ASSESSMENT OF DESIGN AND PROPERTIES FOR FLOWABLE FILL

USAGE IN HIGHWAY PAVEMENT CONSTRUCTION FOR CONDITIONS IN FLORIDA

By

WEBERT LOVENCIN

A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

2007

Copyright 2007

by

Webert Lovencin

I would like to dedicate this dissertation to my parents, my lovely wife, April Adrienne Raines-Lovencin, my sister, Natacha Egland, my nieces and nephews, and to the tax payers who help fund

the public education systems in the state of Florida.

iv

ACKNOWLEDGMENTS

I would like to acknowledge those individuals who were involved in the advance-

ment of this research and throughout my studies. First, I would like to express my most

sincere gratitude to Dr. Fazil T. Najafi, my advisor and supervisory committee chairman.

Dr. Najafi has been a mentor, a friend, and a continuous source of encouragement both

professionally and personally. I thank Dr. Mang Tia, the cochair of my committee, for

his valuable advice and suggestions throughout the research study and dissertation.

I would also like to thank the other members of my committee, Dr. Walter E.

Dukes, Dr. David J. Horhota, Mr. Timothy J. Ruelke, and Mr. Michael J. Bergin, for their

continued support, constructive comments, and recommendations during my tenure at the

University of Florida.

Many debts of gratitude go out to the folks at the Florida Department of Transpor-

tation State Materials Office (Physical Lab and Geotechnical Divisions) and District 2 –

Materials Office in Lake City, who assisted me with this research study. These

individuals include Richard Delorenzo, Craig Roberts, Terry Thomas, Tim Blanton, Mike

Davis, Glenn Johnson, Ben Watson, Willie Henderson, Chris Falade, Bobby Ivory, Scott

Clayton, and Daniel Langley.

I would also like to express my gratitude to Drs. Claude Villiers and Jonathan F.

Earle, and Mrs. Margie Williams for their continuous encouragement and support, as well

as Mrs. Candace J. Leggett for her immense patience and efficient editorial assistance

with writing this dissertation.

v

Finally, I want to specially thank my savior, God (Jehovah), my family in the

United States and abroad from where they have always conferred me their support and

for believing in me the way they do. But above all, I want to deeply thank my beloved

wife, April, for her immense love, indispensable help and patience. April has been the

sole person responsible for my achieving this goal. She has been the wall containing my

worry, my best critic, and my greatest supporter.

vi

TABLE OF CONTENTS page

ACKNOWLEDGMENTS ................................................................................................. iv

LIST OF TABLES...............................................................................................................x

LIST OF FIGURES .......................................................................................................... xii

ABSTRACT.................................................................................................................... xvii

CHAPTER

1 INTRODUCTION ........................................................................................................1

1.1 Background............................................................................................................1 1.2 Problem Statement.................................................................................................2

1.2.1 Strength........................................................................................................2 1.2.2 Shrinkage.....................................................................................................3

1.3 Hypothesis .............................................................................................................5 1.4 Objectives ..............................................................................................................6 1.5 Scope......................................................................................................................6 1.6 Importance of Research .........................................................................................6 1.7 Research Approach................................................................................................7 1.8 Outline of the Dissertation.....................................................................................9

2 LITERATURE REVIEW ...........................................................................................10

2.1 Introduction..........................................................................................................10 2.2 Flowable Fill Technology....................................................................................10

2.2.1 Introduction ...............................................................................................10 2.2.2 Types of Flowable Fill...............................................................................11 2.2.3 Advantages of Using Controlled Low Strength Material (CLSM) ...........11 2.2.4 Engineering Characteristics of CLSM.......................................................13 2.2.5 Uses of Flowable Fill.................................................................................13 2.2.6 Delivery and Placement of Flowable Fill ..................................................14 2.2.7 Limits.........................................................................................................15

2.3 Specifications, Test Methods, and Practices........................................................15 2.3.1 Introduction ...............................................................................................15 2.3.2 ASTM Standard Test Methods..................................................................17

vii

2.3.2.1 Standard Test Method for Preparation and Testing of CLSM Test Cylinders (ASTM D 4832-02) ..............................................17

2.3.2.2 Standard Practice for Sampling Freshly Mixed CLSM (ASTM D 5971-96) ..................................................................................18

2.3.2.3 Standard Test Method for Unit Weight, Yield, Cement Content and Air Content (Gravimetric) of CLSM (ASTM D 6023-96) ................18

2.3.2.4 Standard Test Method for Ball Drop on CLSM to Determine Suitability for Load Application (ASTM D 6024-96)..............................19

2.3.2.5 Standard Test Method for Flow Consistency of CLSM (ASTM D 6103-96) ..................................................................................20

2.3.3 Other Currently Used and Proposed Test Methods...................................20 2.3.4 Specifications by the State Departments of Transportation ......................22 2.3.5 Use of Flowable Fill in the State of Florida ..............................................24

2.3.5.1 Material Specifications (Section 121-2)..........................................24 2.3.5.2 Construction Requirements and Acceptance (Section

121-5, 121-6) ............................................................................................25 2.3.5.3 Guideline for Construction Requirements and Acceptance

(Section 121-5, 121-6) ..............................................................................25 2.4 Early Set and Strength Development...................................................................26

2.4.1 Introduction ...............................................................................................26 2.4.2 Behavior of Slurries...................................................................................26 2.4.3 Early Hydration of Cement Particles.........................................................27 2.4.4 Influence of Water to the Hydration of Cement ........................................28 2.4.5 Effects of Set Accelerator on Hydration of Cement..................................29 2.4.6 Set Time.....................................................................................................29 2.4.7 Strength Development ...............................................................................30 2.4.8 Use of Mineral Admixture (Fly Ash and Granulated Ground Blast

Furnace Slag) in Flowable Fill.........................................................................31 2.4.8.1 Fly ash .............................................................................................31

2.4.8.2 Slag .........................................................................................................34 2.4.8.3 Difference between fly ash and slag................................................36 2.4.8.4 Specific applications .......................................................................36 2.4.8.5 Mixture proportioning/mixture compliance ....................................36

2.4.9 Effect of Moisture on Strength ..................................................................37 2.5 Strength Prediction Models .................................................................................38

2.5.1 Introduction ...............................................................................................38 2.5.2 Hamilton County–Removability Index .....................................................38 2.5.3 Bhat’s Study ..............................................................................................39 2.5.4 NCHRP–Study ..........................................................................................40

2.6 FDOT/UF Flowable Fill Study............................................................................42

3 MATERIALS AND LABORATORY EXPERIMENTAL PROGRAM...................44

3.1 Introduction..........................................................................................................44 3.2 Experimental Design ...........................................................................................44

3.2.1 Rationale for Selecting Mixture Parameters..............................................44 3.2.2 Mixture Proportioning ...............................................................................46

viii

3.2.3 Specimen Sample Collection per Batch Mix.............................................49 3.2.4 Specimen Molds ........................................................................................49 3.2.5 Fabrication of Flowable Fill Specimens....................................................50

3.2.5.1 Preparation of molds .......................................................................50 3.2.5.2 Mixing of flowable fill ....................................................................50 3.2.5.3 Casting of flowable fill....................................................................53

3.3 Limerock Bearing Ratio Test (Florida Test Method 5-515)................................55 3.4 Compressive Strength Test ..................................................................................60 3.5 Proctor Penetrometer Test ...................................................................................64 3.6 Drying Oven ........................................................................................................65 3.7 Drying Shrinkage of Flowable Fill Mixtures.......................................................65

3.7.1 Method 1....................................................................................................66 3.7.2 Method 2....................................................................................................69 3.7.3 Method 3....................................................................................................70

