363R-92 State-of-the-Art Report on High-Strength Concrete · ACI 363R-92 (Reapproved 1997)...

ACI 363R-92(Reapproved 1997)

State-of-the-Art Report on High-Strength Concrete

Reported by ACI Committee 363

Henry G. RussellChairman

Arthur R. AndersonJack O. BanningIrwin G. Cantor*Ramon L. Carrasquillo*James E. CookGregory C. FrantzWeston T. Hester

lMembers responsible for individual chapters

ACI Committee 363 Members Balloting 1992 Revisions

Kenneth L SaucierChairman

Pierre Claude AitcinF. David AndersonClaude BedardRoger W. BlackIrwin G. CantorRamon L. CarrasquilloJudith A. CastelloJames E. CookKingsley D. DrakeGregory C. FrantzThomas G. Guennewig

Anthony N. KojundicBrian R. Mastin*William C. MooreArthur H. Nilson*William F. PerenchioFrancis J. Principe

Weston T. Hester+

Nathan L HowardAnthony N. KojundicMark D. LutherHeshem MarzoukBrian R. MastinWilliam C. MooreJaime MorenoArthur H. NilsonClifford R. Ohwiler

Jaime MorenoSecretary

Kenneth L Saucier*Surendra P. Shah*J. Craig Williams*John Wolsiefer, Sr.J. Francis YoungPaul Zia

William F. PerenchioSecretary

Henry G. RussellMichael T. RussellSurendra P. ShahBryce P. SimonsAva SzypulaDean J. White, IIJ. Craig WilliamsJohn T. WolsieferFrancis J. YoungPaul Zia

Currently available information about high-strength concrete is summar-ized. Topics discussed include selection of materials, concrete mix pro-portioning, batching miring, transporting placing, control procedures,concrete properties, structural design, economics, and applications. Abibliography is included.

Keywords: bibliographies; bridges (structures); buildings; conveying;economics; high-strength concretes; mechanical properties; mixing; mixproportioning; placing; quality control; raw materials; reviews; structural design.

ACI Committee Reports, Guides, Standard Practices,and Commentaries are intended for guidance in design-ing, planning, executing, or inspecting construction andin preparing specifications. Reference to these docu-ments shall not be made in the Project Documents. Ifitems found in these documents are desired to be partof the Project Documents, they should be phrased inmandatory language and incorporated into the ProjectDocuments.

363R

Chapter l-Introduction, pg. 363R-21.l-Historical background1.2-Committee objectives

Chapter 2-Selection of materials, pg. 363R-32.1-Introduction2.2-Cements2.3-Chemical admixtures2.4-Mineral admixtures and slag cement

Copyright cO 1992, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by

any means, including the making of copies by any photo process, or by any elec-tronic or mechanical device, printed or written or oral, or recording for sound orvisual reproduction or for use in any knowledge or retrieval system or device,unless permission in writing is obtained from the copyright proprietors.

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363R-2 ACI COMMITTEE REPORT

2.5-Aggregates2.6-Water2.7-Cited references

Chapter 3-Concrete mix proportions, pg. 363R-83.1-Introduction3.2-Strength required3.3-Test age3.4-Water-cement ratio or water-cementitious ratio3.5-Cement content3.6-Aggregate proportions3.7-Proportioning with admixtures3.8-Workability3.9-Trial batches3.10-Cited references

Chapter 4-Batching, mixing, transporting, placing,curing, and control procedures, pg. 363R-16

4.1-Introduction4.2-Batching4.3-Mixing4.4-Transporting4.5-Placing procedures4.6-Curing4.7-Quality assurance4.8-Quality control procedures4.9-Strength measurements4.10-Cited references

Chapter 5-Properties of high-strength concrete, pg.363R-22

5.1-Introduction5.2-Stress-strain behavior in uniaxial compression5.3-Modulus of elasticity5.4-Poisson’s ratio5.5-Modulus of rupture5.6-Tensile splitting strength5.7-Fatigue strength5.8-Unit weight5.9-Thermal properties5.10-Heat evolution due to hydration5.11-Strength gain with age5.12-Freeze-thaw resistance5.13-Shrinkage5.14-Creep5.15-Cited references

Chapter 6-Structural design considerations, pg. 363R-29

6.1-Introduction6.2-Axially-loaded columns6.3-Beams and slabs6.4-Eccentric columns6.5-Summary6.6-Cited references

Chapter 7--Economic considerations, pg. 363R-417.1-Introduction

7.2-Cost studies7.3-Case histories7.4-Other studies7.5-Selection of materials7.6-Quality control7.7-Areas of application7.4-Conclusion7.9-Cited references

Chapter 8-Applications, pg. 363R-448.1-Introduction8.2-Buildings8.3-Bridges8.4-Special applications8.5-Potential applications8.6-Cited references

Chapter 9-Summary, pg. 363R-48

Chapter 10-References, pg. 363R-49

CHAPTER 1-INTRODUCTION

1.1-Historical backgroundAlthough high-strength concrete is often considered a

relatively new material, its development has been gradualover many years. As the development has continued, thedefinition of high-strength concrete has changed. In the1950s, concrete with a compressive strength of 5000 psi(34 MPa) was considered high strength. In the 1960s,concrete with 6000 and 7500 psi (41 and 52 MPa) com-pressive strengths were used commercially. In the early1970s, 9000 psi (62 MPa) concrete was being produced.More recently, compressive strengths approaching 20,000psi (138 MPa) have been used in cast-in-place buildings.

For many years, concrete with compressive strength inexcess of 6000 psi (41 MPa) was available at only a fewlocations. However, in recent years, the applications ofhigh-strength concrete have increased, and high-strengthconcrete has now been used in many parts of the world.The growth has been possible as a result of recent de-velopments in material technology and a demand forhigher-strength concrete. The construction of Chicago’sWater Tower Place and 311 South Wacker Drive con-crete buildings would not have been possible without thedevelopment of high-strength concrete. The use of con-crete superstructures in long span cable-stayed bridgessuch as East Huntington, W.V., bridge over the OhioRiver would not have taken place without the availabilityof high-strength concrete.

1.2-Committee objectivesSince the definition of high-strength concrete has

changed over the years, the committee needed to definean applicable range of concrete strengths for its activities.The following working definition was adopted: “The im-mediate concern of Committee 363 shall be concretes

HIGH STRENGTH CONCRETE 363R-3

have specified compressive strengths for design of 6000psi (41 MPa) or greater, but for the present time, con-siderations shall not include concrete made using exoticmaterials or techniques.”

The word exotic was included in the definition so thatthe committee would not be concerned with concretessuch as polymer-impregnated concrete, epoxy concrete,or concrete with artificial normal and heavy-weight ag-gregates.

Although 6000 psi (41 MPa) was selected as the lowerlimit, it is not intended to imply that there is a drasticchange in material properties or in production techniquesthat occur at this compressive strength.

In reality, all changes that take place above 6000 psi(41 MPa) represent a process which starts with the lower-strength concretes and continues into high-strength con-cretes. Many empirical equations used to predict prop-erties of concrete or to design structural members arebased on tests using concrete with compressive strengthsless than about 6000 psi (41 MPa). The availability ofdata for higher-strength concretes requires a reassess-ment of the equations to determine their applicabilitywith higher-strength concretes. Consequently, cautionshould be exercised in extrapolating data from lower-strength to high-strength concretes. If necessary, testsshould then be made to develop data for the materials orapplications in question.

The committee also recognized that the definition ofhigh-strength concrete varies on a geographical basis. Inregions where concrete with a compressive strength of9000 psi (62 MPa) is already being produced commercial-ly, high-strength concrete might be in the range of 12,000to 15,000 psi (83 to 103 MPa) compressive strength.However, in regions where the upper limit on commer-cially available material is currently 5000 psi (34 MPa)concrete, 9000 psi (62 MPa) concrete is considered highstrength. The committee recognized that material selec-tion, concrete mix proportioning, batching, mixing, trans-porting, placing, and control procedures are applicableacross a wide range of concrete strengths. However, thecommittee felt that material properties and structuraldesign considerations given in this report should be con-cerned with concretes having the highest compressivestrengths. The committee has tried to cover both aspectsin compiling this state-of-the-art report.

CHAPTER 2-SELECTION OF MATERIALS

2.1-IntroductionThe production of high-strength concrete that con-

sistently meets requirements for workability and strengthdevelopment places more stringent requirements onmaterial selection than for lower-strength concretes.Quality materials are needed and specifications requireenforcement. High-strength concrete has been producedusing a wide range of quality materials based on the re-sults of trial mixtures. This chapter cites the state ofI

knowledge regarding material selection and provides abaseline for the subsequent discussion of mix proportionsin Chapter 3.

Fig. 2.1-Effects of cement on concrete compressivestrength.2.2

2.2-CementsThe choice of portland cement for high-strength con-

strength is the objective, such as in prestressed concrete,there is no need to use a Type III cement. Furthermore,within a given cement type, different brands will have dif-ferent strength development characteristics because ofthe variations in compound composition and fineness thatare permitted by ASTM C 150.

Initially, silo test certificates should be obtained frompotential suppliers for the previous 6 to 12 months. Notonly will this give an indication of strength characteristicsfrom the ASTM C 109 mortar cube test, but also, moreimportantly, it will provide an indication of cement uni-formity. The cement supplier should be required to re-port uniformity in accordance with ASTM C 917. If thetricalcium silicate content varies by more than 4 percent,the ignition loss by more than 0.5 percent, or the finenessby more than 375 cm2/g (Blaine), then problems in main-taining a uniform high strength may result.2.1 Sulfate(SO,) levels should be maintained at optimum with varia-tions limited to ± 0.20 percent.

Although mortar cube tests can give a good indicationof potential strength, tests should be run on trial batches.These should contain the materials to be used in the joband be prepared at the proposed slump, with strengthsdetermined at 7, 28, 56, and 91 days. The effect ofcement characteristics on water demand is more notice-able in high-strength concretes because of the highercement contents.

High cement contents can be expected to result in ahigh temperature rise within the concrete. For example,


the temperature in the 4 ft (1.2 m) square columns usedin Water Tower Place which contained 846 lb cement/yd3

(502 kg/m3), rose to 150 F (66 C) from 75 F (24 C)during hydration.2.2 The heat was dissipated within 6 dayswithout harmful effects. However, when the temperaturerise is expected to be a problem, a Type II low-heat-of-hydration cement can be used, provided it meets thestrength-producing requirements.

A further consideration is the optimization of thecement-admixture system. The exact effect of a water-reducing agent on water requirement, for example, willdepend on the cement characteristics. Strength develop-ment will depend on both cement characteristics and ce-ment content.

2.3-Chemical admixtures2.3.1 General-Admixtures are widely used in the pro-

duction of high-strength concretes. These materials in-clude air-entraining agents and chemical and mineraladmixtures. Air-entraining agents are generally surfac-tants that will develop an air-void system appropriate fordurability enhancement. Chemical admixtures are gener-ally produced using lignosulfonates, hydroxylated car-boxylic acids, carbohydrates, melamine and naphthalenecondensates, and organic and inorganic accelerators invarious formulations. Selection of type, brand, and dos-age rate of all admixtures should be based on perfor-mance with the other materials being considered orselected for use on the project. Significant increases incompressive strength, control of rate of hardening, ac-celerated strength gain, improved workability, and dur-ability are contributions that can be expected from theadmixture or admixtures chosen. Reliable performanceon previous work should be considered during the selec-tion process.

2.3.2 Air-entraining admixtures (ASTM C 260)-Theuse of air entrainment is recommended to enhance dura-bility when concrete will be subjected to freezing andthawing while wet. As compressive strengths increase andwater-cement ratios decrease, air-void parameters im-prove and entrained air percentages can be set at thelower limits of the acceptable range as given in ACI 201.Entrained air has the effect of reducing strength, parti-cularly in high-strength mixtures, and for that reason ithas been used only where there is a concern for durabili-ty. See also Section 5.12.

2.3.3 Retarders (ASTM C 494, Types B and D)-High-strength concrete mix designs incorporate high cementfactors that are not common to normal commercial con-crete. A retarder is frequently beneficial in controllingearly hydration. The addition of water to retemper themixture will result in marked strength reduction. Further,structural design frequently requires heavy reinforcingsteel and complicated forming with attendant difficultplacement of the concrete. A retarder can control therate of hardening in the forms to eliminate cold jointsand provide more flexibility in placement schedules. Pro-jects have used retarders successfully by initially designing

mixtures with sufficient retarder dosage to give the desir-able rate of hardening under the anticipated temperatureconditions.

Since retarders frequently provide an increase instrength that will be proportional to the dosage rate, mix-tures can be designed at different doses if it is expectedthat significantly different rates will be used. However,there is usually an offsetting effect that minimizes thevariations in strengths due to temperature. As tempera-ture increases, later age strengths will decline; however,an increase in retarder dosage to control the rate ofhardening will provide some mitigation of the tempera-ture-induced reduction. Conversely, dosages should bedecreased as temperatures decline.

While providing initial retardation, strengths at 24hours and later are usually increased by normal dosages.Extended retardation or cool temperatures may affectearly (24-hour) strengths adversely.

2.3.4 Normal-setting water reducers (ASTM C 494,Type A-Normal setting ASTM C 494 Type A conven-tional water-reducing admixtures will provide strengthincreases without altering rates of hardening. Theirselection should be based on strength performance. In-creases in dosage above the normal amounts will gener-ally increase strengths, but may extend setting times.When admixtures are used in this fashion to provide re-tardation, a benefit in strength performance sometimesresults.

2.3.5 High-range water reducers 2.4,2.5 (ASTM C 494,Types F and G-High-range water reduction provideshigh-strength performance, particularly at early (24-hour)ages. Matching the admixture to the cement, both in typeand dosage rate, is important. The slump loss character-istics of a high-range water reducer (HRWR) will deter-mine whether it should be added at the plant, at the site,or a combination of each.

Use of a HRWR in high-strength concrete may servethe purpose of increasing strength at the slump or in-creasing slump. The method of addition should distributethe admixture throughout the concrete. Adequate mixingis critical to uniform performance. Supervision is im-portant to the successful use of a HRWR. The use ofsuperplasticizers is discussed further in ACI SP-68.2.6

2.3.6 Accelerators (ASTM C 494, Types C and E)-Ac-celerators are not normally used in high-strength con-crete unless early form removal is critical. High-strengthconcrete mixtures can provide strengths adequate for ver-tical form removal on walls and columns at an early age.Accelerators used to increase the rate of hardening willnormally be counterproductive in long-term strength de-velopment.

2.3.7 Admixture combinations-Combinations of high-range water reducers with normal-setting water reducersor retarders have become common to achieve optimumperformance at lowest cost. Improvements in strengthgain and control of setting times and workability areposstble with optimized combinations. In certain cir-cumstances, combinations of normal-setting or retarding


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water-reducing admixtures plus an accelerating admixturehave also been found to be useful.

When using a combination of admixtures, they shouldbe dispensed individually in a manner approved by themanufacturer(s). Air-entraining admixtures should, ifused, be dispensed separately from water-reducing ad-mixtures.

2.4-Mineral admixtures and slag cementFinely divided mineral admixtures, consisting mainly

of fly ash and silica fume, and slag cement have beenwidely used in high-strength concrete.

2.4.1 Fly ash-Fly ash for high-strength concrete isclassified into two classes. Class F fly ash is normally pro-duced from burning anthracite or bituminous coal andhas pozzolanic properties, but little or no cementitiousproperties. Class C fly ash is normally produced fromburning lignite or subbituminous coal, and in addition tohaving pozzolanic properties, has some autogenous ce-mentitious properties. In general, Class F fly ash is avail-able in the eastern United States and Canada, and ClassC fly ash is available in the western United States andCanada.

Specifications for fly ash are covered in ASTM C 618.Methods for sampling and testing are found inASTM C 311. Variations in physical or chemical proper-ties of mineral admixtures, although within the tolerancesof these specifications, may cause appreciable variationsin properties of high-strength concrete. Such variationscan be minimized by appropriate testing of shipmentsand increasing the frequency of sampling. ACI 212.2Rprovides guidelines for the use of admixtures in concrete.It is extremely important that mineral admixtures be test-ed for acceptance and uniformity and carefully investi-gated for strength-producing properties and compatibilitywith the other materials in the high-strength concretemixture before they are used in the work.

2.4.2 Silica fume - Silica fume and admixtures contain-ing silica fume2.8 have been used in high-strength con-cretes2.9, 2.10 for structural purposes and for surface ap-plications and as repair materials in situations whereabrasion resistance and low permeability are advanta-geous. Silica fume is a by-product resulting from the re-duction of high-purity quartz with coal in electric arcfurnaces in the production of silicon and ferrosilicon al-loys. The fume, which has a high content of amorphoussilicon dioxide and consists of very fine spherical par-ticles, is collected from the gases escaping from thefurnaces.

Silica fume consists of very fine vitreous particles witha surface area on the order of 20,000 m2/kg whenmeasured by nitrogen adsorption techniques 2.29 Theparticle-size distribution of a typical silica fume showsmost par-titles to be smaller than one micrometer (1µm) with an average diameter of about 0.1 µm, which isapproximately 100 times smaller than the average cementparticle. The specific gravity of silica fume is typically 2.2,but may be as high as 2.5. The bulk density as collected

is 10 to 20 lb/ft3 (160 to 320 kg/m3); however, it is alsoavailable in densified or slurry forms for commercialapplication.

Silica fume, because of its extreme fineness and highsilica content, is a highly effective pozzolanic material.The silica fume reacts pozzolanically with the lime duringthe hydration of cement to form the stable cementitiouscompound calcium silicate hydrate (CSH). The availabili-ty of high-range water-reducing admixtures has facilitatedthe use of silica fume as part of the cementing materialin concrete to produce high-strength concretes.2.29 Nor-mal silica fume content ranges from 5 to 15 percent ofportland cement content.

The use of silica fume to produce high-strengthconcrete increased dramatically in the 1980s. Both labor-atory and field experience indicate that concrete incor-porating silica fume has an increased tendency to developplastic shrinkage cracks. 2.29 Thus, it is necessary toquickly cover the surfaces of freshly placed silica-fumeconcrete to prevent rapid water evaporation. Since it isa relatively new material to the concrete industry in theUnited States, the user is referred to several recentsymposia and publications for additional information on

2.4.3 Slag cement - Ground slag cement is producedonly in certain areas of the United States and Canada.Specifications for ground granulated blast furnace slagare given in ASTM C 989. The classes of portland blastfurnace slag cement are covered in ASTM C 595. Slagappropriate for concrete is a nonmetallic product that isdeveloped in a molten condition simultaneously with ironin a blast furnace. When properly quenched and pro-cessed, slag will act hydraulically in concrete as a partialreplacement for portland cement. Slag can be inter-round with cement or used as an additional cement at

the batching facility. Blast furnace slag essentially consistsof silicates and alumino-silicates of calcium and otherbases. Research using ground slag shows much promisefor its use in high-strength concrete.

2.4.4 Evaluation and selection - Mineral admixturesand slag cement, like any material in a high-strength con-crete mixture, should be evaluated using laboratory trialatches to establish the optimum desirable qualities.

Materials representative of those that will be employedater in the actual construction should be used. Particularare should be taken to insure that the mineral admix-ure comes from bulk supplies and that they are typical.enerally, several trial batches are made using varying

ement factors and admixture dosages to establish curveshich can be used to select the amount of cement anddmixture required to achieve the desired results.

When fly ash is to be used, the minimum requirements that it comply with ASTM C 618. Although this specifi-ation permits a higher loss on

2.11ignition, an ignition loss

f 3 percent or less is desirable. High fineness, uni-ormity or production, high pozzolanic activity, and com-atibility with other mixture ingredients are items of pri-ary importance.


2

2.5-Aggregates2.5.1 General - Both fine and coarse aggregates used

for high-strength concrete should, as a minimum, meetthe requirements of ASTM C 33; however, the followingexceptions may be beneficial.

2.5.2 - Grading2.5.2.1 Fine aggregate - Fine aggregates with a

rounded particle shape and smooth texture have beenfound to require less mixing water in concrete and forthis reason are preferable in high-strength concrete2.11

’2.1

The optimum gradation of fine aggregate for high-strength concrete is determined more by its effect onwater requirement than on physical packing. One re-port2.10 stated that a sand with a fineness modulus (PM)below 2.5 gave the concrete a sticky consistency, makingit difficult to compact. Sand with an FM of about 3.0gave the best workability and compressive strength.

High-strength concretes typically contain such highcontents of fine cementitious materials that the gradingof the aggregates used is relatively unimportant com-pared to conventional concrete. However, it is sometimeshelpful to increase the fineness modulus. A NationalCrushed Stone Association report2.13 made several re-commendations in the interest of reducing the water re-quirement. The amounts passing the No. 50 and 100sieves should be kept low, but still within the require-ments of ASTM C 33, and mica or clay contaminantsshould be avoided. Another investigation2.13 found thatthe sand gradation had no significant effect on earlystrengths but that “at later ages and consequently higherlevels of strength, the gap-graded sand mixes exhibitedlower strengths than the standard mixes.”

2.5.2.2 Coarse aggregate

compressive strength with high cement content and lowwater-cement ratios the maximum size of coarse aggre-gate should be kept to a minimum, at ½ in. (12.7 mm) orH in. (9.5 mm). Maximum sixes of ¾ in. (19.0 mm) and1 in. (25.4 mm also have been used successfully. Cordonand Gillespie2.19 felt that the strength increases werecaused by the reduction in average bond stress due to theincreased surface area of the individual aggregate. Alex-ander2.20 found that the bond to a 3 in. (76 mm) aggre-gate particle was only about l/10 of that to a ½-in. (13mm) particle. He also stated that except for very good orvery bad aggregates the bond strength was about 50 to 60percent of the paste strength at 7 days.

Smaller aggregate sixes are also considered to producehigher concrete strengths because of less severe concen-trations of stress around the particles, which are causedby differences between the elastic moduli of the pasteand the aggregate.

Many studies have shown that crushed stone produceshigher strengths than rounded gravel. The most likelyreason for this is the greater mechanical bond which candevelop with angular particles. However, accentuated an-gularity is to be avoided because of the attendant highwater requirement and reduced workability. The ideal ag-

gregate should be clean, cubical, angular, 100 percentcrushed aggregate with a minimum of flat and elongatedparticles.2.13

Because, as stated earlier, bond strength is the limitingfactor in the development of high-strength concrete, themineralogy of the aggregates should be such as to pro-mote chemical bonding. Some work has been done withartificial material such as portland and aluminous cementclinkers and selected slags.2.14,221 The long-term stabilityof the clinkers is in question, however. Harris2.22 statesthat Moorehead measured a potential silica-lime bond ofat least 28,000 psi (193 M Pa). Presumably many siliceousminerals would prove to have good bonding potentialwith portland cement. This would appear to be a promis-ing area for further research.

2.5.3 Absorption -Curing is extremely important in theproduction of high-strength concrete. To produce acement paste with as high a solids content as possible,the concrete must contain the absolute minimum mixwater. However, after the concrete is in place and thepaste structure is established, water should be freelyavailable, especially during the early stages of hydra-tion 2.14,2.23 During this period, a great deal of watercombines with the cement. All of this water loses approx-imately ¼ of its volume after the chemical reactions arecompleted. This creates a small vacuum that is capable ofpulling water short distances into the concrete which, atthis time, is still relatively permeable. Any extra waterwhich can enter the structure will increase the ultimateamount of hydration and, therefore the percent of solidsper unit volume of paste, thereby increasing its strength.If the aggregates are capable of absorbing a moderateamount of water, they can act as tiny curing-water reser-voirs distributed throughout the concrete, thereby pro-viding the added curing water which is beneficial to theselow water-cement ratio pastes.

2.5.4 Intrinsic aggregate strength-It would seem ob-vious that high-strength concrete would require high-strength aggregates and, to some extent, this is true.However, several investigators2.24,2.25 have found that, forsome aggregates, a point is reached beyond which furtherincreases in cement content produce no increase in thecompressive strength of the concrete. This apparently isnot due to having fully developed the compressivestrength of the concrete but to having reached the limitof the bonding potential of that cement-aggregate com-bination.

2.6-WaterThe requirements for water quality for high-strength

concrete are no more stringent than those for conven-tional concrete. Usually, water for concrete is specified tobe of potable quality. This is certainly conservative butusually does not constitute a problem since most concreteis produced near a municipal water supply. However,cases may be encountered where water of a lower qualitymust be used. In such cases, test concrete should bemade with the water and compared with concrete made

TH CONCRETE 363R-7

with distilled water, or it may be more convenient tomake ASTM C 109 mortar cubes. In either case, speci-mens should be tested in compression at 7 and 28 days.If those made with the water in question are at leastequal to 90 percent of the compressive strength of thespecimens made with distilled water, the water then canbe considered acceptable to U.S. Army Corps of En-gineers’ requirements2.26 and ASTM C 94.

For more detailed information on specific contamin-ants refer to the literature in References 2.27, 2.28, and2.29. Test methods for water for special situations aregiven in AASHTO T26.

2.7-Cited references(See also Chapter 10-References)

2.1. Hester, Weston, “High Strength Air-EntrainedConcrete,” Concrete Construction, V. 22, No. 2, Feb. 1977,pp. 77-82.

2.2. “High Strength Concrete in Chicago High-RiseBuildings,” Task Force Report No. 5, Chicago Committeeon High-Rise Buildings, Feb. 1977, 63 pp.

2.3. Freedman, Sydney, “High-Strength Concrete,”Modern Concrete, V. 34, No. 6, Oct. 1970, pp. 29-36; No.7, Nov. 1970 pp 28-32; No. 8, Dec. 1970, pp. 21-24; No.9, Jan. 1971, pp. 15-22; and No. 10, Feb. 1971, pp. 16-23.Also, Publication No. IS176T, Portland Cement Associa-tion.

2.4. “Superplasticizing Admixtures in Concrete,” Pub-lication No. 45.030, Cement and Concrete Association,Wexham Springs, 1976, 32 pp.

2.5. Eriksen, Kirsten, and Nepper-Christensen, Palle,“Experiences in the Use of Superplasticizers in SomeSpecial Fly Ash Concretes,” Developments in the Use ofSuperplasticizers, SP-68, American Concrete Institute,Detroit, 1981, pp. 1-20.

2.6. Developments in the Use of Superplasticizers, SP-68,American Concrete Institute, Detroit, 1981, 572 pp.

2.7. Wolsiefer, John, “Ultra High-Strength Field Place-able Concrete with Silica Fume Admixture,” Concrete In-ternational Design & Construction, V. 6, No. 4, Apr. 1984,pp. 25-31.

2.8. Malhotra, V.M., and Carette, G.G., “Silica Fume,”Concrete Construction, V. 27, No. 5, May 1982, pp. 443-446.

2.9. Fly Ash, Silica Fume, Slag, and other MineralBy-Products in Concrete, SP-79, American Concrete Insti-tute, Detroit, 1983, 1196 pp.

2.10. Blick, Ronald L., “Some Factors InfluencingHigh-Strength Concrete,” Modern Concrete, V. 36, No. 12,Apr. 1973, pp. 38-41.

2.11. Wills, Milton H., Jr., “How Aggregate ParticleShape Influences Concrete Mixing Water Requirementand Strength,” Journal of Materials, V. 2, No. 4, Dec.1967, pp. 843-865.

2.12. Gaynor, R.D., and Meininger, R.C., “EvaluatingConcrete Sands: Five Tests to Estimate Quality,” Con-crete International Design & Construction, V. 5, No. 12,Dec. 1983, pp. 53-60.

2.13. “High Strength Concrete,” Manual of ConcreteMaterials-Aggregates, National Crashed Stone Associa-tion, Washington, D.C. Jan. 1975, 16 pp.

2.14. Perenchio, W.P., “An Evaluation of Some of theFactors Involved in Producing Very High-Strength Con-crete,” Research and Development Bulletin No. RD014,Portland Cement Association, Skokie, 1973, 7 pp.

2.15. “Methods of Achieving High Strength Concrete,”ACI JOURNAL, Proceedings V. 64, No. 1, Jan. 1967, pp.45-48.

2.16. Fowler, Earl W., and Lewis, D.W., “Flexure andCompression Tests of High Strength, Air-Entraining SlagConcrete,” ACI JOURNAL, Proceedings V. 60, No. 1, Jan.1963, pp. 113-128.

2.17. Harris, A.J., “High-Strength Concrete: Manufac-ture and Properties,” The Structural Engineer (London),V. 47, No. 11, Nov. 1969, pp. 441-446.

2.18. Walker, Stanton, and Bloem, Delmar L., “Effectsof Aggregate Size on Properties of Concrete,” ACIJOURNAL, Proceedings V. 57, No. 3, Sept. 1960, pp. 283-298.

2.19. Cordon, William A, and Gillespie, H. Aldridge,“Variables in Concrete Aggregates and Portland CementPaste Which Influence the Strength of Concrete,” ACIJOURNAL, Proceedings V. 60, No. 8, Aug. 1963, pp. 1029-1052.

