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Volume 19/Number 1

April 1998

5420 Old Orchard Road

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Rebar Supports forConcrete in AggressiveEnvironments

Prescriptive versusPerformance Specificationsfor Cements

New Literature

Control of Air Content inConcrete

Air-Void Analyzer

Figure 1. Freeze-thaw deterioration of non-air-entrained concreterailing. (S44517)

Control of Air Content in ConcreteNew manual provides concrete producers and users with tips onachieving and controlling air in concrete.

Air entrainment is a necessary com-ponent of concrete mixtures exposedto freezing and thawing environ-ments. Due to changing materials,conditions of mixing, and methods ofplacing concrete, achieving target aircontents requires attention at the de-sign, specification, and constructionstages. A new reference by NRMCAand PCA titled Manual on Control ofAir Content in Concrete (PCA EB116)–excerpted in this article—bringstogether practical state-of-the-artinformation to control the air contentof fresh and hardened concrete in thefield.

Concrete pavements and structuresin many regions of North Americaare exposed to very severe winter

conditions, including snowfall, the ap-plication of large quantities of deicingagents, and many cycles of freezingand thawing.

Water expands upon freezing, exert-ing forces that exceed the tensilestrength of concrete. Repeated cyclesof freezing and thawing can result incumulative damage in the form ofcracking and scaling (Fig. 1).

Role of Air ContentFor over 50 years, entrained air hasbeen deliberately incorporated in con-crete mixtures to reduce damage dueto cycles of freezing and thawing. Air-entraining admixtures or agents areused to produce a stable system of

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R e t u r n To I n d e x

Concrete Technology Today

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discrete air voids in concrete, termed“entrained air.” Non-air-entrained(left side) and properly air-entrainedconcretes (right side) are shown inFig. 2. Most of the entrained airbubbles are smaller than the head ofa pin (shown). The air voids provideempty spaces within the concretethat act as reservoirs for the freezingwater, relieving pressure and pre-venting damage to the concrete.

Forming Air in ConcreteEntrained air is produced duringmechanical mixing of concrete thatcontains an air-entraining admixture.The shearing action of mixer bladescontinuously breaks up the air into afine system of bubbles. Air-entrain-ing admixtures stabilize these airbubbles.

Air-Void SystemOnce the concrete has set, the casts ofthe original air bubbles are left be-hind in the hardened concrete asvoids. This is commonly referred toas the “air-void system” in hardenedconcrete. The major parameters ofthe air-void system are the total aircontent, average spacing factor be-tween air voids, and specific surface.Entrained air consists of microscopi-cally small bubbles, almost all ofwhich have diameters greater than10 micrometers (0.0004 in.) and lessthan 1 mm (0.04 in.). These bubbles

are uniformly distributed throughoutthe concrete. The relative distance be-tween the voids is termed the spacingfactor. The spacing factor is roughly thedistance water would have to travel be-fore entering an air void, thereby re-ducing the pressure. A smaller spacingis better. The specific surface indicatesthe relative number and size of airbubbles for a given volume of air. Alarger specfic surface is better becauseit indicates a larger number of smallbubbles. A spacing factor of less than0.2 mm (0.008 in.) and specific surfacegreater than 24 mm2/mm3 (600 in.2/in.3) are believed necessary to maintainfreeze-thaw durability.

The total volume of air in concrete isusually measured on the plastic con-crete. Required air content of the con-crete decreases with increasing aggre-

gate size such that approximately9 percent air is maintained in themortar fraction. General recom-mendations on total air content forconcrete are shown in Table 1.

Sampling and Testing for AirThe sample size for air contenttesting of fresh concrete should bea minimum of 0.028 m3 (1 ft3). Thesample should not be taken fromthe very first or last portion of thebatch. A sample should be ob-tained for every 75 m3 (100 yd3) ofconcrete, at least once per day.