3.8 Materials ..............................................................................................................71 3.8.1 Cement.......................................................................................................71 3.8.2 Fly Ash ......................................................................................................72 3.8.3 Blast Furnace Slag.....................................................................................72 3.8.4 Aggregates.................................................................................................73

3.8.4.1 Aggregate gradation ........................................................................74 3.8.4.2 Physical properties, absorption and moisture content .....................76 3.8.4.3 Storage of fine aggregates ...............................................................77

3.8.5 Admixtures ................................................................................................78 3.8.6 Water .........................................................................................................78

4 LABORATORY RESULTS AND DISCUSSIONS ..................................................79

4.1 Introduction..........................................................................................................79 4.2 Laboratory Results...............................................................................................79

4.2.1 Limerock Bearing Ratio (LBR).................................................................79 4.2.2 Compressive Strength (psi) .......................................................................79 4.2.3 Volume Change .........................................................................................84 4.2.4 Proctor Penetrometer Setting Strength (psi)..............................................85 4.2.5 Strength Gained Between 28 and 56 Days ................................................91 4.2.6 LBR Oven Sample Results........................................................................92

4.3 Factors Affecting Strength...................................................................................96 4.3.1 Water-to-Cement (w/c) Ratio ....................................................................96 4.3.2 Cement Content .........................................................................................98 4.3.3 Effect of Air Content on Strength ...........................................................100 4.3.4 Effect of Mineral Admixtures (Fly Ash and Blast Furnace Slag) on

Strength ..........................................................................................................101 4.4 Comparison of Mix Using Type I/II Cement vs. Type I Cement ......................102 4.5 Drying Shrinkage (Volume Change) .................................................................105 4.6 Interpretation of Plastic Test Results.................................................................108

ix

5 STATISTICAL ANALYSIS ....................................................................................111

5.1 Introduction........................................................................................................111 5.2 Statistical Model Derivation ..............................................................................111 5.3 Accelerating Strength Testing ...........................................................................118

5.3.1 Background..............................................................................................118 5.3.2 Accelerated Curing..................................................................................119 5.3.3 Analysis ...................................................................................................119 5.3.4 Confidence Band for Regression Line ....................................................124 5.3.5 Estimate of Later Strength.......................................................................124 5.3.6 Analysis on Other Samples .....................................................................125

5.4 Model Validation and Evaluation of Accuracy .................................................128 5.4.1 Varying Strength Prediction Models for Trend.......................................128 5.4.2 Comparison of Strength Prediction Models ............................................145 5.4.3 Mixture Design Examples to Validate Models .......................................150

5.5 Summary of Model Equations and Limitations.................................................157

6 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS ............................164

6.1 Summary............................................................................................................164 6.2 Conclusions........................................................................................................166 6.3 Recommendations..............................................................................................167

APPENDIX

A FLOWABLE FILL STUDY BATCH MIX DESIGN MATRIX.............................169

B LBR AND COMPRESSIVE STRENGTH DATA OBTAINED IN THE LABORATORY.......................................................................................................185

C ANALYSIS OF VARIANCE (ANOVA), PARAMETERS, AND STANDARD ERROR FOR MODELS....................................................................200

D ESTIMATED 28- AND 56-DAY STRENGTH.......................................................215

LIST OF REFERENCES.................................................................................................252

BIOGRAPHICAL SKETCH ...........................................................................................257

x

LIST OF TABLES

Table page 2-1. Current ASTM standards on controlled low strength material (CLSM) ...................16

2-2. States surveyed and their specification on flowable fill ............................................22

2-3. Specified acceptance strengths and ages ...................................................................23

2-4. Suggested mixture proportions, lb/yd3 .....................................................................23

2-5. FDOT materials specification requirements..............................................................24

2-6. FDOT flowable fill mix design .................................................................................25

2-7. Removability modulus (RE) ......................................................................................39

3-1. Mixture parameters....................................................................................................45

3-2. Summary of sample specimens collected per mix.....................................................49

3-3. Properties of fresh flowable fill (Experiment 1)........................................................56

3-4. Properties of fresh flowable fill (Experiment 2)........................................................57

3-5. Specifications for LBR test equipment......................................................................59

3-6. Chemical composition of cement used......................................................................71

3-7. Physical characteristics of cement.............................................................................72

3-8. Chemical and physical analyses of fly ash ................................................................73

3-9. Chemical and physical analyses of blast furnace slag...............................................73

3-10. Fine aggregate location source ................................................................................74

3-11. ASTM C33-02A and FDOT specifications for fine aggregate gradation ...............75

3-12. Physical properties of fine aggregates (silica sand).................................................76

4-1. LBR strength results for Experiment #1....................................................................80

xi

4-2. LBR strength results for Experiment #2....................................................................81

4-3. Compressive strength results for Experiment #1.......................................................82

4-4. Compressive strength results for Experiment #2.......................................................83

4-5. Volume change results for Experiment #1 ................................................................86

4-6. Volume change results for Experiment #2 ................................................................87

4-7. Mix proportions and proctor penetrometer results for Experiment #1......................88

4-9. Two-day oven LBR strength results for Experiment #1............................................93

4-10. Two-day oven LBR strength results for Experiment #2..........................................94

4-11. Comparison of mixture components and their influence on accelerated 2-day oven and 28-day LBR strength ......................................................................95

4-12. Comparison of mixture components and their influence on percent volume change........................................................................................................106

5-1. Standard error of regression coefficients for equations relating mixture constituents to LBR, compressive strength and percent volume change ...............116

5-2. Estimation of confidence interval for 28-day strength ............................................122

5-3. Summary of regression equations for accelerated (oven) 28-day and 56-day LBR strength .......................................................................................127

5-4. NCHRP’s CLSM mixture proportions and fresh properties [38]............................146

5-5. Comparison of the NCHRP measured and predicted 28-day strength for air-entrained mixtures strength prediction model.............................................147

5-6. Comparison of estimated 28-day compressive strength ..........................................149

5-7. Summary of materials required for validation mixtures..........................................154

5-8. Summary of plastic properties of validation mixture models..................................155

5-9. Comparison of estimated and experimental results for batch mixes 1v through 6v .....................................................................................158

5-10. Comparison of estimated and experimental results for batch mixes 7v through 11v ...................................................................................159

5-11. Summary of recommended strength prediction equations listed with variables and range.........................................................................................162

xii

LIST OF FIGURES

Figure page 1-1. Laboratory task process ...............................................................................................8

2-1. Influence of water/cement (w/c) ratio on the setting of Portland cement paste ........28

2-2. Bhat’s strength prediction model...............................................................................40

3-1. Concrete mixer used in study ....................................................................................51

3-2. Pressure meter test for air content .............................................................................52

3-3. Cast flowable fill in LBR samples.............................................................................53

3-4. Cast flowable fill in 4-in. × 8-in. (compressive strength) samples............................54

3-5. Cast flowable fill in 6-in. × 12-in. (volume change) samples ...................................54

3-6. Cross section of seated LBR penetration piston [30] ................................................58

3-7. LBR machine.............................................................................................................59

3-8. Graph example showing typical load penetration curve that requires no correction...............................................................................................61

3-9. Graph example showing correction of typical load penetration curve for small surface irregularities........................................................................62

3-10. Typical set-up for compressive strength test ...........................................................63

3-11. Typical proctor penetrometer ..................................................................................64

3-12. Test set-up for measuring shrinkage using LVDTs.................................................68

3-13. Schematic of test set-up for measuring shrinkage using LVDTs ............................68

3-14. Three-dial gauge reading method ...........................................................................69

3-15. Dial gauge shrinkage reading being taken...............................................................70

3-16. Gradation of fine aggregates–ASTM specs.............................................................75

xiii

3-17. Gradation of fine aggregates–FDOT specs .............................................................76

