina-

tion of Compressive Strength of Hardened Concrete Cylinders

t This test method is under the junsdiction of ASTM Committee D-18 on Soil and Rock and is the direct responsibility of Subcommittee D 18.15 on Stabll~atton �9 ~4th Admixtures.

Current edition approved Dec. 10. 1995. Pubhshad May 1996. Originally pubhshed as D 4832 - 88. Last prcwous oditlon D 4832 - 88.

2 Annual Book of ASTM Standards, Vo104.02.

D653 Terminology Relating to Soil, Rock, and Con- tained Fluids 3

PS 28 Test Method for Flow Consistency of Controlled Low Strength Material (CLSM) +

PS 29 Test Method for Unit Weight, Yield, and Air Content (Gmvimetric) of Controlled Low Strength Ma- terial (CLSM) +

PS 30 Practice for Sampling Freshly Mixed Controlled Low Strength Material (CLSM) 4

PS 31 Test Method for the Ball Drop on Controlled Low Strength Material (CLSM) to Determine Suitability for Load Application 4

3. Terminology

3.1 Definitions--Except as follows in 3.2, all definitions are in accordance with Terminology D 653.

3.2 Definitions o f Terms Specific to This Standard: 3.2.1 Controlled Low Strength Material ( C L S M ) - - A mix-

tare of soil, cementitious materials, water, and sometimes admixtures, that hardens into a material with a higher strength than the soil but less than 8400 kPa (1200 psi). Used as a replacement for compacted backt'dl, CLSM can be replaced as a slurry, a mortar, or a compacted material and typically has strengths of 350 to 700 kPa (50 to 100 psi) for most applications.

4. Summary of Test Method

4.1 Cylinders of CLSM are tested to determine the compressive strength of the material. The cylinders are prepared by pouring a representative sample into molds, curing the cylinders, removing the cylinders from the molds, and capping the cylinders for compression testing. The cylinders are then tested to obtain compressive strengths. Duplicate cylinders are required.

5. Significance and Use

5.1 This test method is used to prepare and test cylindrical specimens of CLSM to determine the compressive strength of the hardened material.

5.2 CLSM is typically used as a backfill material around structures, particularly in confined or limited spaces. Corn-

Annual Book of ASTM Standards, Vo104.08 4 Annual Book of ASTM Standards, Vo104.09.

* A Summary of Changes section appears at the end of this Test Method.

3 1 9

�9 C o p y r i g h t 1998 by A S T M In te rna t iona l w w w . a s t m . o r g

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pressive strength testing is performed to assist in the design of the mix and to serve as a control technique during construction. Mix design is typically based on 28 day strengths and construction control tests performed 7 days after placement. The compressive strength(s) and other test age(s) will vary according to the requirements for the end product. Addi- tional information on the use and history of CLSM is contained in Appendix X1.

5.3 This test is one of a series of quality control tests that can be performed on CLSM during construction to monitor compliance with specification requirements. The other tests that can be used during construction control o f CLSM are Test Methods PS 28, PS 29, PS 30, and PS 31.

5.4 There are many other combinations of soil, cement, flyash (eementitions or not), admixtures or other materials that could be tested using this method. The mixtures would vary depending on the intended use, availability of materials, and placement requirements.

6. Apparatus 6.1 Single-Use Cylindrical Molds--Plastic single-use 15

em (6-in.) diameter by 30 cm (12-in.) high molds with tight fitting lids, conforming to Specification C 470. Other sizes and types of molds may be used as long as the length to diameter ratio is 2 to 1. The 15 cm by 30 cm (6 in. by 12 in.) molds are preferred because of the low strength of the material and the larger surface area of the ends of the cylinders.

6.2 Sampling and Mixing Receptacle--The receptacle shall be a suitable heavy-gage container, wheelbarrow, etc. of sufficient capacity to allow easy sampling and mixing and to allow preparation of at least two cylinders and for other tests such as described in Test Methods PS 28, PS 29, PS 30, and PS31.

6.3 Storage Container--A tightly constructed, insulated, firmly braced wooden box with a cover or other suitable container for storage of the CLSM cylinders at the construction site. The container shall be equipped, as necessary, to maintain the temperature immediately adjacent to the cylinders in the range of 16 to 27"C (60 to 80"F). The container should be marked for identification and should be a bright color to avoid disturbance.

6.4 Transportation Container--A sturdy wooden box or other suitable container constructed to minimize shock, vibration, or damage to the CLSM cylinders when transported to the laboratory.

6.5 TestingMachine--The testing machine shall meet the requirements as described in Test Method C 39.

NOTE l--Since the compressive strength of CLSM cylinders will typically be 100 kPa (about [5 to 1200 Ibf/in.2), the testing machine mug have a loading range such that valid values of compresslve strength can be obtained.

6.6 Curing Environment--A curing environment (water bath, damp sand, fog room) that meets the requirements of Method C 192. The cylinders may be cured in the same curing environment used for concrete cylinders at the laboratory performing the testing.

6.7 Small Tools--Tools and items that may be required such as shovels, pails, trowels, and scoops.

7. Hazards

7.1 Technical Precaution--The procedure for the preparation of CLSM test cylinders has many similarities to preparing concrete test cylinders (Method C 31 and Method C 192). However, the cylinders are much more fragile than concrete cylinders, and special care should be taken in their preparation, storage, and handling.

7.2 Safety Hazards." 7.2.1 Strictly observe the safety precautions stated in

Practice C 617. 7.2.2 I f the cylinders are capped with molten sulfur

mortar, wear proper personnel protective equipment, including gloves with cuffs at least 15 cm (6-in.) long.

8. Sampling and Test Specimens 8.1 Take samples of the CLSM for each test specimen in

accordance with P$ 30. Record the identity of the CLSM represented and the t ime of casting.

8.2 The sample from the batch should be a min imum of 0.03 m 3 (1 it3) for each two cylinders to be prepared. Prepare a m i n i m u m of two c o m p r e ~ v e strength cylinders for each test age to represent each sampled batch. Additional material may be required if other testing is to be performed, such as in Test Methods PS 28, PS 29, PS 30, and PS 31.

NOTS 2--In the initial stage of CLSM usage, preparation of three cylinders is recommended to obtain reliable compre~ve strength data for each test age. Subsequently, two cylinders may be used to maintain testing records and to ascertain an overall q~ i ty of the mix. However. since the cylinders are fragile and may be damaged during tmnsporta. don, mold removal, and capping, i~eparatlon of an extra cylinder may be necessary to provide the minimum number of test specimens (see Notes 5 and 6). In addition, it may be useful to determine the density of the test cylinders to help evaluate the umfonnity of the compressive strength values.

9. Specimen Molding and Curing 9.1 Place of Molding--Mold specimens promptly on a

level, rigid, horizontal surface free from vibration and other disturbances. The specimens should be prepared at a place as near as practicable to the location where they are to be stored during the first four days.

9.2 Placing the CLSM: 9.2.1 Thoroughly mix the CLSM in the sampling and

mixing receptacle. 9.2.2 With a bucket or pail, scoop through the center

portion of the receptacle and pour the CLSM into the cylinder mold. Repeat until the mold is full. Place a lid on the mold.

Nol'l~ 3--Use of an alr-tight lid has been known to cause low strength materials to crack, possibly due to a creation of a vacuum inside the mold. If an alr.tight lid is contemplated, its use should be evaluated before doing routine testing.

NOTE 4---Some mixtures will bleed rapidly, that is. free water will appear in the mixing receptacle and the mold. Obtaining the material to fill the cylinder must be done quickly after mixing. A few minutes afer filling the mold, thoroughly mix the CLSM in the sampling and mixing receptacle and place a scoopful in the top of the mold, displacing the water. Ifpossiblc, a slight mound of material should be left on the top of the mold. This refilling may be required again after about 15 rain. Leave the mound on the top of the mold and cover.

9.3 Curing." 9.3.1 Store the cylinders at the construction site in the

storage container until the fourth day after preparation.

320

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9.3.2 The cylinders shall be stored under conditions that maintain the temperature immediately adjacent to the cylinders in the range of 16 to 27~ (60 to 80"F). The cylinders must always be protected from freezing. After the first day, provide a high humidity environment by surrounding the cylinders with wet burlap or other highly adsorbent material.

9.3.3 On the fourth day, carefully transport the cylinders to the site of the curing environment in the transportation container and place in a curing environment (see 6.6).

9.3.4 The cylinders are typically left at the controction site for four days and then transported to a curing environment. If extremely low strength CLSM (below 350 kPa) would be damaged by moving on the fourth day, then the cylinders are to be placed in a water storage tank with a temperature between 16" and 27~ (60" and 80"F) at the construction site until they are able to be moved without damage.