2.20. Alexander, K.M., “Factors Controlling theStrength and Shrinkage of Concrete,” ConstructionalReview (North Sydney), V. 33, No. 11, Nov. 1960, pp.19-28.

2.21 “Tentative Interim Report of High StrengthConcrete,” ACI JOURNAL, Proceedings V. 64, No. 9, Sept.1967, pp. 556-557.

2.22. Harris, A.J., “Ultra High Strength Concrete,”Journal, Prestressed Concrete Institute, V. 12, No. 1, Feb.1967, pp. 53-59.

2.23. Klieger, Paul, “Early High Strength Concrete forPrestressing,” Proceedings, World Conference on Pre-stressed Concrete, San Francisco, 1957, pp. A5-1-A5-14.

2.24. Burgess. A. James; Ryell, John; and Bunting,John, “High Strength Concrete for the Willows Bridge,”ACI JOURNAL, Proceedings V. 67, No. 8, Aug. 1970, pp.611-619.

2.25. Gaynor, Richard D., “High Strength Air-En-trained Concrete,” Joint Research Laboratory PublicationNo. 17, National Sand and Gravel Association/NationalReady Mixed Concrete Association, Silver Spring, Mar.1968, 19 pp.

2.26. “Requirements for Water for Use in Mixing orCuring Concrete,” (CRD-C 400-63), Handbook for Con-crete and Cement, U.S. Army Engineer WaterwaysExperiment Station, Vicksburg, 2 pp.

2.27. Concrete Manual, 8th Edition, U.S. Bureau ofReclamation, Denver, 1975, 627 pp.

2.28. McCoy, W.J., “Mixing and Curing Water forConcrete,” Significance of Tests and Properties of Concreteand Concrete-Making Materials, STP-169A, AmericanSociety for Testing and Materials, Philadelphia, 1966, pp.


515-521.2.29. “Silica Fume in Concrete,” preliminary report by

ACI Committee 226, Materials Journal, AmericanConcrete Institute, Detroit, V. 84, No. 2, Mar.-Apr. 1987.

2.30 Fly Ash, Silica Fume, Slag and Natural Pozzolansin Concrete, SP-91, American Concrete Institute, Detroit,1986, 1628 pp.

2.31 Proceedings of the International Workshop on Con-densed Silica Fume in Concrete, CANMET, Montreal,Canada, May 1987.

2.32 Proceedings of the Third International Conferenceon Fly Ash, Silica Fume, and Natural Pozzolans inConcrete, SP-114, American Concrete Institute, Detroit,1989.

CHAPTER 3 - CONCRETE MIX PROPORTIONS

Concrete mix proportions for high-strength concretehave varied widely depending upon many factors. Thestrength level required, test age, material characteristics,and type of application have influenced mix proportions.In addition, economics, structural requirements, manufac-turing practicality, anticipated curing environment, andeven the time of year have affected the selection of mixproportions. Much information on proportioning con-crete mixtures is available in ACI 211.1 and ACISP-46. 3.1 Included in ACI publication SP-46 is the paper“Proportioning and Controlling High Strength Concrete”(SP-46-9).

High-strength concrete mix proportioning is a morecritical process than the design of normal strength con-crete mixtures. Usually, specially selected pozzolanic andchemical admixtures are employed, and the attainment ofa low water-cementitious ratio is considered essential.Many trial batches are often required to generate thedata that enables the researcher to identify optimum mixproportions.

3.2-Strength required3.2.1 ACI 318- The ACI Building Code Requirements

for Reinforced Concrete (ACI 318) describes concretestrength requirements. Normally the concrete has beenproportioned in such a manner that the mean average ofcompressive strength test results has exceeded the spe-cified strength fc' by an amount sufficiently high tominimize the relative frequency of test results below thespecified strength value.

An average value can be calculated for any set ofmeasurement data. The amount that individual test val-ues deviate from the average is usually quantified bycalculation of the standard deviation. Calculation ofstandard deviation on concrete test histories can be avaluable aid in predicting future test result variability.

Many factors can influence the variability of the testresults, including the individual materials, plants, contrac-

tors, inspection agencies, and environmental conditions.All factors which will affect the variability of strengthsand strength measurements should be considered whenselecting mix proportions and when establishing the stan-dard deviation acceptable for strength results. Materialsand proportions used for qualifying the mixture shouldnot be more closely controlled than is planned for theproposed work. Kennedy and Price have identified fac-tors which contribute to the variability of measured com-pressive strengths of concretes in lower strengthranges. 3.3,3.4

Hester identified sources of measured strength vari-ations in high-strength concretes. 3.5 High-strength con-crete is recognized to be more difficult to test accuratelythan normal strength concretes. Testing difficulties maycontribute to lower measured values or higher variability.

A high variance in test results will dictate a higherrequired average strength. If variability is predicted to berelatively low, but proves to be higher, the frequency oftest results below the specified strength may be unaccept-ably high. Therefore, when selecting a target standarddeviation the concrete producer should submit the mostappropriate test record.3.6 A higher required averagestrength may be difficult or impossible to attain whenproducing high-strength concretes because mix propor-tions may already be optimized.

ACI 318 recognizes that some test results are likely tobe lower than the specified strength. The most commondesign approach has been to limit the frequency of testsallowed to fall below the specified strength. The concretehas been judged acceptable if the following requirementsare met:

a) The average of all sets of three consecutive strengthtest results shall equal or exceed the required fc'.

b) No individual strength test (average of two cylin-ders) shall fall below fc' by more than 500 psi (3.4 MPa).

However, some designers have specified higher orlower overdesign strengths than called for in ACI 318regardless of established performance.

Schmidt and Hoffman3.7 report that they do not auto-maticalIy order removal of concrete which is representedby cylinders 500 psi (3.4 MPa) below specified strengthbut do order adjustment of the mixture and correction ofthe deficiency. This is because the ACI 318 Section 4.7.4was established for concretes with strengths in the rangeof 3000 to 5000 psi (21 to 34 MPa). High-strength con-cretes continue to gain considerable strengths above andbeyond design requirements with the passage of time,more than lower-strength concretes.3.7 While the percen-tage gain of compressive strength of high-strength con-cretes from 7 days to 90 days may be equal to or lowerthan concretes in lower strength ranges, the order ofmagnitude of strength gain expressed in psi is actuallymuch higher. For example, a mixture which averages2500 psi (17.2 MPa) in 7 days may average 4200 psi (29MPa) in 90 days. It would have gained strength equal to68 percent of the 7-day strength, or 1700 psi (11.7 MPa)at the age of 90 days. A mixture averaging 7300 psi (50.3


MPa) in 7 days could average 10,000 psi (69 MPa) in 90days. That would be an increase of only 37 percent, butit would have gained 2700 psi (18.6 MPa), a full 1000 psi(6.9 MPa) higher total gain than the lower-strengthmixture.

ACI 318 allows mix designs to be proportioned basedon field experience or by laboratory trial batches. Whenthe concrete producer chooses to select high-strengthconcrete mix proportions based upon laboratory trialbatches, confirming tests results from concretes placed inthe field should also be established.

3.2.2 ACI 214-- Once sufficient test data have beengenerated from the job, a reevaluation of mix propor-tions using “Recommended Practice for Evaluation ofCompression Test Results of Concrete (ACI 214)” maybe appropriate. Analyses affecting reproportioning ofmixtures based upon test histories are described inSections 4.8.1 and 4.8.2.

3.2.3 Other Strength Requirements--In some situations,considerations other than compressive strength may in-fluence mix proportions. Detailed discussion of materialproperties including flexural and tensile strengths is givenin Chapter 5.

3.3- Test ageThe selection of mix proportions can be influenced by

the testing age. This testing age has varied dependingupon the construction requirements. Most often thetesting age has been thought to be the age at which theacceptance criteria are established, for example at 28days. Testing, however, has been conducted prior to theage of acceptance testing, or after that age, dependingupon the type of information required.

3.3.1 Early Age-- Prestressed concrete operations mayrequire high strengths in 12 to 24 hours. Special appli-cations for early use of machinery foundations, pavementtraffic lanes, or slip formed concrete have required highstrengths at early ages. Post-tensioned concrete is oftenstressed at ages of approximately 3 days and requiresrelatively high strengths. Generally concretes which de-velop high later-age strengths will also produce highearly-age strengths. However, the optimum materialsselected, and therefore the mix proportions, may vary fordifferent test ages. For example, Type III cement and nofly ash have been used in a high early-strength design,compared to Type I or II cement and fly ash for a later-age strength design. Early-age strengths may be morevariable due to the influence of curing temperature andthe early-age characteristics of the specific cement.Therefore, anticipated mix proportions should be evalu-ated for a higher required average strength or a later testage.

3.3.2 Twenty-eight days- A very common test age forcompressive strength of concrete has been 28 days. Per-formance of structures has been empirically correlatedwith moist-cured concrete cylinders, usually 6 x 12 in.(152 x 305 mm) prepared according to ASTM C 31 andC 192. This has produced good results for concretes with-

in lower strength ranges not requiring early strengths orearly evaluation. High-strength concretes gain consider-able strengths at later ages and, therefore, are evaluatedat later ages when construction requirements allow theconcrete more time to develop strengths before loads areimposed. Proportions, notably cementitious components,have usually been adjusted depending upon test age.

3.3.3 Later age-- High-strength concretes are frequentlytested at later ages such as 56 or 90 days. High-strengthconcrete has been placed frequently in columns of high-rise buildings. Therefore, it has been desirable to takeadvantage of long-term strength gains so that efficientuse of construction materials can be achieved. This hasoften been justified in high-rise buildings where fullloadings may not occur until later ages.

In cases where later-age acceptance criteria have beenspecified, it may be advantageous for the concrete sup-plier to develop earllater-age strengths.3.8

-age or accelerated tests to predictThe ACI publication SP-56, Accel-

erated StrengthTesting, provides information on acceler-ated testing.3.9 Of course, historical correlation data mustbe developed relative to the materials and proportions tobe used in the work. These tests may not always accur-ately predict later-age strengths; however, these testscould provide an early identification of lower-strengthtrends before a long history of non-compliance isrealized. Later-age acceptance criteria can leave suspectconcrete in question for a long time.

Test cylinders have been held for testing at ages laterthan the specified acceptance age. In cases where thespecified compressive strength fc' was not achieved, sub-sequent testing of later-age or “hold” cylinders has some-times justified the acceptance of the concrete in question.

3.3.4 Test age in relationship to curing- When selectingmix proportions, the type of curing anticipated should beconsidered along with the test age, especially when de-signing for high early strengths. Concretes gain strengthas a function of maturity, which is usually defined as afunction of time and curing temperature.

3.4- Water-cement ratio or water-cementitious ratio3.4.1 Nature of water-cement ratio in high-strength con-

crete- The relationship between water-cement ratio andcompressive strength, which has been identified in low-strength concretes, has been found to be valid for higher-strength concretes also. Higher cement contents andlower water contents have produced higher strengths.Proportioning larger amounts of cement into the con-crete mixture, however, has also increased the waterdemand of the mixture. Increases in cement beyond acertain point have not always increased compressivestrengths. Other factors which may limit maximumcement contents are discussed in Section 3.5.3. Whenpozzolanic materials are used in concrete, a water-cementplus pozzolan ratio by weight has been considered inplace of the traditional water-cement ratio by weight. Flyash meeting requirements of ASTM C 618 with a loss onignition of less than 3.0 percent and ASTM C 494 types


A, D, F, and G chemical admixtures have usually beenused.3.10

Of course the slump of the concrete is related to thewater-cementitious ratio and the total amount of waterin the concrete. While 0 to 2 in. slump concrete has beenproduced in precast operations, special consolidation ef-forts are required. Specified slumps for cast-in-place con-cretes not containing high-range water reducers haveranged from 21/2 to 41/4 in. (64 to 114 mm). Field-placednonplasticized concretes have had measured slumps aver-aging as high as 43/4 in. (121 mm).3.10

The use of high-range water reducers has providedlower water-cementitious ratios and higher slumps.3.11

Water-cementitious ratios by weight for high-strengthconcretes typically have ranged from 0.27 to 0.50. Thequantity of liquid admixtures, particularly high-rangewater reducers, sometimes has been included in thewater-cementitious ratio.

3.4.2 Estimating compressive strength-- The compressivestrength that a concrete will develop at a given water-cementitious ratio has varied widely depending on thecement, aggregates, and admixtures employed.

Principal causes of variations in compressive strengthsat a given water-cementitious ratio include the strength-producing capabilities of the cement and potential forpozzolanic reactivity of the fly ash or other pozzolan ifused. Different types and brands of portland cement haveproduced different compressive strengths as shown in Fig.3.1. 3.2,3.12

CompressiveStrength ,

psi10000

L

Fig. 3.1-- Effects of various brands of cement on concretecompressive strength 3.2,3.12

Specific information pertaining to the range of valuesof compressive strengths of cements has been publishedin ASTM C 917 and Peters.3.13 Fly ashes may vary inpozzolanic activity index from 75 percent to 110 percentof the portland cement control, as defined inASTM C 618. Proprietary pozzolans containing silicafume have been reported to have activity indexes inexcess of 200 percent.3.14 The water requirement of the

particular pozzolan employed has varied and has gener-ally increased with increasing fineness of the pozzolan.Often water requirements for fly ash concrete are lowerthan for portland cement. This helps to lower the water-cementitious ratio of the mixture.

Perenchio 3.15 has reported variable compressivestrength results at given water-cement ratios in laboratoryprepared concretes, depending on the aggregates used. Inaddition, these results have differed from results achievedin actual production with materials from the same area.A range of typical strengths reported at given water-cementitious ratios is represented in Fig. 3.2. Trialbatches with materials actually to be used in the workhave been found to be necessary. Generally, laboratorytrial batches have produced strengths higher than thosestrengths which are achievable in production, as seen inFig. 3.33.2

Krxo

CompressiveStrength ,

psi800

CompressiveStrength,

MPa

Water - Cementitious Ratio

Fig. 3.2-- Strength versus water-cement ratios of variousmixtures 3.2,3.10,3.15,3.16

3.5-Cement contentThe cement quantity proportioned into a high-strength

mixture has been determined best by the fabrication oftrial batches. Common cement contents in high-strengthconcrete test programs range from 660 to 940 lb per yd3

(392 to 557 kg/m3).3.2,3.16 In evaluating optimum cementcontents, trial mixes usually are proportioned to equalconsistencies, allowing the water content to vary accord-ing to the water demand of the mixture.

3.5.1 Strength-For any given set of materials in aconcrete mixture, there may be a cement content thatproduces maximum concrete strength. The maximumstrength may not always be increased by the use of


8000CompressiveStrength,

psi6000

4000

2000

r

1 1

28 56

Age , days

-1190

CompessiveStrength,

MPo

40

Fig. 3.3--Laboratory-molded concrete strengths versusready-mixed field-molded concrete strengths for 9000 psi (62MPa) concrete. 3.2

cement added to the mixture beyond this optimum ce-ment content. The strength for any given cement contentwill vary with the water demand of the mixture and thestrength-producing characteristics of that particularcement as shown in Fig. 3.1. The “Standard Method ofEvaluation of Cement Strength Uniformity from a SingleSource” (ASTM C 917) may prove useful in consideringcement mill sources.3.13 Mortar cube compressivestrength data of cements at ages of up to 90 days havebeen evaluated when proportioning cement in high-strength mixtures.

The strength of the concrete mixture will depend uponthe gel-space ratio, which is defined as the “ratio of thevolume of hydrated cement paste to the sum of the vol-umes of the hydrated cement and of the capillarypores.“ 3.17 This is particularly true when air-entrainingadmixtures are employed. Higher cement contents in air-entrained concrete have not been found to be useful inproducing strengths equivalent to, or approaching,strengths attainable with non-air-entrained concretes.Incorporation of entrained air may reduce strength at aratio of 5 to 7 percent for each percent of air in the mixas shown in Fig. 3.4.

3.5.2 Optimization-- A principal consideration in est-ablishing the desired cement content will be the iden-tification of combinations of materials which will produceoptimum strengths. Ideally, evaluations of each potentialsource of cement, fly ash, liquid admixture, and aggregatein varying concentrations would indicate the optimum ce-ment content and optimum combination of materials.Testing costs and time requirements usually have limited

60. Agg. No. I. Agg. No. 2

50 - . Agg. No.3

Reduction in Comp. 40Strength BelowNon-A .E . Concre te 30of Some W/C, %

Points Represent Avg.of ?-and 28-Day Tests

0 2 4 6 6 IO

Added Air , percent

Fig. 3.4--Strength reduction by air entrainment 3.26

the completeness of the testing programs, but particularattention has been given to evaluation of the brand ofcement to be used with the class and source of pozzolan,if a pozzolan is to be used. Prior to 1977, Chicago high-strength experience was based on concretes using ClassF fly ash, while other high-strength work has been donein Houston using Class C fly ash. 3.2,3.10 Class C fly ashhas been used in Chicago since 1977.

The strength efficiency of cement will vary for differ-ent maximum size aggregates at different strength levels.Higher cement efficiencies are achieved at high strengthlevels with lower maximum aggregate sixes. -* Fig. 3.5illustrates this principle. For example, a maximum ag-gregate size of less than % in. (9.5 mm) yields the highestcement efficiency for a 7000 psi (48.3 MPa) mixture.

Strength Efficiency,

p i / l b o f cemen t / cu

IO

6

Yd

r/ /

= 3.8 to 5.8 in. = 28 days, Moist

No. 4 + $ It 3 6Maximum Size Aggregate , in.

Fig. 3.5-- Maximum size aggregate for strength efficiency en-velop. 3.2

363R-12 ACI COMMlTTEE REPORT

3.5.3 Limiting factors-There are several factors whichmay limit the maximum quantity of cement which may bedesirable in a high-strength mixture. The strength of theconcrete may decrease if cement is added above andbeyond a given optimum content. The maximum desir-able quantity of cement may vary considerably dependingupon the efficiency of dispersing agents, such as high-range water reducers, in preventing flocculation ofcement particles.

Stickiness and loss of workability will be increased ashigher amounts of cement are incorporated into the mix-ture. Combinations of cement, pozzolans, and sandshould be evaluated for the effect of cementitious con-tent upon mixture placeability. Incorporation of an air-entraining admixture may necessitate reevaluation of theeffect of the cement upon mixture workability.

The maximum temperature desired in the concreteelement may limit the quantity or type of cement in themixture. 3.2,3.18 Modification of the mixture with ice, setretarders, or pozzolans may be helpful.

Cement-rich mixtures frequently have very high waterdemands. Therefore, it is possible that special pre-cautions may be necessary to provide adequate curingwater, so that sufficient hydration can occur. It may bepreferable to reduce the amount of cement in the mix-ture and to rely upon more careful selection of aggre-gates, aggregate proportions, etc., optimizing the use ofother constituents.

The amount of slump loss experienced, with attendantincrease in retempering water, and the setting time of theconcrete has varied depending upon the type, brand, andquantity of cement use. Lower cement contents, withinlimits, are desirable in order to enhance the placementcapabilities of the mixture, provided that adequatestrengths can be achieved.

3.6-Aggregate proportionsIn the proportioning of high-strength concrete, the

aggregates have been a very important considerationsince they occupy the largest volume of any of theingredients in the concrete. Usually, high-strengthconcretes have been produced using normal weight ag-gregates. Shideler3.19 and Holm 3.20 have reported onlight-weight high-strength structural concrete. Mather3.21

has reported on high-strength high-density concrete usingheavyweight aggregate.

3.6.1 Fine aggregates-In proportioning a concrete mix-ture, it is generally agreed that the fine aggregates orsand have considerably more impact on mix proportionsthan the coarse aggregates.

The fine aggregates contain a much higher surfacearea for a given weight than do the larger coarse ag-gregates. Since the surface area of all the aggregateparticles must be coated with a cementitious paste, theproportion of fine to coarse can have a direct quan-titative effect on paste requirements. Furthermore, theshape of these sand particles may be either spherical,subangular, or very angular. This property can alter paste

requirements even though the net volume of the sandremains the same.

The gradation of the fine aggregate plays an importantrole in properties of the plastic as well as the hardenedconcrete. For example, if the sand has an overabundanceof the No. 50 and No. 100 sieve sixes, the plastic work-ability will be improved but more paste will be needed tocompensate for the increased surface area. This could re-sult in a costlier mixture, or if the paste volume is in-creased by adding water, a serious loss in strength couldresult. It is sometimes possible, although not always prac-tical economically, to blend sands from different sourcesto improve their gradation and their capacity to producehigher-strength concrete.

Low fine aggregate contents with high coarse aggre-gate contents have resulted in a reduction in paste re-quirements and normally have been more economical.Such proportions also have made it possible to producehigher strengths for a given amount of cementitious ma-terials. However, if the proportion of sand is too low,serious problems in workability become apparent.

Consolidation by means of mechanical vibrators mayhelp to overcome the effects of an undersanded mixture,and the use of power finishing equipment can help tooffset the lack of trowelability.

Particle shape and surface texture of fine aggregatecan have as great an effect on mixing water requirementsas those of coarse aggregate.“” Tests made by Bloemand Gaynor3.22 show that concrete-mixing water require-ments for each cubic yard of concrete change 1 gal. (3.8L) for each change of 1 percent in the void content ofthe sand. Following the work by Bloem and Gaynor, theNSGA-NRMCA Joint Research Laboratory has simpli-fied the procedure for conducting the void content testof sand and a modified gradation is now used. The newprocedure is described in Reference 2.12.

3.6.2 Coarse aggregates-The optimum amount andsize of coarse aggregate for a given sand will depend toa great extent on the characteristics of the sand. Mostparticularly it depends on the fineness modulus (FM) ofthe sand. This is brought out specifically in Table 3.1,which is taken from ACI 211.1. One reference 3.23 sug-gests that the proportion of coarse aggregate shown inTable 3.1 might be increased by up to 4 percent if sandswith low void contents are used. If the sand particles arevery angular, then it is suggested that the amount ofcoarse aggregate should be decreased by up to 4 percentfrom the values in the table. Such adjustments in theproportion of coarse aggregate and sand have been in-tended to produce concretes of equivalent workability,although such changes will alter the water demand for agiven slump. When more or less water is needed in agiven volume of concrete, to preserve the same consis-tency of paste, it is also necessary to adjust the amountof cement or cementitious materials if a given water-cement ratio is to be maintained.

Another possible expedient in the proportioning ofcoarse aggregates for high-strength concrete is to alter


Table 3.1-Volume of coarse aggregate per unit ofvolume of concrete*

I Volume of dry-roddedcoarse aggregate’

per unit volume of concrete fordifferent fineness moduli of sand

*Table 3.1 Taken from ACI 211.1.+Volumes are based on aggregates in dry-rodded condition as described inASTM C 29 for Unit Weight of Aggregate.

These volumes are selected from empirical relationships to produce concretewith a degree of workability suitable for usual reinforced construction. For lessworkable concrete such as required for concrete pavement construction, theymay be increased about 10 percent. For more workable concrete see Section5.3.6.1.

the amount of these aggregates passing certain sieve sixesfrom the amounts shown in ASTM C 33. This method isdescribed in Reference 3.24 and 3.25 as a means ofavoiding “particle interference,” thus permitting a greateramount of coarse aggregate and less total sand. This hashelped to reduce the paste requirements or permit theuse of a more viscous paste, resulting in a higherstrength.

3.6.3 Proportioning aggregates-The amounts of coarseaggregate suggested in Table 3.1 (which is Table 5.3.6 ofACI 211.1) are recommended for initial proportioning.Considerations should be given to the properties of thesand (FM, angularity, etc.) which may alter the quantityof coarse aggregate. In general, the least sand consistentwith necessary workability has given the best strengths fora given paste. Mechanical tools for handling and placingconcrete have helped to decrease the proportion of sandneeded. As previously stated, the use of the smaller sixesof coarse aggregate are generally beneficial, and crushedaggregates seem to bond best to the cementitious paste.

3.7-Proportioning with admixturesNearly all high-strength concretes have contained ad-

mixtures. Changes in the quantities and combinations ofthese admixtures affect the plastic and hardened proper-ties of high-strength concrete. Therefore, special at-tention has been given to the effects of these admixtures(described in Sections 2.3 and 2.4). Careful adjustmentsto mix proportions have been made when changes in ad-mixture quantities or combinations have been made. Ma-terial characteristics have varied extensively, makingexperimentation with the candidate materials necessary.Some of the more common adjustments are described inSections 3.7.1 and 3.7.2.

3.7.1 Pozzolanic admixtures- Pozzolanic admixtures areoften used as a cement replacement. In high-strengthconcretes they have been used to supplement the port-land cement from 10 to 40 percent by weight of the ce-

ment content. In those cases where a net increase in theabsolute volume of the cementitious materials was exper-ienced due to the addition of a pozzolan, a correspond-ing decrease in the absolute volume of the sand was usu-ally made.

The use of fly ash has often caused a slight reductionin the water demand of the mixture, and that reductionin the volume of water (if any) has been compensated forby the addition of sand. The opposite relationship hasbeen found to be true for other pozzolans. Silica fume,for example, dramatically increases the water demand ofthe mixture which has made the use of retarding andsuperplasticizing admixtures a requirement. Proprietaryproducts containing silica fume include carefully balancedchemical admixtures as wel13.14

3.7.2 Chemical admixtures3.7.2.1 Conventional water-reducers and retarders-

The amount of these admixtures used in high-strengthconcrete mixtures has varied depending upon the parti-cular admixture and application. Generally speaking, thetendency has been to use larger than normal or maxi-mum quantities of these admixtures. Typical water re-ductions of 5 to 8 percent may be increased to 10 per-cent. Corresponding increases in sand content have beenmade to compensate for the loss of volume due to thereduction of water in the mixture.

3.7.3.2 Superplasticizers or high-range water-reducingadmixtures-Adjustments to high-strength concrete madewith high-range water reducers have been similar tothose adjustments made when conventional water re-ducers are used. These adjustments have typically beenlarger due to the larger amount of water reduction, ap-proximately 12 to 25 percent. Corresponding increases insand content have been made to compensate for the lossof volume from reduction of water in the mixture.

Some designers have simply added high-range waterreducers to existing mixtures without any adjustments tothe mix proportions to improve the workability of thatconcrete.

Sometimes cement or cementitious content has beenreduced for reasons of economy or to achieve a reduc-tion of the heat of hydration. Usually, however, inhigh-strength concretes high-range water reducers areused to lower the water-cementitious ratio. These ad-mixtures have been effective enough to both lower thewater-cementitious ratio and increase the slump. Due therelatively large quantity of liquid that has been added tothe mixture in the form of superplasticizing admixture,the weight of these admixtures has sometimes been in-cluded in the calculation of the water-cementitious ratio.

3.7.2.3 Air-entraining agents- Although sometimesrequired, air-entraining agents have been found to bevery undesirable in high-strength concretes due the dra-matic decrease in compressive strength which occurswhen these admixtures are used. Modifications to lowerthe water-cementitious ratio and adjust the yield of theconcrete by reduction of sand content have been made.Larger dosage rates of air-entraining admixture have


been found to be required in high-strength concretes,especially in very rich low-slump mixtures and mixturescontaining large quantities of some fly ashes.

3.7.2.4 Combinations- Most but not all high-strength concretes have contained both mineral andchemical admixtures. It has been common for these mix-tures to contain combinations of chemical admixtures aswell. High-range water reducers have performed betterin high-strength concretes when used in combination withconventional water reducers or retarders. This is becauseof the reduced rate of slump loss experienced. It is notunusual for portland-pozzolan high-strength concretes tocontain both a conventional and high-range waterreducer.

3.8-WorkabilityWorkability is defined in ACI 116R “Cement and Con-

crete Terminology” as “that property of freshly mixedconcrete . . . which determines the ease and homogeneitywith which it can be mixed, placed, compacted, andfinished.”

3.8.1 Slump- ASTM C 143 describes a standard testmethod for the slump of portland cement concrete whichhas been used to quantify the consistency of plastic, co-hesive concretes. This test method has not usually beenconsidered applicable to ultra-low and ultra-high slumpconcretes. Other test methods such as the Vebe consist-ometer have been used with very stiff mixes and may bea better aid in proportioning some high-strength con-cretes.

High-strength concrete performance demands a dense,void-free mass with full contact with reinforcing steel.Slumps should reflect this need and provide a workablemixture, easy to vibrate, and mobile enough to passthrough closely placed reinforcement. Normally a slumpof 4 in. (102 mm) will provide the required workability;however, details of forms and reinforcing bar spacingshould be considered prior to development of mix de-signs. Slumps of less than 3 in. (76 mm) have madespecial consolidation equipment and procedures anecessity.

Without uniform placement, structural integrity maybe compromised High-strength mixes tend to lose slumpmore rapidly than lower-strength concrete. If slump is tobe used as a field control, testing should be done at aprescribed time after mixing. Concrete should be dis-charged before the mixture becomes unworkable.