3-18. Storage and removal of fine aggregates ..................................................................77

4-1. Load deformation responses for batch mix #4, at 3-, 28- and 56-day duration.........84

4-2. Percent increase in 56-day strength as compared to 28-day strength (LBR) ............91

4-3. Percent increase in 56-day strength as compared to 28-day strength (psi) ...............92

4-4. Relationship between 28-day bearing strength (LBR) and w/c ratio at 7.5% design air content .....................................................................................................96

4-5. Relationship between 28-day bearing strength (LBR) and w/c ratio at 17.5% design air content .......................................................................96

4-6. Relationship between 28-day compressive strength (psi) and w/c ratio at 7.5% design air content .........................................................................97

4-7. Relationship between 28-day compressive strength (psi) and w/c ratio at 17.5% design air content .......................................................................97

4-8. Relationship between 28-day bearing strength (LBR) and cement content at 7.5% design air content ...............................................................98

4-9. Relationship between 28-day bearing strength (LBR) and cement content at 17.5% design air content .............................................................98

4-10. Relationship between 28-day compressive strength (psi) and cement content at 7.5% design air content ...............................................................99

4-11. Relationship between 28-day compressive strength (psi) and cement content at 17.5% design air content .............................................................99

4-12. Relationship between 28-day LBR strength and cement content............................99

4-13. Relationship between 28-day compressive strength (psi) and cement content .....100

4-14. Effect of mineral admixtures on 28-day LBR strength .........................................101

4-15. Effect of mineral admixtures on 56-day LBR strength .........................................102

4-16. Compressive strength (psi) of Type I/II vs. Type I cement for BM15..................103

4-17. LBR strength of Type I/II vs. Type I cement for BM15 .......................................103

4-18. Compressive strength (psi) of Type I/II vs. Type I cement for BM 25.................103

4-19. LBR strength of Type I/II vs. Type I cement for BM 25 ......................................104

xiv

4-20. Compressive strength (psi) of Type I/II vs. Type I cement for BM 48.................104

4-21. LBR strength of Type I/II vs. Type I cement for BM 48 ......................................104

4-22. Compressive strength (psi) of Type I/II vs. Type I cement for BM 54.................105

4-23. LBR strength of Type I/II vs. Type I cement for BM 54 ......................................105

4-24. Effect of w/c ratio on volume change....................................................................107

4-25. Effect of cement content on volume change .........................................................107

4-26. Effect of mineral admixtures on volume change...................................................108

4-27. Flow diameter vs. sand-to-water ratio ...................................................................110

5-1. Residuals versus fitted values plot (28-day LBR) ...................................................116

5-2. Residuals versus fitted values plot (28-day psi) ......................................................117

5-3. Residuals versus fitted values plot (% volume change) ..........................................117

5-4. Accelerated curing vs. 28-day normal curing strength............................................123

5-5. Accelerated curing vs. 28-day normal curing strength for all mixtures ..................126

5-6. Accelerated curing vs. 56-day normal curing strength for all mixtures ..................126

5-7. Estimated 28-day LBR strength vs. cement content at fixed air (15%) and fixed 0% mineral admixture ............................................................................130

5-8. Estimated 56-day LBR strength vs. cement content at fixed air (15%) and fixed 0% mineral admixture ............................................................................130

5-9. Estimated 28-day compressive strength vs. cement content at fixed air (15%) and fixed 0% mineral admixture...................................................131

5-10. Estimated 28-day compressive strength vs. cement content at fixed air (15%) and fixed 0% mineral admixture...................................................131

5-11. Estimated volume change vs. cement content at fixed air (15%) and fixed 0% mineral admixture ...................................................................................132

5-12. Estimated 28-day LBR strength vs. w/c ratio at fixed air (15%) and fixed 0% mineral admixture ...................................................................................132

5-13. Estimated 56-day LBR strength vs. w/c ratio at fixed air (15%) and fixed 0% mineral admixture ...................................................................................133

xv

5-14. Estimated 28-day compressive strength vs. w/c ratio at fixed air (15%) and fixed 0% mineral admixture ............................................................................133

5-15. Estimated 56-day compressive strength vs. w/c ratio at fixed air (15%) and fixed 0% mineral admixture ............................................................................134

5-16. Estimated volume change vs. w/c ratio at fixed air (15%) and fixed 0% mineral admixture ...................................................................................134

5-17. Estimated 28-day LBR strength vs. cement content at fixed air (8%) and fixed 20% fly ash mineral admixture .....................................................................135

5-18. Estimated 56-day LBR strength vs. cement content at fixed air (8%) and fixed 20% fly ash mineral admixture .....................................................................135

5-19. Estimated 28-day compressive strength vs. cement content at fixed air (8%) and fixed 20% fly ash mineral admixture .......................................136

5-20. Estimated 56-day compressive strength vs. cement content at fixed air (8%) and fixed 20% fly ash mineral admixture .......................................136

5-21. Estimated volume change vs. cement content at fixed air (8%) and fixed 20% fly ash mineral admixture .....................................................................137

5-22. Estimated 28-day LBR strength vs. w/c ratio at fixed air (8%) and fixed 20% fly ash mineral admixture .....................................................................137

5-23. Estimated 56-day LBR strength vs. w/c ratio at fixed air (8%) and fixed 20% fly ash mineral admixture .....................................................................138

5-24. Estimated 28-day compressive strength vs. w/c ratio at fixed air (8%) and fixed 20% fly ash mineral admixture ..............................................................138

5-25. Estimated 56-day compressive strength vs. w/c ratio at fixed air (8%) and fixed 20% fly ash mineral admixture ..............................................................139

5-26. Estimated volume change vs. w/c ratio at fixed air (8%) and fixed 20% fly ash mineral admixture .....................................................................139

5-27. Estimated 28-day LBR strength vs. cement content at fixed air (10%) and fixed 50% ground granulated blast-furnace slag mineral admixture...............140

5-28. Estimated 56-day LBR strength vs. cement content at fixed air (10%) and fixed 50% ground granulated blast-furnace slag mineral admixture...............140

5-29. Estimated 28-day compressive strength vs. cement content at fixed air (10%) and fixed 50% ground granulated blast-furnace slag mineral admixture...............141

xvi

5-30. Estimated 56-day compressive strength vs. cement content at fixed air (10%) and fixed 50% ground granulated blast-furnace slag mineral admixture...............141

5-31. Estimated volume change vs. cement content at fixed air (10%) and fixed 50% ground granulated blast-furnace slag mineral admixture .....................142

5-32. Estimated 28-day LBR strength vs. w/c ratio at fixed air (10%) and fixed 50% ground granulated blast-furnace slag mineral admixture .....................142

5-33. Estimated 56-day LBR strength vs. w/c ratio at fixed air (10%) and fixed 50% ground granulated blast-furnace slag mineral admixture .....................143

5-34. Estimated 28-day compressive strength vs. w/c ratio at fixed air (10%) and fixed 50% ground granulated blast-furnace slag mineral admixture .....................143

5-35. Estimated 56-day compressive strength vs. w/c ratio at fixed air (10%) and fixed 50% ground granulated blast-furnace slag mineral admixture .....................144

5-36. Estimated volume change vs. w/c ratio at fixed air (10%) and fixed 50% ground granulated blast-furnace slag mineral admixture...............................144

5-37. Comparison of measured and predicted 28-days strength.....................................147

5-38. Comparison of estimated 28-day compressive strength for Bhat, NCHRP, and dissertation models...........................................................................150

5-39. Comparison of estimated 28-day compressive strength for NCHRP and dissertation models ..........................................................................................150

5-40. Comparison of measured and predicted 28-day LBR strength of validation mixtures of model...................................................................................................160

5-41. Comparison of measured and predicted 28-day compressive strength of validation mixtures of model..................................................................................160

5-42. Comparison of measured and predicted 28-day (oven) LBR strength of validation mixtures of model..................................................................................161

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Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

ASSESSMENT OF DESIGN AND PROPERTIES FOR FLOWABLE FILL USAGE IN HIGHWAY PAVEMENT CONSTRUCTION

FOR CONDITIONS IN FLORIDA

By

Webert Lovencin

May 2007

Chair: Fazil T. Najafi Cochair: Mang Tia Major Department: Civil and Coastal Engineering

Flowable fill, also known as controlled low-strength material (CLSM), is a self

compacting cementitious material primarily used as a backfill in lieu of compacted soil.