10. Capping the Cylinders 10.1 On the day of testing, carefully remove the molds

from the cylinders and allow the cylinders to air-dry for 4 to 8 h before capping. If the upper surface of the cylinder is not a horizontal plane, use a wire brush to flatten the surface. Brush off all loose particles. Provide a cap for the cylinders using one the following methods:

10.1.1 Cap the cylinders using sulfur mortar in accordance with Practice C 617.

10.1.2 Cap the cylinder using gypsum plaster in accordance with Practice C 617.

10.1.3 Use elastomeric pads in accordance with Practice C 1231. The results of the qualification tests in Practice C 1231 for acceptance of the caps must not indicate a reduction of strength of more than 20 %, rather than 2 % as stated in Practice C 1231. The larger difference is acceptable because of the less critical uses of CLSM and 20 % is estimated to be the inherent variation in compressive strength results because of the lower strength values, for example 350 kPa (50 psi).

10.2 Use the same capping method throughout each project to avoid any variation in the test results from using different capping systems.

NOTE 5--CLSM cylinders are more fragile than concrete cylinde~ and must be handled carefully during the mold removr and during capping.

NOTS 6--1f sulfur mortar is used as the capping compound, oil is placed on the capping plate to ensure release of the cal~pin8 material from the capping plate. More oil may be required on the capping plate when capping CLSM cylirlders than is normally used when capping concrete cylinders. Capped CLSM cylinders will normally contain mote ah" voids between the cap and the cylinder than capped concrete cylinder, and this should be considered i f the caps are tapped to check for voids.

11. Compressive Strength Testing 1 l.l Placing the Specimen--Place the lower bearing

D 4832

block, with its hardened face up, on the table or platen of the testing machine directly under the spherically seated (upper) bearing block. Wipe clean the bearing faces of the upper and lower bearing blocks and of the test specimen, and place the test specimen on the lower bearing block. Carefully align the axis of the specimen with the center of thrust of the spherically seated block. As the spherically seated block is brought to bear on the top of the specimen, rotate its movable portion gently by hand so that uniform seating is obtained.

11.2 Rate of Loading--Apply the load continuously and without shock. Apply the load at a constant rate such that the cylinder will fail in not less than 2 min. Make no adjustment in the controls of the testing machine while a specimen is yielding rapidly immediately before failure.

11.3 Apply the load until the specimen fails, and record the maximum load carried by the specimen during the test. For about one out of every ten cylinders, continue the loading until the cylinder breaks enough to examine the appearance of the interior of the specimen. Note any apparent segregation, lenses, pockets, and the like in the specimen.

12. Calculation 12.1 Calculate and record the compressive strength of the

specimen as follows:

L C = ,K~) I4

where: C = compressive strength, kPa (lbf/in.2), D = nominal diameter of cylinder (normally 15 cm or 6 in.),

and L = maximum load, kN (lb0.

13. Report i3.1 The report shall include the following: 13.1.1 Identification, for example, mix, cylinder number,

location, etc. 13.1.2 Diameter and length, cm (in.). 13.1.3 Cross-sectional area, cm 2 (in.2). 13.1.4 Maximum load, kN (lbf). 13.1.5 Compressive strength, kPa (lbf/in.2). i 3. 1.6 Age of specimen. 13.1.7 Appropriate remarks as to type of failure, defects

noted, or nonuniformity of material.

14. Precision and Bias 14.1 The precision and bias of this test method have not

yet been determined. Data are being sought that will be suitable for use in developing precision and bias statements.

15. Keywords 15.1 b~ckfill; CLSM; compressive strength; construction

control; mix design; quality control; soil stabilization

321


~ D 4832

APPENDIX

(Nonmandatory Information)

XI. HISTORY

X 1.1 This standard was developed to provide an accepted, consensus method of preparing and testing CLSM cylinders. Because the cylinders are more fragile than normal concrete cylinders, the standard provides a workable method of preparation and testing based on much trial and error.

XI.2 CLSM is a combination of soil, portland cement, sometimes admixtures, ~ and enough water so that the mixture has the consistency of a thick liquid. In this form, the CLSM flows readily into openings, filling voids, and provides a hardened material that has a strength greater than the untreated soil used in the mix. Some cementitious fly ashes have been successfully used in place of the cement.

X 1.3 Although the primary use to date of CLSM or other similar materials has been as embedment for pipelines, it also has been used as trench backfill and structure backfill. 5.6

XI.4 Typically, CLSM contains about 5 to 10 % cement. One of the definite advantages is that CLSM may be produced using local soils. As opposed to a lean concrete slurry, the soil for the CLSM can contain up to about 20 to 25 % nonplastic or slightly plastic fines. Although clean concrete sands have been used, the presence of fines can help keep the sand-sized particles in suspension. This allows the mixture to flow easier and helps prevent segregation. Soils that are basically sand sizes work best with the maximum particle compatible with the space to be filled. Central batch plants with the slurry delivered in ready-mix trucks and trench-side, trail-along portable batch plants have been used, with the latter normally used when the soil comes from the trench excavation.

X1.5 Testing Techniques: Xl.5.1 The 15 by 30 cm plastic cylinders (see 6.1) are

Lowitz, C. A., and DcGrcot, O., "Soil-Cement Pipe Bedding, Canadian River Aqueduct," Journal of the Construction Divtsion, ASCE, Vol 94, No. C01, 196S.

6,,Cement.Triter Pipeline Bedding," Portland Cement Association Publica- tion No, PA0011.01.

suggested as a matter of economics; that size is not necessary based on the particle sizes normally used in CSLM. A minimum test age of 7 days is recommended for construction control testing because the cylinders may not be intact enough for transporting and testing in 3 days. In addition, the testing that has been done for 3-day strength has resulted in extremely erratic values.

X1.5.2 The mounding of the material in the cylinders was found to be necessary for mixtures that did not contain many fines; the water bled so quickly that a space was left on top of the cylinders and the hardened cylinders were not of a uniform height.

X1.5.3 At the moisture content required for the mixture to have the necessary flow properties, consolidation of the CSLM in the cylinder mold by vibration is not necessary.

XI.6 Typical Use." XI.6.1 The use of CLSM as pipe embedment illustrates

the relationship between the testing requirements and a typical application. For pipe installations, CLSM is used to fill the gap between the pipe and the excavated trench. The CLSM transfers the load from the pipe to the in situ material, so the native soil must be able to provide the necessary support for the pipe. The circular trench bottom shape is advantageous because it reduces excavation quantities and thus reduces handling of the soil materials. The CLSM eliminates the problem of trying to shape a cradle in the trench bottom to fit the pipe. A cradle is labor intensive and may not result in full contact between the pipe and the soil. The CLSM does ensure uniform support for the pipe. Placement of the CLSM is much faster than compacting the soil in layers alongside the pipe, and potential damage to the pipe from the compacting equipment is eliminated. It is also quicker than flooding and jetting or the saturation and vibration methods of compacting granular bedding materials. This faster installation is a distinct advantage where the construction is in populated areas or through streets.

SUMMARY OF CHANGES

This section identifies the location of changes to this test method since the last edition.

(1) The term "soil-cement slurry" was changed to "Con- trolled Low-Strength Material (CLSM)" and the definition modified.

(2) Capping methods expanded to include gypsum

mortar and elastomeric pads. (3) Reference made to other test methods for CLSM and

procedure modified to include necessary interaction with the other standards.

(4) SI units made the standard. (5) Additional section on keywords added.

The American Socleiy for Testing and Matar~ls takes no position respecting the validity of any patent r~hts asserted in connecllon with any item mentioned in this standard. Users of tNs standard are expressly advised that betormlnMk~n of the validity of any such patent rights, and the risk of Infringement of such r~hts, ere entirely their own r(~vtslblllty.

This standard is B u t U t to revision at any time by the responsible technical r end must be revisweff every five yea~ if not rev~cl, either re#ppl~ved r withdrawn. Your c~lments are invited either for revision of this standard 0r f ~ addittonat stanflarcls and stmukl be ~ to ASTM Headquarters. Your comments will receive careful consideredon at a meatmg of the respo~.sibis technical r which you may at~and. If you feel that your comments have not received ii fair he~lng you should rr~ke your views known to the ASTM Committee on Star~atcis, tO0 Bur Harbor Drive, West Co~Jhohoche& PA t9428,

322


( ~ ) Designation: D 5971 - 96 AMERICAN SOCIETY FOR rESrCt,~3 AND MATERIALS 100 Batr HadOor Dr., W~ t Colshohock~, PA lft428

Repnotod trom The Annual Book of ASTM ~tarKlatds COf~yoght ASTM If rot kste0 m the ctrre~t comb~ed tnOex, wJ appear ~ ~ ~x t edlllon

Standard Practice for Sampling Freshly Mixed Controlled Low-Strength Material I

Mamdald is isaued un~n" the fixed de~t ion D S971; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revi~on. A number in parentheses indicates the year of last ~eapproval. A sup~x~pt ep~ilon (0 iadicates an editorial chanse since the ~ revision or reapproval.