The common method of measur-ing air content in fresh concrete isthe pressure method (Fig. 3). Thismethod is based on the principlethat the only significantly com-pressible ingredient of fresh con-crete is the air. Pressure metersshould not be used for concretemade with lightweight aggregatesor aggregates of high porosity. Inthese instances the volumetric airmeter should be used.

The volumetric method for de-termination of air content relies onsimple displacement of air withwater in a vessel of pre-calibratedvolume.

The gravimetric method is theoldest method of determining aircontent of fresh concrete. The spe-cific gravities (densities) of all ma-terials must be known so that thetheoretical unit weight (with noair) can be determined and thencompared with the actual unitweight to determine air content.The actual unit weight is deter-mined by weighing a known vol-ume of fresh concrete.

Figure 2. Cross-section comparison of non-air entrained (left side)and air-entrained (right side) concrete. (P1104).

Table 1. Recommended Total Target Air Content for Concrete

Air content, percent*aggregate Severe exposure** Moderate Mild

size, mm (in.) exposure† exposure† †

9.5 (3/8) 7-1/2 6 4-1/212.5 (1/2) 7 5-1/2 419.0 (3/4) 6 5 3-1/225.0 (1) 6 4-1/2 3

* Project specifications often allow the air content of the concrete to be within –1 to +2percentage points of the table target values.

** Concrete exposed to wet-freeze-thaw conditions, deicers, or other aggressive agents.† Concrete exposed to freezing but not continually moist, and not in contact with deicers or

aggressive chemicals.† † Concrete not exposed to freezing conditions, deicers, or aggressive agents.

Nominal maximum

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When air content in fresh concreteis compared to air content in hard-ened concrete, differences can exist.Air content in hardened concrete isnormally measured microscopicallyon a polished section of concretetaken from a laboratory beam, fieldcylinder, or core. Differences be-tween fresh and hardened air con-tent from the same lot of concreteare generally less than plus-or-mi-nus 1 to 2 percentage points.

Effects of Concrete IngredientsThe materials used to produce con-crete–portland cement, supplemen-tary cementitious materials, chemi-cal admixtures, aggregates, and mix-ing water–can have a significant ef-fect on air content. A discussion ofthe qualitative effects of these mate-rials on the trends in air content iscovered in the manual along withguidance to correct unintendedchanges in air content resulting fromchanges in materials. Table 2 sum-marizes just some of the effects con-crete ingredients have on air.

Production Procedures,Construction Practices, andField ConditionsThe way concrete is produced andhandled can also have a significant

Figure 3. A Type B pressure meter usedto measure total air content of freshconcrete. (P66113)

Table 2. Effects of Concrete Ingredients on Air Content

Material Effects GuidanceCement

Alkali content Air content increases Changes in alkaliwith increase in cement content require thatalkali level. air-entraining agent

dosage be adjusted.Fineness Decrease in air content Adjust agent if

with increased fineness cement source orof cement. fineness changes.

Cement Decrease in air content Increase air-entrain-content with increase in cement ing admixture

content. dosage rate.Fly ash Air content decreases Changes in L.O.I. or

with increase in L.O.I. fly ash source require(carbon content). that air-entraining

agent dosage beadjusted.

Water reducers Air content increases Reduce dosage ofwith increase in dosage air-entraining agent.of lignin-based materials.

Aggregate Air content increases with Decrease air-increased sand content. entraining agent

dosage.

Table 3. Effects of Production and Construction Variables on Air Content

Variable Effects Guidance

Mixer capacity Air increases as capacity Run mixer close to fullis approached. capacity. Avoid over-

loading.Temperature Air content decreases with Increase air-entraining

increase in temperature. agent dosage astemperature increases.

Haul time and Long hauls, even without Optimize deliveryagitation agitation, reduce air, schedules. Maintain

especially in hot weather. concrete temperaturesin recommended ranges.

Pumping Reduction in air content Use loop in descendingranges from 2 to 3%. pump line. Keep the

pumping pressure aslow as possible.