Flowable fill is an extremely versatile construction material that has been used in a wide

variety of applications. There are two types of flowable fill, excavatable and

nonexcavatable. An excavatable flowable fill mixture is considered excavatable when

the 28-day compressive strength is 100 psi. Nonexcavatable mixtures are mixes in which

the minimum design strength is at 125 psi or greater. The ability to control and predict

the strength and volume change (shrinkage) is an important aspect to consider when

designing a flowable fill mixture. Various studies have been conducted to better

understand and predict quality control measures such as the strength and the occurrence

of shrinkage in flowable fill.

xviii

The aim of this research was to vary components of excavatable flowable fill

mixtures. A 4 × 3 × 2 × 3 factorial design (i.e., 4 levels of cement, 3 levels of mineral

admixtures, 2 levels of air content, and 3 levels of water/cement ratio) was applied to

evaluate the compressive strength, limerock bearing ratio (LBR) strength, and shrinkage.

With this study’s objective in mind, a total of 58 mixtures were selected from the

factorial design matrix and batched in a laboratory. The strength of the mixtures was

evaluated at 6 hours, 1 day, 2 days oven cured, 3 days, 28 days and 56 days.

Mathematical models were developed to predict the LBR, compressive strength,

and volume change. An accelerated curing method, along with prediction models, was

developed to help estimate long-term strength of flowable fill. Based on the performance

of the statistical analysis, it was found that the models developed from this study

provided good correlations for estimating strength and volume change of excavatable

flowable fill mixture. Though the models were found to provide good correlations, the

formula developed for estimating the volume change was found to be unacceptable for

design application. This study provides a rational method for engineers to utilize when

designing flowable fill mixture.

1

CHAPTER 1 INTRODUCTION

1.1 Background

The construction industry searches for the most cost and time efficient means for

completing its projects. Many of these projects include cutting and backfilling trenches

for structure and drainage pipe installation. Often cutting and backfilling trenches

disrupts major traffic arteries. Standard practice for backfilling trenches includes soil

being placed in 6-inch lifts and compacted until a minimum density threshold is achieved.

The soil tests required to set and verify the density threshold in the field require several

days to complete. To help in this matter, newer forms of construction material have been

introduced. The most common is called controlled low strength material (CLSM), also

known as flowable fill. The use of flowable fill negates the need for placing the 6-inch

lifts and eliminates the need for practically all tests, excluding a simple in-place soil test.

Flowable fill is an extremely versatile construction material that has been used in a

wide variety of applications. Among the many successful applications of flowable fill are

slurried backfill for walls, culverts, pipe trenches, bridge abutments and retaining walls;

backfill for abandoned underground structures (including mines) or tanks; and floating

slab foundation for lightweight structures [1,2]. Flowable fill offers a number of

advantages over conventional earthfill materials that require controlled compaction in

layers [2]. The advantages include ease of mixing and placement, the ability to flow into

hard-to-reach places, and the self-leveling characteristic of the fill.

2

1.2 Problem Statement

1.2.1 Strength

Flowable fill answers the need for a fill that allows prompt return to traffic flow,

does not settle, does not require vibration or other means of compaction, can be

excavated, is fast to place, and safer than other forms of fill. One requirement typically

encountered with flowable fill is the need to limit the maximum compressive strength [3].

This requirement is necessary in cases where future excavation may be required for

maintenance and repair of embedded utilities. To predict the long-term strength and the

excavatability of flowable fill using conventional excavating equipment, many

approaches are employed. One approach for predicting whether or not a flowable fill mix

is excavatable is to develop a correlation using its early age strength and long-term

strength. For example, a mixture exhibiting strength that is less than 100 psi would be

classified as being excavatable. Mixtures resulting in strengths higher than 100 psi would

be very difficult to excavate and would be termed nonexcavatable.

According to Digiola and Brenda [4], the proper control of strength in flowable fill

is an important criterion used to develop a mix design. Despite this known criterion, a

review of literature shows few studies published in proper control of strength in flowable

fill. In using flowable fill, not only is it required to meet minimal strengths to maintain

and provide suitable structural support, but the maximum strength development must also

be controlled to allow for future excavation. A study by Pons et al. [3] shows that in

1994, about 80% of the concrete producer market producing flowable fill carried the

understanding or expectation for excavatability. For these reasons, design strengths often

must be assigned a range of strengths from “minimally acceptable” to “maximum

allowable.”

3

Many state agencies specify acceptance strengths at a curing age of 28 days, while

others include 56-day strength in their specifications [5]. In some cases, the maximum

strengths are listed to enable excavation for a later date. Some state agencies, however,

list the target strengths instead of maximum strengths which causes some concrete plants

to produce flowable fill mixes with minimum strength, as they would normally for

Portland cement concrete. In general, the desired strength is the maximum hardness that

can be excavated at a later date using conventional excavating equipment. The existing

Florida Department of Transportation (FDOT) flowable fill specification requires field

tests to verify that a minimum penetration resistance is achieved.

Flowable fill mixtures are usually designed on the basis of compressive strength

development. Little information is available in which the terminology used for

describing the strength of flowable fill is something other than compressive strength.

This method of describing the quality of flowable fill is conventional throughout the

ready mix industry. Because flowable fill is used as a backfill material similar to soil, a

suitable unit instead of compressive strength, such as limerock bearing ratio (LBR), is

needed to describe the in-place bearing strength of the flowable fill mixture. Making

such a change would alter the state-of-the-art for relating the quality of strength for

flowable fill mixtures.

1.2.2 Shrinkage

To understand why shrinkage occurs, one must first understand the materials in

flowable fill. Just as shrinkage occurs in concrete, it also occurs in flowable fill.

Cement, a key ingredient in flowable fill, when mixed with water forms a paste and a

chemical reaction called “hydration” occurs. The hardened cement paste is what binds all

the other ingredients together to create flowable fill.

4

During the process of hydration, tiny voids filled with water and air form in the

paste. The more porous the cement paste is in a mixture, the weaker the mixture. Studies

have shown that voids in concrete play a vital role in shrinkage. After pouring, concrete

will change volume as moisture levels change. In flowable fill this phenomenon also

takes place. Another condition playing a key role in concrete shrinkage is temperature.

Expansion and shrinkage due to changes in temperature can put stress on flowable fill,

resulting in cracks.

Studies have shown that high water/cement (w/c) ratio and high water content are

the two factors known to cause unwarranted drying-shrinkage in concrete. Although

flowable fill has a higher w/c ratio and higher water content than concrete, studies on

drying shrinkage have indicated that flowable fill exhibits shrinkage to a lesser extent

than concrete. Typical reports of linear-shrinkage values on flowable fill are in the range

of 0.002 to 0.05 percent (6). These values are similar to concrete with low drying

shrinkage. The shrinkage and expansion of flowable fill tend to continue varying

throughout testing. A study by Grandham et al. (7) found that the maximum shrinkage

and expansion values of flowable fill were generally less than the acceptable limit

established for concrete (7).