1. Scope

1.1 This practice explains the procedure for obtaining a representative sample to test o f freshly mixed controlled low- strength material (CLSM) as delivered to the project site (Note 1). This practice includes sampling from revolving- drum truck mixers and from agitating equipment used to transport central-mixed CLSM.

1.2 The values stated in inch-pound units are to be regarded as standard. The metric equivalents of inch-pound units may be approximate.

NOT~ l--Composite samples arc required by this practice unless specifically excepted by procedures governing the tests to be performed, such as tests to determine uniformity of consistency and mixer efficiency. Procedures used to select the specific test batches are not described in this practice. It is recommended that random sampling be used to determine overall specification compliance.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applica. bility of regalatory limitations prior to use.


2.1 ASTM Standards: D 653 Terminology Relating to Soil, Rock, and Contained

Fluids 2 D4832 Test Method for Preparation and Testing of

Controlled Low Strength Material Test Cylinders 2 PS 28 Test Method for Flow Consistency of Controlled

Low Strength Material 3 PS 29 Test Method for Unit Weight, Yield and Air Con-

tent (Gravimetric) of Controlled Low Strength Material 3

3. Terminology

3.1 Definitions--Except as follows in 3.2, all definitions are in accordance with Terminology D 653.

3.2 Definitions of Terms Specific to This Standard: 3.2.1 composite sample, n---a sample that is constructed

by combining equal portions of grab samples taken at two or more regularly spaced intervals during discharge of the middle portion of the batch of CLSM.

3.2.2 controlled low-strength material (CLSM), n--a mixture of Portland cement, fly ash, aggregates, water, and

i This prance is under the jurisdiction of ASTM Committee D- 18 on Soil and Rock and is the direct reslmmibility of Subcommittee D18.15 on Stabilization with Admixture.

~ t edition approved May 24, 1996. Publiflled August 1996. Orisinaily published as PS 30- 95. Last p~vious edition PS 30- 95.

2 A~ttal Book of ASTM Standarda, Vol 04.08. 3 Annual Book of ASTM Standards, Vo104.09.

possibly chemical admixtures that, as the cement hydrates, forms a soil replacement material. The CLSM is a self compacting, flowable, cementitious material that is primarily used as a baekt'dl or structural fill instead of compacted fdl or unsuitable native soil. Depending on the amount of water used in the CLSM mixture, it can be placed as a nonflowable compacted material or as a mortar.

3.2.3 flow consistency, n - - m e ~ u r e d by the average diameter of the spread achieved by removal of the flow cylinder.

4. Significance and Use

4.1 This practice shall be used to provide a representative sample of the material for the purpose of testing various properties. The procedures used in sampling shall include the use of every precaution that will assist in obtaining samples that are truly representative of the nature and condition of the CLSM.

5. Sampling

5.1 Size of Sample--The sample of CLSM for compressive strength testing shall be a m in imum of 0.5 ft 3 (14 L). For other tests, the composite size shall be large enough to perform the test and to ensure a representative sample of the batch was taken.

6. Procedure

6.1 Sampling from Revolving-Drum Truck Mixers or Agitators--Sample the CLSM at two or more regularly spaced intervals during discharge of the middle portion of the batch. These grab samples shall be obtained within the time limit specified in 6.2 and composited into one sample for test purposes. In any case do not obtain samples until aRer all water has been added to the mixer; also do not obtain samples from the very first or last portions of the batch discharge. Sample by repeatedly passing a receptacle through the entire discharge stream or by completely di- verting the discharge into a sample container. Regulate the rate of discbargc of the batch by the rate of revolution of the drum and not by the size of the gate opening.

No'rB 2--Sampling normally should be performed on the CLSM as delivered from the truck to the job site excavation.

6.2 The elapsed time between obtaining the first and final portions of the composite sample shall be as short as possible and in no instance shall it exceed 2 rain.

6.3 Transport the composite samples to the place where fresh CLSM tests are to be performed or where test specimens are to be molded. The composite sample shall be combined and remixed with a shovel or scoop the min imum

323


q~ D $971

amount necessary to ensure uniformity and compliance with the minimum time limits specified in 6.4.

6.4 Start tests for flow consistency (Test Method PS 28), unit weight, and air content (Test Method PS 29) within 5 rain after obtaining the final portion of the composite sample. Complete these tests as expeditiously as possible. Start molding specimens for strength tests (Test Method D 4832) within 10 min after obtaining the flnai portion of

the composite sample. Keep the elapsed time between obtaining and using the sample as short as possible and protect the sample from the sun, wind, and other sources of rapid evaporation, and from contamination.

7. Keywords

7.1 air content; CLSM; composites; flow consistency; quality control; sampling; unit weight

The ,4merlcan Society for TeM~ng and Matw~a~ tak~ ~ `~siti~n r~A~ct~ng th~ v~dtty of a~y l~t~nt tigms a~u~t1~ ~ ~ with tony Item mentioned in ttgr itandalO, U~mr~ of t t~ st~toWO ale axl~eaaiy mOvlBeO thM o~ltero1#t~lon OI tt~ tlllMIty of ~ 41uch ~ t fl~t,% at~ tlw r ~ of l t ~ t ~ of 41ueh f~ ts , 41tl ~ l r ~ thl~ ~vn t ~ l t M i l l ~ .

Th~ ~t~nd~t~ ~8 ~ u b ~ ~ ~-ev~n K a~y t~trm W rhe reg~n~3i~ t~cht t~ ~ m m l t ~ ~ ~ ~ ~ ~ ~ ~ ~ ff t)ot twl#ed, ettfmr rego~covod ot wlthdrawn. Your oommett~ ~ lnv#ed elther for ret, l~on ol ttgg ltw)d~,d or for et~tBotml #tend,,id$ and should be eddlwalmd to ASTM Heedqueners. Your comments will tecelve (~#td conslderltlon et ll mNtlng of trm rlmpor41~ t~m~c~ ~ which y~u m4y Kt~nd~ ~ ~ u ~ thet ~ur ~mm~tO h ~ ~ t ~eiv~d ~ f~lr ~mr~g y~u ~ ~ ~ vlews known to tho A~rM ~ on ,~w~wd#, lOO Bur Halt~ot Dd~l, West Cotttbohoclcen, PA 19428.

324


( • 1 [ • ) Designation: D 6023 - 96 ^ue,~s soccer, F~ r~s .~ ~ ~ r e . ~ s 10o ~ Hsrbor Dr, WeSt Cot~shohocke~. PA 19428

Reprlnted ~om the A~qtm/Book o~ ASTM S t ~ CAZOy~ ASTM ~ not l~ted t~ the c~,re~ oom~ned index, w~ appeK m ttw rmxt edmoe

Standard Test Method for Unit Weight, Yield, Cement Content, and Air Content (Gravimetric) of Controlled Low Strength Material (CLSM) I

standard il issued under the fixed de - -on D 6023; the number immediately fonowi~l the dmlo~.don indlcatel the year of miginal sdoption or, in the cme of revi,~on, the year of hu~ tevilaon, A number in parenthmm indicates the Year of lint ral~P~rovaL A supe~cript elniloo (~) indicatee an edJtodal change since the last revi~on or real~ov~.

1. Scope* 1.1 This test method explains determination of the mass

per cubic foot (cubic meter) of freshly mixed Controlled Low Strength Material (CLSM) and gives formulas for calculating the yield, cement content, and the air content of the CLSM. This test method is based on Test Method C 138 for Concrete.

NOTE l - -Uni t Weight is the traditional terminology used to describe the property determined by this test method. The proper term is density. It has also been termed unit mires or bulk density. To be compatible with terminology used in the concrete indusav, unit weight is referenced in this test method.

1.2 The values stated in SI units are to br regarded as standard. The inch-pound equivalents are shown for information only.

1.3 CLSM is also known as fiowable fill, controlled density fill, soil-cement slurry, soil-cement grout, unshrinkable fdl, "K-Kxete," and other similar names.

1.4 This standard does not purport to address all of the safety concerns, i f any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.


2.1 ASTM Standards: C 29/C 29M Test Method for Unit Weight and Voids in

Aggregate 3 C 125 Terminology Relating to Concrete and Concrete

Aggregates 3 C 128 Test Method for Specific Gravity and Absorption of

Fine Asgregates 3 C 138 Test Method for Unit Weight, Yield and Air

Content (Gravimetric) of Concrete 3 C 150 Specification for Portland Cement 3 C231 Test Method for Air Content of Freshly Mixed

Concrete by the Pressure Method 3 D 653 Terminology Relating to Soil, Rock, and Contained

~ d s 4

t This trot method is uadex the jurhldlction of ASTM Comm/ttee D- 18 om Soil and Rock and is the direct r of Sub~mmittee DI 8.15 on StYlization with Admixturm.