3.8.2 Placeability-- High-strength concrete, oftendesigned with % in. (12 mm) top size aggregate and witha high cementitious content, is inherently placeable pro-vided attention is given to optimizing the ratio of sand tocoarse aggregate. Local material characteristics have amarked effect on proportions. Cement fineness and par-ticle size distribution influence the character of themixture. Admixtures have been found to improve theplaceability of the mixture.

Placeability has been evaluated in mock-up formsprior to final approval of the mix proportions. At that

time placement procedures, vibration techniques, andscheduling have been established since they greatly affectthe end product and will influence the apparent place-ability of the mixture.

3.8.3 Flow properties and stickiness-Slumps needed foralmost any flow can be designed for the concrete; how-ever, full attention must be given to aggregate selectionand proportioning to achieve the optimum slump. Elon-gated aggregate particles and poorly graded coarse andfine aggregates are examples of characteristics that haveaffected flow and caused higher water content for place-ability with attendant strength reduction.

Stickiness is inherent in high-fineness mixtures re-quired for high strengths. Certain cements or cement-pozzolan or cement-admixture combinations have beenfound to cause undue stickiness that impairs flowability.The cementitious content of the mixture normally hasbeen the minimum quantity required for strength devel-opment combined with the maximum quantity of coarseaggregate within the requirements for workability.

Mixtures that were designed properly but appear tochange in character and become more sticky can be con-sidered suspect and quickly checked for proportions, pos-sible false setting of cement, undesirable air entrainment,or other changes. A change in the character of a high-strength mixture could be a warning sign for quality con-trol and, while a subjective judgment, may sometimes bemore important than quantitative parameters.

3.9- Trial batchesFrequently the development of a high-strength con-

crete pro ram has required a large number of trialbatches.3.2,3.10 In addition to laboratory trial batches,field-sized trial batches have been used to simulate typ-ical production conditions. Care should be taken that allmaterial samples are taken from bulk production and aretypical of the materials which will be used in the work.To avoid accidental testing bias, some researchers havesequenced trial mixtures in a randomized order.

3.9.1 Laboratory trial batch investigations- Laboratorytrial batches have been prepared to achieve several goals.They should be prepared according to “Standard Methodof Making and Curing Concrete Test Specimens in theLaboratory” (ASTM C 192). However, whenever possible,timing, handling, and environmental conditions similar tothose which are likely to be encountered in the fieldshould be approximated.

Selection of material sources has been facilitated bycomparative testing, with all variables except the can-didate materials being held constant. In nearly everycase, particular combinations of materials have proven tobe best. By testing for optimum quantities of optimummaterials, the investigator is most likely to define the bestcombination and proportions of materials to be used.

Once a promising mixture has been established, fur-ther laboratory trial batches may be required to quantifythe characteristics of those mixtures. Strength charac-teristics at various test ages may be defined. Water

TH CONCRETE 363R-15

demand, rate of slump loss, amount of bleeding, seg-regation, and setting time can be evaluated. The unitweight of the mixture should be defined and has beenused as a valuable quality control tool. Structuralconsiderations such as shrinkage and elasticity may alsobe determined. While degrees of workability andplaceability may be difficult to define, at least asubjective evaluation should be attempted.

3.9.2 Field-production trial batches- Once a desirablemixture has been formulated in the laboratory, fieldtesting with production-sized batches is recommended.Quite often laboratory trial batches have exhibited astrength level significantly higher than that which can bereasonably achieved in production as shown in Fig. 3.33.2

Actual field water demand, and therefore concrete yield,has varied from laboratory design significantly. Ambienttemperatures and weather conditions have affected theperformance of the concrete. Practicality of productionand of quality control procedures have been better eval-uated when production-sized trial batches were preparedusing the equipment and personnel that were to be usedin the actual work.

3.10-Cited references(See also Chapter l0-References)

3.1. Proportioning Concrete Mixes, SP-46, AmericanConcrete Institute, Detroit, 1974, 240 pp.

3.2. Blick, Ronald L.; Petersen, Charles F.; andWinter, Michael E., “Proportioning and Controlling HighStrength Concrete,” Proportioning Concrete Mixes, SP-46,American Concrete Institute, Detroit, 1974, p. 149.

3.3. Kennedy, T.B., “Making and Curing ConcreteSpecimens,” Significance of Tests and Properties ofConcrete and Concrete-Making Materials, STP-169A,American Society for Testing and Materials, Phila-delphia, 1966, pp. 90-101.

3.4. Price, Waller H., “Factors Influencing ConcreteStrength,” ACI JOURNAL, Proceedings V. 47, No. 6, Feb.1951, pp. 417-432.

3.5. Hester, Weston T., “Testing High Strength Con-cretes: A Critical Review of the State of the Art,”Concrete International Design & Construction, V. 2, No.12, Dec. 1980, pp. 27-38.

3.6. Gaynor, Richard D., “Mix Design SubmissionUnder ACI 318 and ACI 301--(or Which Test RecordShould I Use?),” NRMCA Technical Information LetterNo. 372, National Ready Mixed Concrete Association,Silver Spring, May 8, 1980, 7 pp.

3.7. Schmidt, William, and Hoffman, Edward J., “9000psi Concrete-Why? Why Not?,” Civil Engineering-ASCE, V. 45, No. 5, May 1975, pp. 52-55.

3.8. Gaynor, Richard D., “An Outline on HighStrength Concrete,” Publication No. 152, National ReadyMixed Concrete Association, Silver Spring, May 1975, pp.3, 4, and 10.

3.9. Accelerated Strength Testing, SP-56, AmericanConcrete Institute, Detroit, 1978, 328 pp.

3.10. Cook, James E., “A Ready-Mixed Concrete

Company’s Experience with Class C Fly Ash,” PublicationNo. 163, National Ready-Mixed Concrete Association,Silver Spring, Apr. 1981, 11 pp.

3.11. Hester, Weston, T., and Leming, M., “Use ofSuperplasticizing Admixtures in Precast, PrestressedConcrete Operations.”

3.12. “High Strength Concrete,” National CrushedStone Association, Washington, D.C., Jan. 1975, 16 pp.

3.13. Peters, Donald J., “Evaluation of CementVariability-The First Step,” Publication No. 161,National Ready Mixed Concrete Association, SilverSpring, Apr. 1980, 9 pp.

3.14. Wolsiefer, John, “Ultra High-Strength FieldPlaceable Concrete with Silica Fume Admixture,” Con-crete International: Design & Construction, V. 6, No. 4,Apr. 1984, pp. 25-31.

3.15. Perenchio, William F., and Khieger, Paul, “SomePhysical Properties of High Strength Concrete,” Researchand Development Bulletin No. RD056.01T, PortlandCement Association, Skokie, 1978, 7 pp.

3.16. Freedman, Sydney, “High-Strength Concrete,Modern Concrete, V. 34, No. 6, Oct. 1970, pp. 29-36; No.7, Nov. 1970, pp. 28-32; No. 8, Dec. 1970, pp. 21-24; No.9, Jan. 1971, pp. 15-22; and No. 10, Feb. 1971, pp. 16-23.Also, Publication No. IS176T, Portland Cement Associa-tion.

3.17. Neville, A.M., Properties of Concrete, 3rd Edition,Pitman Publishing Limited, London, 1981, 779 pp.

3.18. Bickley, John A, and Payne, John C., “HighStrength Cast-in-Place Concrete in Major Structures inOntario,” paper presented at the ACI Annual Conven-tion, Milwaukee, Mar. 1979.

3.19. Shideler, J.J., “Lightweight-Aggregate Concretefor Structural Use, ACI JOURNAL, Proceedings V. 54, No.4, Oct. 1957, pp. 299-328.

3.20. Holm, T.A., “Physical Properties of HighStrength Lightweight Aggregate Concretes,” Proceedings,2nd International Congress on Lightweight Concrete(London, Apr. 1980), Ci8O, Construction Press,Lancaster, 1980, pp. 187-204.

3.21. Mather, Katharine, “High Strength, High DensityConcrete,” ACI JOURNAL, Proceedings V. 62, No. 8, Aug.1965, pp. 951-962. Also, Technical Report No. 6-635, U.S.Army Engineer Waterways Experiment Station.

3.22. Bloem, Delmar L., and Gaynor, Richard D.,“Effects of Aggregate Properties on Strength of Con-crete,” ACI JOURNAL, Proceedings V. 60, No. 10, Oct.1963, pp. 1429-1456.

3.23. Tobin, Robert E., “Flow Cone Sand Tests,” ACIJOURNAL, Proceedings V. 75, No. 1, Jan. 1978, pp. l-12.

3.24. Ehrenburg, D.O., “An Analytical Approach toGap-Graded Concrete,” Cement, Concrete, and Aggregates,V. 2, No. 1, Summer 1980, pp. 39-42.

3.25. Tuthill, Lewis H., “Better Grading of ConcreteAggregates,” Concrete International Design & Construc-tion, V. 2, No. 12, Dec. 1980, pp. 49-51.

3.26. Gaynor, Richard D., “High Strength Air-En-trained Concrete,” Joint Research Laboratory Publication


No. 17, National Sand and Gravel Association/NationalReady Mixed Concrete Association, Silver Spring, Mar.1968, 19 pp.

CHAPTER 4- BATCHING, MIXING,TRANSPORTING, PLACING, CURING,

AND CONTROL PROCEDURES

4.1-IntroductionThe batching, mixing, transporting, placing, and con-

trol procedures for high-strength concrete are not dif-ferent in principle from those procedures used for con-ventional concrete. Thus ACI 304 can be followed. Somechanges, some refinements, and some emphasis on criti-cal points are necessary. Maintaining the unit water con-tent as low as possible, consistent with placing require-ments, is good practice for all concrete; for high-strengthconcrete it is critical. Since the production of high-strength concrete will normally involve the use of rela-tively large unit cement contents with resulting greaterheat generation, some of the recommendations given inChapter 3 on Production and Delivery and Chapter 4 onPlacing and Curing in ACI 305R, “Hot Weather Con-creting,” may also be applicable.

In addition, the production and testing of high-strength concrete requires well-qualified concrete pro-ducers and testing laboratories, respectively.

4.2 - Batching4.2.1 Control, handling and storage of materials- The

control, handling, and storage of materials need not besubstantially different from the procedures used for con-ventional concrete as outlined in ACI 304. Proper stock-piling of aggregates, uniformity of moisture in thebatching process, and good sampling practice are essen-tial. It may be prudent to place a maximum limit of 170F (77 C) on the temperature of the cement as batched inwarm weather and 150 F (66 C) in hot weather. Wherepossible, batching facilities should be located at or nearthe job site to reduce haul time.

The temperature of all ingredients should be kept aslow as possible prior to batching. Delivery time should bereduced to a minimum and special attention paid toscheduling and placing to avoid having trucks wait tounload.

4.2.2 Measuring and weighing- Materials for produc-tion of high-strength concrete may be batched in manual,semiautomatic, or automatic plants. However, sincespeed and accuracy are required, ACI 304 recommendsthat cements and pozzolans be weighed with automaticequipment. Automatic weigh batchers or meters are re-commended for water measurement. To maintain theproper water-cement ratios necessary to secure high-strength concrete, accurate moisture determination in thefine aggregate is essential. A combination of warmweather and high cement content often requires thecooling of mixing water. ACI 305R notes that the use of

cold miring water effects a moderate reduction in con-crete placing temperature. The use of ice is more effec-tive than cold water; however, this will require icemaking or chipping equipment at the batch plant.

4.2.3 Charging of materials-Batching procedures haveimportant effects on the ease of producing thoroughlymixed uniform concrete in both stationary and truckmixers. The uniformity of concrete mixed in centralmixers is generally enhanced by ribbon loading the aggre-gate, cement, and water simultaneously. However, iftruck mixers are being used, ribbon loading will preventdelayed miring, which is sometimes used to prevent hy-dration of the cement during long hauls. This procedureinvolves stopping the mixer drum after aggregates andthree-quarters of the water are charged and before thecement is loaded and not starting the drum again untilthe job site is reached. Slump loss problems may thus beminimized. High-range water-reducing admixtures areanother consideration. These admixtures are very likelyto be used in the production of high-strength concrete.According to the guidelines in the Canadian StandardsAssociation’s Preliminary Standard A 266.5-M 1981, testshave shown that high-range water-reducing admixturesare most effective and produce the most consistentresults when added at the end of the mixing cycle afterall other ingredients have been introduced and tho-roughly mired. If there is evidence of improper mixingand nonuniform slump during discharge, procedures usedto charge truck and central mixers should be modified toinsure uniformity of mixing as required by ASTM C 94.

4.3- MixingHigh-strength concrete may be mixed entirely at the

batch plant, in a central or truck mixer, or by a combin-ation of the two. In general, mixing follows the recom-mendations of ACI 304. Experience and tests4.0,4.2 andstandards documents of the Concrete Plant Manufactur-ers Bureau have indicated that high-strength concrete canbe mired in all common types of mixers.4.3,4.4,4.5 It mayprove beneficial to reduce the batch size below the ratedcapacity to insure more efficient mixing.

4.3.2 Mixer performance- The performance of mixersis usually determined by a series of uniformity tests(ASTM C 94) made on samples taken from two to threelocations within the concrete batch being mixed for agiven time period.4.6 Some work4.2,4.7 has indicated thatdue to the relatively low water content and high cementcontent and the usual absence of large coarse aggregate,the efficient mixing of high-strength concrete is moredifficult than conventional concrete. Special precautionsor procedures may by required. Thus, it becomes moreimportant for the supplier of high-strength concrete tocheck mixer performance and efficiency prior to produc-tion mixing.

4.3.3 Mixing time- The mixing time required is basedupon the ability of the central mixer to produce uniformconcrete both within a batch and between batches. Man-ufacturers’ recommendations, ACI 304, and usual specifi-


cations, such as 1 min for 1 yd 3 (0.75 m3) plus ‘/4 min foreach additional yd 3 of capacity, are used as satisfactoryguides for establishing mixing time. Otherwise, mixingtimes can be based on the results of mixer performancetests. The mixing time is measured from the time all in-gredients are in the mixer. Prolonged miring may causemoisture loss and result in lower workability,4.8 which inturn may require retempering to restore slump, therebyreducing strength potential.

4.3.4 Ready-mixed concrete-High strength concretemay be mixed at the job in a truck mixer. However, notall truck mixers can mix high-strength concrete, especiallyif the concrete has very low slump. Close job control isessential for high-strength ready-mixed concrete opera-tions to avoid causing trucks to wait at the job site due toslow placing operations. (Note Section 4.7.) Retardingadmixtures are used to prolong the time the concrete willrespond to vibration after it has been placed in theforms. Withholding some of the mixing water until thetruck arrives at the job site is sometimes desirable. Thenafter adding the remaining required water, an additional30 revolutions at mixing speed are used to incorporatethe additional water into the mixture adequately. (SeeACI 304.) When loss of slump or workability cannot beoffset by these measures, complete batching and miringcan be conducted at the job site. If a high-range water-reducer is added at the site, a truck mounted dispenseror an electronic field dispenser is usually required.

4.4-Transporting4.4.1 General considerations- High-strength concrete

can be transported by a variety of methods and equip-ment, such as truck mixers, stationary truck bodies withand without agitators, pipeline or hose, or conveyor belts.Each type of transportation has specific advantages anddisadvantages depending on the conditions of use, mix-ture ingredients, accessibility and location of placing site,required capacity and time for delivery, and weather con-ditions.

4.4.2 Truck-mixed concrete- Truck miring is a processin which proportioned concrete materials from a batchplant are transferred into the truck mixer where allmixing is performed. The truck is then used to transportthe concrete to the job site. Sometimes dry materials aretransported to the job site in the truck drum with themiring water carried in a separate tank mounted on thetruck. Water is added and mixing is completed. Thismethod, which evolved as a solution to long hauls andplacing delays, is adaptable to the production of high-strength concrete where it is desirable to retain theworkability as long as possible. However, free moisture inthe aggregates, which is part of the mixing water, maycause some cement hydration.

4.4.3 Stationary truck body with and without agitator-Units used in this form of transportation usually consistof an open-top body mounted on a truck. The smooth,streamlined metal body is usually designed for dischargeof the concrete at the rear when the body is tilted. A

discharge gate and vibrators mounted on the body areprovided at the point of discharge. An apparatus thatribbons and blends the concrete as it is unloaded isdesirable. However, water is not added to the truck bodybecause adequate mixing cannot be obtained with theagitator.

4.4.4 Pumping- High-strength concrete will in manycases be very suitable for pumping. Pumps are availablethat can handle low-slump mixtures and provide highpumping pressure. High-strength concrete is likely tohave a high cement content and small maximum size ag-gregate--both factors which facilitate concrete pumping.Chapter 9 of ACI 304 provides guidance for the use ofpumps for transporting high-strength concrete. In thefield, the pump should be located as near to the placingareas as practicable. Pump lines should be laid out witha minimum of bends, firmly supported, using alternatelines and flexible pipe or hose to permit placing over alarge area directly into the forms without rehandling.Direct communication is essential between the pump op-erator and the concrete placing crew. Continuous pump-ing is desirable because if the pump is stopped, move-ment of the concrete in the line may be difficult orimpossible to start again.

4.4.5 Belt conveyor- Use of belt conveyors to trans-port concrete has become established in concrete con-struction. Guidance for use of conveyors is given in ACI304.4R. The conveyors must be adequately supported toobtain smooth, nonvibrating travel along the belt. Theangle of incline or decline must be controlled to elim-inate the tendency for coarse aggregate to segregate fromthe mortar fraction. Since the practical slump range forbelt transport of concrete is 1 to 4 in. (25 to 100 mm),belts may be used to move high-strength concrete onlyfor relatively short distances of 200 to 300 ft (60 to90 m). Over longer distances or extended time lapses,there will be loss of slump and workability.4.9 Enclosuresor covers are used for conveyors when protection againstrain, wind, sun, or extreme ambient temperatures isneeded to prevent significant changes in the slump ortemperature of the concrete. As with other methods oftransport for high-strength concrete, proper planning,timing, and control are essential.

4.5-Placing procedures4.5.1 Preparations- Preparations for placing high-

strength concrete should include recognition at the startof the work that certain abnormal conditions will existwhich will require some items of preparation that cannotbe provided readily the last minute before concrete isplaced. Since workability time is expected to be reduced,preparation must be made to transport, place, consoli-date, and finish the concrete at the fastest possible rate.This means, first, delivery of concrete to the job site mustbe scheduled so it will be placed promptly on arrival, par-ticularly the first batch. Equipment for placing the con-crete must have adequate capacity to perform its func-tions efficiently so there will be no delays at distance


portions of the work. There should be ample vibrationequipment and manpower to consolidate the concretequickly after placement in difficult areas. All equipmentshould be in the first class operating condition. Break-downs or delays that stop or slow the placement can ser-iously affect the quality of the work. Due to more rapidslump loss, the strain on vibrating equipment will begreater. Accordingly, provision should be made for anample number of standby vibrators, at least one standbyfor each three vibrators in use. A high-strength concreteplacing operation is in serious trouble, especially in hotweather, when vibration equipment fails and the standbyequipment is inadequate.

4.5.3 Equipment- A basic requirement for placingequipment is that the quality of the concrete, in terms ofwater-cement ratio, slump, air content, and homogeneity,must be preserved. Selection of equipment should bebased on its capability for efficiently handling concrete ofthe most advantageous proportions that can be consoli-dated readily in place with vibration. Concrete should bedeposited at or near its final position in the placement.Buggies, chutes, buckets, hoppers, or other means may beused to move the concrete as required. Bottom-dumpbuckets are particularly useful however, side slopes mustbe very steep to prevent blockages. High-strength con-crete should not be allowed to remain in buckets forextended periods of time, as the delay will cause stickingand difficulty in discharging.

4.5.3 Consolidation- Proper internal vibration is themost effective method of consolidating high-strength con-crete. The advantages of vibration in the placement ofconcrete are well established. The provisions of ACI 309must be followed. Hi h-strength concrete can be very”sticky" material. 4.1,4.10 indeed, effective consolidationprocedures may well start with mix proportioning. Coarsesands have been found to provide the best workability.4.10

The im ortance of full compaction cannot be overstated.Davies4.11 has shown that up to 5 percent loss in strengthmay be sustained from each 1 percent void space in con-crete. Thus, vibration almost to the point of excess maybe required for high-strength concrete to achieve its fullpotential.

4.5.4 Special considerations- Where different strengthconcretes are being used within or between differentstructural members, special placing considerations arerequired. To avoid confusion and error in concrete place-ment in columns, it is recommended that, where practi-cal, all columns and shearwalls in any given story beplaced with the same strength concrete. For formworkeconomy, no changes in column size in the typical high-rise buildings are recommended.4.12 In areas where twodifferent concretes are being used in column and floorconstruction, it is important that the high-strength con-crete in and around the column be placed before thefloor concrete. With this procedure, if an unforeseen coldjoint forms between the two concretes, shear strength willstill be available at the column interface.4.13

4.6-Curing4.5.1 Need for curing- Curing is the process of main-

taining a satisfactory moisture content and a favorabletemperature in concrete during the hydration period ofthe cementitious materials so that desired properties ofthe concrete can be developed. Curing is essential in theproduction of quality concrete; it is critical to the pro-duction of high-strength concrete. The potential strengthand durability of concrete will be fully developed only ifit is properly cured for an adequate period prior to beingplaced in service. Also, high-strength concrete should bewater cured at an early age since partial hydration maymake the capillaries discontinuous. On renewal of curing,water would not be able to enter the interior of the con-crete and further hydration would be arrested.4.14

4.5.3 Type of curing- Water curing of high-strengthconcrete is highly recommended4.14 due to the low water-cement ratios employed. At water-cement ratios below0.4, the ultimate degree of hydration is significantlyreduced if free water is not provided. Water curing willallow more efficient, although not complete, hydration ofthe cement. Klieger4.15 reported that for low water-cement ratio concretes it is more advantageous to supplyadditional water during curing than is the case withhigher water-cement ratio concretes. For concretes withwater-cement ratio of 0.29, the strength of specimensmade with saturated aggregates and cured by pondingwater on top of the specimen was 850 to 1000 psi (5.9 to6.9 M Pa) greater at 28 days than that of comparablespecimens made with dry aggregates and cured underdamp burlap. He also noted that although early strengthis increased by elevated temperatures of mixing andcuring, later strengths are reduced by such temperatures.However, work by Pfieffer 4.16 has shown that laterstrengths may have only minor reductions if the heat isnot applied until after time of set. Others 4.1,4.17 havereported that moist curing for 28 days and thereafter inair was highly beneficial in securing high-strength con-crete at 90 days.

4.5.3 Methods of curing- As pointed out in ACI 308,the most thorough but seldom used method of watercuring consists of total immersion of the finished con-crete unit in water. “Ponding” or immersion is an excel-lent method wherever a pond of water can be created bya ridge or dike of impervious earth or other material atthe edge of the structure. Fog spraying or sprinkling withnozzles or sprays provides satisfactory curing when im-mersion is not feasible. Lawn sprinklers are effectivewhere water runoff is of no concern. Intermittentsprinkling is not acceptable if drying of the concretesurface occurs. Soaker hoses are useful, especially onsurfaces that are vertical. Burlap, cotton mats, rugs, andother coverings of absorbent materials will hold water onthe surface, whether horizontal or vertical. Liquid mem-brane-forming curing compounds retain the originalmoisture in the concrete but do not provide additionalmoisture.


4.7-- Quality assurance4.7.1 Materials- Once the high-strength concrete mix-

ture has been proportioned, the concrete supplier orsampling and testing program is recommended to assurethe physical properties required. The use of ASTMStandard Method for Evaluation of Cement StrengthUniformity from a Single Source (ASTM C 917) with ap-propriate limits will provide the proper basis for suchuniformity. It is desirable that the aggregates and ad-mixtures specified in the mixture be uniform and comefrom the same source for the duration of the project.

4.7.2 Control of operations4.10- Effective coordinationand control procedures between the supplier and thecontractor are critical to the operations. The suppliernormally has full control of high-strength concrete untilit is placed in the forms. Control of the slump, time onjob, mixing, and mixture adjustments is under the juris-diction of the supplier. The contractor must be preparedto handle, place, and consolidate the concrete promptlyas received. Cement hydration, temperature rise, slumploss, and aggregate grinding during mixing all increasewith passage of time; thus it is important that the periodbetween initial mixing and delivery be kept to an abso-lute minimum. The dispatching of trucks is coordinatedwith the rate of placement to avoid delays in delivery.When elapsed time from batching to placement is so longas to result in significant increases in mixing waterdemand, or in slump loss, mixing in the trucks is delayeduntil only sufficient time remains to accomplish mixingbefore the concrete is placed.

4.7.3 Communication equipment- Equipment for directcommunication between the supply and placement loca-tions for use by the inspection force is essential. Theneed for other equipment such as signaling and identi-fying devices depends on the complexity of the projectand the number of different concrete mixtures employed.The project engineer will normally advise the contractorof the equipment that is necessary and require him topresent plans or descriptions of the equipment for reviewwell in advance of the start of placement.

4.7.4 Laboratoy 4.10-- A competent concrete laboratorymust be available for testing the concrete delivered to thejob site. This laboratory should be inspected regularly bythe Cement and Concrete Reference Laboratory (CCRL)and conform to the requirements of ASTM E 329. Aminimum of one set of cylinders is normally made foreach 100 yd3 (76 m3) of concrete placed, with at leasttwo cylinders cast for each test age; that is, 7, 28, 56, and90 days.

4.7.5 Contingency plans-Plans need to be developedto provide for alternate operations in case difficulty isexperienced in the basic placing concept. Backup equip-ment is essential, especially vibrators. Batch sixes arereduced if placing procedures are slowed. For truck-mixed concrete, rush hour traffic delays can cause seriousproblems. It may be desirable to reduce the elapsed timebetween contact of the cement and water (mixing andtransporting), especially during warm weather. A maxi-

mum elapsed time of 11/2 hr after the cement has enteredthe drum until completion of discharge is frequently spe-cified (See ASTM C 94). Reduction to 45 minutes maybe necessary under hot weather conditions or wheresevere slump loss is experienced. For extreme job tem-peratures, field production trial batches are often made.

4.8-Quality control procedures4.8.1 Criteria- The first consideration for selecting

quality control procedures is determining that the dis-tribution of the compressive strength test results followsa normal distribution curve. It has been suggested4.18 thata skew distribution may prevail due to the mean ap-proaching a limit. This may be the case for very-high-strength concrete, 15,000ever available data4.19,4.20

psi (103 MPa) or higher. How-indicate that in the range of

6000; to 10,000 psi (41 to 69 MPa) normal distribution isachieved. Thus ACI 214 will normally be a convenienttool for quality control procedures for high-strengthconcrete. Another point which needs consideration bothin the quality control and the design phase is the ques-tion of the age at the time of testing for acceptance forhigh-strength concrete. Compressive strength tests showthat a considerable strength gain may be achieved after28 days in high-strength concrete. To take advantage ofthis fact, several investigators 4.10,4.13,4.20 have suggestedthat the specification for compressive strength should bemodified from the typical 28-day criterion to either 56 or90 days. This extension of test age would then allow, forexample, the use of 7000 psi (48 MPa) concrete at 56days in lieu of 6000 psi (41 MPa) at 28 days for designpurposes. In this case the same mixture could be used tomeet this criterion. High-strength concrete is generallyused in high-rise structures; therefore, the extension ofthe time for compressive strength test results is reason-able since the lower portion of the structure will notattain full dead load for periods up to one year andlonger.

4.8.2 Method of evaluation- To satisfy strength perfor-mance requirements, the average strength of concretemust be in excess of fc', the design strength. The amountof excess strength depends on the expected variability oftest results as expressed by a coefficient of variation orstandard deviation and on the allowable proportion oflow tests. Available information4.14,4.19,4.20 indicates thatthe standard deviation for high-strength concrete be-comes uniform in the range of 500 to 700 psi (3.5 to 4.8MPa), and therefore, the coefficient of variation willactually decrease as the average strength of the concreteincreases. This, of course, may be the result of increasedvigilance and quality assurance on the part of the pro-ducer. Thus, the method of quality control is closely re-lated to the factors noted in Section 4.7. Assuming thatthe producer will devote a reasonable effort to properquality assurance measures, the standard deviation meth-od of evaluation appears to be a logical quality controlprocedure. Consider, for example, that good quality con-trol may be expected on a job where an fc' of 10,000 psi


(69 MPa) is required. A required average strength fc' ofonly 11,000 psi (76 MPa) is thus required with a standarddeviation of 645 psi (4.4 MPa)

f ’CI = f,’ + 134s= 10,000 + 1.34 x 645= 10,864 psi (75 MPa) (4-la)

or

f,’ = f,’ + 2.33s - 500= 10,000 + 2.33 x 645 - 500= 11,000 psi (76 MPa)

s = standard deviation.