Since flowable fill is often placed underneath roadways as a road base, varying

volume change is an important attribute to investigate. In various parts of Florida

moisture is greatly abundant. Because this is so, when flowable fill is used in these areas,

it is affected, forcing the flowable fill volume to alter. From the volume change

activities, cracks are often created, leading to water seepage through the cracks causing

5

roadbed damage and deficiencies in the roadway. The final result may include pavement

depressions or pavement humps.

Various problems encountered while using flowable fill arise from the lack of

documented procedures to measure or determine long-term strength for future excava-

tion. Some areas that need further investigation and documentation are as follows:

• A practical method for designing flowable fill mixtures.

• A thorough investigation of the effects of shrinkage in flowable fill.

• A developed flowable fill design method that utilizes commonly used units for describing the strength of backfill materials, such as limerock bearing ratio (LBR) instead of compressive strength.

• A study identifying long-term performance of flowable fill, particularly how the plastic properties of flowable fill affect its long-term strength and excavatability.

It is critical that research be conducted at this time given there is a large number of

roadway construction, maintenance, and rehabilitation projects taking place throughout

Florida.

1.3 Hypothesis

Several factors in flowable fill are found to be similar to those identified in concrete

as a controlled measure for predicting strength. The factors include w/c ratio, cement

content, fly ash content, and plastic properties. The following hypothetical questions

may be asked: (1) Is it possible to get target strength (100 LBR) for flowable fill if

quantities of its mixture components are known? (2) If so, can varying the components of

flowable fill mix help target strength and shrinkage?

Laboratory experiments can be conducted to identify key components to help lay a

foundation for developing rational methods to approach development of flowable fill

mixture design for construction. In addition, models can be developed to employ known

6

component parameters to produce reliable results for predicting strength and field

performance (i.e., shrinkage) of flowable fill.

1.4 Objectives

The primary objectives of this research are as follows:

• Vary mixture components of flowable fill, to help predict strength using prediction models.

• Vary mixture components to predict shrinkage in flowable fill using a prediction model.

• Develop mix design procedures utilizing fine aggregate materials commonly used for flowable fill in the state of Florida.

• Identify setting behavior of flowable fill.

• Provide recommendations where warranted from findings.

1.5 Scope

This is a continuance of a preliminary study in which the key goal was to evaluate

the performance of flowable fill in pavement sections using accelerated and nonacceler-

ated mixtures. Using knowledge acquired from the findings of the preliminary study, the

scope of the current research will focus on developing strength prediction models that

incorporate flowable fill mix parameters. It is critical to vary known components (i.e., air

content, cementitious content, etc.) for establishing the framework and creating the

database to use for prediction models. Thus, this research will focus on the effects of the

following:

• strength in LBR for flowable fill mixtures; and • change in flowable fill volume due to shrinkage.

1.6 Importance of Research

The proper control of strength development in flowable fill applications is an

important criterion in developing a design mixture. Very few studies have been

7

published evaluating the long-term strength of flowable fill in LBR. This research will

help to develop mix design procedures for concrete producers using flowable fill and will

benefit the construction industry.

The volume changes due to shrinkage are of considerable importance. If the

amount of volume change in flowable fill due to shrinkage is derivable, producers will be

able to modify their mixes for obtaining optimal mixtures. Also, contractors can

compensate as necessary.

1.7 Research Approach

To meet the research objectives, this study was conducted utilizing the process

categorized as tasks provided below.

• Task 1 – Literature search: − Examine existing ideas, theories and results published about flowable fill

reviewing various properties affecting its mixtures − Review work done on concrete and geotechnical engineering practices − Review past and current flowable fill practices – materials, design mixes,

properties, and testing practices to measure performance. • Task 2 – Data collection:

− Prepare laboratory design mixtures − Design the experiment for laboratory mixtures

Use factorial design Vary mixture components (i.e., cement, fly ash/slag, and

water/cement ratio) Prepare mixture proportions and samples

− Run small-scale design mixes obtained from the study’s factorial design − Obtain test results from all design mixes performed.

• Task 3 – Data analysis:

− Analyze experimental results obtained from laboratory tests carefully to meet the objectives of the study.

• Task 4 – Model development using empirical approach:

− Develop model using SAS and Minitab. • Task 5 – Model interpretation:

− Evaluate reliability and effectiveness of models.

8

• Task 6 – Final dissertation writing process:

− After completing Tasks 1 through 5, prepare a final report in the form of a dissertation to highlight the achievements and original contributions of the research.

The flowchart presented in Figure 1-1 gives a schematic view of the laboratory task

process to be conducted as part of the research.

Figure 1-1. Laboratory task process

YesNo

Make modifications

Run batch mixtures

Attain target air content and plastic properties

Are the analyzed

results viable?

Randomly select mixtures

Assessing the design and properties for controlled low strength materials (CLSM)

usage in highway pavement

Determine performance

Develop model and framework

9

1.8 Outline of the Dissertation

This dissertation is comprised of six chapters. A brief summary of each chapter is

provided below.

Chapter 1 describes the background, problem statement, hypothesis, objectives,

scope, and importance of this research and the approach used to conduct the research.

Chapter 2 presents a literature review of basic information relating to flowable fill.

The review focuses on flowable fill technology, current practices, strength development,

and strength prediction models.

Chapter 3 explains information pertaining to the materials and experimental testing

program evaluated in the study. The method of preparation of the flowable fill mixtures,

design mix selection, mixture proportions, test specimens, testing procedure, testing

equipment and testing procedures utilized in this study are also presented.

Chapter 4 provides the laboratory results of the flowable fill mixtures. Detailed

discussions on the results are included, along with influencing strength factors affecting

the long-term behavior of flowable fill.

Chapter 5 discusses the results and statistical analysis performed on the laboratory

data. Models predicting strength and volume change are provided. An accelerated

strength testing method is presented for estimating the long-term strength of flowable fill.

Chapter 6 summarizes the research and its conclusions and offers recommendations

for further research.

10

CHAPTER 2 LITERATURE REVIEW

2.1 Introduction

A comprehensive literature search was conducted to identify and examine existing

publications dealing with the following subject matter:

• strength • set time • cement; and • admixtures.

2.2 Flowable Fill Technology

2.2.1 Introduction

Flowable fill, also referred to as controlled low strength material (CLSM), is a

relatively new technology whose use has grown over the years. It describes a fill

technology that is used in place of compacted backfill. Flowable fill is self-leveling with

a consistency similar to pancake batter; it can be placed with minimal effort and no

vibration or tamping is required.

Flowable fill, or CLSM, is a highly flowable cementitious slurry typically

comprised of water, cement, fine aggregates, and often fly ash and chemical admixtures,

including air-entraining agents, foaming agents, and accelerators. Other names used for

this material are “flowable mortar” and “lean-mix backfill” [8].

Flowable fill is defined by the ACI Committee 229 as a “self compacting

cementitious material that is in a flowable state at the time of placement and that has a

specified compressive strength of 200 lb/in2 or less at 28 days” [6, p. 56]. Flowable fill

11

has a low cementitious content for reduced strength development, which makes future

excavation a possibility. This mixture is capable of filling all voids in irregular

excavations and hard-to-reach places (such as under and around pipes) and hardens in a

matter of a few hours without the need for compaction in layers.

2.2.2 Types of Flowable Fill

There are a variety of CLSM types available for various engineering purposes. The

most obvious distinction between types is the possible need for future removal. Thus, the

current FDOT specification divides flowable fill into two main classes: (i) excavatable

fill; and (ii) nonexcavatable fill.