Internal vibration Air content decreases Do not overvibrate.under prolonged vibration Avoid high-frequencyor at high frequencies. vibrators (>10,000 vpm).

effect on its air content and entrainedair-void system. Variables associatedwith concrete production include themethods of batching, mixing proce-dures, and time and speed of mixing.Construction-related variables andfield conditions such as transport anddelivery, retempering, placement,consolidation, finishing, and tem-perature also can affect the air con-tent of concrete. Table 3 summarizesthe effect of some of these variableson air content.

ExcerptThe information presented in this articleis a brief excerpt taken from the Manualon Control of Air Content in Concrete(EB116), published in 1998 by NRMCAand PCA. The document presents practi-cal information on achieving and con-trolling target air contents. It is availablethrough NRMCA and PCA (see NewLiterature).

PCA R&D Serial No. 2093a


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Air-Void AnalyzerBy Tine Aarre, Ph. D.Dansk Beton Teknik A/S

A new test determines the air-voidsystem of fresh concrete.

It is generally accepted that entrainingair in concrete improves its frost resis-tance. It is also recognized that it is thenumber of very small closely spacedair voids and not the volume of airthat determines the efficiency of the(entrained) air-void system.

Most conventional methods for ana-lyzing air in fresh concrete, such as thepressure-meter method, measure thetotal air content only, and conse-quently provide no information aboutthe parameters that determine thequality of the air-void system.

These parameters–the size and num-ber of voids and spacing betweenthem–can be measured on polishedsamples of hardened concrete (ASTMC 457) but the result of such analysiswill only be available several days af-ter the concrete has hardened.

A New Test MethodThis problem has now been overcomeby new test equipment called the air-void analyzer (AVA) or commonly re-ferred to in North America as theDanish air test (see Fig. 1 and Ref. 2).

The AVA was developed to deter-mine the standard ASTM C 457 air-void parameters in fresh samples ofair-entrained concrete. The test appara-tus determines the volume and sizedistributions of entrained air voids andthus allows an estimation of the spac-ing factor, the specific surface, and thetotal amount of entrained air.

Fresh concrete samples can be takenat the ready mix plant and on site.Testing concrete before and afterplacement into forms can verify howthe applied methods of transporting,placing, and consolidation affect theair-void system. Since the samples aretaken on fresh concrete, the air con-tent and air-void system can be ad-justed during production.

Principle of the MethodIn this test method, air bubbles from asample of fresh concrete rise througha viscous liquid, enter a column ofwater above it, then rise through thewater and collect under a submerged

buoyancy recorder. The viscous liq-uid retains the original bubble sizes.Large bubbles rise faster than smallones through the liquids. The changein buoyancy is recorded as a func-tion of time and can be related to thenumber of bubbles of different size.

Figure 1. Equipment for the air-void analyzer. (67961)

Test Procedure• A 20 cm3 mortar sample is ex-

tracted from the concrete.• The sample is injected into the bot-

tom of a column filled with the vis-cous liquid and water (see Fig. 2).The mortar is stirred for 30 secondsto release the air bubbles into theviscous liquid.

• The bubbles rise through the liquidand enter the column of waterabove it. Bubbles collect under asubmerged buoyancy recorder thatis attached to a balance.

• The computer calculates voids lessthan 3.0 mm, spacing factor, andspecific surface.

These parameters correspond tothose that would be obtained fromlinear traverse measurements(ASTM C 457) on a hardened con-crete sample. Comparison with thatmethod yields an accuracy of ±10%for a data collection period of 25minutes. A curve, similar to particlesize distribution, shows voids versusvoid diameter, and a bar chartshows actual void volume in differ-ent ranges of void diameter.

Figure 2. Air bubbles rising throughliquids in column. (67962)

Documentation and UseExtensive testing and documentationof the accuracy of the AVA have beencarried out. Currently no standard ex-ists for the method. The AVA was notdeveloped for measuring the total aircontent of concrete, and because ofthe small sample size, may not giveaccurate results for this quantity.However, this does not impact theuse of the method for assessing thequality of the air-void system.