Current edition approved ~ 10, 1996. I~blished May 1997. Odginally imbligxd at P$ 29 - 95,

a See Section 13 of the Refula~o~ ~ AS'rM TeclmlcM Commi~es. s Annun/Book qfASTM Standards, Vo104.02. �9 Ann~ Book of ASTM Standords, Vol 04.08.

D 3740 P r a n c e for Minimum Requirements for Agencies Engaged in the Testing and/or Inspection of Soil and Rock as used in Engineering Design and Construction 4

D4832 Test Method for Preparation and Testing of Controlled Low Strength Material (CLSM) Test Cyfinders 4

D 6024 Test Method for the Ball Drop on Controlled Low Strength Material (CLSM) to Determine Suitability for Load Application 4

PS 28 Test Method for Flow Consistency of Controlled Low Strength Material (CLSM) 4

PS 30 Practice for Sampling Freshly Mixed Controlled Low Strength Material s

3. Terminology 3. l Definitions--Except as follows in 3.2, all definitions

are in accordance with Terminology C 125 and D 653. 3.1.1 Controlled Low Strength Material (CLSM)--a mix-

tore of soil or aggregates, cementitious material, fly ash, water, and sometimes chemical admixtures, that hardens into a material with a higher strength than the soil, but le~ than 8400 kPa (1200 psi).

3.1A.I Discassion--Used as a replacement for compacted backfill, CLSM can be placed as a slurry, a mortar, or a compacted material and typically has strengths of 350 to 700 kPa (50 to 100 psi) for most applications.

3.1.2 mass, n-- the quantity of matter in a body. (See weight.)

3.1.2.1 Discassian--Units of mass are the kilogram (kg), the pound (lb) or units derived from these. Masses are compared by weighing the bodies, which amounts to Com- paring the forces of gravitation acting on them.

3.1.3 weight, n--the force exerted on a body by gravity. (see mass.)

3.1.3.1 Discussion--Weight is equal to the mass of the body multiplied by the acceleration due to gravity. Weight may be expressed in absolute units (newtons, poundals) or in gravitational units (kgf, lbt). Since weight is equal to mass times the acceleration due to gravity, the weight of a body will vary with the location where the weight is determined, while the mass of the body rema/ns constant. On the surface of the earth, the force of gravity imparts to a body that is free to fall an acceleration of approximately 9.81 m/s 2 (32.2

3.2 Description of Term Spec~qc to This Standard:

s Annua/Book ofASTM S~u/ards, Vo[ 04.09.

* A Sammm-y of Chang~ sectiea apl~trs at the cad of thlg Test Methed.

325


r D 6023

3.2.1 yield--the volume of CLSM produced from a mix- tore of known quantities of the component materials.

4. Summary of Test Method 4. I The density of the CLSM is determined by fdling a

measure with CLSM, determining the ma~ , and calculating the volume of the measure. The density is then calculated by dividing the mass by the volume. The yield, cement content, and the air content o f the CLSM is calculated based on the masses and volumes of the batch components.

5. Significance and Use 5.1 This test method provides the user with a procedure to

calculate the density of freshly mixed CLSM for determination of compliance with specifications, for determining mass/volume relationships or conversions such as those found in purchase agreements, and also for quality control purposes.

5.2 This test method is intended to assist the user for quality control purposes and when specified to determine compliance for air content, yield, and cement content of freshly mixed CLSM.

5.3 This test method is not meant to predict the air content of hardened CLSM, which may be either higher or lower than that determined by this test method.

5.4 This test is one of a series of quality control tests that can be performed on CLSM during construction to monitor compliance with specification requirements. The other tests that can be used during construction control are Test Method D 4832, Provision Test Methods PS 28 and PS 31.

No're 2--Notwithstanding the statements on precision and bias contained in this test method: The prec~ion of this test method is dependent on the competence of the personnel performing it and the sultab~lity of the equipment and facilities used. Agencies which meet the criteria of Practice D 3740 are generally considen~ capable of competent and objective te~in 8. Users of this method are cautioned that compliance with Practice D 3740 does not in itself ensure reliable testing. Reliable testing depends on several factor~; Practice D 3740 provides It means of evaluation some of those facton.

6. Apparatus 6.1 Balance---A balance or scale accurate to within 0.3 %

of the test load at any point within the range of use. The range of use shall be considered to extend from the mass of the measure empty to the mass of the measure plus the CLSM.

6.2 Filling Apparatus--Scoop, bucket or pail of sufficient capacity to facilitate filling the measure in a rapid, efficient manner.

6.3 Sampling and Mixing Receptacle---The receptacle shall be a suitable container, wheelbarrow, and the like of sufficient capacity to allow easy sampling and remixing of the CI~M.

6.4 Measure.--A cylindrical container made of steel or other suitable metal (Note 3). It shall be watertight and sufficiently rigid to retain its form and calibrated volume under rough usage. Measures that are machined to accurate dimensions on the inside and provided with handles are preferred. All measures, except for measuring bowls of air meters shall conform to the requirements of Test Method C 29/C 29M. The min imum capacity o f the measure shall conform to the requirements of Table 1. When measuring

TABLE 1 Minimum Cal~olty of I~hmmmt

Nomln~ Mexlmum ~ z , o( O ~ ' m , ~ W q i n # Camcay o~ t.~mem, rein*

in. mm ~ L

1 28.0 0.2 6 1 ~.41 ~7.w 0.4 11 2 50 0.8 14

A Aggm~W of t glwn n ~ n ~ m ~ x x n :~ze m ~ cent~ up to 10 z of Im~t~s mtm~d ce the Me~ rt~m:d to.

m u Wovtde tot w~r, momums may be up te 5 ~ Umdw tflan Ind~nod In e~

bowls of air meters are used, they shall conform to the requirements of Test Method C 231. The top rim of the air meter bowls shall be smooth and plane within 0.01 in. (0.25 m m ) (Note 4).

NOTE 3--Tbe metal shoukl not be readily subject to attack by cement page. However, nmcfive materiah inch u aluminum alloys may be used in instances where, as a consequence of an initial reaction, a surface film is ral~dly formed which proteoas the metal against further corce~on.

Note 4---Tbe top rim is satisfactorily plane ira 0.01-in. (0.25-ram) feeler gage cannot be imetted between the rim and a piece of V, in. (6 ram) or thicker plate Itlau laid over the top of tbe mca~are.

6.5 Strike-Off Plate---A flat rectangular metal plate at least I/4 in. (6 ram) thick or a glass or acrylic plate at least i/= in. (12 ram) thick with a length and width at least 2 in. (50 ram) greater than the diameter of the measure with which it is to be used. The edges of the plate shall be straight and smooth within a tolerance of IAe in. (1.5 ram).

6.6 Calibration Equipment--A piece of plate glass, preferably at least I/4 in. (6 ram) thick and at least 1 in. (25 ram) larger than the diameter of the measure to be calibrated. A thin film of vacuum, water pump or chassis grease smeared on the flange of the bowl will make a watertight joint between the glass plate and the top of the bowl.

7. Sample

7.1 Obtain the sample for freshly mixed CLSM in accordance with Practice PS 30.

7.2 The size of the sample shall be approximately 125 to 200 % of the quantity required to fill the measure.

8. Calibration of Measure

8.1 Calibrate the measure and determine the calibration factor (1/volume), following the procedure outlined in Test Method C 29/C 29M.

NOTE 5--For the calculation of unit weight, the volume of the measure in acceptable metric units thonid be expreued in cubic metres, or the factor as I/m 3. However, for convenience the ~ of the measure may be expressed in lite~

8.2 Measures shall be recalibrated at least once a year or whenever there is reason to question the accuracy of the cafibration.

9. Procedure

9.1 Place the measure on a level, rigid, horizontal surface free from vibration and other disturbances.

9.2 Placing the CLSM: 9.2.1 Start this procedure within 5 rain after obtaining the

sample of CLSM and complete as expeditiously as possible. 9.2.2 Thoroughly mix the sample of CLSM in the sam-

3 2 6

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q~ D 6023

pfing and mixing receptacle to ensure uniformity. 9.2.3 With the filling apparatus, scoop through the center

portion of the sample and pour the CLSM into the measure. Repeat until the measure is full.

9.3 On completion of filling, the measure shall not contain a substantial excess or deficiency of CLSM. An excess of CLSM protruding approximately Vs in. (3 m m ) above the top of the mold is optimum. To correct a deficiency, add a small quantity of CLSM.

9.4 Strike-Off--ARer tilting, strlke-off the top surface of the C I ~ M and finish it smoothly with the flat strike-offplate using great care to leave the measure just level full. The strike-off is best accomplished by pressing the strike-off plate on the top surface of the measure to cover about two thirds of the surface and withdrawing the plate with a sawing motion to finish only the area originally covered. Then place the plate on the top of the measure to cover the original two thirds of the surface and advance it with a vertical pressure and a sawing motion to cover the whole surface of the measure. Several final strokes with the inclined edge of the plate will produce a smooth finished surface.