(4-lb)

Of course, a close check of the field results and main-tenance of records in the form of control charts or othermeans are necessary to maintain the desired control.Early-age control of concrete strength such as the accel-erated curing and testing of compression test specimensaccording to ASTM C 684 is often used, especially wherelater-age (56 or 90 days) strength tests are the final ac-ceptance criterion.

4.9 - Strength measurements4.9.1 Conditions-since much of the interest in high-

strength concrete is limited to strength only in com-pression, compressive strength measurements are ofprimary concern in the testing of high-strength concrete.Standard test methods of the American Society for Test-ing and Materials (ASTM) are followed except wherechanges are dictated by the peculiarities of the high-strength concrete. The potential strength and variabilityof the concrete can be established only by specimensmade, used, and tested under standard conditions. Thenstandard control tests are necessary as a first step in thecontrol and evaluation of the mixture. Curing concretetest specimens at the construction site and under jobconditions is sometimes recommended since this is con-sidered more representative of the curing applied to thestructure. Tests of job-cured specimens may be highlydesirable and are necessary when determining the timeof form removal, particularly in cold weather, and whenestablishing the rate of strength development of struc-tural members. They should never be used for qualitycontrol testing. Strength specimens of concrete made orcured under other than standard conditions provide addi-tional information but are analyzed and reported separ-ately. ASTM C 684 requires that a minimum of twocylinders be tested for each age and each test condition.

4.9.2 Specimen size and shape- ASTM standards speci-fy a cylindrical specimen 6 in. (152 mm) in diameter and12 in. (305 mm) long. This size specimen has evolvedover a period of time, apparently from practical con-siderations. It is about the maximum weight one personcan handle with reasonable effort and is large enough tobe used for concrete containing 2 in. (50 mm) maximumsize aggregate and smaller, which encompasses the

majority of concrete being placed today. Designers gen-erally assume 6 x 12 in. (152 x 305 mm) specimens as thestandard for measured strengths. Recently some 4 x 8 in.(102 x 204 mm) cylinders have been used for determiningcompressive strength.4.18,4.19 However, 4 x 8 in. (102 x 204mm) cylinders exhibit a higher strength and an increasein variability compared to the standard 6 x 12 in. (152 x305 mm) cylinder.4.23,4.24 Regardless of the specimen size,as the compressive stress is transferred through theloading platen-specimen interface, a complex, triaxial dis-tribution of stresses in the specimen end may developwhich can radically alter the specimen failure mode andaffect results.

4.9.3 Testing apparatus- Testing machine character-istics that may affect the measured compressive strengthinclude calibration accuracy, longitudinal and lateralstiffness, stability, alignment of the machine components,type of platens, and the behavior of the platen sphericalseating. Testing machines should meet the requirementsof ASTM C 39 when used for testing compressivestrength of cylindrical specimens. Overall testing machinedesign including longitudinal and lateral stiffness andmachine stability will affect the behavior of the specimenat its maximum load. The type of platens and behavior ofthe spherical seating will affect the level of measuredcompressive strength.4.23

Sigvaldason 4.25 recommended a minimum lateral stiff-ness of 10 xl04 lb/in. (17.5 x l0 6 N/m), and a longi-tudinal stiffness of 10 x l06 lb/in. (17.5 x l06 N/m). Hereported that a longitudinally “flexible” machine wouldcontribute to an explosive failure of the specimen at themaximum stress, but that the actual stress achieved wasinsensitive to machine flexibility. However, he also notedthat a machine which is longitudinally stiff but laterallyflexible deleteriously influences the measured compres-sive strengths. Sigvaldason and Cole4.26 reported that useof proper platen size and design is critical if strengths areto be maximized and variations reduced. The upperplaten must have a spherical bearing block seating and beable to rotate and achieve full contact with the specimenunder the initial load and perform in a fixed mode whenapproaching the ultimate load. Cole demonstrated thata testing machine with a spherical bearing block seating(able to rotate under load) measured increasingly er-roneous results for higher strength concretes, withreductions as high as 16 percent for 10,000 psi (69 MPa)cubes.

The diameters of the platen and spherical bearingsocket are critically important.4.23 Ideally, the platen andspherical bearing block diameters should be approximate-ly the same as the bearing surface of the specimen.Bearing surfaces larger than the specimen will be re-strained (due to size effects) against lateral expansion willprobably not expand as rapidly as the specimen, and willconsequently create confining stresses in the specimenend. Bearing surfaces and spherical seating blocks smallerin diameter than those of the specimen may result inportions of the specimens remaining unloaded and bend-


ing of the platen around the socket with a consequentnonuniform distribution of stresses.

4.9.4 Type of mold-- The choice of mold materials, andspecify construction of the mold regardless of the typesof material used, can have a significant effect onmeasured compressive strengths. A given consolidationeffort is more effective with rigidly constructed molds,and sealed waterproofed molds reduce leakage of mortarpaste and inhibit the dehydration of the concrete.Blick4.15 compared high-strength specimens cast in steeland high-quality paper molds and reported that use ofthe rigid steel molds increased strengths approximately 13percent but that use of either mold material did not con-sistentlyHester4.7

affect variability of the measured strengths.evaluated a number of mold materials used

under actual field conditions. Measured compressivestrengths achieved with properly prepared specimenswere compared. Specimens cast in steel molds achievedapproximately 6 percent higher strengths but had aslightly higher coefficient of variation compared tospecimens cast in tin molds. Specimens cast in steelmolds achieved approximately 16 percent higher strengththan specimens cast in plastic molds.

4.9.5 Specimen preparation- For many years concretetechnologists have recognized the need to cap or grindthe ends of cast concrete test specimens prior to testingfor compressive strength. The detrimental effects of non-planeness, irregulariwell documented.4.23

din and grease, etc., have beenFor high-strength concrete the

strength of the cap, if used, is another consideration.Troxell,4.27 Wemer,4.28 and other have compared the rel-ative merits of sulfur mortars, gypsum plaster, high-alumina cements, and other capping materials. If thecompressive strength or modulus of elasticity of thecapping material is less than that of the specimen, loadsapplied through the cap will not be transmitted uni-formly.

Sulfur mortar is the most widely used capping mater-ial. Most commercially available sulfur mortar cappingcompounds are combinations of sulfur with inert mineralsand fillers and, when properly prepared, are economical,convenient to apply, and develop a relatively highstrength in a short period of time. However, these mater-ials are sensitive to the material formulations andhandling practices. Kennedy4.29 and Werner investigatedthe effect of the thickness of sulfur mortar caps on com-pressive strengths of moderate strength concretes. Capthicknesses in the range of 1/16 to ‘/s in. (1.5 to 3 mm)are desirable for use on high-strength concrete. However,caps consistently thinner than Ya in. (3 mm) are difficultto obtain. Kennedy4.26 and Hester4.23 note that the prin-cipal problems with thin caps are air voids at the spe-cimen-cap interface and cracking of the specimen capunder load. Caps with a thickness of ‘/ in. (6 mm) areapparently satisfactory. Low-strength thick caps maycreep laterally under load and therefore contribute toincreased tensile stresses in the specimen ends and con-sequently substantially reduce measured compressive

strengths for the concrete specimen. Gaynor 4.30 andSaucier 4.31 indicate that concrete strengths up to 10,000psi (69 MPa) may be determined using high-strength cap-ping materials, including sulfur mortar, which havestrengths in the range of 7000 to 8000 psi (50 to 60MPa), if the cap thickness is maintained at approximatelyl/4 in. (6 mm). For expected compressive strengths above10,000 psi (69 MPa), the ends are usually formed orground to tolerance.4.29.4.30

4.10- Cited References(See also Chapter l0-- References)

4.1. Saucier, K.L.; Tynes, W.O.; and Smith, E.F.,“High-Compressive-Strength Concrete-Report 3, Sum-mary Report,” Miscellaneous Paper No. 6-520, U.S. ArmyEngineer Waterways Experiment Station, Vicksburg,Sept. 1965, 87 pp.

4.2. Saucier, K.L., “Evaluation of Spiral-Blade Con-crete Mixer, Shelbyville Reservoir Project, Shelbyville,Illinois,” Miscellaneous Paper No. 6-975, U.S. ArmyEngineer, Waterways Experiment Station, Vicksburg,Mar. 1968, 17 pp.

4.3. Strehlow. Robert W., “Concrete Plant Production,”Concrete Plant Manufacturers Bureau, Silver Spring,1973, 112 pp.

4.4. “Concrete Plant Standards of the Concrete PlantManufacturers Bureau,” 7th Revision, Concrete PlantManufacturers Bureau, Silver Spring, Jan. 1, 1983, 11 pp.

4.5. “Concrete Plant Mixer Standards of the PlantMixer Manufacturers Division, Concrete Plant Manufac-turers Bureau,” 5th Revision, Concrete ManufacturersBureau, Silver Spring, July 18, 1977, 4 pp.

4.6. Concrete Manual, 8th Edition, U.S. Bureau ofReclamation, Denver, 1975. 627 pp.

4.7. Saucier, K.L., “Evaluation of a 16-cu-ft LaboratoryConcrete Mixer,” Miscellaneous Paper No. 6-692, U.S.Army Engineer Waterways Experiment Section,Vicksburg, Jan. 1965.

4.8. Bloem, Delmar L., “High-Energy Mixing,” Techni-cal Information Letter No. 169. National Ready MixedConcrete Association, Silver Spring, Aug. 1961, pp. 3-8.

4.9. Saucier Kenneth L., “Use of Belt Conveyors toTransport Mass Concrete,” Technical Report No. C-74-4,U.S. Army Engineer Waterways Experiment Station,Vicksburg, 1974, 42 pp.

4.10. Blick, Ronald L., “Some Factors InfluencingHigh-Strength concrete,” Modern Concrete, V. 36, No. 12,Apr. 1973, pp. 38-41.

4.11. Davies, R.D., “Some Experiments on the Com-paction of Concrete by Vibration,” Magazine of ConcreteResearch (London), V. 3, No. 8, Dec. 1951, pp. 71-78.

4.12. Schmidt, William, and Hoffman, Edward J.,“9000-psi ConcreteWhy?-Why Not?,” Civil Engineering-ASCE, V. 45, No. 5, May 1975, pp. 52-55.

4.13. “High-Strength Concrete in Chicago High-RiseBuildings,” Task Force Report No. 5, Chicago Committeeon High-Rise Buildings, 1977, 63 pp.

4.14. Neville, A.M., Properties of Concrete, 2nd Edition,


John Wiley and Sons, New York, 1973, 686 pp.4.15. Klieger. Paul, “Early High Strength Concrete for

Prestressing,” Proceedings, World Conference on Pre-stressed Concrete, San Francisco, 1957, pp. A5-l-A5-14.

4.16. Pfieffer, D.W., and Ladgren, J.R., “Energy Ef-ficient Accelerated Curing of Concrete-A LaboratoryStudy for Plant-Produced Prestressed Concrete,” Tech-nical Report No. 1, Prestressed Concrete Institute,Chicago, Dec. 1981.

4.17. Price, Walter H., “Factor Influencing ConcreteStrength,” ACI JOURNAL, Proceedings V. 47, No. 6, Feb1951, pp. 417-432.

4.18. Mather, Brant, “Stronger Concrete,” HighwayResearch Record No. 210, Highway Research Board, 1967,pp. l-28.

4.19. Day, K.W., “Quality Control of 55 MPa Concretefor Collins Place Project, Melbourne, Australia,” ConcreteInternational Design & Construction, V. 3, No. 3, Mar.1981, pp. 17-24.

4.20. Cook, James E., “Research and Application ofHigh-Strength Concrete Using Class C Fly Ash,” ConcreteInternational: Design & Construction, V. 4, No. 7, July1982, pp. 72-80.

4.21. Fortie, Douglas A, and Schnoreier, P.E., “Four-by-Eight Test Cylinder Are Big Enough,” Concrete Con-struction, V. 24, No. 11, Nov. 1979, pp. 751-753.

4.22. Wolsiefer, John, private communication withACI Committee 363, 1982.

4.23. Hester, Weston T., “Field Testing High-StrengthConcretes: A Critical Review of the State-of-the-Art,”Concrete International Design & Construction, V. 2, No.12, Dec. 1980, pp. 27-38.

4.24. Carrasquillo, Ramon L.; Nilson, Arthur H.; andSlate, Floyd O., “Properties of High-Strength ConcreteSubject to Short-Term Loads,” ACI JOURNAL, Proceed-ings V. 78, No. 3, May-June 1981, pp. 171-178.

4.25. Sigvaldason, O.T., “The Influence of TestingMachine Characteristics Upon the Cube and CylinderStrength of Concrete, Magazine of Concrete Research(London), V. 18, No; 57, Dec. 1966, pp. 197-206.

4.26. Cole, D.G., “Some Mechanical Aspects of Com-pression Testing Machines,” Magazine of ConcreteResearch (London), V. 19, No. 61, Dec. 1967, pp. 247-251.

4.27. Troxell, G.E., “The Effect of Capping Methodsand End Conditions Before Capping Upon the Compres-sive Strength of Concrete Test Cylinder,” Proceedings,ASTM, V. 41, 1941, pp. 1038-1052.

4.28. Werner, George, “The Effect of Type of CappingMaterial on the Compressive Strength of ConcreteCylinder,” Proceedings, ASTM V. 58, 1958, pp. 1166-1186.

4.29. Holland, Terrence C., “Testing High StrengthConcrete,” Concrete Construction, June 1987, pp. 534-536.

4.30. Godfrey, K.A., Jr.,"Concrete Strength recordJumps 36%,” Civil Engineering, Oct. 1987, pp. 84-88.

4.31. Saucier, K.L., “Effect of Method of Preparationof Ends of Concrete Cylinders for Testing," MiscellaneousPaper No. C-72-12, U.S. Army Engineer Waterways Ex-

periment Station, Vicksburg, Apr. 1972, 51 pp.

CHAPTER 5-PROPERTIES OFHIGH-STRENGTH CONCRETE

5.1-IntroductionConcrete properties such as stress-strain relationship,

modulus of elasticity, tensile strength, shear strength, andbond strength are frequently expressed in terms of theuniaxial compressive strength of 6 x 12-m. (152 x 305-mm) cylinders. Generally, the expressions have beenbased on experimental data of concrete with compressivestrengths less than 6000 psi (41 MPa). Various propertiesof high-strength concrete are reviewed in this chapter.The applicability of current and proposed expressions forpredicting properties of high-strength concrete areexamined.

5.2-Stress-strain behavior in uniaxial compressionAxial-stress versus strain curves for concrete of com-

pressive strength up to 12,000 psi (83 MPa) are shown inFig. 5.1. The shape of the ascending part of the stress-strain curve is more linear and steeper for high-strengthconcrete, and the strain at the maximum stress is slightlyhigher for high-strength concrete.5.5-5.6 The slope of thedescending part becomes steeper for high-strength con-crete. To obtain the descending part of the stress-straincurve, it is generally necessary to avoid the specimen-testing system interaction; this is more difficult to do forhigh-strength concrete. 5.3,5.5,5.8

A simple method of obtaining a stable descending partof the stress-strain curve is described in References 5.3

Stress,ksi

Strain, percent

Fig. 5.1 -Complete compressive stress-strain curves 5.I


and 5.7. Concrete cylinders were loaded in parallel witha hardened steel tube with a thickness such that the totalload exerted by the testing machine was always increas-ing. This approach can be employed with most conven-tional testing machines. An alternate approach is to usea closed-loop testing machine.‘.’ In a closed-loop testingmachine, specimens can be loaded so as to maintain aconstant rate of strain increase and avoid unstablefailure.

High-strength concrete exhibits less internal micro-cracking than lower-strength concrete for a given im-posed axial strain.5.9 As a result, the relative increase inlateral strains is less for high-strength concrete (Fig.5.2).5.10 The lower relative lateral expansion during theinelastic range may mean that the effects of triaxialstresses will be proportionally different for high-strengthconcrete. For example, the influence of hoop reinforce-ment is observed to be different for high-strength con-crete.5.11 It was reported that the effectiveness of spiralreinforcement is less for high-strength concrete.5.11

Fig. 5.2-- Axial stress versus axial strain and lateral strainfor plain normal weight concrete5.10

5.3-Modulus of elasticityIn 1934, Thoman and Raede5.12 reported values for

the modulus of elasticity determined as the slope of thetangent to the stress-strain curve in uniaxial compressionat 25 percent of maximum stress from 4.2 x l06 to 5.2 xl06 psi (29 to 36 GPa) for concretes having compressivestrengths ranging from 10,000 (69 MPaMPa). Many other investigators5.4,5.13-5.18

to 11,000 psi (76have reported

values for the modulus of elasticity of high-strength con-cretes of the order of 4.5 to 6.5 x l0 6 psi (31 to 45 GPa)depending mostly on the method of determining themodulus. A comparison 5-19 of experimentally determinedvalues for the modulus of elasticity with those predictedby the expression given in ACI 318, Section 8.5 forlower-strength concrete, based on a dry unit weight of145 lb/ft 3 (2346 kg/m3) is given in Fig. 5.3. The ACI 318expression overestimates the modulus of elasticity forconcretes with compressive strengths over 6000 psi (41MPa) for the data given in Fig. 5.3.

A correlation between the modulus of elasticity Ec andthe compressive strength fc' for normal weight concretes

(see Fig. 5.3) was reported in Reference 5.19 as

Ec= 40,000 K + 1.0 x l06 psi

for 3000 psi < f,’ < 12,000 psi

(EC = 3320 &’ + 6900 M P afor 21 MPa c<f,’ < 83 MPa) (5-l)

Other empirical equations for predicting elastic modu-lus have been proposed.5.17,5.18 Deviation from predictedvalues are highly dependent on the properties and pro-portions of the coarse aggregate. For example, highervalues than predicted by Eq. (5-l) were reported byRussell,5.20 Saucier,5.21 and Pfeiffer. 5.22

5.4-Poisson’s ratioExperimental data on values of Poisson’s ratio for

high-strength concrete are very limited. Shideler5.23 andCarrasquillo et al5.2 reported values for Poisson’s ratio oflightweight-aggregate high-strength concrete having uni-axial compressive strengths up to 10,570 psi (73 MPa) at28 days to be 0.20 regardless of compressive strength,age, and moisture content. Values determined by the dy-namic method were slightly higher.

On the other hand, Perenchio and Klieger5.24 reportedvalues for Poisson’s ratio of normal weight high-strengthconcretes with compressive strengths ranging from 8000to 11,600 psi (55 to 80 MPa) between 0.20 and 0.28. Theyconcluded that Poisson’s ratio tends to decrease with in-creasing water-cement ratio. Kaplan5.25 found values forPoisson’s ratio of concrete determined using dynamicmeasurements to be from 0.23 to 0.32 regardless of com-pressive strength, coarse aggregate, and test age for con-cretes having compressive strengths ranging from 2500 to11,500 psi (17 to 79 MPa).

Based on the available information, Poisson’s ratio ofhigh-strength concrete in the elastic range seems compar-able to the expected range of values for lower-strengthconcretes.

5.5-Modulus of ruptureThe values reported by various investigators 5.23,5.26-5.28

for the modulus of rupture of both lightweight and nor-mal weight high-strength concretes fall in the range of 7.5

&r to 12 g where both the modulus of rupture andthe compressive strength are expressed in psi. The fol-lowing equation was recommended 5.2 for the predictionof the tensile strength of normal weight concrete, asmeasured by the modulus of rupture f,’ from the com-pressive strength as shown in Fig. 5.4

fr ’ = 11.7 &r psifor 3000 psi < f,’ < 12,000 psi

c- = 0.94 &r MPafor 21 MPa < f,’ < 83 MPa) (5-2)

C 8’1- \\\

0


ModulusRupture

f; , psi

q, MPa

0 2 4 6 8 1OI I I I /

f’,.MPo

Modulus ofRupturef’, , MPa

Fig. 5.4-- Tensile strength based on modulus of rupturetest 5.2

5.6-Tensile splitting strengthDewar5.27 studied the relationship between the indirect

tensile strength (cylinder splitting strength) and the com-pressive strength of concretes having compressivestrengths of up to 12,105 psi (83.79 MPa) at 28 days. Heconcluded that at low strengths, the indirect tensilestrength may be as high as 10 percent of the compressivestrength but at higher strengths it may reduce to 5 per-cent. He observed that the tensile splitting strength wasabout 8 percent higher for crushed-rock-aggregate con-crete than for gravel-aggregate concrete- In addition, hefound that the indirect tensile strength was about 70 per-cent of the flexural strength at 28 days. Carrasquillo,Nilson, and Slate 5.2 reported that the splitting strengthdid not vary much from the usual range shown in Fig.5.5, although as the compressive strength increases, thevalues for the splitting strength fall in the upper limit ofthe expected range. The following equation for the pre-diction of the tensile splitting strength &,’ of normalweight concrete was recommended5.2

f 'SP = 7.4 K psifor 3000 psi c f,’ < 12,000 psi

(fJp’ = 0.59 g MPafor 21 MPa < f,’ < 83 MPa)

5.7-Fatigue strength

(5-3)

The available data on the fatigue behavior of high-strength concrete is very limited. Bennett and Muir.5.29

studied the fatigue strength in axial compression of high-strength concrete with a 4-in. (102-mm) cube compressivestrength of up to 11,155 psi (76.9 MPa) and found thatafter one million cycles, the strength of specimens sub-

q,MP*0 2 4 6 8I

MPa

12000

t; I20 40 60 80

4-x6" (102mm r203mml

1000

SplittingTensile 800

Strength t;p

psi 6 0 0

400

OOI I 1 I

2000 6000 10000 14000Cylinder Strength t; . psi

I I / / I I L

0 20 40 R.psi 8 o 1 0 0 120

Fig. 5.5-Tensile strength based on split cylinder test 5.2

jected to repeated load varied between 66 and 71 percentof the static strength for a minimum stress level of 1250psi (8.6 MPa). The lower values were found for thehigher-strength concretes and for concrete made with thesmaller-size coarse aggregate, but the actual magnitudeof the difference was small. To the extent that is known,the fatigue strength of high-strength concrete is the sameas that for concretes of lower strengths.

5.8-Unit WeightThe measured values of the unit weight of high-

strength concrete are slightly higher than lower-strengthconcrete made with the same materials.

5.9-Thermal propertiesThe thermal properties of high-strength concretes fall

within the a proximatecretes.5.21,5.26

range for lower-strength con-Quantities that have been measured are

specific heat, diffusivity, thermal conductivity, and co-efficient of thermal expansion.

5.10-Heat evolution due to hydrationThe temperature rise within concrete due to hydration

depends on the cement content, water-cement ratio, sizeof the member, ambient temperature, environment, etc.Freedman 5.15 has concluded from data of Saucier et al.in Fig. 5.6 that the heat rise of high-strength concreteswill be approximately 11 to 15 F/l00 lb of cement/yd 3 (6to 8 C per 59 kg/m3 of cement). Values for temperaturerise of the order of 100 F (56 C) in high-strength con-crete members containing 846 lb of cement/yd 3 (502kg/m3) were measured in a building in Chicago as shownin Fig. 5.7.5.16

5.11-Strength gain with ageHigh-strength concrete shows a higher rate of strength

gain at earl a es as compared to lower-strength con- crete5.1,5.2,5.13,5.15but at later ages the difference is not


Temp. ,F

40 -

0 I I I I0 20 40 60 80 100

Time, hours

Fig. 5.6-Temperature rise of high-strength field-cast 10 x20 x 5-ft (3 x 6 x 1.5-m) blocks 5.21

200

150

yeroture. ,oo , -1

50

0

C o l u m n c3 i

I t

5 10 15 20

Age, days

Fig. 5.7-- Measured concrete temperatures at Water TowerPlace.5.16

100 -

Compressive Strength

Compressive Strengtha t 9 5 d a y s

@---I

0 7 28 95

Age, days

Fig. 5.8-- Normalized strength gain with age for moist-curedlimestone concretes 5.2

significant (see Fig. 5.8). Parrott 5.26 reported typicalratios of 7-day to 28-day strengths of 0.8 to 0.9 for high-

strength concrete and 0.7 to 0.75 for lower-strength c o n -crete, while Carrasquillo, Nilson, and Slate5.2,5.9 foundtypical ratios of 7-day to 95-day strength of 0.60 forlow-strength, 0.65 for medium-strength, and 0.73 forhigh-strength concrete. It seems likely that the higherrate of strength development of high-strength concrete atearly ages is caused by (1) an increase in the internalcuring temperature in the concrete cylinders due to ahigher heat of hydration and (2) shorter distance betweenhydrated particles in high-strength concrete due to lowwater-cement ratio.

5.12-Freeze thaw resistanceInformation about air content requirement for high-

strength concrete to produce adequate durability iscontradictory. For example, Saucier, Tynes, and Smith5.21

concluded from accelerated laboratory freeze-thaw teststhat, if high-strength concrete is to be frozen under wetconditions, air-entrained concrete should be considereddespite the loss of strength due to air entrainment. Incontrast, Perenchio and Klieger5.24 obtained excellentresistance to freezing and thawing of all of the high-strength concretes used in their study, whether air en-trained or non-air-entrained. They attributed this to thegreatly reduced freezable water contents and the in-creased tensile strength of high-strength concrete.

Little information is available on the shrinkage be-havior of high-strength concrete. A relatively high initialrate of shrinkage has been reported, 5.26,5.30 but afterdrying for 180 days there is little difference between theshrinkage of high-strength and lower-strength concretemade with dolomite or limestone. Reducing the curingperiod from 28 to 7 days caused a slight increase in theshrinkage. 5.26 Shrinkage was unaffected by changes inwater-cement ratio5.15 but is approximately proportionalto the percentage of water by volume in the concrete.Other laboratory studies 5.31 and field studies 5.16,5.22,5.28

have shown that shrinkage of high-strength concrete issimilar to that of lower-strength concrete. Nagataki andYonekuras 5.32 reported that the shrinkage of high-strength concrete containing high-range water reducerswas less than for lower-strength concrete.

5.14-- CreepParrott5.26 reported that the total strain observed in

sealed high-strength concrete under a sustained loadingof 30 percent of the ultimate strength was the same asthat of lower-strength concrete when expressed as a ratioof the short-term strain. Under drying conditions, thisratio was 25 percent lower than that of lower-strengthconcrete. The total long-term strains of drying and sealedhigh-strength concrete were 15 and 65 percent higher, re-spectively, than for a corresponding lower-strength con-crete at a similar relative stress level. Ngab et a1.5.31

found little difference between the creep of high-strengthconcrete under drying and sealed conditions. The creep


of high-strength concrete made with high-range waterreducers is reported5.32 to be decreased significantly. Themaximum specific creep was less for high-strength con-crete than for lower-strength concrete loaded at the sameage.5.16,5.20,5.31 An example is shown in Fig. 5.9. 5 .28

However, high-strength concretes are subjected to higherstresses. Therefore, the total creep will be about thesame for any strength

found 5.22 h concrete. No problems due to

creep were in columns cast with high-strengthconcrete. As is found with lower-strength concrete, creepdecreases as the age at loading increases,5.31 specificcreep increases with increased water-cement ratio,5.24 andthere is a linear relationship with the applied stress.5.31

This linearity extends to a higher stress-strain ratio thanfor lower-strength concrete.

Some additional information on properties of high-strength concrete can be obtained from References 5.33to 5.42.

1.75

1.50

1.25

CreepCoefficient,

CcI.00

0 7 5

0.50

0.25

0

,-De- Unsealed- Sealed

yft;=48DD psi

1000 psi = 6.895 M PO

= 0.45 in All Cases

Age at Loading = 2 DaysAfter 28 Days Curing

, I I I0 15 30 45 60 75

T i m e A f t e r L o a d i n g , d a y s

Fig. 5.9-- Relationship between creep coefficient and timefor sealed and unsealed concrete specimens 5.31


5.1 Wischers, Gerd, “Applications and Effects ofCompressive Loads on Concrete,” BetontechnischeBerichte 1978, Betone Verlag GmbH, Dusseldorf, 1979,pp. 31-56. (in German)

5.2. Carrasquiho, Ramon L.; Nilson, Arthur H.; andSlate, Floyd O., “Properties of High Strength ConcreteSubjected to Short-Term Loads,” ACI JOURNAL, Proceed-ings V. 78, No. 3, May-June 1981, pp. 171-178, andDiscussion, Proceedings V. 79, No. 2, Mar.-Apr. 1982, pp.162-163.

5.3. Wang, P.T.; Shah, S.P.; and Naaman, A.E.,

“Stress-Strain Curves of Normal and LightweightConcrete in Compression,” ACI JOURNAL, Proceedings V.75, No. 10, Nov. 1978, pp. 603-611.

5.4. Kaar, P.H.; Hanson, N.W.; and Capell, H.T.,“Stress-Strain Characteristics of High-Strength Concrete,”Douglas McHenry International Symposium on Concreteand Concrete Structures, SP-55, American Concrete Insti-tute, Detroit, 1978, pp. 161-185. Also, Research andDevelopment Bulletin No. 051.01D, Portland CementAssociation.