The AVA is used in Europe, NorthAmerica, and Japan, and it was usedon the Great Belt Project in Denmark.The method is used in conjunctionwith traditional methods for measur-ing air content.

References1. Standard Test Method for Microscopical

Determination of Parameters of the Air-Void System in Hardened Concrete, ASTMC 457, ASTM, West Conshohocken,Pennsylvania, 1990.

2. Quality Assurance of Concrete Based onTesting of the Fresh, Still Plastic Material,EC-Contract No. BRE-CT90-0.58, 1991-1995.

3. Henrichsen, A., and Vyncke. J., “QualityAssurance of Air-Void Structures inConcrete,” International Symposium onNon-Destructive Testing in Civil Engineer-ing (NDT-CE), German Society for Non-Destructive Testing (DGZfP), Berlin,September 1995.

Editor’s NoteFurther information can be obtained bycontacting Dansk Beton Teknik A/S,Helleruplund Alle 21, DK-2900 Hellerup,Denmark, Telephone: 011-45-39-61-23-66,Fax: 011-45-39-62-28-33, e-mail: [email protected].

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April 1998


Rebar Supports for Concretein Aggressive EnvironmentsBy Ole T.K. Vik, P. Eng.President, Con Sys Inc.

New reinforcement supports combat corrosion inreinforced concrete and enhance durability ofreinforced concrete structures.

• Plastic supports – only permittedin structures not exposed to chlo-rides.

• Concrete supports – silica fumecontent of 5-10% of portland ce-ment by mass; shall not have anoily/smooth surface, for example,from form release agent used inproduction, nor be sealed by sur-face impregnating or by the use ofhydrophobic-enhancing additives;at least 7 days of moist curing at aminimum of 15°C (59°F); maxi-mum water absorption 5.0% after30 minutes and 8.5% after 24 hrs.

Bar supports and side-wall spacersmade from high performance con-crete have been developed in orderto meet the new specification re-quirements (see Fig. 1). This wasnecessary because none of the exist-ing products on the market in theearly 1990s met the new require-ments. The new reinforcement sup-ports have been used in bridgeprojects and other major concretestructures in Norway since 1994 andin North America since 1997.

The City of Winnipeg, Manitoba,is using concrete bar supports meet-ing these new specifications for theircurrent Norwood Bridge and YorkAvenue Underpass projects. Fig. 2shows the spacers attached to the re-inforcement before side forms areplaced. The concrete supports pro-vided the solution to the city’s re-

tion must pen-etrate the pro-tective cover,minimize ef-fects that other-wise couldcompromisethe integrity ofthe protectivecover? One an-swer isNorway’s NewCode for Ensur-ing ConcreteCover, which addresses this questionin specifications for bar supportsand their installation.(2) Require-ments of these specifications in-clude:• Material – non-metallic and non-

corrosive.• Geometric shape – complete em-

bedment without significantvoids, minimal visual effect onfinished surfaces, and stabilityagainst overturning under con-struction loads.

• Dimensional tolerance – ± 2 mmfor heights < 70 mm (± 0.08 in. for< 2.75 in.).

• Strength and stiffness – mini-mum load-carrying capacity 6 kN(1350 lbs) for individual supports,maximum 1 mm (0.04 in.) com-pressive deformation of supportunder construction loading or 2mm (0.08 in.) including heat load-ing (e.g., steam cleaning, hotweather conditions).

• Provisions for fastening – condi-tional requirements for fasteningsupport to the form and rein-forcement to the support, nailsshall be stainless steel with dis-tance between the nail and rein-forcement a minimum 50% ofsupport height, tie wire shall beannealed steel (plastic coatedonly if all reinforcement is coated)with concrete cover a minimum50% of the support height.