9.5 Cleaning and Mass Measuremem--ARcr strike.off, clean all excem CLSM from the exterior of the measure and dctermine thc gross mass of the CLSM in the measure to an accuracy consistent with the requirements of 6. I.

10. Calculation 10.1 DensiO~-.Calcolate the mass of the CLSM in

mcgngrams or grams (pounds) by subtracting the mass of the measure from the gross mass. Calculate the density, W, by multiplying the mass of the CLSM by the calibration factor for the measure determined in 8.1.

10.2 Yield--Calculate the yield as follows: Y/(ft 3) - W,/W (l)

or, y (yd 3) = W1/(27 W) (2)

or, y (m 3) = WI/W (3)

where: Yf = volume of CLSM produced per batch, I~ 3, Y = volume CLSM produced per batch, m 3 (~3), W = density of CI.~M, kg/m 3 (lb/ft3), and WI = total mass of all materials batched, kg (lb) (Note 6).

NOTe 6---The total mare of all materials b a ~ is the sum of she masses of the cement, the fly ash, the filler aggregate in she condition used, She mixing water added to the batch, and any other solid or liquid ~ nsod.

10.3 Relative Yield--Relative yield is the ratio of the actual volume of CLSM obtained to the volume as designed for the batch calculated as follows:

R~,- Y/Y# (4)

where: Ry = relative yield,

Y = volume CLSM produced par batch, m 3 (ydS), and I"# = volume of CLSM which the batch was designed to

produce, m s (yd3). NOTe 7--A value fro" R~ greater than 1.00 indicates an exce~ of

CLSM being produced whereto a value less shan this indicates She batch to be "short" of its "tmiLm~d volume.

10.4 Cement Content (Note 8 ~ c u l a t e the actual cement content as follows:

N - N,/Y (5)

where: N = actual cement content ks/m 3 (IblydS), N, = mass of cement in the batch, kg (Ib), and Y = volume CLSM produced par batch, m 3 (yd3).

No'r~ 8--In detcrmininl cemanl content on CI~M's that contain Cbiss C fly mh, she actust msm of Chin C fly mh shail be i,ld,'d to she mass of cement.

10.5 Air Content---Calculate the ~ content as follows:

A - [ ( r - W ) / T ] x 100 (6)

or, A -- [(Yf-- V)/Yf] X 100 (inch-pound units) (7)

or, A - [ ( Y - v)/Y] x IO0 (sl units) (8)

where: A = air content (percentage of voids) in the C l a M , T = theoretical den~ty of the CLSM computed on an air

free basis, kg /m s (lb/fl 3) (Note 7), W = density of CLSM, kg/m 3 (lh/fts), Y/ - volume of C I ~ M produced per batch, f0, V = total absolute volume of the component ingredients in

the batch, t3 or m 3, and Y = volume CLSM produced per batch, m 3 (ydS).

Nor~ 9--The theoretical demity is, cnstommily, s laboratory duty- ruination, she value for which is assumed to remain constant for all batches made using idcoticeJ component ingredients and proportions. It is calculated from the following equation:

T= W, lV The absolute volume of each ingredient in cubic feet is equal to the quotient of the mare of that ingredient divided by she product of its specific gravity times 62.4. The absolute volume of each ingredient in cubic meters is equal to the mau of the ingredient in kltollran~ divided by 1000 times its specific gravity. For She ag~egatc cumpouan~ the bulk specific gravity and mau should be determined by Test Method C 128. A value of 3.15 may be umd for cements manufactured to meet she requirements of Specification C 150.

11. Report I 1.1 Report the results for the density to the nearest 1

lb/fl 3 (10 kg/m3). The density may be l~,-ported as un/t weight to be compatible with the terminology used in the concrete industry.

I 1.2 Report the following information: I 1.2. I Yield, to the second decimal. I 1.2.2 Relative yield, to the second decimal. I 1.2.3 Cement content, to the second decimal. 11.2.4 Air content, to the nearest 0.5 %.

327


I~ D 6023

12. Precision and Bias

12.1 Precision--Data are being evaluated to determine the precision of this test method. In addition, Subcommittee D 18.15 is seeking pertinent data from users of the test method.

12.2 Bias--The procedure in this test method for mea-

suring unit weight has no bias because the value for unit weight can be defined only in terms of a test method.

13. Ke~ovords 13.1 air content; backfill; cement content; CLSM; con-

struction control; density; flowable fill; mix design; quality control; relative yield; soil stabilization; unit weight; yield

SUMMARY OF CHANGES

This section identifies location of changes to this test method since the last edition.

(l) This test method previously had the designation PS 29 - 95, a provisional test method.

(2) The differences between this version of the test method and the previous one are as follows:

(3) Sections 1.3, 3.L2, 3.1.3, 3.2 and 5.4, Notes L, 2, and 5 were added.

(4) SI units were made the standard, unit weight was changed to density, weight was changed to mass.

(5) Sections 3.2, 4.1, 8.1, l l . I and 12 were rewritten. (6) Units in Table I were corrected. (7) In 6.6 vacuum grease was added. (8) Composite sample was changed to sample in 9.2.1 and

9.2.2. (9) Section 13, additional keywords were added.

The Amef~n s~c~y t~r T~Jr~ ~ ~ t e ~ i ~ tak~ n~ ~s~t~n r ~ e ~ # ~ tt~ va~ty ~ w)y p ~ n t ~ t ~ ~ t~ te~ ~ ~ w ~ my ltem mentloned ln t l ~ ~wm~rd. U~er~ of t t~ stand~vd are ~ ~o~lsed th~t domnnkW, t ~ ~ ~ ~ ~ ~ y ~ p~tent ~ t t~ , md the r~X of ~lrtngem~nt ot such tA~ts, w~ enOm~ rlWr own nmon~lbll~.

Th~ smr, d~d ~. ~*bloct m mv~on K w~y tln~ by Um re~on~L~ lechn~ ~ w ~ mu~ be mvlowed ~ety ~ ~ ~ It not r e v ~ , ettr4t reqopmved or ~ Yout commera are lnvtted elthK for mvlslon ol Um ~w~ard or lat ~ t t loml l mmndw~m and should be ~ M N d to ASTM Ite~VlLw~ers. Your commwt~ wlll mceive cuelul cona~demtlon wt a mNtlr~ of the maponalble t @ ~ / ~ ~mmltt~, whlch yau mly wth~d, if you feel tlmt yout commw~ hlve not m~Ned a ~ r hew~ng you should ttWt@ your vlews lrnown to th@ ASTM Commlthm on St&-x;~al~, 10O B~r Hubot DtivL West ~ PA 19428.

328

Copyr igh t by ASTM In t ' l ( a l l r i gh t s r e se rved) ; Thu Feb 7 18 :46 :02 EST 2013Downloaded /p r in t ed byKar ina Agama (F reyss ine t+Tie r ra+Armada+Peru+S .A.C . ) pu r suan t t o L icense Agreemen t . No fu r the r r ep roduc t ions au tho r i zed .

(1~) Designation: D 6024-96 . . . . . . . 100 Barr ~SOC . . . . . . . . . . . . . . . . . . . . . . De. West C4~f, hONocketl, PA 19428

If not ~ ~ me ~ comtY~ed ~dex, w~ apoear m the ~xt edmon

Standard Test Method for Ball Drop on Controlled Low Strength Material (CLSM) to Determine Suitability for Load Application 1

stlmda~ it i~ued under the fixed demgnation D 6024; the number immedialely following the d e ~ t i o n indicates the year of onlpnal adoption or, in the r of r~.vision, the year of last revis A number in psrenthee~ indimttm the year of last reapptoval. A supetscnp~ ep~lon O) indicates an editm'i~ chan~ sinc~ the last revbaon or nmppmval.

1. Scope* 1.1 This specification explains the determination of the

ability of Controlled Low Strength Material (CLSM) to withstand loading by repeatedly dropping a metal weight onto the in-place material.

1.2 The values stated in SI units are to be regarded as the standard. The inch-pound equivalents are shown for infor- marion only.

1.3 CLSM is also known as flowable fill, controlled density fill, soil-cement slurry, soil-cement grout, unshrinkable fill, "K-Krete," and other similar names.

1.4 This standard does not purport to address all of the safety concerns, i f any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.


2.1 ASTM Standards: C 125 Terminology Relating to Concrete and Concrete

Aggregates 3 C 360 Test Method for Ball Penetration in Freshly Mixed

Hydraulic Cement Conca'e~ ~ D 653 Terminology Relating to Soil, Rock, and Contained

Fluids" D 3740 Practice for Minimum Requirements for Agencies

Engnged in the Testing and/or Inspection of Soil and Rock as used in the Engineering Design and Con- struetion 4

D4832 Test Method for Preparation and Testing of Controlled Low Strength Material (C].~M) Test Cylinder#

D6023 Test Method for Unit Weight, Yield, and Air Content (Gravimetrir of Controlled Low Strength MateriM 4

PS 28 Provisional Test Method for Flow Consistency of Controlled Low Strength Material 4

I TI~ rut method il under the juriadiction of ASTM CommJt~e D- I S on Soil and Rock and k the ~ R~on~bility of Subcommlttee DI 8.1S on ~ t l o n with Admixttm~

~ t edition approved Oct. 10, 1996. Publigaed JuDe 1997. Ot~imflly publkhed u PS 31 - 95.