Controlled low strength material (CLSM) excavatability is dependent on many

factors including binder strength, binder density, aggregate quantity, aggregate gradation,

and the excavating equipment used. The National Ready Mixed Concrete Association

(NRMCA) recommends that excavatable CLSM mixes have a 20+ psi compressive

strength at 3 days, a 30+ psi compressive strength at 28 days, and ultimate compressive

strength less than 150 psi. Compliance with these recommendations is typically

established with cylinder compressive strength tests [2].

2.2.3 Advantages of Using Controlled Low Strength Material (CLSM)

There are various inherent advantages of using CLSM over compacted soil and

granular backfills. Some of these are listed below [8].

1. It has a fast setup time.

2. It hardens to a degree that precludes any future trench settlement.

3. The extra cost for the material, compared to compacted backfill, is offset by the fact that it eliminates the costs for compaction and labor, reduces the manpower required for close inspection of the backfill operation, requires less trench width, and reduces the time period and costs of public protection measures.

12

4. There are no problems due to settlement, frost action, or localized zones of increased stiffness.

5. Flowable fill mix designs can be adjusted to meet specific fill requirements, thus making the fill more customized and efficient.

6. Flowable fill is stronger and more durable than compacted soil or granular fill.

7. During placement, soil backfills must be tested after each lift for sufficient compaction. Flowable fill self-compacts consistently and does not need this extensive field testing.

8. It allows fast return to use by traffic.

9. Flowable fill does not form voids during placement nor settle or rut under loading.

10. Since it reduces exposure to possible cave-ins, flowable fill provides a safer environment for workers.

11. It reduces equipment needs.

12. It makes storage unnecessary because ready-mix trucks deliver flowable fill to the jobsite in the quantities needed.

13. Flowable fill containing fly ash benefits the environment by making use of this industrial waste by-product.

These benefits also include reduced labor and equipment costs (due to self-leveling

properties and absence of need for compaction), faster construction, and the ability to

place material in confined spaces. The relatively low strength of CLSM is advantageous

because it allows for future excavation, if required. Another advantage of CLSM is that

it often contains by-product materials, such as fly ash and foundry sand, thereby reducing

the demands on landfills, where these materials might otherwise be deposited.

Despite these benefits and advantages over compacted fill, the use of CLSM is not

currently as widespread as its potential might warrant. CLSM is somewhat a hybrid

material; it is a cementitious material that behaves more like a compacted fill. As such,

much of the information and discussions on its uses and benefits are lost between

concrete materials engineering and geotechnical engineering. Although there is

13

considerable literature available on the topic, CLSM is often not given the level of

attention it deserves by either group.

2.2.4 Engineering Characteristics of CLSM

When a CLSM mixture is designed, a variety of engineering parameters needs to be

evaluated prior to, during, and after placement in the field. Optimum conditions for each

parameter depend on the application. Typically, 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]:

1. strength development 2. time of set 3. flowability and fluidity, or consistency of the mixture 4. permeability 5. consolidation characteristics 6. California bearing-ratio test; and 7. freeze-thaw durability.

The performance criteria for flowable fills are outlined in ACI 229R-94. Flowable

fill is a member of the family of grout material. ACI Committee 229 calls it “controlled

low strength material,” and does not consider it concrete. If it is anticipated or specified

that the flowable lean-mix backfill may be excavated at some point in the future, the

strength must be much lower than the 1200 psi that ACI uses as the upper limit for

CLSM. The late-age strength of removable CLSM materials should be in the range of 30

to 150 psi as measured by compressive strength in cylinders [8].

2.2.5 Uses of Flowable Fill

CLSM is typically specified and used as compacted fill in various applications,

especially for backfill, utility bedding, void fill and bridge approaches. Backfill includes

applications such as backfilling walls, sewer trenches, bridge abutments, conduit

14

trenches, pile excavations, and retaining walls. As structural fill, it is used in foundation

subbase, subfooting, floor slab base, and pipe bedding. Utility bedding applications

involve the use of CLSM as a bedding material for pipes, electrical and other types of

utilities, and conduits. Void-filling applications include the filling of sewers, tunnel

shafts, basements or other underground structures such as road base, mud jacking,

subfooting, and floor slab base. CLSM is also used in bridge approaches, either as a

subbase for the bridge approach slab or as backfill with other elements. Other uses of

flowable fill include abandoned underground storage tanks, wells, abandoned utility

company vaults, voids under pavement, sewers and manholes, and around muddy areas

[8,10].

Conventional backfill in trenches and around small structures usually involves

placement of aggregate material in thin layers with labor-intensive compaction. Poorly

constructed backfill or lack of control of compaction often creates excessive settlement of

the road surface and may produce unacceptable stresses on buried utilities and structures.

Use of CLSM removes the necessity for mechanical compaction with the associated

safety hazards for workers. It can also provide more efficient placement and may permit

reduced trench dimensions [10].

2.2.6 Delivery and Placement of Flowable Fill

CLSM can be delivered in ready-mix concrete trucks and placed easily by chute in

a flowable condition directly into the cavity to be filled or into a pump for final

placement. For efficient pumping, some granular material is needed in the mixture [8].

CLSM can even be transported as a dry material in a dump truck. It can be proportioned

to be self-leveling thus not requiring compaction, and so can be placed with minimal

15

effort without vibration or tamping. It hardens and develops strength, and can be

designed to meet specific strength criteria or density requirements.

Precautions against the following need to be taken into account while working with

flowable fill [8]:

1. Fluidized CLSM is a heavy material and during placement (prior to setting) will exert a high fluid pressure against any forms, embankment, or wall used to contain the fill.

2. Placement of flowable fill around and under tanks, pipes, or large containers such as swimming pools, can cause the container to float or shift.

2.2.7 Limits

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 [11]:

1. Requires lighter-weight pipes to be anchored.

2. Needs to undergo confinement before setting.

3. May not allow higher-strength mixtures to be excavated.

4. Forms or pipes used must resist lateral pressures (lateral pressure is applied while in the fluid condition).

2.3 Specifications, Test Methods, and Practices

2.3.1 Introduction

The Environmental Protection Agency (EPA) recommends that procuring agencies

use ACI229R-94 and the ASTM standards listed in Table 2-1 when purchasing flowable

fill or contracting for construction that involves backfilling or other fill applications.

More than 20 states have specifications for flowable fill containing coal fly ash. They

include California, Colorado, Delaware, Florida, Georgia, Illinois, Indiana, Kansas,

Kentucky, Maryland, Massachusetts, Michigan, Minnesota, Nebraska, New Hampshire,

16

New Mexico, North Carolina, Ohio, Texas, Washington, West Virginia, and Wisconsin.

The history of the current standard test methods for CLSM is rather short but quite

important [12].

Table 2-1. Current ASTM standards on controlled low strength material (CLSM) ASTM Specification Number

Title

D 4832-02

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

D 5971-01 (PS 30)

Standard Practice for Sampling Freshly Mixed Controlled Low Strength Material

D 6023-02 (PS 29)

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

D 6024-02 (PS 31)

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

D 6103-97 (PS 28)

Standard Test Method for Flow Consistency of Controlled Low Strength Material

One or more of the following ASTM test methods listed in Table 2-1 are used

primarily as a quality measure during backfilling and construction in the following areas

[8,12]:

1. Sampling–Obtaining samples of the flowable fill for control tests shall be in accordance with Practice D 5971.

2. Unit weight, yield (ASTM C 138) and air content (ASTM C 231)–Determining the unit weight, yield, or air content of a flowable fill mixture shall be in accordance with Test Method D 6023.

3. Flow consistency–Measuring the flowability of the flowable fill mixture shall be in accordance with Test Method D 6103.

4. Compressive strength–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 reliability of the mix ingredients and proportions.

5. Load application–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 [5].

17

6. Penetration resistance–Tests such as ASTM C 403 may be useful in judging the setting and strength development up to a penetration resistance number of 4000 (roughly 100 psi compressive cylinder strength).