5.5. Shah, S.P.; Gokoz, U.; and Ansari, F., “AnExperimental Technique for Obtaining Complete Stress-Strain Curves for High Strength Concrete,” Cement,Concrete and Aggregates, V. 3, No. 1, Summer 1981, pp.21-27.

5.6. Shah, S.P., “High Strength Concrete-A Work-shop Summary,” Concrete International Design & Con-struction, V. 3, No. 5, May 1981, pp. 94-98.

5.7. Shah, S.P.; Naaman, A.E.; and Moreno, J., “Effectof Confinement on the Ductility of Lightweight Con-crete,” International Journal of Cement Composites andLightweight Concrete (Harlow, Essex), V. 5, No. 1, Feb.1983, pp. 15-25.

5.8. Holm, T.A., “Physical Properties of High StrengthLightweight Aggregate Concrete,” Proceedings, 2nd Inter-national Congress on Lightweight Concrete (London,Apr. 1980) Ci80, Construction Press, Lancaster, 1980,pp. 187-204.

5.9. Carrasquillo, Ramon L.; Slate, Floyd 0.; andNilson, Arthur H., “Microcracking and Behavior of High-Strength Concrete Subject to Short-Term Loading,” ACIJOURNAL, Proceedings V. 78, No. 3, May-June 1981, pp.179-186.

5.10. Ahmad, Schuaib, and Shah, Surendra P.,“Complete Triaxial Stress-Strain Curves for Concrete,”Proceedings, ASCE, V. 108, ST4, Apr. 1982, pp. 728-742.

5.11. Ahmad, S.H., and Shah, S.P., “Stress-StrainCurves Of Concrete Confined by Spiral Reinforcement,ACI JOURNAL, Proceedings V. 79, No. 6, Nov.-Dec. 1982,pp. 484-490.

5.12. Thoman, William H., and Raeder, Warren, “Ulti-mate Strength and Modulus of Elasticity of HighStrength Portland Cement Concrete,” ACI JOURNAL,Proceedings V. 30, No. 3, Jan-Feb. 1934, pp. 231-238.

5.13. Smith, E.F.; Tynes, W.O.; and Saucier, K.L.,“High-Compressive-Strength Concrete, Development ofConcrete Mixtures,” Technical Documentary Report No.RTD TDR-63-3114, U.S. Army Engineer Waterways Ex-periment Station, Vicksburg, Feb. 1964, 44 pp.

5.14. Nedderman, Howard, “Flexural Stress Distri-bution in Very-High-Strength Concrete,” MSc thesis,University of Texas at Arlington, Dec. 1973, 182 pp.

5.15. Freedman, Sydney, High-Strength Concrete,”Modern Concrete, V. 34, No. 6, Oct. 1970, pp. 29-36; No.7, Nov. 1970, pp. 28-32; No. 8, Dec. 1970, pp. 21-24; No.9, Jan. 1971, pp. 15-22; and No. 10, Feb. 1971, pp. 16-23.Also, Publication No. lS176T, Portland Cement Associ-ation.


5.16. “High-Strength Concrete in Chicago High-RiseBuildings,” Task Force Report No. 5, Chicago Committeeon High-Rise Buildings, Feb. 1977, 63 pp.

5.17. Teychenne, D.C.; Parrott, L.J.; and Pomeroy,C.D., “The Estimation of the Elastic Modulus of Con-crete for the Design of Structures,” Current Paper No.CP23/78, Building Research Establishment, Garston,Watford, 1978, 11 pp.

5.18. Ahmad, S.H., “Properties of Confined ConcreteSubjected to Static and Dynamic Loading,” PhD thesis,University of IIIinois at Chicago Circle, Mar. 1981.

5.19. Martinez, S.; NiIson, AH.; and Slate, F.O.,“Spirally-Reinforced High-Strength Concrete Columns,”Research Report No. 82-10, Department of StructuralEngineering, Cornell University, Ithaca, Aug. 1982.

5.20. Russell, H.G., and Corley, W.G., “Time-Dependent Behavior of Columns in Water Tower Place,Douglas McHenry International Symposium on Concreteand Concrete Structures, SP-55, American ConcreteInstitute, Detroit, 1978, pp. 347-373, Also, Research andDevelopment Bulletin No. RD052.01B, Portland CementAssociation.

5.21. Saucier, K.L.; Tynes, W.O.; and Smith, E.F.,“High Compressive-Strength Concrete-Report 3, Sum-mary Report,” Miscellaneous Paper No. 6-520, U.S. ArmyEngineer Waterways Experiment Station, Vicksburg,Sept. 1965, 87 pp.

5.22. Pfeifer, Donald W.; Magura, Donald D.; Russell,Henry G.;, and Corley, W.G., “Time Dependent Defor-mations in a 70 Story Structure,” Designing for Effects ofCreep, Shrinkage, Temperature in Concrete Structures,SP-37, American Concrete Institute, Detroit, 1971, pp.159-185.

5.23. Shideler, J J., “Lightweight-Aggregate Concretefor Structural Use,” ACI JOURNAL, Proceedings V. 54,No. 4, Oct. 1957, pp. 299-328.

5.24. Perenchio, William F., and Khieger, Paul, “SomePhysical Properties of High Strength Concrete,” Researchand Development Bulletin No. RD056.01T, PortlandCement Association, Skokie, 1978, 7 pp.

5.25. Kaplan, M.F., “Ultrasonic Pulse Velocity,Dynamic Modulus of Elasticity, Poisson’s Ratio and theStrength of Concrete Made with Thirteen DifferentCoarse Aggregates,” RILEM Bulletin (Paris), New SeriesNo. 1, Mar. 1959, pp. 58-73.

5.26. Parrot, LJ., “The Properties of High-StrengthConcrete,” Technical Report No. 42.417, Cement andConcrete Association, Wexham Springs, 1969, 12 pp.

5.27. Dewar, J.D., “The Indirect Tensile Strength ofConcretes of High Compressive Strength,” TechnicalReport No. 42.377, Cement and Concrete Association,Wexham Springs, Mar. 1964, 12 pp.

5.28. Kaplan, M.F., “Flexural and CompressiveStrength of Concrete as Affected by the Properties of theCoarse Aggregates, ACI JOURNAL, Proceedings V. 55,No. 11, May 1959, pp. 1193-1208.

5.29. Bennett, E.W., and Muir, S.E. St. J., “SomeFatigue Tests of High-Strength Concrete in Axial Com-

pression,” Magazine of Concrete Research (London), V.19, No. 59, June 1967, pp. 113-117.

5.30. Swamy, R.N., and Anand, K.L., “Shrinkage andCreep of High Strength Concrete,” Civil Engineering andPublic Works Review (London), V. 68, No. 807, Oct. 1973,pp. 859-865, 867-868.

5.31. Ngab, A.S.; Slate, F.O.; and Nilson, A.H.,“Behavior of High-Strength Concrete Under SustainedCompressive Stress,” Research Report No. 80-2, Depart-ment of Structural Engineering, Cornell University,Ithaca, Feb. 1980, 201 pp. Also, PhD dissertation, CornellUniversity, 1980, and “Shrinkage and Creep of HighStrength Concrete,” ACI JOURNAL, Proceedings V. 78,No. 4, July-Aug. 1981, pp. 255-261.

5.32. Nagataki, S., and Yonekura, A., “Studies of theVolume Changes of High Strength Concretes with Super-plasticizer,” Journal, Japan Prestressed ConcreteEngineering Association (Tokyo), V. 20, 1978, pp. 26-33.

5.33. Ahmad, S.H. and Shah, S.P. “Behavior of HoopConfined Concrete Under High Strain Rates,” ACIJOURNAL, Proceedings V. 82, No. 5. Sept.-Oct. 1985, pp.634-647.

5.34. “Research Needs for High-Strength Concrete,”reported by ACI Committee 363, ACI Materials Journal,Proceedings V. 84, No. 6, Nov.-Dec. 1987, pp. 559-561.

5.35. Proceedings of Symposium on Utilization of High-Strength Concrete, Stavanger, Norway, June 15-18, 1987,Tapir, Publishers, N-7034 Trondheim-N7H, Norway, 688PP.

5.36. Yogendram, Langan, Hagne and Ward, “SilicaFume in High Strength Concrete,” ACI Materials Journal,V. 84, No. 2, Mar.-Apr. 1987, pp. 124-129.

5.37. Carrasquillo, P., and Carrasquillo, R., “CurrentPractice in Evaluation of High Strength Concrete,”ACI Materials Journal, V. 85, No. 1, Jan.-Feb., 1988, pp.49-54.

5.38. Smadi, M.M., Slate, F.O., and Nilson, A.H.,“Shrinkage and Creep of High, Medium, and LowStrength Concretes Including Overloads,” ACI MaterialsJournal, Proceedings V. 84, No. 3, May-June 1987, pp.224-234.

5.39. Smadi, M.M., Slate, F.O., and Nilson, AH.,“High, Medium, and Low Strength Concrete Subject toSustained Loads-Strains, Strengths and FailureMechanisms,” ACI JOURNAL, Proceedings V. 82, No. 5,Sept.-Oct. 1985, pp. 657-664.

5.40. Ahmad, S.H., and Shah, S.P., “StructuralProperties of High Strength Concrete and Its Impli-cations on Precast and Prestressed Concrete,” Journal ofPrestressed Concrete Institute, Nov.-Dec. 1985.

5.41. Ahmad, S.H., and Shah, S.P., “High StrengthConcrete-A Review,” Proceedings of International Sym-posium on Utilization of High Strength Concrete,Stavanger, Norway, June 15-18, 1987.

5.42. Shirley, T. Scott, Burg, G. Ronald, and Fiorato,E. Anthony, “Fire Endurance of High Strength ConcreteSlabs,” ACI Materials Journal, Mar.-Apr. 1988, pp. 102-108.


CHAPTER 6-STRUCTURAL DESIGNCONSIDERATIONS

High-strength concretes have some characteristics andengineering properties that are different from those oflower-strength concretes. Internal changes resulting fromshort-term and sustained loads and environmental factorsare known to be different. Directly related to these inter-nal differences are distinctions in mechanical propertiesthat must be recognized by design engineers in predictingthe performance and safety of structures. These distinc-tions are increasingly important as strengths increase.Tests of unreinforced high-strength concrete have shown,for example, that such material in many cases may beclosely characterized as linearly elastic up to stress levelsapproaching the maximum stress. Thereafter, the stress-strain curve of high-strength concrete decreases at amuch greater rate than lower-strength concretes.6.1-6.10

Extensive experimentation at several research centershas provided a fundamental understanding of the be-havior of high-strength concrete. While substantial infor-mation is now available on many aspects, some final re-commendations must await the results of current andfuture work.

In this chapter, the emphasis will be placed on designof members and structures.6.11 Where recommendationsare made, they are based on the best current experi-mental information and in most cases must be consideredtentative.

6.2-Axially-loaded columnsFew columns in practice are subjected to truly axial

loads. Bending moments, due to eccentric application ofload or associated with rigid frame action, are usuallysuperimposed on axial loads. ACI 318-83 requirementsfor design and ACI 318R-83 reflect this. However, it isuseful to look first at the behavior of columns carryingaxial load only.

6.2.1 Strength contribution of steel and concrete-Theattribute of main interest is the ultimate strength. Presentdesign practice, in calculating the nominal strength of anaxially loaded member, is to assume a direct addition lawsumming the strength of the concrete and that of thesteel. The justification for this is seen in Fig. 6.1, whichsuperimposes typical stress-strain curves in compressionfor three concretes with that for reinforcing steel having60,000 psi (414 MPa) yield strength (the last curve isdrawn to a different vertical scale for convenience). Theusual assumption is made that steel and concrete strainsare identical at any load stage.

For lower-strength concrete, when the concretereaches the range of significant nonlinearity (about 0.001strain), the steel is still in the elastic range and con-sequently starts to pick up a larger share of the load.When the strain is close to 0.002, the slope of the con-crete curve is nearly zero and it can be thought of as de-forming plastically, with little or no increase in stress.

The steel reaches its yield point at about the same strainin this case; thus, concrete is at its maximum stress, steelis at fy, and the strength of the column is predicted by

P = 0.85 fc' Ac + fy As (6-l)

where fc' = cylinder compressive strength of the con-crete

fy = yield strength of steelAc = area of concrete sectionAs = area of steel

The factor 0.85 is used to account for the observed dif-ference in strength of concrete in columns compared withconcrete of the same mix in standard compression-testcylinders.

A similar analysis holds for high-strength concretecolumns, except the steel will yield before the concretereaches its peak strength. However, the steel will con-tinue to yield at essentially constant stress until theconcrete is fully stressed. Prediction of strength maytherefore still be based on Eq. (6-l). Experimentaldocumentation also supports use of the factor 0.85 forhigh-strength concrete.6.12-6.13

6.2.2 Effects of confinement steel-Lateral steel incolumns, preferably in the form of continuous spirals, hastwo beneficial effects on column behavior: (a) it greatlyincreases the strength of the core concrete inside thespiral by confining the core against lateral expansionunder load, and (b) it increases the axial strain capacityof the concrete, permitting a more gradual and ductilefailure, i.e., a tougher column.6.12-6.16

The basis for design of spiral steel under the 1977 andlater versions of ACI 318 is that the strengthening effectof the spiral must be at least equal to the columnstrength lost when the concrete shell outside of the spiralspalls off under load. The ACI 318 equation for mini-

70 r

O?0 0 2 0 4 0 6

1,sM PO

-60 “c,M PO

440

-2-o

JO

Strain, percent

Fig. 6.1-- Concrete and steel stress-strain curves


mum volumetric ratio of spiral is

= 0.45 2 - 1 -Li I

f'ps E 4

P-2)

where ps = ratio of volume of spiral reinforcement tovolume of concrete core

Ag = gross area of concrete section

r”:= area of concrete core

6= cylinder compressive strength of concrete= yield strength of spiral steel

The increase in compressive strength of columns pro-vided by spiral steel is based on an experimentallyderived relationship for strength gain

where x =

f,” =

f.2' =

x - fcl’ = 4.oJy (6-3a)

compressive strength of spirally reinforc-ed concrete columncompressive strength of unconfined con-crete columnconcrete confinement stress produced byspiral

This relationship can be shown to lead directly to Eq.(6-2). The concrete confinement stress produced by spiralf2' is calculated on the basis that the spiral steel hasyielded, using the familiar hoop tension equation.

or2J4 f

f2' = dscwhere ASP = area of spiral steel

4 = diameter of concrete coreS = pitch of spiral

and other terms are as already defined.Recent work by Ahmad and Shah 6.14 has shown that

spiral reinforcement is less effective for columns ofhigher-strength concrete and for lightweight concretecolumns. They found also that the stress in the steelspiral at peak load for high-strength concrete columnsand lightweight concrete columns is often significantlyless than the yield strength assumed in the developmentof Eq. (6-2).

These conclusions are consistent with results of experi-mental research at Cornell University.6.13 In the Cornellresearch, an “effective” confinement stress f2 (1 - s/dc)was used in evaluating results, where f2 is the confine-ment stress in the concrete, calculated using the actualstress in the spiral steel, often less than fy . The term (1 -s/dc) reflects the reduction in effectiveness of spirals

associated with increasing spacing of the spiralwires.6.13,6.17 Thus an improved version of Eq. (6-3a) is

z - fc,’ = 4.Of, (1 - s/d,) (6-3b)

Fig. 6.2 shows the results of the Cornell tests oncolumns using different strength concretes. It is clear thatthe strength gain predicted by Eq. (6-3b) is valid for nor-mal weight concrete of all strengths for confinementstress up to at least 3000 psi (21 MPa). A similar plotbased on Eq. (6-3a) shows a somewhat unconservativeprediction for higher confinement stresses, but it can beshown that typical confinement stresses for practicalcolumn spirals are seldom more than about 1000 psi (7MPa). For this range Eq. (6-3a) gives good results. Fromthe strength viewpoint, the present ACI 318 equation forminimum spiral steel ratio can be used safely for high-strength normal weight columns as well as for lower-strength concrete columns.

Fig. 6.2 also shows that a spiral has much less con-fining effect in lightweight concrete columns. The light-weight concrete tends to crush under the spirals at heavyloads, relieving the confining pressure.6.13 For lightweightspirally reinforced columns, Martinez has suggested thatEq. (6-3a) be replaced by

z - fcl’ = 1.8fi’ (6-4a)

and Eq. (6-3b) be replaced by

x - fcl’ = 1.8 f2’ (1 - s/d,) (6-4b)

This important difference in behavior means that Eq.(6-2) found in ACI 318 must be reexamined. It appearsthat lightweight concrete columns would require about2.5 times more spiral steel than corresponding normalweight columns to satisfy strength requirements after thecover spalls off, a requirement that is not reflected inACI 318. Whether or not such heavy spirals are practicalmay be questioned.

There is not yet general agreement on the effective-ness of spiral steel for improving the ductility of high-strength concrete columns, that is, for increasing thestrain limit and flattening the negative slope of thestress-strain curve past the point of peak stress. A paperby Ahmad and Shah6.14 indicates that confining spiralsare about as effective in flattening the negative slope ofthe stress-strain curve for high-strength concrete columnsas for lower-strength concrete columns. However, theCornell work6.13 showed significant differences. Fig. 6.3shows experimental stress-strain curves for differentstrengths of normal weight concrete columns with varyingspiral reinforcement. Three groups of curves are identi-fied by the three concrete strength levels studied. Eachof these groups consists of three sets of curves corres-ponding to three different amounts of lateral reinforce-ment. Indicated in each set of curves with a short hori-zontal line is the average unconfined column strengthcorresponding to that particular set of confined columns.


Effective Confinement Stress f,(l- s/d,) , MPa

0 5 IO 15 20t I I I I I

StrengthIncrememt

T,- f’; ,

ksi

12 -

10 -

6 -

Normal Weight ConcreteA High- Strength. Medium - Strengthl Low- Strength

Lightweight ConcreteA High- Strengtha Medium - Strengtho Low- Strength

- 80

- 60

StrengthIncrementTc-f‘, )

MPa

fc= f;t l.Bfe(l-s/d,) - 2 0

4 x 16 - in. (102 x 406 -mm) CylinderStroke Rote: 12,000 p-in (0.30 mm)/min.

I 02000 3000

Effective Confinement Stress 1,(1-s/d,) , psi

Fig. 6.2-Strength increment provided by spiral reinforcement action on 4 x 16-in. columns

AxialStress,

ksi

Normal Weight Spiral Columns

4 x 16 - in. (102 x 406 -mm) CylinderStroke Rate: 12.000 p-in.(O 30mmtlnun1; = Unconfined Column Strength(2500) = Effective Ccnfinement

stress ‘L, t- l/d&

AxialStress ,M Pa

Axial Strain , in. / in.

Fig. 6.3-Experimental stress-strain curves of 4 x 16-in. normal weight spiral columns

Referring to Fig. 6.3, the curves for high-strengthconcrete columns NC167 that had an effective confine-ment stress of 767 psi (5 MPa) are compared with thecurves for lower-strength concrete columns NC163 withan effective confinement stress of 800 psi (6 MPa). Dif-ferent behavior for comparable confinement stress isevident. Not only is the strain at peak stress much lessfor high-strength concrete, but the stress falls off sharplyjust past the peak value. This last fact is seen to be trueeven for columns NC169 with a very high confinementstress of 2500 psi (17 MPa) (probably not attainable inpractical columns).

Based on the available evidence, one may concludethat normal density high-strength concrete columns withspiral steel show strength gain due to the spirals that is

predicted well by present equations, but that their pro-perties past peak stress may be deficient compared withlower-strength columns. The design of lightweight con-crete columns with spiral steel should be approached verycarefully. 6.13,6.17

Another interesting and important observation relatingto spirally reinforced columns generally is that the levelof confinement stress corresponding to spirals designedby ACI 318 is rather low for all columns. The confine-ment stress becomes significantly lower for larger dia-meter columns, assuming that the cover requirements re-main constant. This follows directly from Eq. (6-2). Forlarger columns, the ratio Ag/Ac becomes much smaller;consequently the required spiral steel ratio becomessmaller and the effective confinement stress becomes


proportionately smaller. Confinement stress produced byspirals designed to ACI 318 for lower-and high-strengthconcrete, for 15 and 50 in. column core diameters arecompared in Table 6.1.

Table 6.1-Confinement stress produced by spiralsdesigned by ACI 318

4. f’ (1 - s/a, s,in. (mm) A, /A Ps* psi (MPa) in. (mm)

f,’ = 3000 psi (21 MPa) (#3 spiral bar)

15(38) ;:;“: 0.0099 238 (1.64) 2.96 (75)50( 172) 0.0028 83 (0.57) 3.17 (81)

f: = 10,000 psi (69 MPa) (#5 spiral bar)

0.0330 825(5.69) 2.50(64)5 0 ( 1 2 7 ) 0.0093 263(1.81) 2.67(68)

*Ratio of volume of spiral reinforcement to total volume of core(out-to-out of spirals).

Tests show that for lower-strength concrete even thereduction in confinement stress from 238 to 83 psi (1.64to 0.57 MPa) obtained under ACI 318 wilI produce a col-umn with very large strain capacity without significantloss of resistance. For high-strength concrete, thereduction of confinement stress from 825 to 263 psi (5.69to 1.81 MPa) produces a column with virtually no post-peak strain capacity. Even the higher confinement stressof 825 psi (5.69 MPa) produces a column with the unde-sirable characteristic of a sharpimmediately after peak stress.6.13

drop-off of resistance

While some experimental data are available at thistime for high-strength concrete columns using lateral tiesrather than spirals,6.18,6.19 more work must be done forsuch members.

6.2.3 Repeated loading-High-strength concrete is rela-tively free of internal microcracking, even close to ulti-mate load, when loaded monotonically.6.1 On the otherhand, high-strength concrete is reported to be morebrittle than lower-strength concrete,6.2 lacking much ofthe ductility that accompanies progressive crack growth.Some experimental research indicates that fatiguestrength is essentially independent of compressivestrength.6.20 Recent research indicates that failure ofconcrete subject to repeated loading can be approximate-ly predicted by the concept of the envelope curve, di-rectly related to the short-term monotonic stress-straincurve. 6.21 For high-strength concrete, each load appli-cation causes relatively less incremental damage. How-ever, the number of cycles to failure may not be neces-sarily larger because of the greater negative slope of thepost-peak envelope curve.

While important work has been done,6.20,6.22,6.23 it isclear that additional research is needed on all aspects ofhigh-strength concrete, with and without confinementsteel, subject to various repeated load regimens, beforedesign recommendations can be made.

6.2.4 Sustained loading-In most structures, concreteis subjected to sustained loads. The time-dependent

strains associated with these stresses have a profound ef-fect on the structural behavior. Such strains are directlyrelated to long-term deflection, losses in prestress force,and cracking. Column strength may be reduced due tosustained loading of high intensity. It may also be in-creased because of the capability of a concrete structureto adjust itself to local high over-stresses through creep.

Creep may be described either in terms of the creepcoefficient

Cc = creep straininitial elastic strain (6-5)

or by the coefficient of specific creep (unit creep coef-ficient)

6, = creep strain per unit stress (6-6)

The two can be related through the modulus of elasticity

cc = E,6, (6-7)

There is general agreement that creep of high-strengthconcrete is significantly less than that of a lower-strengthconcrete6.7,6.24-6.27 The most recent information, for con-cretes with strength up to about 10,000 psi (69-MPa), in-dicates that high-strength concrete has a specific creeponly about 20 percent that of lower-strength concrete anda creep coefficient about 30 percent as high.6.27

As a result, for axially loaded high-strength concretecolumns, creep shortening at a given stress level will beless than that of lower-strength columns, a fact of pos-sible significance in high-rise concrete structures.6.30 Inaddition, the distribution of load between concrete andsteel of high-strength concrete columns will be less sub-ject to change with the passage of time. Elastic distri-bution of stresses may be more nearly maintained. Lossof stress in a prestressed member due to creep shorten-ing will be much less at a given concrete stress level, butthis advantage may be largely canceled if higher sustainedload stresses are permitted.

6.3-Beams and slabsThe material properties described in Chapter 5 and in

Section 6.2 may effect the characteristic behavior of high-strength concrete beams.6.31-6.34 In some cases, improve-ments are seen; in other cases less satisfactory behaviorwill result. In many ways, high-strength beams may be-have according to essentially the same rules that havebeen used to describe behavior of beams made of lower-strength concrete. However, some questions remain to beanswered.

6.3.1 Compressive stress distribution-The compressivestress distribution in beams is directly related to theshape of the stress-strain curve in uniaxial compression.Consequently, for high-strength concrete, which displaysdifferences in that shape, as shown in Fig. 6.1, it isreasonable to expect differences in flexural compressive


stress distribution, particularly at loads approachingultimate.

In present U.S. practice as in ACI 318 and ACI 318R,proportioning of beam sections is generally based on con-ditions at a hypothetical state of incipient collapse atfactored loads. Fig. 6.4(a) shows the generally parabolicshape of the compressive stress distribution in a beammade of lower-strength concrete. The nominal resistingmoment may be calculated knowing the internal forces Tand C and the internal lever arm between them. The act-ual shape of the compressive stress distribution at in-cipient failure, always highly variable even within a givenrange of concrete strengths, may be considered irrelevantif one knows (a) the magnitude of the compressive resul-tant C, and (b) the level in the beam at which it acts.These may be established in terms of three parameterscharacteristic of a given stress distribution [see Fig.6.4(a)].

k 1 = ratio of average to maximum compressive stressin beam

k 2 = ratio of depth to compressive resultant to neutralaxis depth

k 3 = ratio of maximum stress in beam to maximumstress in corresponding axially loaded cylinder

C=k,k,f;bc

-> T = Asfs

C-O.85 f’,ab

drp- C=$.f;bc

T=A,f,

Fig. 6.4-Concrete stress distributions for rectangular beams

For ordinary design purposes, it is convenient to workwith an equivalent rectangular compressive stress distri-bution, shown in Fig. 6.4(b), with magnitude of compres-sive resultant and line of action the same as before. Suchan equivalent distribution is specifically referenced andpermitted in ACI 318 and its Commentary, ACI 318R.With the uniform value of concrete compression assumedequal to 0.85fc', a single parameter PI is sufficient todefine both magnitude and line of action.

For high-strength concrete, the stress-strain curve ismore linear than parabolic. Therefore, there is reason tosuspect that the stress block parameters may be different.Experimental research has confirmed that differences doexist, and alternatives to the rectangular stress block havebeen proposed, such as in Fig. 6.4(c).6.34 However, differ-ences in calculated strength values for beams and eccen-tric columns depend on steel ratios and other factors.

ACI 318R suggests, based on an equivalent rectangu-lar stress block, that the nominal flexural strength of asingly reinforced beam that is under-reinforced can becalculated by

where Mn = nominal moment strength at section,in-lb

;= area of tension reinforcement, in.2

= specified yield strength of reinforcement,psi

d = distance from extreme compression fiberto centroid of tension reinforcement, in.

if= ratio of tension reinforcement= specified compressive strength of con-

crete, psiThe coefficient 0.59 can be shown to be equivalent tok2/k1k3. The experimental variation of k2/k1k3 with con-crete compressive strength based on research at severalcenters is shown in Fig. 6.5. 6.6,6.31-6.35 While a detailedstudy of the separate k values indicates that significantdifferences in the separate values exist depending onconcrete strength, it is clear from Fig. 6.5 that thedifferences are compensative and that the combined coef-ficient is well-represented by the constant value 0.59. Thisstatement is reinforced by the results shown in Fig. 6.6,which compares flexural strength predictions obtainedusing the usual rectangular stress block, a triangularstress block, and a distribution based on experimentallyderived stress-strain curves with test data for beams ofvarying reinforcement ratios and concrete strengths to11,000 psi (76 MPa). Test values were best predictedusing actual stress-strain curves, but either the rec-tangular or triangular distributions gave acceptable lowerbounds to the experimental and theoretical values.6.36

Based on these and similar studies, it appears that, forunder-reinforced beams, the present ACI 318 methodscan be used without change, at least for concretestrengths up to 12,000 psi (83 MPa). For over-reinforced


F

Concrete Strength , M Pa

0 8I

0.6

k2

k,

i

. . 0.500- & - - - - A - - - - - -

0.4 t

0.2

0 L

. Rectangular

t I 1 I

0 4 8 I2 16 20

Concrete Strength , ksi

Fig. 6.5-- Stress block parameter k2/k1k3 versus concretestrength

140

100Mu,

k i p - f t80

60

4 0

20

Test Dato 0ACI Cods -4.-

TriangularStress Block --*-

Theoretical I*--

0.5 I 2 3

Reinforcement Ratio p ,%

Fig. 6.6-- Comparison of flexural strength Mu, of beams forseveral compressive stress distributions

beams, which are not allowed by ACI 318, or formembers combining axial compression and bending,important differences may occur.6.33

6.2.3 Limiting compressive strain-While high-strengthconcrete reaches its peak stress at a compressive strainslightly higher than that for lower-strength concrete, theultimate strain is lower for high-strength concrete, bothin uniaxial compression tests and in beam tests.6.13,6.34 Ithas been suggested that this result apparently is due to

energy release from the testing equipment. Fig. 6.76.5

shows the variation of concrete strain at failure at theextreme compression face of singly reinforced concretebeams or eccentrically loaded columns without lateralconfinement steel. The constant value of strain at ex-treme concrete compression fiber of 0.003 prescribed byACI 318 is seen to represent satisfactorily the experi-mental results for high-strength as well as lower-strengthconcrete, although it is not as conservative for high-strength concrete.