See Section 13 of the Reg, ulalioas Governing ASTM Technical CommitteeJ. 3 Ammal Book ofASTM ~tandards, V~ 04.02. ' Annum Ba~k q/'ASTM ,~arda~, Vo104.08.

3. Terminology 3.1 Definitions--Except as follows in 3.2, all defimtions

are in accordance with Terminology C 125 and D 653. 3.2 Definition of Term Specific to This Standard: 3.2.1 Controlled Low Strength Material (CLSM)~a mix-

tore of soil or ~ t e s , cementirious material, fly ash, water and sometimes chemical admixtures, that hardens into a material with a higher strength than the soil, but less than 8400 kPa (1200 psi).

3.2.1.1 Discu.~sion.--Usedasareplacementforcompaeted backfill, CLSM can be placed as a slurry, a mortar, or a compacted material and typically has strengths of 350 to 700 kPa (50 to 100 pal) for most applications.

4. Summary of Test Method 4.1 A standard cylindrical weight is dropped five times

from a specific height onto the surface of in-placo CLSM. The diameter of the resulting indentation is measured and compared to established criteria. The indentation is in- speeted for any free water brought to the surface from the impact.

5. Significance and Use 5.1 This test method is used primarily as a field test m

determine the readiness of the CLSM to accept loads prior to adding a temporary or permanent wearing surface.

5.2 This test method is not meant to predict the load bearing strength of a CLSM mixture.

5.3 This test is one of a series of quality control tests that can be performed on CLSM during construction to monitor compliance with specification requirements. The other tests that can be used during construction control are Test Methods D4832, D6023, and Provisional Test Method PS 28.

NOTe I--Notwith~tanding the statements on prec.'on and contained in this t a t method: the prec~on of this test method is dependent on the mmpeten~ of the pemonnel peffonming it and the mitahih'ty of the equipment and facilities ueed. Apncies which meet the criteria of Pmcti~ D 3740 are lenendly comldered capable of competent and objective testing. Utem of this test method are cautioned that compliance with Practice D 3740 does not in it . l l ensure relialde testing. Reliable tearing depends on several factors; Practice D 3470 provkles a means of evaluating some of tho~ facton.

6. Apparatus

6.1 Ball.drop Apparatus--a cylinder with a hemispheri- cally shaped bottom and handle with a mass of 14 + 0.05 k8

* A ~mmmry of Cimages s~den mpp~u~ s t ~ e eud of this T ~ Method.

329


D 6 0 2 4

Meetc Ecutvetmts In, rnm in, rnm I~ 3.2 MYe 117 i,~ 13 5'Ai 140

16 5 ~ 143 1 25 9 228

ltA~ 38 12 305 3 76

FIG. 1 Bali-drop Apparatus

(30 + 0.1 lb), and a stirrup or frame to guide the handle (Fig. l).

6.1.1 Weight~The cylindrical weight (ball) shall be approximately 15 cm (6 in.) in diameter and 12 cm (45/J in.) in height, with the top surface at right angles to the axis and the bottom in the form of a hemisphere of 75 mm (3 in.) radius. The cylindrical weight may be machined from metal stock or cast or spun provided the dimensions and weight with the handle meet requirements, and the finish is smooth.

6.1.2 Handle--The handle shall be a metal rod, 13 mm (IA in.) in diameter. The handle may be T-shaped or a closed rectangle at the top to permit grasping by the hand.

6.1.3 Stirrup--The stirrup shall be at least 38 mm (IV2 in.) in width. The stirrup frame is attached securely to blocks elevating it 9 cm (3tA in.).

6.1.4 Blocks--pie~s of wood, or ultra high molecular weight plastic (UHMW) that are 9 cm (31/2 in.) high are used to elevate the stirrups to the proper height. The stirrups must be centered on the blocks to avoid tipping, and attached securely to the stirrups so shifting does not occur. The blocks shall be parallet to each other and perpendicular to the main stirrup frame. The blocks must not interfere with the ball-drop apparatus. Each block shall have the minimum dimension of 9-cm (3V2 in.) wide by 18-cm (7-in.) long with a minimum bearing area of 155 cm 2 (24 in2).

6.2 Measuring Device---capable of measuring the diameter of the indentation. It must be capable of measuring a minimum of 3 mm (I/8 in.).

7. Procedure 7. I The surface of the CLSM will need to be as level as

possible either by self-leveling or by slight brooming action with hand tools. Set the elevated base of the apparatus on the leveled CLSM surface, with the handle in a vertical position and free to siide through the frame. Put slight pressure on the frame with your free hand to stabilize the device. Lift the handle as far as possible allowing the top surface of the ball to contact the underside of the stirrup frame. Release the weight allowing it to free fall to the surface of the CLSM. Repeat this for a total of five times at each location tested. Before testing a new location of the in-place CLSM remove any material that has adhered to the ball from previous testing,

7.2 Measure the diameter of the indentation left by the ball with a measuring device (Note 2). If the diameter of indentation is 76 mm (':3 in.) then the CLSM is suitable for the load application. If the diameter of indentation is 76 mm (>3 in.) then the CLSM is unsuitable or not ready for load application.

NOTe 2--It has been shown under limited use that an indentation of ~75 mm (3 in.) is suitable for normal load application.

7.3 Inspect the indentation for visible surface water or sheen brought to the surface by the dropping action of the ball. The surface should look similar to that before the test with the exception of an indentation. The presence of surface water indicates that the CLSM is unsuitable or not ready for load application.

8. Report 8.1 Report the following: 8.1.1 Project Identification, 8.1.2 Location of test, 8.1.3 Identification of individual performing the test

method, and 8.1.4 Date test is performed. 8.2 Report the following information: 8.2.1 V~ble surface water or sheen brought to the surface

by the dropping action, 8.2.2 Irregularities on the surface of the in place CLSM

such as indentations left by the blocks or severe cracking, and

8.2.3 Diameter of indentation to nearest 3 mm (V, in.).

9. Precision and Bias

9.1 Predsion--Data are being evaluated to determine the preeision of this t~'-t method. In addition, Subcommittee D18.15 is seeking pertinent data from users of the test m e t h o d .

10. Keywords 10.1 backfill; bali drop apparatus; bearing; CLSM; con-

struction control; early load; flowable fill; mix design; quality control; soil stabilization; surface weter, wearing surface

3 3 0


IJ~ O 6024

SUMMARY OF CHANGES

This section identifies the location of changes to this test method since the last edition.

(1) This test method previously had the designa~on PS 31 - 9 5 , a provisional standard.

(2) The differences between this version of the test method and the previous one are as follows:

(3) Sections 1.3, 5.3 and 6.2 were added. (4) Notes 1 and 2 were added. (5) SI units were made the standard. (6) Sections 3.2.1, 4.1, 6.1.3, 6.1.4, 7.1, 7.2, 8, 9.1, and I0

were mvritten. (7) Fig. I blocks were added to the drawing.

The Am~can S~.te~ for Testlng w)d M~erla~ ~ no po~Oon re~oectln~ t ~ valk~W of ~ y ~ ~ ~ ~ ~ w ~ wty ttom nwntlon~ ln t t ~ ~.rm'~Wd. U s ~ ol t . ~ g, andard w~ expr~O/ ~mVl~d ttW d~omOr, e t ~ of t l~ wOlOlO/ ot ~ny .~.h pstent r l l ~ , md tt~ r~l( ol ln#tnl~,w~ of suc~ r;gt~, ~re enUr~ ttWr own rem~m//:O~.

T ~ mr , Oetd k. ~ to rev,~,~ at Jmy r#r,e by the n m o n a ~ techr, k ~ cor, vn4~m w-,r mu~ ~ rev~m,~ m ~ ~ ~ # nor r m , ~ , a(Itmr rl~oproved or w/thc~r~, y ~ r commera w~ tm/ t~ ~VW" for twts,~n of t t l mmcfard or ~ ~ ~ ar~,~ ' .a~ tB ~ a M x ~ to ~I3TM H~'q~artt~. Y,x,t c , ~ . n w n w~ re~#~ ~ t d ~ r W a meat~g ~' the r , m ~ r w l ~ teo/Wca/torero/tree, wh/ch you may ~t~,r # you ~et ~ yow (xwsr, w m tur,,o not rJc~v~ o f~r/werlng )~u ~ mab~ ymr view~ kntwsn to the ASTM ~ on St'w)dar~, 100 Botr Hsrbor Dr~e, W~t ~ , PA19428.