7. Density tests–These are not required since it becomes rigid after hardening.

8. Setting and early strength–These may be important where equipment, traffic, or construction loads must be carried. Setting is judged by scraping off loose accumulations of water and fines on top and seeing how much force is necessary to cause an indentation in the material. ASTM C 403 penetration can be run to estimate bearing strength.

9. Flowability of the CLSM–Flowability is important, so that the mixture will flow into place and consolidate.

Many states have developed specifications governing the use of CLSM. In some

cases, these are provisional. However, specifications differ from state to state, and

moreover, a variety of different test methods are currently being used to define the same

intended properties. This lack of conformity, both on specifications and testing methods,

has also hindered the proliferation of CLSM applications. There are also technical

challenges that have served as obstacles to widespread CLSM use. For instance, it is

often observed in the field that excessive long-term strength gain makes it difficult to

excavate CLSM at later stages. This can be a significant problem that translates to added

cost and labor. Other technical issues deserving attention are the compatibility of CLSM

with different types of utilities and pipes, and the durability of CLSM subjected to

freezing and thawing cycles [13].

2.3.2 ASTM Standard Test Methods

2.3.2.1 Standard Test Method for Preparation and Testing of CLSM Test Cylinders (ASTM D 4832-02)

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 them, removing the cylinders from the molds, and capping the cylinders for

18

compression testing. The cylinders are then tested by machine to obtain compressive

strengths by applying a load until the specimen fails. Duplicate cylinders are required

[14].

The compressive strength of a specimen is calculated as follows:

cPfA

= (2-1)

where fc = compressive strength in pounds per square inch (lb/in2); P = maximum failure load attained during testing in pounds (lb); and A = load area of specimen in square inches (in2).

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.

2.3.2.2 Standard Practice for Sampling Freshly Mixed CLSM (ASTM D 5971-96)

This practice explains the procedure for obtaining a representative sample of the

freshly mixed flowable fill as delivered to the project site for control and properties tests.

Tests for composite sample size shall be large enough to perform so as to ensure that a

representative sample of the batch is taken. This includes sampling from revolving-drum

truck mixers and from agitating equipment used to transport central-mixed CLSM [14].

2.3.2.3 Standard Test Method for Unit Weight, Yield, Cement Content and Air Content (Gravimetric) of CLSM (ASTM D 6023-96)

This practice explains the procedure for obtaining a representative sample of the

freshly mixed flowable fill (as delivered). The density of the CLSM is determined by

filling a measure with CLSM, determining the mass, calculating the volume of the

measure, then dividing the mass by the volume. The yield, cement content, and air

content of the CLSM are calculated based on the masses and volumes of the batch

components [14].

19

a) Yield:

1WYW

= (2-2)

where Y = volume of CLSM produced per batch in cubic feet (ft3); W = density of CLSM in pounds per cubic foot (lb/ft3); and W1 = total mass of all materials batched, lb.

b) Cement content:

tNNY

= (2-3)

where N = actual cement content in pounds per cubic yard (lb/yd3); Nt = mass of cement in the batch, lb; and Y = volume of CLSM produced per batch in cubic yards (yd3).

c) Air content:

100T WAT−

= ∗ (2-4)

where A = air content (percent of voids) in the CLSM; T = theoretical density of the CLSM computed on an air free basis, lb/ft3;

and W = density of CLSM, lb/ft3.

2.3.2.4 Standard Test Method for Ball Drop on CLSM to Determine Suitability for

Load Application (ASTM D 6024-96)

This test method is used primarily as a field test to determine the readiness of the

CLSM to accept loads prior to adding a temporary or permanent wearing surface. A stan-

dard cylindrical weight is dropped five times from a specific height onto the surface of

in-place CLSM. The diameter of the resulting indentation is measured and compared to

established criteria. The indentation is inspected for any free water brought to the surface

from the impact [14].

20

2.3.2.5 Standard Test Method for Flow Consistency of CLSM (ASTM D 6103-96)

This test method determines the fluidity and consistency of fresh CLSM mixtures

for use as backfill or structural fill. It 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-mm sieve. 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 [14].

2.3.3 Other Currently Used and Proposed Test Methods

The American Concrete Institute (ACI) classifies CLSM as a mixture design

having a maximum 28-day compressive strength of 1200 lb/in2. A CLSM mixture that is

considered to be excavatable at a later age using hand tools should have a compressive

strength lower than 101.5 psi at the 28-day stage [14]. This is used to minimize the cost

of excavating a mix at a later stage. 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 utilizing the

flow cone method is most applicable for grout mixtures that use no aggregate filler. A

maximum flow cone measurement of 35 seconds or a minimum slump of 9 in. would be

two practical design parameters. Other methods to specify CLSM consistency have also

been suggested. One such method is very similar to the ASTM standard test

specification, “Flow Table for Use in Tests of Hydraulic Cement” (C 230), for deter-

mining the consistency or flow of mortar mixtures [14].

Permeability of the CLSM mixtures has been measured using the ASTM “Test

Method for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using

a Flexible Wall Permeameter” (D 5084). Loss on ignition of CLSM mixtures, and

21

mineralogy of the hardened CLSM has been determined on the basis of similar tests for

cement. It has been 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 (NRMCA) performance recommendations [14].

The gradation has been determined per ASTM C136-01, “Standard Test Method

for Sieve Analysis of Fine and Coarse Aggregates” and ASTM C117, “Standard Test

Method for Materials Finer than 75 μm (No. 200) Sieve in Mineral Aggregates by

Washing.” Also, AASHTO M43 #10 screening aggregate specifications [15] has been

used to determine the suitability of utilizing the compliance of aggregates used with these

standards [14].

A new ASTM standard, “Standard Practice for Installing Buried Pipe Using

Flowable Fill” has been proposed, which describes how to use flowable fill for installing

buried pipe. ASTM Committee C 3 on Clay Pipe has already initiated mentioning the use

of flowable fill in the Standard C 12 that covers installation of clay pipe [14].

A summarized overview of the test standards currently in use and that of provi-

sional test methods is as follows [14]:

• Provisional methods of testing

1) AASHTO Designation: X7 (2001)–“Evaluating the Corrosion Performance of Samples Embedded in Controlled Low Strength Material (CLSM) via Mass Loss Testing”

2) AASHTO Designation: X8 (2001)–“Determining the Potential for

Segregation in Controlled Low Strength Material (CLSM) Mixtures” 3) AASHTO Designation: X9 (2001)–“Evaluating the Subsidence of Controlled

Low Strength Materials (CLSM).”

22

• Other ASTM test methods used in CLSM technology

1) ASTM C231-97–“Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method”

2) ASTM C403/C 403M-99–“Standard Test Method for Time of Setting of

Concrete Mixtures by Penetration Resistance” 3) ASTM D560-96–“Standard Test Methods for Freezing and Thawing

Compacted Soil-Cement Mixtures” 4) ASTM D5084-90 (Reapproved 1997)–“Standard Test Method for Measure-

ment of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter”

5) ASTM G51-95 (Reapproved 2000)–“Standard Test Method for Measuring

pH of Soil for Use in Corrosion Testing.” 2.3.4 Specifications by the State Departments of Transportation

From a survey of six southeastern states (shown in Table 2-2) carried out by Riggs

and Keck [12], it is apparent that all of the specifications were issued after 1990, and so

the use of CLSM is relatively new to standard transportation road construction. Tables

2-3 and 2-4 show the comparison of similarities and differences for various requirements

based on the survey.