Concrete Strength , M Pa

0 20 4 0 60 80 l00 1200.005 r I I 1 I I I

.

0001 t

0 I I I I I

0 4 8 12 16 20

Concrete Strength , ksi

ig. 6.7-- Ultimate concrete flexural strain Q, versus con-crete compressive strength

6.3.3 Influence of confinement steel and compressionSteel-Considering the more limited strain capacity ofhigh-strength concrete in compression, it is necessary toevaluate the ductility of beams made of high-strengthconcrete. Deflection ductility index /1 will be definedhere as

where4 = beam deflection at failure load

4, = beam deflection at the load producing yieldingof tensile steel

Tests by Pastor et al6 . 3 4 of beams made of relatively high-strength concrete are summarized in Table 6.2 (Series A)and Table 6.3 (Series B). Beams of Series A were singlyreinforced with no compression steel and no confinementsteel. The series includes beams with concrete strengthsfrom 3700 to 9265 psi (26 to 64 MPa). For the high-strength beams, tensile steel ratio varied from 0.29 &, to1.11 pb where ,,b = reinforcement ratio for balancedstrain conditions.

The results show a lower ductility for the beams with


Table 6.2-Deflection ductility index for Series Abeams 6.34

Ductilityindex

*Ratio of tension reinforcement divided by reinforcement ratio producingbalanced strain conditions.

the higher concrete strengths. Based on these results, thesecond series summarized in Table 6.3 was performed.These beams included varying amounts of compressionsteel (50 to 100 percent of tensile steel area) and lateralconfinement steel in the form of closed hoops at spacingof 3, 6, and 12 in. (7.6, 15.2, and 30.5 mm). All beamswere of high-strength concrete and comparable to BeamA4 of the first series, which had no ties and no com-pression steel.

Table 6.3-Deflection ductility index for Series Bbeams 6.34

Beam

Bl

i:

EB6

psi

853486058578847885168466

Tp/p,0.570.550.570.590.560.58

DuctilityindexWA.2.362.644.888.325.616.14

From Beams Bl and B2, compared with Beam A4, itcan be concluded that ties at 12 in. (30.5 mm) increasedthe ductility index, but not significantly. Ductility indexincreased markedly when the tie spacing was reduced to6 in. (15.2 mm) in Beams B3 and B4, but showed no up-ward trend when the spacing was further reduced to 3 in.(7.6 mm).

A comparison between Beams B3 and B4 indicates abeneficial effect in adding more compression steel, al-though this trend is not clearly reflected in a comparisonof Beams B5 and B6.

6.3.4 Minimum tensile steel ratios-ACI 318 sets anupper limit on the tensile steel ratio for beams at 75percent of the balanced ratio to insure that failure,should it occur, will be a gradual, yielding type. A lowerlimit of tensile steel ratio is set to guard against suddenfailure of very lightly reinforced beams upon concretecracking, when the tension formerly carried by the con-crete is transferred to the steel reinforcement.

The present ACI 318 expression for minimum steelratio

PmfJl = 7 for fy in psiY

P#&= 1.7 for 4 in MPa (6.10)Y

is derived on the basis that the resisting moment of thecracked section should be at least as great as the momentthat caused the member to crack, based on the modulusof rupture. Since the latter is known to be greater forhigh-strengthcrete, 6.2,6.12

concrete than for lower-strength con-it is evident that the strength of concrete

should be included in a revised version of Eq. (6.10).With modulus of rupture taken at 7.5 &r (0.62 q), itcan be shown that

Pmi?a_ i-7 $r

42 m/l’y (1.38/f,) (6.11)

would be an appropriate equation for all concretestrengths from 3000 to 12,000 psi (21 to 83 MPa).6.28

6.3.5 Shear and diagonal tension-In current US. prac-tice, design for shear is based on conditions at factoredloads. The total shear resistance is made up of two parts:Vs provided by the stirrups and Vc, nominally the “con-crete contribution.” The nominal concrete contributionincludes, in an undefined way, the contributions of thestill uncracked concrete at the head of a hypotheticaldiagonal crack, the resistance provided by aggregateinterlock along the diagonal crack face, and the dowelresistance provided by the main reinforcing steel.

High-strength concrete loaded in uniaxial compressionfractures suddenly and, in so doing, may form a failuresurface that is smooth and nearly a plane.6.1-6.3 This is incontrast to the rugged failure surface characteristic oflower-strength concrete. In beams controlled by shearstrength, the state of stress is biaxial, combining diagonalcompression in the direction from the load point to thesupport with diagonal tension in the perpendicular direc-tion. Diagonal tension cracks in high-strength concretebeams can be expected to have a smooth surface, likelyto be deficient in aggregate interlock.

Tests confirm that aggregate interlock decreases asconcrete strength increases. Thus, a shear strengthdeficiency may be produced which is not accounted forby present design equations. Data from Frantz 6.38,6.39 atthe University of Connecticut have indicated that the cal-culated concrete contribution Vc is ade uate for high-strength concrete. Data byNilson 6.40,6.41 at CornellUniversity indicates that current design methods are notconservative for high strength concrete. Experimental re-search by Ahmad et al. 6.42,6.43 indicates that the shearstrength contribution of the concrete is conservativelypredicted by ACI 318-83 Eq. (11-3) for shear-span ratiosof 2.5 or less, but for higher ratios, more typical inordinary construction, and for relatively low steel ratios,the ACI equation may be unconservative. It was further


shown by their research that the more complex ACI 318-83 Eq. (11-6) is unconservative for high-strength concretebeams with low steel ratios. Recent research by Russelland Roller6.37 indicates that, for beams with high flexuralsteel ratios, the current ACI Code equations are safe.The beneficial effects of high-strength concrete for pre-stressed beams was demonstrated, using an analysis basedon truss models, by Kaufman and Ramirez.6.44 Higherstrength concrete increases the strength of the diagonaltruss members, resulting in increased efficiency of theweb reinforcement through the mobilization of more stir-rups as well as increased load-carrying capacity of thestruts themselves. Currently, no research data are avail-able regarding the minimum requirement of web reinfor-cement to prevent brittle failure resulting from theformation of a critical diagonal crack.

6.3.6 Bond, anchorage, and development length-Present ACI 318 methods of design for developmentlength and anchorage of tensile steel are based on tests,generally using concretes with compressive strengths notgreater than about 4000 psi (28 MPa). Although some in-formation has recently become available for high-strengthconcrete, not enough data have been obtained to permitrecommendations.

6.3.7 Cracking-The modulus of rupture, which is theappropriate measure of concrete tensile strength for usein predicting flexural cracking load, has been reported inChapter 5 to be 11.7 K for normal weight concreteswith strengths in the range from 3000 to 12,000 psi (21 to83 MPa). It thus appears that the ACI 318 value of 7.5g is too low. However, for curing conditions such asseven days moist curing followed by air drying, a value of7.5 K is probably fairly close for the full strengthrange. It may, therefore, be recommended with nochange. The assumption of a modulus of rupture lowerthan the actual value for a flexural member is neitherconservative nor unconservative but simply results in aninaccurate prediction of cracking load. This will result ininaccurate estimation of both elastic and creep deflec-tions.

The direct tensile strength is seldom measured but isof interest in studying web-shear cracking in prestressedconcrete members, for one example. Both modulus ofrupture and tensile splitting strength of high-strengthconcrete are well above the corresponding values forlower-strength concrete. In this respect, at least, em-pirically derived equations for flexural shear and torsionalshear strength could be used for high-strength concretecalculations based on the lower-strength material. How-ever, other aspects of concern are discussed in Section6.3.5.

6.3.8 Elastic deflections--The main uncertainties inpredicting elastic deflections of reinforced concretebeams are (a) elastic modulus Ec; (b) modulus of rupturefr; and (c) effective moment of inertia, which depends onthe extent of cracking of the beam.

For the elastic modulus, the following equation of

Chapter 5 mayare known.

be used unless actual values of modulus

Ec = 40,000 K + 1.0 x 106 psi

(Ec= 3320 K + 6900 MPa) (6-12)

Eq. (6.12) should be modified by the correction factor(w/c/145)1.5 [for SI units (wc/2300)1.5 for concrete densitiesother than 145 lb/ft3 (2320 kg/m3).6.2,6.13,6.46

The modulus of rupture has been discussed in Section6.3.7. For prediction of deflections a value of 7.5 Emay be used to calculate the flexural cracking moment ofthe beam. The eauation for effective moment of inertiaIe included in the ACI 318 is

whereMcr = cracking momentMa = maximum moment

(6-13)

Ig = gross moment of inertia of sectionIcr = moment of inertia of cracked transformed

section

This provides a basis for beam deflection calculation thatappears valid for high-strength concrete as well as normalconcrete beams, based on information currently avail-ablee 6.34,6.47,6.48

6.3.9 Time-dependent deflections-Time-dependent de-flections of beams due to creep and shrinkage arepresently calculated by applying multipliers too computedelastic deflections. This procedure is generally valid forhigh-strength concrete members, but experimental dataindicates that the multipliers may be significantly lessbecause of the lower creep coefficient typical of high-strength concrete. According to ACI 318, additional long-term deflections are obtained using the following multi-plier

f1 + 5Op’

where= reinforcement ratio for nonprestressed

compression reinforcement= time-dependent factor

The time-dependent factor is given by Fig. 6.8, takenfrom ACI 318R.

Research in progress,6.47,6.48 providing an indication oflong-term multipliers and their variation with time, issummarized in Fig. 6.9. Results are currently available upto about 1 year loading age, and clear trends are evident,as follows:


0 1 3 6 12 18 24 3 0 36 4 8 6 0

Duration of Load , months

Fig. 6.8-ACI 318R Commentary multiplier for long-timedeflections of beams

Multiplier

Multiplier

Multiplier

f’c=36w psi

0 I I I

0 l00 200 300

Duration of Load, days

f;=6500 psiI 1 1

100 200 300


/ 1 I

l00 200 300


Fig. 6.9-- Multipliers for long-term deflections for differentstrength concrete beams

a. For 3600 psi (2.5 MPa) concrete beams, l-year mul-tipliers of 0.85, 0.60, and 0.50 for beams with p’/p, re-spectively, equal to 0, 0.5, and 1.0 are less than the ACI318 l-year values of 1.40, 1.10, and 0.80, which weredetermined for lower-concrete strengths.

b. For high-strength concrete beams, deflection multi-pliers are still lower than the ACI 318 values. For ex-

ample, for high-strength beams with no compressionsteel, the value of 0.55 at 1 year is only 40 percent of theACI 318 value and 65 percent of the experimental valuefor lower-strength concrete.

c. The influence of compression steel may be less im-portant for high-strength concrete beams than for lower-strength beams. For beams of lower-strength concrete,addition of compression steel having an area equal tothat of the tensile steel reduces l-year deflections by 41percent. For high-strength concrete, the beam with com-pression steel shows about 35 percent reduction. Thiscould be expected because the role of compression steelis mainly to reduce the creep of the concrete in the com-pression zone under sustained loads, the high-strengthconcrete with lower creep coefficient needs less help inthis respect.

Deflection measurements are continuing in the re-search described. Results over a longer period of timewill be available as well as information for beams withcompressive strengths fc' to 12,000 psi (83 MPa). Con-crete strength should appear as a parameter in equationsto predict long-term deflections. Concrete strength notonly influences long-term deflections directly because ofthe lower creep coefficient but also influences the effect-iveness of compression steel.

6.3.10 Repeated Loading-With reference to Section6.2.3, it appears that high-strength concrete, because ofits relative freedom from internal microcracking at ser-vice loads, would be more resistant to repeated loadingconsisting of a large number of cycles at relatively lowstress ranges such as in bridges. If ductility is an im-portant consideration, as is the case in seismic resistantdesign, it would be important to include lateral confine-ment steel in the form of closed hoop stirrups as well ascompression reinforcement. While the subject has beenthoroughly studied for lower-strength concrete,6.20,6.22,6.23

little information on high-strength concrete beams subjectto repeated loads is available at this time.

6.3.11 Prestressed concrete beams-Characteristics ofhigh-strength concrete, discussed previously in thischapter in the context of axially loaded members andreinforced concrete beams, affect the behavior of pre-stressed concrete beams in corresponding ways. Specialmention must be made, however, of the effects of a verylow creep coefficient.

At the same concrete stress levels, time-dependentdeflection of high-strength beams will be less. On theother hand, low concrete creep may have little effect onprestressed beam deflections because upward creep de-flection due to prestress is, in many cases, canceled bydownward creep deflection due to sustained loads. Thisresults in only very small net deflections associated withall sustained loads.

For a given level of concrete stress, loss of prestressforce due to creep could be expected to be much smallerfor prestressed beams using high-strength concrete.Higher sustained concrete stress would negate this ad-vantage.


6.4-Eccentric columns6.4.1 Compressive stress distribution-It was pointed out

in discussing beams in Section 6.3.1 that the shape of thecompressive stress distribution in high-strength concretebeams is apt to be different from that in lower-strengthconcrete beams, reflecting the different shape of thecompressive stress-strain curve as shown in Fig. 6.1. Forunder-reinforced concrete beams, with strength con-trolled by the yield strength of the reinforcement, theactual shape of the compressive stress block used in cal-culation of the nominal flexural strength is of littleimportance so long as the internal lever arm to the com-pressive resultant is close to the true value. The con-ventional rectangular stress block and equations for de-termining nominal flexural strength based on the rec-tangular stress block will normally be satisfactory. Over-reinforced beams are not permitted according to ACI318, and so one concludes that present procedures willproduce adequate results for all beams designed underprovisions of ACI 318, whether lower- or high-strengthconcrete is used.

In the case of combined bending and axial load, i.e.,eccentric columns, members failing in flexural compres-sion cannot be avoided. For members with relatively loweccentricity, failure will be initiated by the concretereaching its limiting strain, while the steel on the far sideof the column may be well below tensile yielding or mayremain in compression at the failure load. For such cases,a more accurate representation of the concrete compres-sive stress block could be important.

6.4.2 Interaction diagram for strength of short columns-Limited analytical studies have been made of eccentriccolumns comparing the predictions of the current ACI318R Commentary approach based on the equivalent rec-tangular stress block, with a trapezoidal concrete stressdistribution.6.49 The general shape of the trapezoid wouldvary, ranging from nearly rectangular for lower-strengthconcrete to nearly triangular for very-high-strength asdiscussed in Section 6.3.1. Fig. 6.10 shows a comparisonof the strength interaction diagram relating axial loadcapacity Pn and flexural capacity Mn for a 14 x 14 in.column made of 12,000 psi (83 MPa) strength concrete.Reinforcement is provided by four No. 11 comer barshaving yield strength fy = 60,000 psi (414 MPa). Strengthunder combined axial load and bending was computedfirst using the conventional rectangular stress block (solidline), then using a variable-proportioned trapezoid(dashed line).

3000

2000

Nominal AxialLoad Strength

at givenEccentricity

Pn, kips

1000

0

“r

0 200 400 500

Nominal M o m e n t Strength Mu,ff-klp

Fig. 6.10-- Comparative interaction diagrams for high-strength concrete column

For relatively large eccentricities, when moment dom-inates and failure is initiated by tensile reinforcementyielding, the two curves are almost indistinguishable. Forintermediate to small eccentricities, ACI 318 results inlarger values for both moment and axial force at a giveneccentricity at failure than those obtained by the moreexact calculation. Differences of up to 15 percent in theinteraction diagram relating moment to axial load havebeen found based on comparative calculations.6.49

ACI 318 procedures in corporate an assumed concrete

strain limit in compression of 0.003. It has been shown inSection 6.3.2 that this is less conservative for high-strength concrete than for lower-strength concrete. In thepresence of effective lateral confinement, such as provid-ed by continuous spirals in normal weight concrete col-umns, the effective strain limit is larger than this value,and strain compatibility analysis can be based on 0.003strain. However, there is no apparent justification for in-creasing limiting strain assumptions above present values.

6.4.3 Slenderness effects-The moment magnificationmethod for dealing with slenderness effects in reducingthe strength of reinforced concrete columns appears tobe generally valid for high-strength concrete. An excep-tion may be in the equations for calculating effectiveflexural rigidity. Two alternative equations are given inACI 318 for flexural rigidity, both of which include fac-tors to account for the effect of concrete creep in anapproximate way. The validity of these equations forhigh-strength concrete may at least be questioned, recog-nixing the significantly lower creep coefficient for high-strength concrete. No experimental information is avail-able at this time. In addition, calculations shouldincorporate estimates of Ec as given by Eq. (6-12).

6.5-Summary6.5.1 Review-A brief summary has been given of the

special characteristics of high-strength concrete as theybear upon the behavior and design of reinforced concretemembers and structures.

For axially loaded columns, the direct addition of con-crete and steel strength contributions is generally valid,as for lower-strength concrete members. Lateral steelplays a particularly important role in that it is necessaryto improve ductility and toughness. Of special concern is


the sharp drop-off of load after peak stress and theapparent diminished effectiveness of lateral steel inincreasing ductility compared with lower-strength con-crete columns. Further studies are needed. High-strengthconcrete columns will exhibit less shortening under loadthan lower-strength concrete columns because of thehigher elastic modulus and lower creep coefficient.

For beams, use of the conventional equivalent rec-tangular stress block appears to give satisfactory resultsfor under-reinforced members required by ACI 318 pro-cedures. The compressive strain limit is less than foundfor lower-strength concrete but still may be taken at0.003. Confinement steel and compressive steel should beused in designing concrete beams where ductility is im-portant as for seismic resistant structures. Changes havebeen recommended for ACI 318 values for minimum ten-sile steel ratio to reflect the influence of concretestrength, as well as in the modulus of elasticity to be usedin deflection calculations. Significant changes should alsobe considered in the calculation of long-term beamdeflections to reflect the much lower creep coefficientand reduced effectiveness of compression steel in thecase of high-strength concrete beams.

The calculation of eccentric column strength may beinfluenced by the shape of the compressive stress blockused, particularly for columns with relatively small ec-centricity with neutral axis at failure close to an edge.Limited trial calculations comparing rectangular stressblock with trapezoidal stress block indicate only smalldifferences. In determining slenderness effects, specialconsideration should be given to the lower creep coef-ficient for high-strength concrete, as it affects theeffective flexural rigidity used in the calculations, and toimproved values of modulus of elasticity.

6.5.2 Research needs-The material of Chapter 6should be considered to be subject to revision based onfuture research results. Areas in which information islacking include shear, diagonal tension, torsion, bond,anchorage, development length, and the effects of re-peated loading. Research programs are now in progressin several centers that are aimed at filling some of thesegaps. In this way, the research base will be expanded sothat the many advantages of high-strength concrete maybe used safely and with confidence based on thoroughdocumentation of material properties and behavioralcharacteristics of members.

6.6-Cited references(See also Chapter l0--References)

6.1. Carrasquillo, Ramon L.; Nilson, Arthur H.; andSlate, Floyd O., “Microcracking and Engineering Pro-perties of High-Strength Concrete,” Research Report No.80-1, Department of Structural Engineering, CornellUniversity, Ithaca, Feb. 1980, 254 pp.

6.2. Carrasquillo, Ramon L.; Nilson, Arthur H.; andSlate, Floyd O., “Properties of High Strength ConcreteSubject to Short-Term Loads,” ACI JOURNAL, Proceed-ings V. 78, No. 3, May-June 1981, pp. 171-178.

6.3. Carrasquillo, Ramon L.; Slate, Floyd 0.; andNilson, Arthur H., “Microcracking and Behavior of HighStrength Concrete Subject to Short-Term Loading,” ACIJOURNAL, Proceedings V. 78, No. 3, May-June 1981, pp.179-186.

6.4. “High Strength Concrete in Chicago High-RiseBuildings,” Task Force Report No. 5, Chicago Committeeon High-Rise Buildings, 1977, 63 pp.

6.5. Kaar, P.H.; Hanson, N.W.; and Capell, H.T.,“Stress-Strain Characteristics of High-Strength Concrete,”Douglas McHenry International Symposium on Concreteand Concrete Structures, SP-55, American Concrete Inst-itute, Detroit, 1978, pp. 161-185. Also, Research andDevelopment Bulletin No. RD051.01D, Portland CementAssociation.

6.6 Perenchio, William F., and Klieger, Paul, “SomePhysical Properties of High Strength Concrete,” Researchand Development Bulletin No. RD056.01T, PortlandCement Association, Skokie, 1978, 7 pp.

6.7. Shah, S.P., Editor, Proceedings, National ScienceFoundation Workshop on High Strength Concrete, Uni-versity of Illinois at Chicago Circle, Dec. 1979, 226 pp.

6.8. Wang, P.T.; Shah, S.P.; and Naaman, A.E.,“Stress-Strain Curves of Normal and Lightweight Con-crete in Compression,” ACI JOURNAL, Proceedings V. 75,No. 11, Nov. 1978, pp. 603-611.

6.9. “Research Needs for High-Strength Concrete,”reported by ACI Committee 363, ACI Materials Journal,Proceedings V. 84, No. 6, Nov.-Dec. 1987, pp. 559-561.

6.10. Proceedings of Symposium on Utilization of High-Strength Concrete, Stavanger, Norway, June 15-18, 1987,Tapir Publishers, N-7034 Trondheim-NTH, Norway, 688pp.

6.11. Nilson, A.H., “Design Implications of CurrentResearch on High-Strength Concrete,” High-StrengthConcrete, SP-87, American Concrete Institute, Detroit,1985, pp. 85-118.

6.12. Martinez, S., Nilson, AH., and Slate, F.O.,“Spirally-Reinforced High-Strength Concrete Columns,”Research Report No. 82-10, Department of StructuralEngineering, Cornell University, Ithaca, Aug. 1982.

6.13. Martinez, S., Nilson, AH., and Slate, F.O.,“Spirally-Reinforced High-Strength Concrete Columns,ACI JOURNAL, Proceedings V. 81, No. 5, Sept.-Oct. 1984,pp. 431-442.

6.14. Ahmad, S.H., and Shah, S.P., “Stress-StrainCurves of Concrete Confined by Spiral Reinforcement,”ACI JOURNAL, Proceedings V. 79, No. 6, Nov.-Dec. 1982,pp. 484-490.

6.15. Fafitis, A., and Shah, S.P., “Lateral Rein-forcement for High-Strength Concrete columns,” High-Strength Concrete, SP-87, American Concrete Institute,Detroit, 1985, pp. 213-232.

6.16. Yong, Y.K., Nour, M.G., and Nawy, E.G., “Be-havior of Laterally-Confined High-Strength ConcreteUnder Axial Loads,” Journal of Structural Engineering, V.114, No. 2, Feb. 1988, pp. 332-351.

6.17. Slate, F.O., Nilson, A.H., and Martinez, S.,


“Mechanical Properties of High-Strength LightweightConcrete,” ACI JOURNAL, Proceedings V. 83, No. 4, July-Aug. 1986, pp. 606-613.

6.18. Vallenas, J.; Bertero, V.V.; and Popov, E.P.,“Concrete Confined by Rectangular Hoops and Subjectedto Axial Loads,” Report No. UCB/EERC-77/13, Earth-quake Engineering Research Center, University of Cali-fornia, Berkeley, 1977.

6.19. Sheikh, S.A. and Uzumeri, S.M., “Strength andDuctility of Tied Concrete Columns,” Journal of Structur-al Division, ASCE, V. 106, No. ST5, May 1980, pp. 1079-1102.

6.20. Bennett, E.W., and Muir, S.E. St. J., “SomeFatigue Tests on High Strength Concrete in UniaxialCompression,” Magazine of Concrete Research (London),V. 19, No. 59, June 1967, pp. 113-117.

6.21. Ahmad, S.H., “Properties of Confined ConcreteSubject to Static and Dynamic Loading,” PhD thesis,University of Illinois at Chicago Circle, Mar. 1981.

6.22. Bertero, V.V.; Bresler, B.; and Liao, H.,“Stiffness Degradation of Reinforced Concrete MembersSubject to Cyclic Flexural Moments,” Report No. EERC-69/12, University of California, Berkeley, Dec. 1969.

6.23. Bresler, B., and Bertero, V.V., “Influence of HighStrain Rate and Cyclic Loading Behavior of Unconfinedand Confined Concrete in Compression,” Proceedings,2nd Canadian Conference on Earthquake Engineering,Department of Civil Engineering, McMaster University,Hamilton, June 1975, pp. 15-1 - 15-38.

6.24. Ngab, AS.; Slate, F.O.; and NiIson, A.H.,“Behavior of High-Strength Concrete Under SustainedCompressive Stress,” Research Report No. 80-2, Depart-ment of Structural Engineering, Cornell University,Ithaca, Feb. 1980, 201 pp.

6.25. Ngab, Ali S.; NiIson, Arthur H.; and Slate, FloydO., “Shrinkage and Creep of High Strength Concrete,ACI JOURNAL, Proceedings V. 78, No. 4, July-Aug. 1981,pp. 255-261.

6.26. Ngab, Ali S.; Slate, Floyd 0.; and Nilson, ArthurH., “Microcracking and Time-Dependent Strains in High-Strength Concrete, ACI JOURNAL, Proceedings V. 78, No.4, JuIy-Aug. 1981, pp. 262-268.

6.27. Smadi, M.M.; Slate, F.O.; and NiIson, A.H.,“Time-Dependent Behavior of High-Strength ConcreteUnder High Sustained Compressive Stresses,” ResearchReport No. 82-16, Department of Structural Engineering,Cornell University, Ithaca, Nov. 1982.

6.28. Smadi, M.M., Slate, F.O., and Nilson, A.H.,“Shrinkage and Creep of High-, Medium-, and Low-Strength Concretes, Including Overloads,” ACI MaterialsJournal Proceedings V. 84, No. 3, May-June 1987, pp.224-234.

6.29. Smadi, M.M., Slate, F.O., and Nilson, A.H.,“High-, Medium-, and Low-Strength Concrete Subject toSustained Overloads--Strains, Strengths, and FailureMechanisms,” ACI JOURNAL, Proceedings V. 82, No. 5,Sept.-Oct. 1985, pp. 657-664.

6.30. Russell, H.G., and Corley, W.G., “Time-

Dependent Behavior of Columns in Water Tower Place,”Douglas McHenry International Symposium on Concreteand Concrete Structures, SP-55, American Concrete Insti-tute, Detroit, 1978, pp. 347-373. Also, Research andDevelopment Bulletin No. RD052.01B, Portland CementAssociation.

6.31. Leslie, Keith E.; Rajagopalan, K.S.; and Everard,Noel J., “Flexural Behavior of High-Strength ConcreteBeams,” ACI JOURNAL, Proceedings V. 73, No. 9, Sept.1976, pp. 517-521.

6.32. Nedderman, H., “Flexural Stress Distribution inVery-High Strength Concrete,” MSc thesis, University ofTexas at Arlington, Dec. 1973, 182 pp.

6.33. Zia, Paul, “Structural Design with High StrengthConcrete,” Report No. PZIA-77-01, Civil EngineeringDepartment, North Carolina State University, Raleigh,Mar. 1977, 65 pp.

6.34. Pastor, J.A.; NiIson, A.H.; and Slate, F.O.,“Behavior of High Strength Concrete Beams,” ResearchReport No. 84-3, Department of Structural Engineering,Cornell University, Ithaca, Feb. 1984.

6.35. Wang, Pao-Tsan; Shah, Surendra P.; andNaaman, Antoine E., “High Strength Concrete in Ulti-mate Strength Design,” Proceedings, ASCE, V. 104, ST11,Nov. 1978, pp. 1761-1773.

6.36. Discussion of “Flexural Behavior of High-Strength Concrete Beams” by Keith E. Leslie, K.S.Rajagopalan, and Noel J. Everard, ACI JOURNAL, Pro-ceedings V. 74, No. 3, Mar. 1977, pp. 140-145.

6.37. Russell, H., and Roller, J.J., “Shear Strength ofHigh-Strength Concrete Beams,” accepted for publicationin ACI Structural Journal.

6.38. Mphonde, A.G., and Frantz G.C., “Shear Testsof High and Low Strength Concrete Beams WithoutStirrups,” ACI JOURNAL, Proceedings V. 81 No. 4, July-Aug. 1984.

6.39. Mphonde, A.G., and Frantz G.C., “Shear Testsof High- and Low-Strength Concrete Beams with Stir-rups,” High-Strength Concrete, SP-87, American ConcreteInstitute, Detroit, 1985, pp. 179-196.