The function of reinforcing steelsupports, also referred to as bar sup-ports and side-wall spacers, is tohold reinforcing bars securely inproper position during concretingand to ensure correct concrete coverover the reinforcement in the fin-ished structure. Proper positioningof reinforcement is necessary for itsstructural function and durability.Correct concrete cover over the rein-forcement helps protect it from cor-rosive chemicals that may be presentin the service environment.

Corrosion of the reinforcementwill occur if corrosive chemicalssuch as water-dissolved chloridesgain passage through the cover tothe reinforcing steel, or if carbon-ation of the concrete, which starts atthe exposed surface, reaches the re-inforcing steel.(1) Although the con-ditions inducing corrosion in rein-forced concrete may vary, properposition and correct cover are essen-tial requirements for all concretestructures, especially in aggressiveenvironments.

Aggressive environments includecoastal climates with seawater andsalt air, or climates where roadsalts/deicing agents are used, andother locations where corrosivechemicals are present. In coastal ar-eas, practically all outdoor struc-tures, and in particular marine struc-tures, are subjected to an aggressiveenvironment. Elsewhere, concretestructures most often subjected toaggressive environments includebridges, parking garages, industrialplants, and agricultural facilities.

Many of today’s new bridges inEurope and North America are tar-geting 100 years of service life. Thisrequires a sound, good-quality con-crete cover to protect reinforcementfrom chemical attack by preventingwater, chloride, and carbon dioxideingress.(1) How then can bar sup-ports, which by virtue of their func-

Figure 1. Bar supports and side-wall spacers madefrom high performance concrete featuring highstrength (minimum 75 MPa [10,900 psi]); lowpermeability to air, water, and chloride ions; highresistance to chemicals; and geometrically andmaterially designed to become an integral part ofthe host concrete structure. (67925)


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Who Uses Deicers?Throughout North America, con-crete is regularly subjected to someform of chloride by direct or indi-rect application, or by environmen-tal exposure. Required air contentsand chloride limits depend onwhether or not deicers will be used.A limited survey of deicer usagewas performed by PCA’s MarketResearch Department. Only stateswith severe freeze-thaw conditionswere polled. Of those 35 State De-partments of Transportation con-tacted, 29 responded.

Which deicers are regularlyused? There are four:• Sodium chloride (NaCl)• Calcium chloride (CaCl2)• Magnesium chloride (MgCl2)• Calcium magnesium acetate (CMA).

Results:• NaCl is still used most frequently

by over 93% of respondents, al-though some states use it as a 1:1salt-sand mix.

• Some amount of CaCl2 (less than1% of total deicer salts) is also used

regularly by 41% of the states, of-ten in liquid form. It is primarilyused to improve the effectivenessof sodium chloride.

• 14% of states use a small amountof MgCl2 (less than 1% of total).

• 10% of states use a small amountof CMA (less than 1%), most re-spondents citing cost (comparedwith other deicers) as prohibitiveto more widespread use.

• Colorado uses salt-sand mix of1:9 (10% salt).

• Massachusetts reports that CaCl2accounts for 14% of its total de-icer usage.

Figure 3. Reinforcing support in thebottom flange of a precast girder will,because of its shape, be completelyembedded and barely visible on thegirder’s surface when the form isremoved. Norwood Bridge,Winnipeg, Manitoba. (67927)

Figure 4. Precast sections made with concrete barsupports being placed at Norwood Bridge. Photocourtesy of Lafarge Canada Inc.-Winnipeg Precast andThomas Young Productions (photographer).

Figure 2. Side-wall spacers in the web ofa precast bridge girder ensure correctcover over reinforcement when the steelform is closed. Norwood Bridge,Winnipeg, Manitoba. (67926)

quirements of ensuringadequate and uniformcover over the steel re-inforcement withoutleaving an unsightlyconcrete surface withexposed non-concretematerials that might bepotential weak spots inthe protective cover.The combination ofEuropean technologyand high performanceconcrete present aninnovative solution toa common durabilityissue.