Table 2-2. States surveyed and their specification on flowable fill State Specification and Title of Section Issue Date

Alabama Section 260, Low Strength Cement Mortar 1996 Florida Section 121, Flowable Fill” (revised 1996) 1997 Georgia Section 600, Controlled Low Strength Flowable Fill 1995 North Carolina Controlled Low Strength Material Specification 1996 South Carolina Specification 11, Specification for Flowable Fill 1992 Virginia Special Provisions for Flowable Backfill 1991

According to the survey, the general acceptance age is 28 days with two states

having 56-day requirements (Table 2-3). As a result of the high levels of pozzolans in

many CLSM mixtures, there can be significant strength increases after 28 days. Several

23

states have both excavatable and nonexcavatable mixtures. If the CLSM is to be

removed at a later date, its strength must be limited to less than 300 psi, which can be

assured only if later age strengths are evaluated [12].

Table 2-3. Specified acceptance strengths and ages Strength, psi (MPa in parentheses)

State Age (days) Minimum Maximum

Alabama 28 80 (0.55) 200 (1.4) Florida 28 100 (0.7) 125 (0.9) Georgia 28 100 (0.7) 125 (0.9) North Carolina 28; 56 125 (0.9) 150 (1.0) South Carolina 28; 56 80 (0.55) 125 (0.86) Virginia 28 30 (0.2) - 200 (1.4)

Note: Maximum strengths are restricted to enable excavation at later stages, if desired or needed.

Table 2-4. Suggested mixture proportions, lb/yd3 (values in kilograms per cubic meter,

kg/m3, are in parentheses)

State Cement Pozzolan Fine Aggregate Water Air Range

Alabama

61 (36) 185 (110) 195 (116) 195 (116) 517 (307)

331 (196) 0 572 (339) 572 (339) 0

2859 (1696) 2637 (1586) 2637 (1586) 2673 (1586) 413 (245)

509 (302) 500 (297) 488 (290) 488 (290) 341 (202)

Not given ″ ″ ″ ″

Florida

75-100 (44-89) 75-150 (44-89)

0 150-600 (89-356)

(a) (a)

(b) (a) (b)

5-35 15-35

Georgia

75-100 (44-89) 75-150 (44-89)

0 150-600 (89-356)

(a) (a)

(b) (a) (b)

15-35 5-15

N. Carolina

40-100 (24-59) 100-150 (59-89)

(a) (a)

(a) (a)

(b) (a) (b)

0-35 0-35

S. Carolina

50 (30) 50 (30)

600 (356) 600 (356)

2500 (1483) 2500 (1483)

458 (272) 541 (321)

None (c) None (c)

Virginia Contractor must submit his own mixture (“mix design”)

Note: (a) Proportion to yield 1 yd3 (1 m3) (b) Proportion to produce proper consistency (c) Air up to 30% may be used if required.

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2.3.5 Use of Flowable Fill in the State of Florida

Flowable fill has been used throughout the state of Florida as a construction

material. The FDOT has used the material for bedding, encasements, tank enclosures,

pipes, and general backfill for trenches. Occasionally, the use of flowable fill has been

specified for placement under a base with a set time of four hours or more prior to the

placement of the base materials [16].

The current specification divides the flowable fill into two classes: excavatable and

nonexcavatable. The maximum allowable 28-day compressive strength of excavatable

flowable fill is 100 psi. The minimum compressive strength for nonexcavatable flowable

fill is 125 psi. The suggested range of cement and fly ash has been specified for each

class of excavatable and nonexcavatable fill. Prior to use on projects, flowable fill mix

designs must be approved by FDOT. The approval of the mix design is based on the

specified range of material and laboratory test data, such as air content, compressive

strength, and unit weight [16].

2.3.5.1 Material Specifications (Section 121-2)

According to Section 121 of the FDOT “Standard Specifications for Roadway and

Bridge Construction,” the material requirements a flowable fill mix design must meet in

order to be approved by FDOT are noted in Table 2-5 below [16].

Table 2-5. FDOT materials specification requirements Fine aggregatea ...............................................................................Section 902 Portland cement (Types I, II, or III)................................................Section 921 Fly ash, slag and other pozzolanic materials ................................. Section 929 Air-entraining admixturesb .............................................................Section 924 Water...............................................................................................Section 923 aAny clean fine aggregate with 100% passing a 3/8-in. (9.5-mm) mesh sieve and not more than 15% passing a No. 200 (75 µm) sieve may be used.

bHigh air generators or foaming agents may be used in lieu of conventional air-entraining admixtures and may be added at jobsite and mixed in accordance with manufacturer’s recommendation.

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All materials used should meet other specification requirements on a consistent

basis (see Section 2.3.5.3 below).

2.3.5.2 Construction Requirements and Acceptance (Section 121-5, 121-6)

FDOT specifications require the ambient air temperature to be 40° F (4° C) or

higher and the mix be delivered at a temperature of 50° F (10° C) or higher. FDOT does

not permit placement during rain or when the temperature is below 40° F. Specification

requires the material to remain undisturbed until it reaches a penetration resistance of 35

psi or higher. A soil penetrometer (ASTM C 403, “Standard Test Method for Time of

Setting of Concrete Mixtures by Penetration Resistance”) is used to measure setting time

[16].

2.3.5.3 Guideline for Construction Requirements and Acceptance (Section 121-5, 121-6)

To assist in designing a flowable fill mix, Section 121 of the specifications

provides a guideline shown in Table 2-6 for one to use in preparing a mix design [16].

Table 2-6. FDOT flowable fill mix design Excavatable Nonexcavatable

Cement, Type I

75-100 lb/yd3 (45-60 kg/m3)

75-150 lb/yd3 (45-90 kg/m3)

Fly ash

None

150-600 lb/yd3 (90-335 kg/m3)

Water –a –a Airb 5-35% 5-15% 28-day compressive strengthb

Maximum 100 psi (690 kPa)

Minimum 125 psi (860 kPa)

Unit weightb (wet)

90-110 lb/yd3 (1440-1760 kg/m3)

100-125 lb/yd3 (1600-2000 kg/m3)

aMix design shall produce a consistency that will result in a flowable self-leveling product at a time of placement. bThe requirements for percent air, compressive strength and unit weight are for laboratory designs only and are not intended for jobsite acceptance requirements. Fine aggregate shall be proportioned to yield 1 yd3 (1 m3).

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2.4 Early Set and Strength Development

2.4.1 Introduction

The early strength of flowable fill in a plastic state comes primarily from the

friction of particles of its constituents. This theory originates from the behavior of

particles in slurry flow, powder technology, and tribology (the science and technology of

interacting surfaces in relative motion and all related practices, including friction,

lubrication, and wear). Although slurry flow does not have any cementing agents, an

explanation of the role of particle friction in slurry is an important base to fully

understanding the early strength of flowable fill.

The end of the plastic state is indicated by hydration of cement particles and the

role of cohesion appears to begin in this stage. The hydration process in flowable fill can

be explained based on the chemical reaction of cement and fly ash in the concrete.

2.4.2 Behavior of Slurries

The behavior of slurries as described by Kendall is similar to that of coulomb

materials, with a flow stress dependent on the high friction between the solid grains [17].

Three simple tests were conducted by Kendall, a plastimeter test, an extrusion test, and a

bubble collapse test. The result was that the slurries became unmoldable, nonextrudable

or noncompactable when the solid grains in the slurry became frictionally locked

together. However, this effect can be prevented by addition of a polymer lubricant which

reduces friction between the grains thereby improving slurry flow.

According to an experiment by Kendall involving wet concrete slurry, if the slurry

is truly plastic, then at a pressure equal to the yield pressure, one’s foot would sink into

the slurry (as in the Bingham model) [17]. In that experiment, the foot did not sink

because the cement grains under the foot were pushed together, experienced friction, and

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so resisted flow. However, when some polymer lubricant is mixed into the slurry, the

friction between th