6.40. El-Zanaty, AH., Nilson, AH., and Slate, F.O.,“Shear Capacity of Prestressed Concrete Beams UsingHigh-Strength Concrete,” ACI JOURNAL, Proceedings V.83, No. 3, May-June 1986, pp. 359-368.

6.41. El-Zanaty, A.H., Nilson, A.H., and Slate, F.O.,“Shear Capacity of Reinforced Concrete Beams UsingHigh-Strength Concrete,” ACI JOURNAL, Proceedings V.83, No. 2, Mar.-Apr. 1986, pp. 290-296.

6.42. Ahmad, S.H., Khaloo, A.R., and Poveda, A.,“Shear Capacity of Reinforced High-Strength ConcreteBeams,” ACI JOURNAL, Proceedings, V. 83, No. 2, Mar.-Apr. 1986, pp. 297-305.

6.43. Ahmad, S.H., and Lue, D.M., “Flexure-ShearInteraction of Reinforced High-Strength ConcreteBeams,” ACI Structural Journal, V. 84, No. 4, July-Aug.1987, pp. 330-341.

6.44. Kaufman, M.K., and Ramirez, J.A., “Re-eval-uation of the Ultimate Shear Behavior of High-Strength


F

Concrete Prestressed I-Beams,” ACI Structural Journal,Proceedings V. 85, No. 3, May-June 1988, pp. 295-303.

6.45. Treece, R.A., and Jima, J.O., “Bond Strength ofEpoxy-Coated Reinforcing Bars,” ACI Materials Journal,V. 86, No. 2, Mar.-Apr. 1989.

6.46. Pauw, Adrian, “Static Modulus of Elasticity ofConcrete as Affected by Density,” ACI JOURNAL, Pro-ceedings V. 57, No. 6, Dec. 1960, pp. 679-688.

6.47. Leubkeman, C.H., Nilson, A.H., and Slate, F.O.,“Sustained Load Deflection of High-Strength ConcreteBeams,” Research Report No. 85-2. Department of Struc-tural Engineering, Cornell University, Ithaca, Feb. 1985,164 PP.

6.48. Paulson, K.A., and Nilson, A.H., “Deflections ofHigh-Strength Concrete beams Under SustainedLoading,” Research Report (in preparation), Departmentof Structural Engineering, Cornell University, Ithaca.

6.49. Garcia, D.T., and Nilson, AH., “A ComparativeStudy of Eccentrically Loaded High-Strength ConcreteColumns,” Research Report (in preparation), Departmentof Structural Engineering, Cornell University, Ithaca.

CHAPTER 7-- ECONOMIC CONSIDERATIONS

As earlier chapters have demonstrated, high-strengthconcrete is a state-of-the-art material, and like moststate-of-the-art materials, it commands a premium price.In some instances, the benefits are well worth the addi-tional effort and expense; in others they are not. Beforethe cost/benefit trade-offs in specific applications arediscussed, the economic considerations regarding the useof high-strength concrete generally will be examined.

In many areas and for many uses, the benefits of high-strength concrete more than compensate for the in-creased costs of raw materials and quality control.Basically, high-strength concrete will carry a compressionload at less cost than any lower-strength concrete.7.1

Chicago-based structural engineers William Schmidt andEdward S. Hoffman compiled charts indicating the costof supporting 100,000 lb (445 kN) of service load comesto $5.02 per story with 6000 psi (41 MPa) concrete, $4.21with 7500 psi (52 MPa), and drops to $3.65 with 9000 psi(62 MPa) concrete (which the authors report they had nodifficulty obtaining in the Chicago area).7.2

While the figures reflect 1975 costs, the ratio shouldremain similar. The reason for these economies is that,although the concrete itself is more costly than lower-strength mixtures, the cost differential is offset by sig-nificant reduction in the given member size. This capa-bility is particularly attractive for use in columns.

Since column size is so important for architectural andrental reasons, the ability to limit the sixes for tallerstructures often allows the use of a concrete solution inlieu of one of structural steel.

In 1976, Architectural Record noted that ". . . a 30 x30-in. column of 6,000 psi concrete might require an

amount of reinforcing steel equal to 4 percent of thecolumn area for a given load, whereas the same columnin 9,000 psi would require only 1 percent steel-theminimum allowed by code."7.3

7.2-Cost studiesThe Material Service Corporation7.4 conducted a

pricing study that dramatically demonstrated the costadvantage of replacing percentages of steel with high-strength concrete in short tied columns. This 1983 studywas made for a column supporting a design load (1.4D+ 1.7L) of 1000 kips (4.45 MN) and based on the follow-ing prices:

Reinforcing steel $760/ton in place7000 psi concrete $80/yd3 in place9000 psi concrete $85/yd3 in place11,000 psi concrete $104/yd 3 in place14,000 psi concrete $129/yd 3 in placeFormwork $280/yd 3 in place

As Fig. 7.1 shows, using high-strength concrete with aminimum of steel is the most economical solution.

Compressive Strength , MPa60 80

30 I I

Cost of 40 x 40 in.Column per Foot of 20 -Length per 1000kips of Design Load(1.4 D’+l.7L), $ 10 _

0, 1 I I6 8 IO 12 14

Compressive Strength , ksi

ig. 7.1-- Cost of columns

7.3-Case historiesTwo examples might help translate this savings into

actual dollars.7.3.1 Case history No. 1-In 1968, Philadelphia’s first

high-rise office building using 6000 psi (41 MPa) concretewas designed. To meet the span requirements [approxi-mately 30 ft (9m) square bays] while avoiding unaccept-able oversized columns on the lower floors, the columnsof the first three floors were built of structural steel.However, a comparison study made by the designing en-gineers for 8000 psi (55 MPa) concrete showed that

7.3.1.1- With the same column sixes as the originalunacceptable sixes, a 60 percent reduction in reinforcingsteel with the 8000 psi (55 MPa) concrete would havebeen made. This would also have resulted in 24 fewersplices per column, a side benefit in labor and time costsavings.

7.3.12- With the same amount of reinforcing used


as in the original column, the column size could havebeen reduced from 36 x 46 in. (915 x 1170 mm) to 30 x30 in. (760 x 760 mm). This size would have been ac-ceptable to the architect and owner and would haveeliminated the need for an additional trade-structuralsteel-on the job.

Rough calculations show that 8000 psi (55 MPa) con-crete for the lower-floor columns with a stepped strengthreduction, as the building reached the upper floors, to3000 psi (21 MPa) concrete at the top would have result-ed in a column size that met the demands of the archi-tect, owner, and rental agent. This would have savedclose to $530,000 in 1968 dollars.

7.3.2 Case history No. 2-- The economies of high-strength concrete were more dramatically demonstratedin the construction of New York City’s first buildingusing 8000 psi (55 MPa) concrete, The Palace Hotel builtin 1979. The building was originally conceived usingstructural steel for the lower floors, designated forballroom and restaurant functions, with a reinforcedconcrete superstructure for the hotel facilities. However,the engineers were able to convert the entire design,except for two columns on the lowest four levels, toreinforced concrete through the use of 8000 psi (55 MPa)concrete. These ballroom and restaurant areas requiredlarge column spacing. The common limitations of 6000psi (41 MPa) concrete would have made the columnsprohibitively large and uneconomical. A presentation tothe New York City Building Department about the val-ues of high-strength concrete, together with the proposedcontrols to insure quality, resulted in its acceptance foruse in New York.

Concrete with compressive strengths of 8000 and 7000psi (55 and 48 MPa) was used in the columns of thebuilding only. Lightweight concrete with compressivestrength of 3500 psi (24 MPa) was used for floor slabs,and 5000 to 6000 psi (34 to 41 MPa) concrete was usedin wall construction. On the lower five levels of the hotel,column sixes were reduced by approximately 25 percent.Approximately 10 percent less reinforcing steel was usedbecause of the strength of the concrete. In addition, No.11 reinforcing bars remained a viable size, avoiding theneed for mechanical connections between the reinforcingbars, thus considerably reducing the floor-framing timerequirements. Further economies were realized by mini-mixing changes in column sixes and reducing columnreinforcement on the upper floors.

The ability to reduce the amount of costly reinforcingsteel without sacrificing strength is an attractive benefitto owners, builders, and engineers, but the use of high-strength concrete in building columns has a corollaryeconomic benefit. It enables the lower floors of high-risebuildings to maintain an acceptable column size, while atthe same time increasing the number of possiblestories7.1

This is a case of a relatively new material meeting theneeds of market economics. The Chicago Committeestudy7. 5 noted “The potential number of stories in

high-rise buildings is limited by the required largecolumns if they were to be built with ordinary low-strength concrete. Real estate properties in prime loca-tions had to be developed with maximum rental floorarea. Architectural layout of apartment or condominiumunits demanded flexibility, which is restricted by largecolumns. High-strength concrete satisfied this conditionby allowing column sixes to be reduced to a minimum.”

7.4-Other studiesIn Ontario, Canada, the Richmond-Adelaide Center’s

use of high-strength concrete columns enabled the arch-itect to increase the use of the underground parkinggarage by approximately 30 percent.7.6 In times when allbuilding construction is difficult to capitalize, a materialthat both reduces construction costs and substantiallyincreases the amount of revenue-gathering space withina building can be a tremendous factor in the decision tobuild.

7.5-Selection of materialsThe economic consequences of requiring fly ash may

vary. On The Royal Bank Plaza Project in Ontario, Can-ada, a 43-story building constructed from 1973-1976 (oneof the first to use fly ash in high-strength concrete), all ofthe various strength concrete mixtures on the projectwere converted to local fly ash. This resulted in a savingof approximately $100,000 over the contract and pro-duced concretes with extremely good fresh and hardenedproperties. 7.6

The Scotia Plaza-A 68-story building in Toronto,Canada, constructed in 1988--is one of the first buildingsto employ the use of silica fume in concrete as an ele-ment in increasing strength. Strengths of up to 10,000 psihave been achieved. Two Union Square in Seattle em-ploys 19,000-psi concrete containing silica fume-thehighest strength used to date in a conventional building.

7.6-Quality controlWhile selection of materials will influence costs, an-

other factor, and one more exclusively the result of theuse of high-strength concrete, is the cost of the increasedtesting, quality control, and inspection that the use ofhigh-strength concrete requires. The quality and consis-tency of the concrete is crucial, and additional steps mustbe taken to insure that quality and consistency.

In the Royal Bank Plaza Project, a number of precau-tions were necessary. The supplier had to have a qualitycontrol person at the site to control both the schedulingof trucks and the consistency of the concrete at the timeit was delivered. For this central plant project, the suppli-er agreed that there would be no water added to thetrucks after they had come onto the site and that anyminor adjustments would be made prior to sending thetruck to the site. Regular visits were made to the batchplant to check batching procedures and to obtain the testsamples. Furthermore, a full-time technician was employ-ed to carry out sampling and testing on site. This was


found to be an essential feature of quality control.On a later project, Richmond-Adelaide Center, Phase

II, Ontario, Canada, 1977-1979, by the same engineers,not only did the supplier maintain full-time inspection onthe site to insure that the delivered material met require-ments but the engineers employed by the owner alsomaintained full-time inspection and regularly inspectedthe batch plant. Often this type of stringent qualitycontrol is required by regulation. For The Palace Hotel,the New York City Building Department stipulated thatat least two suppliers of concrete prequalify the concretemixtures to strengths up to 8000 psi (55 MPa). The pre-qualification was to be performed by an independenttesting laboratory, and a full-time professional engineerwould be required to continuously inspect the progress ofthe work, performing no other work during the construc-tion.7.7 For hot weather concreting, the engineers re-quired mixing water limited to no more than 50 F (10 C)and the truck drums to be hosed down if standing indirect sunlight. Further, all trucks were limited to 10 yd3

(7.6 m3) loads, despite capacities of 16 yd3 (12.2 m3).While the professional inspection does add to cost, thecontinuing education of the suppliers and concrete sub-contractors in the areas of quality control should ul-timately create better concretes of all strengths and resultin better and more economical use of materials.

7.7-Areas of applicationIn general, the economic advantages of high-strength

concrete are most readily realized when the concrete isused in the columns of high-rise buildings. In this appli-cation, engineers may take full advantage of its increasedcompressive strength: reducing the amount of steel, re-ducing column size to increase usable floor space, or al-lowing additional stories without detracting from lowerfloors. These benefits overshadow the increased qualitycontrol costs and possible higher cost of raw materialsdiscussed earlier. Yet the use of high-strength concretehas also spread to other applications, primarily slabs,beams, and long-span bridges. The economic considera-tions of these uses should also be examined.

Parking garages, bridge decks, and other installationsrequiring improved density, lower permeability, and in-creased resistance to freeze-thaw and corrosion havebecome prime candidates for consideration of the use ofhigh-strength materials.

The primary advantage of high-strength concrete inslabs is the resulting reduction in dead load.7.8 However,as Schmidt and Hoffman point out, significant economiescan be achieved only by reducing the thickness that isrequired for stiffness; the additional reinforcementrequired may offset the concrete savings. Used for rec-tangular beams, T-beams, and one-way slabs, high-strength concrete yields reduced section width or thick-ness and allows for longer spans, but (as with slabs) lessexpensive lightweight concrete continues to perform thisjob satisfactorily. Presently, there is no economic justi-fication, under normal circumstances, for the use of a

premium material such as high-strength concrete forslabs or beams.

Long-span bridges are another area where the quali-ties of high-strength concrete are proving themselveseconomically attractive. High-strength concrete’s com-paratively greater compressive strength per unit weightand unit volume allows lighter, more slender bridge piers.This provides improved horizontal clearances. In addi-tion, the increased stiffness of high-strength concrete isadvantageous when deflections or stability govern thebridge design. Increased tensile strength of high-strengthconcrete is helpful in service load design in prestressedconcrete.7.9

In bidding to build a cable-stayed bridge across theOhio River, a concrete deck proposal beat steel by 29percent-roughly $10 million. The two-lane crossing be-tween Huntington, West Virginia, and Proctorville, Ohio,includes the first major asymmetrical stayed-girder struc-ture in the United States. The bridge has a main span of900 feet over one pier. The three bids to construct thebridge using concrete ranged from $23.5 million to $29.7million, all well below the lowest steel bid ($33.3 million).The designer, Arvid Grant Associates, specified box gir-ders only 5 ft (1.5 m) deep cast of 8000 psi (55 MPa)high-strength concrete.7.8

7.8-ConclusionThe economic benefits of high-strength concrete are

just now becoming fully apparent. Certainly as the use ofhigh-strength concrete increases, additional and possiblyeven greater benefits will be realized. In any case, thoseprojects that have led the way in the use of high-strengthconcrete have clearly demonstrated its economic advan-tages. For now, it allows the profession to engineer mostcost effectively and space effectively. In the future, thoseconsiderations may tip the balance on whether certainprojects are constructed at all.

7.9-Cited references(See also Chapter 10--References)

7.1. “High Strength Concrete--Costs More in theTruck, Costs Less in the Structure,” PCA Concrete Tech-nology Today, No. 4, Dec. 1980, p. 3.

7.2. Schmidt, William, and Hoffman, Edward S.,“9,000-psi Concrete-Why?, Why Not?,” Civil Engineering-ASCE, V. 45, No. 5, May 1975, pp. 52-55.

7.3. “High-Strength Concrete Allows Bigger Loads onSmaller Columns,” Architectural Record, V. 159, No. 7,June 1976, pp. 133-135.

7.4. Private correspondence from J. Moreno ofMaterial Service Corp. to Irwin G. Cantor, May 12, 1983.


7.6. Bickley, John A., and Payne, John C., “HighStrength Cast-in-Place Concrete in Major Structures inOntario,” paper presented at the ACI Annual Conven-tion, Milwaukee, Mar. 1979.


7.7. Private correspondence from J. T. Walsh, Depart-ment of Buildings, New York, to Irwin G. Cantor, Aug.11, 1977.

7.8. “Concrete Beats Steel by 29%,” EngineeringNews-Record, V. 206, May 14, 1981, p. 16.

7.9. Carpenter, James E., “Applications of HighStrength Concrete for Highway Bridges,” Public Roads,V. 44, No. 2, Sept. 1980, pp. 76-83.

CHAPTER 8-APPLICATIONS

Some specific applications of high-strength concreteare described in this chapter. Separate sections describeapplications in buildings, bridges, and special structures.The applications are not all-inclusive but demonstrate arange of applications of high-strength concrete. Some po-tential applications for high-strength concrete are alsodiscussed.

8.2-BuildingsThe largest application of high-strength concrete in

buildings has been for columns of high-rise structures.The history of high-strength concrete columns in theChicago area has been described in Task Force ReportNo.58.1 of the Chicago Committee on High-Rise Build-ings. Since 1972, more than 30 buildings in the Chicagoarea have been constructed with columns having a designcompressive strength of 9000 psi (62 MPa). The develop-ment of concrete for use in two buildings in Toronto hasbeen reported by Bickley and Payne. 8.2 Other applica-tions have been reported in New York,8.3 Houston,8.4,8.5

Minneaplis,8.6 Melbourne, Australia,8.7 Dallas,8.25 andSeattle.8.26 Information obtained from these and othersources is summarized in Table 8.1.

Table 8.1-- Buildings with high-strength concrete

TotalBuilding Location

S.E. Financial center MiamiPetrocanada Building CalgaryLake Point Tower Chicago1130 S. Michigan Ave. ChicagoTexas Commerce Tower HoustonHelmsley Palace Hotel New YorkTrump Tower New YorkCity Center Project MinneapolisCollins Place MelbourneLarimer Place Condominium Denver499 Park Avenue New YorkRoyal Bank Plaza TorontoRichmond-Adelaide Center TorontoMidcontinental Plaza ChicagoWater Tower Place ChicagoRiver Plaza ChicagoChicago Mercantile Exchange ChicagoColumbia Center SeattleInterfirst Plaza DallasEugene Terrace Chicago311 S. Wacker Drive Chicago900 N. Michigan Annex ChicagoTwo Union Square Seattle225 W. Wacker Drive ChicagoScotia Plaza Toronto

* Year in which high-strength concrete was cast.t ‘Avo experimental columns of 11,000 psi strength were included.$ Two experimental columns of 14,000 psi strength were included.~9,CN~psiakousedhflowskbroflowerkvek.

Year*1982 531982 341965 70

19811978

1981

1980

19751978197219751976198219831983198719881986198719881988

755368524431274333507956407672447015623068

Maximumdesign

concretestrength,

psi7000725075007500750080008000800080008000850088008800900090009Qwg@m9500

10,00011,00012,000 ss14,000

14,000**14,00010,000

l * 19,000 psi indirectly specified to achieve a high modulus of elasticity.

8.3-BridgesThere have been many applications of high-strength

concrete in precast prestressed bridge girders. However,published information on actual structures is limited.


The effect of using high-strength concrete in fourdifferent solid-section girders has been described byCarpenter.8.8 For integral deck bulb tees, span capabilityfor closely spaced girders increased with increase inconcrete strength. For wider spaced girders, capabilityincreased when concrete strength was increased up to8000 psi (55 MPa). Above 8000 psi (55 MPa) compres-sive strength, span capability did not increase becausesufficient prestress forces could not be provided. Similarresults were obtained for other cross sections.

For post-tensioned box girder bridges, Carpenter re-ported that high-strength concrete can be used to in-crease span capability. However, for higher-strength con-cretes, maximum available prestress force again limitedmaximum spans. For segmental box girder bridges, heshowed that high-strength concrete is feasible in regionswhere member thickness is controlled by stress. However,where thickness is controlled by other factors, high-strength concrete may not be beneficial.

Some actual bridges in which the use of high-strengthconcrete has been reported are listed in Table 8.2. Per-haps the most significant application in the United Statesis the Huntington, West Virginia, to Proctorville, Ohio,crossing for which a compressive strength of 8000 psi (55MPa) was specified.8.9 The bridge consists of an asym-metrical stayed-girder superstructure with a main span of900 ft (274 m).

Table 8.2-- Bridges with high-strength concrete

San Diego to CoronadoLinn Cove Viaduct 8.13 I

CaliforniaNorth Carolina

Pasco-Kennewick IntercityCoweman River Bridges 8.14

Huntington to ProctorvilleAnnicis BridgeNitta Highway BridgeKaminoshima Highway BridgeTower RoadFukamitsu Highway BridgeOotanabe Railway BridgeAkkagawa Railway Bridge

WashingtonWashingtonW. Va. to OhioBritish ColumbiaJapanJapanWashingtonJapanJapanJapan

* Lightweight concreteMetric equivalent: 100 psi = 6.895 MPa

MaximumYear span, ft1967 1581981 7501969 1401979 1801978 981

1461984 9001986 15261968 981970 2821987 1611974 851973 791976 150

Maximumdesign

concretestrength,

psi

6,0006,000

6,000 L*6,0006,0007,0008,0008,0008,5008,5009,000

10,00011,40011,400

The use of concrete with compressive strengths up to11,000 psi (76 MPa) in railway bridges in Japan has alsobeen reported.8.10,8.11 Nagataki8.11 reports that strengthsof 11,400 psi (79 MPa) can be easily obtained in the fieldin Japan.

8.4-Special applicationsIn 1948, concrete with a specified compressive strength

of 9000 psi (62 MPa) was used for precast panels for apowerhouse at Fort Peck Dam, Montana. High-strengthconcrete was specified to provide an extremely dense

concrete that would withstand the harsh exposure. Actualcompressive strengths of concrete were reported 8.15 to beconsiderably higher than 9000 psi (62 MPa).

The use of 10,000 psi (69 MPa) concrete for pre-stressed concrete polesdescribed by Skrastins8.16

produced by spinning has beenm 1970. High-strength concrete

was selected to reduce the size of the poles.Copen 8.17 has indicated that the use of 10,000 psi (69

MPa) concrete in thin arch dams would usually result ingreater economy through reduced volume of concrete.High-strength concrete would tend to reduce deflectionsin a dam and may improve strength of construction jointsand permit earlier removal of formwork. Disadvantagesof high-strength concrete listed by Copen include de-velopment of stress concentrations, particularly in thefoundation for the dam; tendency toward more crackingin concrete; increased temperature control problems; andcomplications involved with openings through the damand railways over the dam.

The application of high-strength concrete in twograndstand roofs has been described by Bobrowski8.18

Lightweight concrete with a density of 118 lb/ft3 (1.89Mg/m3) and a minimum cube strength of 7500 psi (52MPa) at 28 days was used in the roof beams at Don-caster racecourse, England. Roof beams at Leopardstownracecourse, Ireland, had 28 day cube compressivestrengths between 7200 and 8850 psi (50 and 61 MPa)and an average density of 115 lb/ft3 (1.84 Mg/m3).

Anderson has reported8.19 the use of high-strengthconcrete in piles for marine foundations in northwesternUnited States. Measured 28 day compressive strengthsranged between 7900 and 9900 psi (55 to 68 MPa). High-strength concretes with compressive strengths up to 9400psi (65 MPa) have also been used for decks of dockstructures in the northwestern United States.

In 1984, the Glomar Beaufort Sea I8.27 was placed inthe arctic, This exploratory drilling structure containsabout 12,000 yd3 (9200 m3) of high-strength lightweight


concrete with unit weights of about 112 lb/ft3 (1794kg/m3) with 56-day compressive strength of 9000 psi (62MPa) and about 6500 yd3 (5000 m3) of high-strength nor-mal-weight concrete with unit weights of about 145 lb/ft3

(2323 kg/m3) and 56-day compressive strengths of about10,000 psi (69 MPa).

Field placements of high-strength, low-permeability,and chemical-resistant concretes for industrial manufac-turing applications were reported by Wolsiefer.8.20 Spe-cial applications have included several modular bankvaults placed at slumps of 9 in. (230 mm) with measuredcompressive strengths of 12,000 psi (83 MPa) at 45 days.

The protection of reinforcing steel from corrosion canbe expected to be enhanced when high-strength concreteis used. The resultant low porosity should increase theelectrical resistivity and reduce the rate at which oxygenreaches the steel, both of which will reduce corrosionrates. Moreover, the ease with which chloride ions fromdeicing salts can reach the steel and initiate corrosion isalso reduced.

Although there are many studies evaluating the corro-sion of steel embedded in regular strength concrete, nosystematic studies in the influence of concrete strengthappear to have been reported. Published data for high-strength concrete can be extracted from studies investi-gating other factors, particularly the influence of silicafume. The conclusions obtained with regular concretesare also applicable to high-strength concrete: namely,there is an increase in electrical resistivity 8.28,8.29 and areduction in chloride permeability8.29,8.30 with increasedstrength. Data linking these parameters with laboratorycorrosion data are given in Table 8.3. The corrosion be-havior of a very high-strength mortar has also been re-ported.8.31 Useful discussions regarding the factors af-fecting the corrosion of steel in concretes with silica fumeare to be found in references.8.31,8.32,8.33

Table 8.3-- Corrosion resistance data for selected high-strength concrete (data from reference 8.29)

Strength hficrosilicat Chloride Electrical 18 month Corrosion Data(psi) (mpa) (wt. %) Permeability* Resistivity %orl~ ‘4

(Coulombs) (ohm.cm) (mv) ( pohm/cm’)5,160 35.6 0 3,663 8 -456 227,360 50.8 15 198 95 -26 48,580 59.2 15 98 118 -53 49,290 64.1 8 132 74 -3 112,120 83.6 15 75 161 +53 4

t By weight of portland cement.* Measured by AASHTO-T-227 rapid chloride permeability tat at 28 days age.$ Corrosion potential measured with respect to a copper sulfate reference electrode.Q F$ is the polarization current; its reciprocal is a measure of the rate of corrosion.

8.5-- Potential applicationsMost applications of high-strength concrete have used

the strength property of the material. However, high-strength concrete may possess other characteristics thatcould be used advantageously in concrete structures.

LeMessurier 8.21 proposed the use of high-strength con-crete to satisfy the need for a high modulus of elasticity.Similarly, high-strength concrete can be used in slabs toallow early removal of formwork and avoid reshoring.8.22

This takes advantage of both the high modulus of elasti-city and lower creep of high-strength concrete. Ander-son8.19 had suggested that the low creep of high-strengthconcrete should be taken into account when consideringprestress losses. Since most of the prestress loss is at-tributable to creep and shrinkage, prestress losses forhigh-strength concrete members should be less than forlower-strength concrete members.

Rabbat and Russell 8.23 have reported that the maxi-mum span capability of solid-section girders can be in-creased by 15 percent when the concrete compressivestrength is increased from 5000 to 7000 psi (34 to 48MPa). Finally, Manning 8.24 has suggested that the rela-tionship between high-strength concrete and high-qualityconcrete may make high-strength concrete attractive notfor its strength but for its long-term service performance.

More recently, high-strength concrete has been speci-fied for applications in warehouses, foundries, parkinggarages, bridge deck overlays, dam spillways, and heavyduty industrial floors. In these applications, high-strengthconcrete is being used to provide a concrete with im-proved resistance to chemical attack, better abrasion re-sistance, improved freeze-thaw durability, and reducedpermeability.



8.2. Bickley, John A., and Payne, John C., “High-Strength Cast-in-Place Concrete in Major Structures inOntario,” paper presented at the ACI Annual Conven-tion, Milwaukee, Mar. 1979.

8.3. “New York City Gets Its First High-StrengthConcrete Tower,” Engineering News-Record, V. 202, Nov.2, 1978, p. 22.

8.4. Pickard, Scott S., “Ruptured Composite Tube


Design for Houston’s Texas Commerce Tower,” ConcreteInternational: Design & Construction, V. 3, No. 7, July1981, pp. 13-19.

8.5. Cook, James E., “Research and Application ofHigh-Strength Concrete Using Class C Fly Ash,” ConcreteInternational Design & Construction, V. 4, No. 7, July1982, pp. 72-80.

8.6. Venema, T.P., and Regnier, H.J., “Placement,Batching, and Tests of High Strength Concrete forMinneapolis City Center Project,” submitted to ACI forpublication.

8.7. Day, K.W., “Quality Control of 55 MPa Concretefor Collins Place Project, Melbourne, Australia,” ConcreteInternational Design & Construction, V. 3, No. 3, Mar.1981, pp. 17-24.

8.8. Carpenter, James E., “Applications of HighStrength Concrete for Highway Bridges,” Public Roads,V. 44, No. 2, Sept. 1980, pp. 76-83.

8.9. “Concrete Beats Steel by 29%,” EngineeringNews-Record, V. 206, May 14, 1981, p. 16.

8.10. “Stronger Concrete,” EngineeringNews-Record, V.189, June 8, 1982, p. 12.

8.11. Nagataki, Shigeyoshi, “On the Use of Superplasti-cizers,” Seminar on Special Concretes, 8th FIP Congress(London, 1978), Federation Intenationale de la Pre-contrainte, Wexham Springs, 1978, 15 pp.

8.12. “Concrete Box Girder Span Establishes U.S.Record,” Engineering News-Record, V. 208, No. 1, Jan. 7,1982, pp. 22-25.