References1. Montani, R., and Sohanghpurwala, A.A., Corrosion

in Reinforced Concrete, Seminar, World of Concrete’98, Orlando, Florida, January 18, 1998.

2. Nye regler for sikring av overdekning, Spesifikasjonerfor sikring av armeringens overdekning (New Code forEnsuring Concrete Cover, Specifications for Ensur-ing Cover over Reinforcement) Publication No. 78,Norwegian Road Research Laboratory, Oslo, Nor-way, May 1995.

Editor’s NoteAdditional information can be obtained from ConSys Inc., Box 341, Pinawa, MB, Canada R0E 1L0, Tele-phone 204-753-2404, Fax 204-753-8329/800-442-8850,or e-mail [email protected].

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April 1998


Prescriptive versus PerformanceSpecifications for CementsA description of the differences between performance specificationsand prescriptive specifications outlines some of the potential benefitsand drawbacks of each.

Specifications, or standards, are thebasis to verify quality and maintainproduct uniformity. Conformance tostandards can be determined usingeither prescriptive or performancespecifications. A prescriptive specifi-cation gives chemical or physical re-quirements that are indirectly re-lated to performance. A performancespecification sets limits for physicaltest results only.

In the U.S., specifications for ce-ment have had both prescriptive andperformance features. Performancefeatures have included requirementsfor setting time, strength, and dura-bility. Prescriptive features have in-cluded limits on chemical composi-tion, some physical properties, andrestrictions on ingredients. BothASTM C 150 (for portland cement)and ASTM C 595 (for blended hy-draulic cement) have prescriptiveand performance elements. In 1992,the first performance-only specifica-tion for cements, ASTM C 1157, wasissued.

As an example of the differencebetween prescriptive and perfor-mance requirements, ASTM C 150limits the tricalcium aluminate (C3A)level in portland cement to providesulfate resistance for concrete (ormortar). The C3A level is obtainedfrom results of chemical analyses ofthe cement. In ASTM C 1157, sulfateresistance of concrete (or mortar) iscontrolled by evaluating laboratorytests of mortar prisms made with thecement. The laboratory test is in-tended as a predictor of field perfor-mance of concrete.

Prescriptive specifications providea well-defined means for the manu-facturer to demonstrate compliancewith chemical composition, but maylimit the options of cement manufac-turers (by restricting the use of con-stituent materials) and thus posesomewhat of a barrier to innovation.Compliance with performance speci-fications, on the other hand, allowsthe use of different constituent mate-

rials but is more sensitive to the testmethods used to predict performance.

Blended cements offer attractivemethods of manufacturing a materialto minimize environmental impactand result in very efficient use of raw,recycled, and by-product materials.Currently, the ASTM C 595 specifica-tion would not allow the most inno-

vative and potentially efficient com-bination of materials. That is whereC 1157 can fill in the current gaps.Users potentially can choose thesecements to address particular dura-bility or construction needs. A com-parison of some features of the threecement specifications is given below.

Feature ASTM ASTM ASTMC 150 C 595 C 1157

Specification limits on:Minimum compressive strength? Yes Yes YesAutoclave expansion? Yes Yes YesTime of setting? Yes Yes YesAlkalies? Optional No NoChemical composition? Yes Yes NoFineness? Yes No NoMortar air content? Yes Yes No

Number of basic types 5 6 6

Total number of types 8 16 6

Type designation for:General concrete construction I IS, IP, I(PM), I(SM), P GUHigh early strength III — HEModerate sulfate resistance II IP(MS), IS(MS) MSHigh sulfate resistance V — HSLow heat of hydration IV P(LH) LHModerate heat of hydration II IS(MH), IP(MH), MH

I (PM)(MH),I(SM)(MH)