331


( ~ ) Designation: D 6103- 97

Standard Test Method for Flow Consistency of Controlled Low Strength Material (CLSM) 1

This standard is issued under the fixed designation D 6103; the number immediately following the deslg~ation inthcates the year of original adoption or, in the case of revision, the year of last revision. A number in parentbeses iod]cates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapprovaL

1. Scope * 1.1 This test method covers the procedure for determination

of the flow consistency of fresh Controlled Low Strength Material (CLSM). This test method applies to flowable CLSM with a maximum particle size of 19.0 mm (3/4 in.) or less, or to the portion of CLSM that passes a 19.0 ram (3/4 in.) sieve.

1.2 The values stated in SI units are to be regarded as standard. The inch-pound equivalents are given for information only.

1.3 CLSM is also known as flowable fill, controlled density fill, soil-cement slurry, soil-cement grout, unshrinkable fill, K-Krete, and other similar names.

1.4 This standard does not purport to address all o f the safety concerns, i f any, associated with its use. It is the responsibility o f the user o f this standard to establish appropriate safety and health practices and determine the applicability o f regulatory limitations prior to use.


2.1 ASTM Standards: C 143 Test Method for Slump of Hydraulic Cement Con-

crete 2 C 172 Practice for Sampling Freshly Mixed Concrete 2 D 653 Terminology Relating to Soil, Rock, and Contained

Fluids a D 3740 Practice for Minimum Requirements of Agencies

Engaged in the Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction 3

D 4832 Test Method for Preparation and Testing of Con- trolled Low Strength Material (CLSM) Test Cylinders 3

D 5971 Practice for Sampling Freshly Mixed Controlled Strength Material 4

1)6023 Test Method for Unit Weight, Yield, and Air Con- tent (Gravimetric) of Controlled Low Strength MateriaP

D 6024 Test Method for Ball Drop on Controlled Low Strength Material to Determine Suitability for Load Ap- plication '~

t This test method ts under the jurisdiction of ASTM Committee DI 8 on Soil and Rock mid ]s the direct responsiblhty of Subeommittee DIS.15 on Stabilization with Admixtures.

Current edition approved March 10, 1997. Published September 1997. 2 Annual Book of ASTM Standards, Vot 04.02. �9 Annual Book of ASTM Standards, Vo104.08. *Annual Book of.4STM Standards, Vo104.09.

3. Terminology

3.1 Definitions--Except as follows in 3.2, all definitions are in accordance with Terminology D 653

3.2 Definitions o f Terms Specific to This Standard: 3.2.1 controlled low strength material (CLSM), n - -a mix-

ture of soil or aggregates, cementitious material, fly ash, water and sometimes chemical admixtures, that hardens into a material with a higher strength than the soil, but less than 84 00 kPa (1200 psi). Used as a replacement for compacted backfill, CLSM can be placed as a slurry, a mortar, or a compacted material and typically has strengths of 350 to 700 kPa (50 to 100 psi) for most applications.

3.2.2 f low consistency, n - -a measurement of the spread of a predetermined volume of CLSM achieved by removal of the flow cylinder within a specified time.

4. Summary of Test Method

4.1 An open-ended cylinder is placed on a flat, level surface and filled with fresh CLSM. The cylinder is raised quickly so the CLSM will flow into a patty. The average diameter of the patty is determined and compared to established criteria.

5. Significance and Use 5.1 This test method is intended to provide the user with a

procedure to determine the fluidity of CLSM mixtures for use as backfill or structural fill.

5.2 This test method is considered applicable to fresh CLSM containing only sand as the aggregate or having coarse aggregate small than 19.0 mm (3/4 in.). I f the coarse aggregate is larger than 19.0 nun (3Ain.), the test method is applicable when it is made on the fraction of CLSM passing a 19.0 m m (~/4 in.) sieve, with the larger aggregate being removed in accordance with the section on Additional Procedures for Large Maximum size Aggregate Concrete in Practice C 172.

No~ l--Removing the coarse aggregate will alter the characteristics of the mix and therefore will give information only about the remaining material It is suggested that for mixes containing coarse aggregate 19.0 nun (3/4 in.) or larger, a measurement of the slump is more appropriate.

5.3 For nonflowable CLSM, or for mixtures that do not come out of the flow cylinder easily, measure the slump as outlined in Test Method C 143.

5.4 This test method is one of a series of quality control tests that can be performed on CLSM during construction to monitor compliance with specification requirements. The other testa

*A Summary of Changes section appears at the end of this standard.

3 3 2


that can be used during construction control are Test Methods D 4832, D 6023, and D 6024.

Nol~ 2 Not withstanding the statements on precision and bias contained in this test method, the precision of this test method is dependent on the competence of the personnel performing it and the suitability of the equipment and facihties used. Agencies that meet the criteria of Practice D3740 generally are considered capable of competent and objective testing. Users of this test method are cautioned that compliance with Practice D 3740 does not in itself assure rehable testing. Rehable testing depends on several factors. Practice D 3740 provides a means of evaluating some of those factors.

6. Apparatus 6.1 Flow Cylinder--The flow cylinder shall be a 150 mm (6

in.) length of 76 m m (3 in.) inside diameter, straight tubing of steel, plastic or other non-absorbent material, non-reactive with CLSM containing Portland cement. Individual diameters and lengths shall be within +- 3 mm (l/s in.) of the prescribed dimensions. The flow cylinder shall be constructed such that the planes of the ends are parallel to one another and perpendicular to the longitudinal axis of the cylinder. The flow cylinder shall have a smooth interior, open at both ends and a rigid shape that is able to hold its dimensions and under conditions of severe use.

6.2 Sampling and Mixing Receptacle--The receptacle shall be a suitable container, wheelbarrow, etc., o f sufficient capacity to allow easy sampling and remixing of the CLSM.

6.3 Filling Apparatus--Scoop, bucket, or pail of sufficient capacity to facilitate filling of the flow cylinder in a rapid, efficient manner.

6.4 Nonporous Surface--A 0.6 m (2-fl) square, or larger, made of a nonporous material that is also noncorroding, such as acrylic, cast aluminum, or stainless steel. The surface must be smooth, free of defects, and rigid.

6.5 Miscellaneous Equipment: 6.5.1 Eming Device---Watch, clock, or stopwatch capable

of timing 1 s intervals. 6.5.2 Straight edge---A stiffmetal straightedge of any con-

venient length but not less than 254 mm (10 in.). The total length of the straightedge shall be machined straight to a tolerance of +0A mm (+0.005 in). The metal shall be made of suitable material that is noncorroding.

6.5.3 Measuring device, capable of measuring spread diameter. Must be able to measure a minimum of 6 ram (~,4 in.).

7. Test Sample 7.1 Obtain the sample of freshly mixed CLSM in accor-

dance with D 5971.

8. Procedure

8.1 Place the nonporous surface on a flat, level area that is free of vibration or other disturbances.

8.2 Dampen the flow cylinder with water and place it on end, on a smooth nonporous level surface. Hold firmly in place during filling.

8.3 Thoroughly remix the CLSM, the minimum amourtt necessary to ensure uniformity, in the sampling and mixing receptacle.

Noa~ 3---The test for flow consistency, unit weight, and air content (D 6023) must be started within 5 rain aries obtaining the final portion of

D 6103

the composite sample, Complete these tests as expothtiously as possible.

8.4 With the filling apparatus, scoop through the center portion of the receptacle and pour the CLSM into the flow cylinder. Fill the flow cylinder until it is just level full or slightly overfilled.

8.5 Strike offthe surface with a suitable straight edge, until the surface is flush with the top of the flow cylinder, while holding the flow cylinder in place. Remove any spillage away from the cylinder after strike off.

8.6 Within 5 s of filling and striking off, raise the flow cylinder quickly and carefully in a vertical direction. Raise the flow cylinder at least 15 cm (6 in.) by a steady upward lift with no lateral or torsional motion in a time period between 2 and 4 s. Complete the entire test from the start of filling through removal o f the flow cylinder without interruption within an elapsed time of 11/2 min.

8.7 Immediately measure the largest resulting spread diameter of the CLSM. Take two measurements of the spread diameter perpendicular to each other. The measurements are to be made along diameters which are perpendicular to one another.

Note 4--As the CLSM spreads, segregation may occur, with the water spreading beyond the spread of the cohesive mixture. The spread of the cohesive mixture should be measured. NOTE 5---For ease in measuring perl:,enthcuMr diameters, the surface

that the flow cylinder will be placed on can be marked with perpendicular lines and the cylinder centered where the lines cross.

Note 6~The average diameter of the CLSM patty typically is established by the specifying organization and may vary depending on how the CLSM is being used. For flowable CLSM used to readily fill spaces (without requiring vibration), the average diameter of the patty typically is 20 to 30 cm (8 to 12 in.).

9. Report 9.1 Include the following information in the report: 9.1.1 Sample identification. 9.1.2 Identification of individual performing the test

method. 9.1.3 Date the test is performed. 9.1.4 Record the two measurements to the nearest I era(�89

in.). Compute the average of the two measurements rounded offto the nearest 5 mm (lAin.), and report as the average flow consistency of the CLSM.

10. Precision and Bias 10.1 Precision---Data are being evaluated to determine the

precision of this test method. Additionally, Subcommittee D 18.15 is seeking pertinent data from users of the test method. 5

10.2 Bias--No statement on bias can be prepared because there are no standard reference materials.

11. Keywords

11.1 backfill; CLSM; construction control; flowable fill; flow consistency; flow cylinder; mix design; quality control; soil stabilization

s Anyone having data pertinent to the precision of this test method or wishing to participate in a round robin test, contact the D18.15 Subcommittee Chairman at ASTM Headquarters.

333


q~') D 6103

APPENDIX

(Nonmandatory Information)

XL Rationale

XI.1 This test method was developed to provide an accepted, consensus method of measuring the flow characteristics of CLSM. Although CLSM may be mixed and delivered like concrete, the mixture typically is much more fluid than

concrete so that it readily will fill voids and spaces. This test method provides a procedure to quantify the flow characteristics.

SUMMARY O F CHANGES

This test method previously was provisional standard (PS) 28 and has been revised and approved as a full consensus standard.

(1) This standard previously had the designation PS 28-95, a provisional standard. (2) The differences between this version of the standard and the previous one are as follows: (3) Addition of Sections 1.3, 5.4, 6.4, 6,5, 8.1, 8.2, 8.3, 8.4,

Note 2, Note 4, Note 5, Note 6, Appendix XI . I and this section. (4) Revised wording m Sections 3.2.1, 3.2.2, 4.1, 6. l, 8.2, 8.4, 8.5, 8.6, 9.1, 10.1, 11 and Note 4 (5) SI units made the standard

The American Society for Testing and Materials takes no position respecting the validity of any patent tights asserted in connection with any item mentioned m this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the nak of infringement of such rights, are entirbiy their own responsibility.

ThiS standard is subject to rewsion at any time by the responsible technical committee and must be reviewed every five yeats and i f not revised,, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for ~ l i t i ona l standards and shou/d be addressed to ASTM Headquarters. Your comments will receive careful consideration at a meeting of the responsible technic.a/committee, which you may attend ff you fee/that your comments have not received a fair hearing you should make your views known to the ASTM Committee on Standards. 100 Barr Harbor Drive, Wast Conshohocken, PA 19428.

334


STP1331 -EB/May 1998

Author Index

A

Abelleira, A., 124 Ash, J. R., 200

B

Baker, T. H. W., 275 Benavidez, A. A., 213 Bennet, D., 151 Benson, J. M, 165 Berke, N. S., 124 Black, D. C., 180 Brinkley, D., 231 Brogdon, J. F., 45

C

Clem, D. A., 137 Crouch, L. K., 45

D

Davidson, J. S., 108 Dockter, B. A., 13 Dolen, T. P., 213

E

Eaton, S. J., 255

G

Gamble, R., 45 Gardner, M. R., 194 Gray, D. D., 180 Green, B. H., 151

H

Hegarty, J. R., 255 Hepworth, H. K., 108 Hitch, J. L., 3 Hook, W., 137 Hoopes, R. J., 87, 265 Hooyman, J.L., 108 Howard, A., 285

335

K

Keck, R. H., 296 Kerns, L., 67 Kraus, R. N., 27 Kunzer, B. A., 306

L

Landwermeyer, J. S., 67

M

Mason, T. F., 210 McGrath, T. J., 237, 265 Mueller, P. E., 231 Mullarky, J. I., 102

N

Naik, T. R., 27

O

Ohlheiser, T. R., 60

P

Pickering, D. G., 124 Pons, F., 67

R

Ramme, B. W., 27 Reddy, T. P., 180 Riggs, E. H., 296

S

Scavuzzo, R., 306 Selig, E. T., 237 Snethen, D. R., 165 Staheli, K., 151 Sturzl, R. F., 27



T Walley, D. M., 151 Webb, M. C., 237

Tucker, C. J., 45

W Z

Walker, M. P., 200 Ziemkiewicz, P. F., 180


STP1331 -EB/May 1998

Subject Index

A

Access holes, 210 Acid mine drainage, 180 Admixtures, 108 Aggregate, 45, 60, 194

base, 67 Air entrainment, 45, 124 Airport runways, 255 American Concrete Institute, 3 Approach embankments, 165 Asphalt surface, 275 ASTM standards, 102, 151, 194,

285 C 618, 13 C 670, 306 C 802, 306

B

Backfill, 3, 67, 102, 194, 296 electrical resistivity, 124 embankment/abutment, 165 field test, 237 foundation, 137 frost penetration, 275 granular, 210 hydraulic, 180 low strength, 231 pipelines, 137 sequential application use, 200 tests, 87 utility trench, 102, 231

Bearing strength, 67 Bedding factor, 265 Bentonite, 151 Bleeding, 27, 87 Boring machine, 151 Bridge applications, 137, 165

C

California bearing ratio, 67, 87 Cement, 306 Clay, 237, 255 Coal ash, 3, 13, 27, 151, 180

337

Compression, 87 triaxial, 265

Compressive strength, 27, 45, 87, 213, 237

cylinder unconfined, 67 plastic portland cement concrete,

231 Concrete, 237

cutoff walls, 213 plastic, 213 portland cement, 231 roller compacted, 306 seawall, 210

Conductivity, 87 Construction application,

recycled glass, 60 Construction, bridge, 165 Construction control, 285

field test, 306 Construction procedures, 137 Corrosion, 124 Cross-contamination, 108

D

Deflections, pipe, 237 Deformation, 213 Drainage characteristics, 124 Dry scrubber, 13 Durability requirements, 306

E

Earth dams, 213 Electrical resistivity, 124 Erosion, water, 210 Excavatability, 67, 102 Excavation

restoration, 231 sequential, 200

F

Field test, 237, 285, 306 microtunneling, 151

Finite element analyses, 265



Fluidized bed ash, 180 Fluidized bed boiler, 27 Fly ash, 13, 237, 265, 296

Class C, 151 tests using, 3, 27

Foundation, building, backfill, 137

Freeze-thaw, 87 Frost action, 275

G

Glass, recycled, 60 Groundwater control, 200 Grout, 180 Grout pump emplacement

equipment, 108

H

Heat of neutralization, 306 Hydraulic backfilling, 180

K

K-Krete, 3

L

Leachates, 27 Limestone screenings, 45 Load bearing characteristics, 87

M

Microtunneling, 151 Mines, abandoned, hydraulic

backfilling, 180 Mix proportion, 27, 45, 137 Model, gravity spread prediction,

180 Modulus of subgrade reaction,

67 Mortar, flowable, 108, 296

N

National Ready Mixed Concrete Association, 45, 102

P

Penetration resistance, hand-held, 67

Performance, non-shrink slurry backfill, 231

Permeability, 27, 87 flow-pump, 213

Pipe, 60, 137, 200, 275 bedding, 265 buried, 255, 265, 285 buried, field test, 237, 285 high density polyethylene, 237 trench restoration, 231

Plastic, high density polyethylene, 237

Plastic concrete, 213 Processed glass aggregate, 60

Q

Quality control, 194, 285

R

Radioactively contaminated systems, 108

Recycling, 60

S

Sand, tunnel excavation, 151 Scrubber, dry, 13 Seawall, concrete, 210 Segregation, 45 Selig bulk modulus, 265 Settlement, 27

differential, 165 Shaft stabilization, 151 Shear, 87

strength, triaxial, 213 Shrinkage, 27 Slump, 231 Slurry, 231, 285 Soil, 87, 124, 296

soil-cement, 306 Duncan hyperbolic, 265 granular, 255 movement, 200 native, 194 stabilization, 285


Specification, composite, CI_SM, 296

Steel, corrugated, 237 Steel coupon corrosion

experiments, 124 Street/cut repair applications,

67 Strength, 265, 306

gain, 102 mix design lowering, 237

Subgrade modulus, 67 Subsidence, 67, 87, 180

T

Tank stabilization, 108 Thermal conductivity, 87, 275 Thermal properties, 275 Transportation agencies, state,

296 Tremie backfill, 200 Tremie placing, 213 Trenches, 194, 200, 231,275

bedding factors, 265 safety, 255

INDEX 339

U

Underwater injection, 108 Utility trench applications, 102,

231, 275 Void, 210 Void filling, 3, 108

W

Water erosion, 210 Water leaching tests, 27 Water service lines, 275 Water treatment facility, 108

Y

Yield stress fluid, 180 Young's moduli, 237


ISBN 0-8031-2477-5