Accepted by:ASTM C 55 (Concrete brick)? Yes Yes YesASTM C 90 (Concrete block)? Yes Yes YesASTM C 94 (Ready mix specification)? Yes Yes NoACI 301 (Structural concrete Yes Yes Nospecification)?ACI 318 (Building Code)? Yes Yes NoUniform Building Code? Yes Yes Yes

ASTM C 150: Standard Specification for Portland CementASTM C 595: Standard Specification for Blended Hydraulic CementsASTM C 1157: Standard Performance Specification for Blended Hydraulic Cement

Comparison of ASTM Cement Specifications


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R e t u r n To I n d e xPL981.01B

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Intended for decision makers associatedwith design, management, and construc-tion of building projects, Concrete Technol-ogy Today is published triannually by theConstruction Information Services Depart-ment of the Portland Cement Association. Our purpose is to show various waysof using concrete technology to your

PUBLISHER'S NOTE: Direct all correspondence toSteve Kosmatka, EditorJamie Farny, Assistant EditorConcrete Technology TodayPortland Cement Association5420 Old Orchard RoadSkokie, Illinois 60077-1083Phone: 847/966-6200 Fax: 847/966-8389E-mail: [email protected]: [email protected]

Printed in U.S.A.

This publication is intended SOLELY for use by PROFESSIONAL PERSONNEL who are competent to evaluate the sig-nificance and limitations of the information provided herein, and who will accept total responsibility for the applicationof this information. The Portland Cement Association DISCLAIMS any and all RESPONSIBILITY and LIABILITY for theaccuracy of and the application of the information contained in this publication to the full extent permitted by law.

NEW LITERATUREThe following publications are nowavailable. To purchase any of these, inthe United States, contact PortlandCement Association, Order Process-ing, P. O. Box 726, Skokie, IL 60076-0726; telephone 800/868-6733, or fax847/966-9666. They can also be or-dered via PCA's web sitewww.portcement.org. In Canada,please direct requests to the nearestregional office of the Canadian Port-land Cement Association (Halifax,Montreal, Toronto, and Vancouver).

Manual on Control of AirContent in Concrete, EB116While use of air-entrained concrete is awell-established practice, quality con-trol issues may arise during produc-tion and placement of air-entrainedconcrete. The way concrete is pro-duced can have a significant effect onits air content and entrained air-voidsystem. By focusing on the variables

that can affect the air content of con-crete, the manual gives the reader suf-ficient knowledge to obtain the de-sired air content in concrete as well astroubleshoot any difficulties arisingfrom mixing or placing. A compactdisk version of the document is in-cluded. See an excerpt in this issue ofConcrete Technology Today.

Ettringite and Oxyanion-Substituted Ettringites—TheirCharacterization andApplications in the Fixation ofHeavy Metals: A Synthesis ofthe Literature, RD116The term ettringite, a mineral pro-duced when tricalcium aluminatecombines with sulfate during normalhydration of portland cement, de-scribes a number of chemically simi-lar substances. This report discussesthe sulfate form, and also focuses onthe forms of ettringite producedwhen other substances are incorpo-

rated into ettringite. Ettringite for-mation has significant potential forstabilizing wastes containing heavymetals by using portland cement.This is a valuable reference for any-one interested in the chemistry ofettringite as found in concrete aswell as anyone involved with stabi-lizing waste with cement.

Rectangular Concrete Tanks,IS003This newly revised publication pre-sents the latest technical guidelinesand procedures for structural designof rectangular above- or below-ground concrete tanks. The text con-siders various combinations of endconditions and aspect ratios, adaptsdesign coefficients for multicelltanks, and presents design coeffi-cients for twisting moments to covermost design situations in practice.Numerous examples are provided.

advantage and avoiding problems. If thereare problems or ideas readers would likediscussed in future issues, please let usknow. Items from this newsletter may bereprinted in other publications subject toprior permission from the Association. Forthe benefit of our readers, we occasionallypublish articles on products. This does notimply PCA endorsement.