8.13. Pfeifer, Donald W., “Development of the Con-crete Technology for a Precast Prestressed ConcreteSegmental Bridge,” Journal, Prestressed Concrete Insti-tute, V. 27, No. 5, Sept.-Oct. 1982, pp. 78-99.

8.14. Hurlbut, Roger, “146-ft Long Precast PrestressedBridge Girders in Washington State, “Journal, PrestressedConcrete Institute, V. 24, No. 1, Jan.-Feb. 1979, pp. 88-92.

8.15. “Unusual Strengths Attained in Precast SlabsUsed for Facing Power House Walls,” Concrete, V. 57,No. 5, May 10, 1949, pp. 9-10.

8.16. Skrastins, Janis I., ‘Toward High-Strength Con-crete,” Modern Concrete, V. 34, No. 1, May 1970, pp. 44-48.

8.17. Copen, Merlin D., “Problems Attending Use ofHigher Strength Concrete in Thin Arch Dams,” ACIJOURNAL, Proceedings V. 72, No. 4, Apr. 1975, pp. 138140.

8.18. Bobrowski, J., and Bardham-Roy, B.K., “Struc-tural Assessment of Lightweight Aggregate Concrete,”Concrete (London), V. 5, No. 7, July 1971, pp. 229-234.

8.19. Anderson, Arthur R., “Research Answers Neededfor Greater Utilization of High Strength Concrete,”Journal, Prestressed Concrete Institute, V. 25, No. 4,July-Aug. 1960, pp. 162-164.

8.20. Wolsiefer, John, “Ultra High-Strength FieldPlaceable Concrete with Silica Fume Admixtures,” Con-

crete International Design & Construction, V. 6, No. 4,Apr. 1984, pp. 25-31.

8.21. Fischer, R.E., “Round Table--Concrete in Archi-tecture: A Current Assessment,” Architectural Record,Nov. 1982.

8.22. Nilson, AH., “Structural Design Considerationsfor High Strength Concrete,” Proceedings, NationalScience Foundation Workshop on High Strength Con-crete, University of Illinois at Chicago Circle, Dec. 1979.

8.23. Rabbat, Basile G., and Russell, Henry G., “Op-timized Sections for Precast, Prestressed Bridge Girders,”Journal, Prestressed Concrete Institute, V. 27, No. 4,July-Aug. 1982, pp. 88-104.

8.24. Young, F.J., and Russell, H.G., “Session V--Summary of Floor Discussion,” Proceedings, NationalScience Foundation Workshop on High Strength Con-crete, University of Illinois at Chicago Circle, Dec. 1979.

8.25. “Tower Touches Few Bases,” Engineering News-Record, V. 210, No. 24, June 16, 1983, pp. 24-25.

8.26 Godfey, K.A., Jr., “Concrete Strength RecordJumps 36%,” Civil Engineering, V. 57, No. 10, Oct. 1987,pp. 84-88.

8.27. Fiorato, A.E., Person, A, and Pfeifer, D.W.,“The First Large-Scale Use of High Strength LightweightConcrete in the Arctic Environment,” Second Symposiumon Artic Offshore Drilling Platforms, Houston, Texas, Apr.1984.

8.28. Vennesland. O., and Gjorv, O.E., “Silica Con-crete-- Protection Against Corrosion of Embedded Steel,”Fly Ash, Silica Fume and Other Mineral By-Products inConcrete, ACI SP-79, V. 2, 1983, pp. 719-730.

8.29. Burke, N.S., and Weil, T.G., “Corrosion Protec-tion Through the Use of Concrete Admixtures,” Supple-mentary Paper, Proceedings, 2nd International Confer-ence on Performance of Concrete in the Marine Environ-ment, St. Andrews-by-the-Sea, New Brunswick, Aug.1988.

8.30. Preece, C.M., Frolund, T., and Bager, D.H.,“Chloride Ion Diffusion in Low Porosity Silica CementPaste,” Condensed Silica Fume in Concrete, Report BML82.610, Norwegian Institute of Technology, Trondheim,1982, pp. 51-58.

8.31. Preece, C.M., Frolund, T., and Bager, D.H.,“Electrochemical Behavior of Steel in Dense Silica-Cement Mortar,” Fly Ash, Silica Fume and Other MineralBy-Products in Concrete, ACI SP-79, V. 2, 1983, pp. 785-796.

8.32. Fidjestol, P., “Reinforcement Corrosion and theUse of CSF-Based Additives,” Concrete Durability, ACISP-100, V. 2, 1987, pp. 1445-1458.

8.33. Scali, M.J., Chin, D., and Burke, N.S., “Effect ofMicrosilica and Fly Ash Upon the Microstructure andPermeability of Concrete,” Proceedings, Ninth Inter-national Conference on Cement Microscopy, Internation-al Cement Microscopy Association, Texas, 1987, pp. 375-397.


CHAPTER 9-- SUMMARY

The objective of this report was to present state-of-the-art information on concrete with strengths in excessof about 6000 psi (41 MPa) but not including concretemade using exotic materials or techniques. This sectionof the report presents a summary of the material con-tained in the previous chapters.

All materials for use in high-strength concrete must becarefully selected using all available techniques to insureuniform success. Items to be considered in selecting ma-terials include cement characteristics, aggregate size, ag-gregate strength, particle shape and texture, and the ef-fects of set-controlling admixtures, water reducers, silicafume, and pozzolans. Trial mixtures are essential to in-sure that required concrete strengths will be obtainedand that all constituent materials are compatible.

Mix proportions for high-strength concrete generallyhave been based on achieving a required compressivestrength at a specified age. Depending on the appropriateapplication, a specified age other than 28 days has beenused. Factors included in selecting concrete mix propor-tions have included availability of materials, desiredworkability, and effects of temperature rise. All materialsmust be optimized in concrete mix proportioning toachieve maximum strength. High-strength concrete mixeshave usually used high cement contents, low water-cement ratios, normal weight aggregate, and chemicaland pozzolanic admixtures. Required strength, specifiedage, material characteristics, and type of application havestrongly influenced mix design. High-strength concretemix proportioning has been found to be a more criticalprocess than the proportioning of lower-strength concretemixes. Laboratory trial batches have been required inorder to generate necessary data on mix design. In manycases, laboratory mixes have been followed by field pro-duction trial batches.

Batching, mixing, transporting, placing, and controlprocedures for high-strength concrete are not essentiallydifferent from procedures used for lower-strength con-cretes. However, special attention is required to insure ahigh-strength uniform material. Special considerationshould be given to minimizing the length of time betweenconcrete batching and final placement in the forms. De-lay in concrete placement can result in a subsequent lossof long-term strength or difficulties in concrete place-ment. Special attention should also be paid to the testingof high-strength concrete cylinders since any deficiencywill result in an apparent lower strength than that actu-ally achieved by the concrete. Items deserving specificattention include manufacture, curing, and capping ofcontrol specimens for compressive strength measure-ments; characteristics of testing machines; type of moldused to produce specimens; and age of testing. In manyinstances, strength measurements at early ages have beenmade even though the compressive strength has not beenspecified until 56 or 90 days.

Some research data have indicated that the modulus

of elasticity of high-strength concrete is lower than wouldhave been predicted from data on lower-strength con-cretes. However, values of Poisson’s ratio appear to be inthe expected range, based on lower-strength concretes.The modulus of rupture for high-strength concretes ishigher than would have been anticipated. However, thetensile splitting strength values appear to be consistentwith lower-strength concretes. Unit weight, specific heat,diffusivity, thermal conductivity, and coefficient of ther-mal expansion have been found to fall generally withinthe usual range for lower-strength concretes. High-strength concrete has shown a higher rate of strengthgain at early ages as compared to lower-strength con-crete, but at later ages the difference is not significant.Information on creep and shrinkage of high-strength con-crete has indicated that the shrinkage is similar to thatfor lower-strength concrete. However, specific creep ismuch less for high-strength concretes than for lower-strength concretes.

In the area of structural design, it has been found thataxially loaded columns with high-strength concrete can bedesigned in the same way as lower-strength columns. Ithas also been identified that high-strength concrete col-umns exhibit less shortening under load than lower-strength columns because of the higher modulus of elasti-city and lower creep coefficients. For beams, use of theconventional equivalent rectangular stress block appearsto give satisfactory results for under-reinforced concretemembers. The compressive strain limit of 0.003 appearsto be acceptable. However, changes have been recom-mended for present code values for minimum tensilesteel ratio, modulus of rupture, modulus of elasticity,shear strength, and development length. Changes are alsoneeded in the area of calculating long-term beam de-flections.

The economic advantages of using high-strength con-crete in the columns of high-rise buildings have beenclearly demonstrated by applications in many cities. Theability to reduce the amount of reinforcing steel incolumns without sacrificing strength and to keep, thecolumns to an acceptable size has been an economicbenefit to owners of high-rise buildings. Consequently,concrete with compressive strengths in excess of 6000 psi(41 MPa) has been used in the columns of high-risebuildings in cities throughout North America. Studieshave also indicated advantages in the use of high-strengthconcrete in long-span concrete bridges. However, this ap-plication has yet to be fully implemented. There havealso been applications where high-compressive-strengthconcrete has been needed to satisfy special local re-quirements. These have included dams, prestressed con-crete poles, grandstand roofs, marine foundations,parking garages, bridge deck overlays, heavy duty indus-trial floors, and industrial manufacturing applications.

Although high-strength concrete is often considered arelatively new material, it is becoming accepted in moreparts of North America as shown by the many examplesof its usage. At the same time, material producers are


responding to the demands for the material and arelearning production techniques. As with many devel-opments of new materials, research data supporting thegrowth has also increased. However, the need foradditional research has been documented in ACI 363.1R.Some research projects are underway to satisfy theseneeds. However, further work is needed to fully use theadvantages of high-strength concrete and to affirm itscapabilities. This report has documented existingknowledge of high-strength concrete so that the directionfor future development may be ascertained.

CHAPTER 10-REFERENCES

10.1-Recommended referencesThe documents of the various standards-producing or-

ganizations referred to in this document are listed belowwith their serial designation.

American Association of State Highway and TransportationOfficialsT-26 Quality of Water to be Used in Concrete

American Concrete Institute116R Cement and Concrete Terminology20l.lR Guide for Making a Condition Survey of Con-

crete in Service211.1 Standard Practice for Selecting Proportions for

Normal, Heavyweight, and Mass Concrete212.2R Guide for Use of Admixtures in Concrete214 Recommended Practice for Evaluation of

Strength Test Results of Concrete304 Guide for Measuring, Mixing, Transporting, and

Placing Concrete304.4R Placing Concrete with Belt Conveyors305R Hot Weather Concreting308 Standard Practice for Curing Concrete309 Guide for Consolidation of Concrete318 Building Code Requirements for Reinforced

Concrete318R Commentary on Building Code Requirements

for Reinforced Concrete

American Society for Testing and MaterialsC 31 Standard Method of Making and Curing Con-

crete Test Specimens in the FieldC 33 Standard Specification for Concrete AggregatesC 39 Standard Test Method for Compressive Strength

of Cylindrical Concrete SpecimensC 94 Standard Specification for Ready-Mixed Con-

creteC 109 Standard Test Method for Compressive Strength

of Hydraulic Cement, Mortars (using 2 in. or50 mm cube specimens)

C 143 Standard Test Method for Slump of PortlandCement Concrete

C 150C 192

C 260

C 311

C 494

C 595

C 618

C 684

C 917

C 989

E 329

Standard Specification for Portland CementStandard Method of Making and Curing Con-crete Test Specimens in the LaboratoryStandard Specification for Air-EntrainingAdmixtures for ConcreteStandard Methods of Sampling and Testing FlyAsh or Natural Pozzolans for Use as a MineralAdmixture in Portland Cement ConcreteStandard Specification for Chemical Admixturesfor ConcreteStandard Specification for Blended HydraulicCementsStandard Specification for Fly Ash and Raw orCalcined Natural Pozzolan for Use as a MineralAdmixture in Portland Cement ConcreteStandard Method of Making, AcceleratedCuring, and Testing of Concrete CompressionTest SpecimensStandard Method for Evaluation of CementStrength Uniformity from a Single SourceStandard Specification for Ground Iron Blast-Furnace Slag for use in Cement and MortarsStandard Recommended Practice for Inspectionand Testing Agencies for Concrete, Steel, andBituminous Materials as Used in Construction

Canadian Standards AssociationA 266.5-M1981 Guidelines for the Use of Super-

plasticizing Admixtures in Concrete

Concrete Plant Manufacturers BureauConcrete Plant Manufacturers Standards of the PlantMixer Manufacturers Division

The above publications may be obtained from the fol-lowing organizations:

American Association of State Highway and Transporta-tion Officials333 N Capitol St. N.W.Suite 225Washington, D.C. 20001

American Concrete InstituteP.O. Box 19150Detroit, MI 48219

American Society for Testing and Materials1916 Race StreetPhiladelphia, PA 19103

Canadian Standards Association178 Rexdale Blvd.Rexdale, Ont.Canada M9W 1R3


Concrete Plant Manufacturers Bureau900 spring St.Silver Spring, Md. 20910

10.2-- Cited referencesCited references are provided at the end of each

chapter.

10.3-- BibliographyThe purpose of this bibliography is to call attention to

literature on high-strength concrete in addition to thatlisted at the ends of chapters in this report. The entriesare organized alphabetically by author. Anonymous refer-ences are listed alphabetically according to their titles.

10.1. Abeles Paul W., “Experience with High-StrengthConcrete in Combination with High-Strength Steel inPrecast Reinforced and Prestressed Concrete,” Materialsand Structures, Research and Testing (RILEM Paris) V. 6,No. 36, Nov.-Dec. 1973, pp. 464-472.

10.2. Ahmad, S.H., and Shah, S.P., “Complete Stress-Strain Curve of Concrete and Nonlinear Design,” ProgressReport, National Science Foundation Grant PFR 7822878, University of Illinois at Chicago Circle, Aug. 1979,29 pp. Also, Nonlinear Design of Concrete Structures, Uni-versity of Waterloo Press, 1980, pp. 61-81.

10.3. Aitcin, Pierre-Claude, “How to Produce HighStrength Concrete,” Concrete Construction, V. 25, No. 3,Mar. 1980, pp. 222-230.

10.4. Albinger, John, and Moreno, Jaime, “High-Strength Concrete, Chicago Style,” Concrete Construction,V. 26, No. 3, Mar. 1981, pp. 241-245.

10.5. Alexander, K.M.; Bruere, G.M.; and Ivanusec, I.,“The Creep and Related Properties of Very High-Strength Superplasticized Concrete,” Cement and Con-crete Research, V. 10, No. 2, Mar. 1980, pp. 131-137.

10.6. Anderson, Arthur R., “Some Examples of Energyand Resource Conservation Utilizing High-Strength Con-crete,” presented at the ACI Annual Convention, Mil-waukee, Mar. 1979.

10.7. Bache, H.H., “Compression Failure in BrittleMaterials. Fracture Hardening (Trykbrud I Skore Materi-aler),” Nordisk Betong (Stockholm), No. 1, 1977, pp. 7-10.(in Swedish)

10.8. Bazant, Z.P., “High Strength Concrete: Discus-sion on Material Behavior Under Various Types of Load-ing,” Proceedings, National Science Foundation Workshopon High Strength Concrete, University of Illinois atChicago Circle, 1979, Report D-l, 13 pp.

10.9 Bennett, E.W., “Fatigue in Concrete,” Concrete(London), May 1974, pp. 43-45.

10.10. Berntsson, L.; Hedberg, B.; and Malinowski, R.,“Triaxial Deformations by Uniaxial Load on Heat-Curedand High-Strength Concrete (Triaxiala DeformationerTill Foljd av Enaxlig Tryckbelastning pa Varmerhardad,hoghallfast betong),” Cement-och-Betonginstitutet, V. 45,No. 2, May 1970, pp. 205-224. (in Swedish)

10.11. Berry, E.E., and Malhotra, V.M., “Fly Ash forUse in Concrete-A Critical Review,” ACI JOURNAL,

Proceedings V. 77, No. 2, Mar.-Apr. 1980, pp. 59-73.10.12. Bertero, Vitelmo V., “Inelastic Behavior of

Structural Elements and Structures,” Proceedings, Na-tional Science Foundation Workshop on High StrengthConcrete, University of Illinois at Chicago Circle, 1979,Report E-l, 70 pp.

10.13. Bickley, J.A., “Concrete Optimization,” ConcreteInternational: Design & Construction, V. 4, No. 6, June1982, pp. 38-41.

10.14. Billington, C.J., “Underwater Repair of Con-crete Offshore Structures,” Proceedings, 11th Annual Off-shore Technology Conference (Houston, 1979), OffshoreTechnology Conference, Dallas, 1979, V. 2, pp. 927-937.

10.15. Bloss, D.R.; Hubbard, S.J.; and Gray, B.H.,“Development and Evaluation of a High-Strength Poly-ester Synthetic Concrete,” Technical Report No. M-2, U.S.Army Construction Engineering Research Laboratory,Champaign, Mar. 1970, 70 pp.

10.16. Bremer, F., “Prestressed Concrete Pressure Ves-sels for Nuclear Reactors,” Technical Session on Designand Construction of Nuclear Power Plants, 7th FIP Con-gress (New York, 1974), Federation Internationale de laPrecontrainte, Wexham Springs, 1975, pp. 34-40.

10.17. Bromham, S.B., “Superplasticizing Admixturesin High Strength Concrete,” Symposium on Concrete inEngineering: Engineering for Concrete (Brisbane, Aug.1977), National Conference Publication No. 77/8, Insti-tution of Engineers, Australia, Brisbane, 1977, pp. 17-22.

10.18. Brooks, J.J., and Neville, AM., “PredictingLong-Term Creep and Shrinkage from Short-TermTests,” Magazine of Concrete Research (London), V. 30,No. 103, June 1978, pp. 51-61.

10.19. Brown, Colin B., “A Discussion on the Micro-mechanics of Achieving High Strength and Other Super-ior Properties,” National Science Foundation Workshopon High Strength Concrete, University of Illinois atChicago Circle, Dec. 1979, Report No. B-l, 5 pp.

10.20. Carrasquillo, R.L.; Nilson, A.H.; and Slate,F.O., “High-Strength Concrete: An Annotated Biblio-graphy 1930-1979,” Cement, Concrete, and Aggregates, V.2, No. 1, Summer 1980, pp. 3-19.

10.21. Carrasquillo, R.L.; Nilson, A.H.; and Slate,F.O., “The Prediction of High-Strength Concrete,” ReportNo. 78-1, Department of Structural Engineering, CornellUniversity, Ithaca, May 1978, 91 pp. Also, MSc thesis,Cornell University, Ithaca, May 1978, 90 pp.

10.22. Carrasquillo, R.L.; Nilson, A.H.; and Slate,F.O., “Very High-Strength Concrete-An Annotated Bib-liography 1930-1976,” Report No. 367, Department ofStructural Engineering, Cornell University, Ithaca, Apr.1977, 46 pp.

10.23. Carrasquillo, Ramon L., and Slate, Floyd O.,“Micro-cracking and Definition of Failure of High- andNormal-Strength Concretes,” Cement, Concrete, and Ag-gregates, V. 5, No. 1, Summer 1983, pp. 54-61.

10.24. Chernobaev, V.I., “Investigation of the CarryingCapacity of High Strength Concrete Flexible Columns(Issledovanie Nesush-ehei Sposobnosti Gibkikh Kolonn


Iz Vysokoprochnykh Betonov),” Beton i Zhelezobeton(Moscow), No. 4, Apr. 1975, pp. 9-11. (in Russian)

10.25. Chung, H.; Hayashi, S; and Kokusho, S.,“Experimental Study on the Shear Strength of HighStrength Concrete Beams,” Transactions, Japan ConcreteInstitute, Tokyo, V. 2, 1980, pp. 233-240.

10.26. Chung, H.; Hayashi, S.; and Kokusho, S.,“Reinforced High Strength Concrete Columns Subjectedto Axial Forces, Bending Moments and Shear Forces,”Transactions, Japan Concrete Institute, Tokyo, V. 2, 1980,pp. 335-342.

10.27. Colaco, Joseph P.; Ames, Jay B.; and Dubinsky,Eli, “Concrete Shear Walls and Spandrel Beam MomentFrame Brace New York Office Tower,” Concrete Interna-tional Design & Construction, V. 3, No. 6, June 1981, pp.23-28.

10.28. Collepardi, Mario, and Corradi, Mario, “Influ-ence of Naphthalene-Sulfonated Polymer Based Super-plasticizers on the Strength of Ordinary and LightweightConcretes,” Superplasticizers in Concrete, SP-62, AmericanConcrete Institute, Detroit, 1979, pp. 315-336.

10.29. Collins, A.R., “The Principles of Making High-Strength Concrete,” Civil Engineers Review, V. 4, May-June 1954, pp. 172-176, 203-206. Also, Civil Engineeringand Public Works Review (London), V. 45, No. 524, Feb.1950, pp. 110-112, and No. 525, Mar. 1950, pp. 170-171,180.

10.30. “Concrete Strength Secret: Dry Mix,” En-gineering News-Record, V. 189, June 15, 1972, p. 3.

10.31. Coppetti, G.; Cambini, F.; and Tognon, G.,“Use of Very High-Strength Concrete for the Manufac-ture of Centrifuged Piles (Impiego Di Calcestruzzi AdAltissime Resistenze Per la Producione De Pali Centri-fugati),” Industria Italiana del Cemento (Rome), V. 50,No. 2, Feb. 1980, pp. 121-130. (in Italian)

10.32. Craven, M.A., “High-Strength and LightweightConcretes for Prestressing,” New Zealand Concrete Con-struction (Wellington), V. 11, No. 3, Mar. 1967, pp. 40-41.

10.33. Cross, Hardy, “Design of Reinforced ConcreteColumns Subject to Flexure,” ACI JOURNAL, ProceedingsV. 26, No. 2, Dec. 1929, pp. 157-169.

10.34. Crow, L.J., and Bates, R.C., “Strengths of Sul-fur-Basalt Concretes,” Report Investigations No. 7349, U.S.Bureau of Mines, Washington, D.C., 1970, 21 pp.

10.35. Dawson, P., “Design and Construction of a Pre-stressed Concrete Pressure Vessel for a Working Pres-sure of 69 N/mm2 (10,000 psi),” Transactions, 4th Inter-national Conference on Structural Mechanics in ReactorTechnology (San Francisco, Aug. 1977) Committee of theEuropean Communities, Luxemburg, 1977, Volume H,Paper H l/5, 13 pp.

10.36. Desov, A.E., “Basic Principles of High StrengthConcrete,” Transportation Research Record No. 504,Transportation Research Board, 1974, pp. 37-42.

10.37. “Development of Prestressed Concrete HighStrength Concrete,” Concrete and Constructional En-gineering (London), V. 57, No. 7, July 1962, p. 268.

10.38. Diamond, Sidney, and Gomez-Toledo, Carlos,

“Consistency, Setting, and Strength Gain Characteristicsof a ‘Low Porosity’ Portland Cement Paste,” Cement andConcrete Research, V. 8, No. 5, Sept. 1978, pp. 613-621.

10.39. Dikeou, J.T.; Kukacka, L.E.; Backstrom, J.E.;and Steinberg, M., “Polymerization Makes Tougher Con-crete,” ACI JOURNAL, Proceedings V. 66, No. 10, Oct.1969, pp. 829-839.

10.40. Erntroy, H.C., and Shacklock, B.W., “Design ofHigh Strength Concrete Mixes,” Reprint No. 32, Cementand Concrete Association, London, 1954.

10.41. “Federal Complex Strikes Low-Key Note,”Building Design and Construction, V. 22, No. 11, Nov.1981, pp. 92-94.

10.42. FIP 7th Congress (New York, 1974), Proceed-ings, V. 2, Lectures and General Reports, FederationInternationale de la Prewntrainte, Wexham Springs,1975, 137 pp.

10.43. Fintel, Mark, “Creep, Shrinkage and Tempera-ture Effects in Tall Buildings,” Concrete Industry Bulletin,V. 14, No. 3, Mar. 1974, pp. 4-11.

10.44. French, P.J.; Montgomery, R.G.J.; and Robson,T.D., “High Concrete Strength Within the Hour,” Con-crete (London), V. 5, No. 8, Aug. 1971, pp. 253-258.

10.45. Fukuchi, Toshio, and Ohama, Yoshihiko, ‘Pro-cess Technology and Properties of 2500 kg/cm2--StrengthPolymer-Impregnated Concrete,” Proceedings, 2nd Inter-national Congress on Polymers in Concrete (Austin, Oct.1978), University of Texas at Austin, 1979, pp. 45-56.

10.46. Fukuchi, Toshio, et al., “Effect of CourseAggregate on Compressive Strength of Polymer-Impreg-nated Autoclaved Concrete,” Proceedings, 22nd JapanCongress on Materials Research (Kyoto, Sept. 1978),Society of Materials Science, Kyoto, 1979, pp. 373-376.

10.47. Funakoshi, M., and Okamoto, T., “The ShearStrength of Prestressed Beams for which Very HighStrength Concrete is Employed,” Transactions, JapanConcrete Institute, Tokyo, V. 2, 1980, pp. 271-278.

10.48. Gallagher, J.E., “Acrylic-Latex Additives CreateExtra Strength New Concretes,” Architectural Record,Mar. 1967, pp. 199-200.

10.49. Galwey, AK., et al., “Relatively High Strengthof a Chalk-Aggregate Concrete,” Journal of AppliedChemistry, May 1966, pp. 159-162.

10.50. Garas, F.K., “Research and Development inSupport of the Design of a Prestressed Concrete PressureVessel for a Working Pressure of 69 N/mm2 (10,000 psi),”International Journal of Pressure Vessels Piping, V. 8, No.3, May-June 1980, pp. 233-244.

10.51. Gaynor, R.D., “Producing High Strength Air-Entrained Concrete,” unpublished discussion paper. Fordetailed information of the test data, see Gaynor,Richard D., “High Strength Air-Entrained Concrete,”Joint Research Laboratory Publication No. 17, NationalSand and Gravel Association/National Ready Mixed Con-crete Association, Silver Spring, Mar. 1968, 19 pp.

10.52. Ghosh, R.S., and Malhotra, V.M., “Use ofSuper-plasticizers as Water Reducers,” Cement, Concrete,and Aggregates, V. 1, No. 2, 1979, pp. 56-63.


10.53. Givens, J.J., Jr., and Carter, G., “Rehabilitationof Offshore Platforms,” Civil Engineering-- ASCE, V. 40,No. 4, Apr. 1970, pp. 47-49.

10.54. Golikov, A.E., “The Effect of High-StrengthConcrete Moulding Technology on the Physico-Mech-anical Properties,” Beton i Zhelezobeton (Moscow), No. 9,1967, pp. 34-35. (in Russian)

10.55. Green, Arthur N., “Low Dosage Super WaterReducer,” presented at the International Symposium onSuperplasticizers in Concrete, Ottawa, May 1978.

10.56. Gupchup, V.N.; Jayaram, S.; and Kulkarni, J.A.,“Effect of Admixtures on Properties of High-StrengthConcrete Mixes,” Indian Concrete Journal (Bombay), V.53, No. 12, Dec. 1979, pp. 331-335.

10.57. Guy, I.N., Editor, Advances in Concrete (Sym-posium Proceedings, University of Birmingham, Sept.1971), The Concrete Society, London, 1972.

10.58. Hanson, J.A, “Shear Strength of LightweightReinforced Concrete Beams,” ACI JOURNAL, Proceed-ings V. 55, No. 3, Sept. 1958, pp. 387-403.

10.59. Harris, Alan, “Optimization of Concrete Hulls,”Proceedings, Conference on Concrete Ships and FloatingStructures (Berkeley, Sept. 1975), University of Califor-nia, Berkeley, 1976, pp. 270-273.

10.60. Hattori, Kenichi, ‘Experiences with MightySuperplasticizer in Japan,” Superplasticizers in Concrete,SP-62, American Concrete Institute, Detroit, 1979, pp.37-66.

10.61. Hattori, K., “Properties of Admixtures for HighStrength Concrete and Their Water Reducing Meehan-ism,” Concrete Journal (Tokyo), V. 14, No. 3, 1976, pp.12-19. (in Japanese)

10.62. Hester, Weston T., “High Strength, Superplasti-cized Concrete: The Significance of Mix Water-CementRatio, Mortar-Aggregate Bond and Cement Efficiency,presented at the ACI Annual Convention, Atlanta, Jan.1982.

10.63. “High-Strength Concrete,” Building (London),V. 211, No. 6436, 1966, pp. 129-130.

10.64. “High-Strength Concrete-Crushed Stone Ag-gregate Makes the Difference,” National Crushed StoneAssociation, Washington, D.C., Nov. 1974, 31 pp.

10.65. Hognestad, E., and Perenchio, W.F., “Devel-opments in High-Strength Concrete,” Proceedings, 7thFIP Congress (New York, 1974), Federation Inter-nationale de la Prewntrainte, Wexham Springs, 1975, V.2, Lectures and General Reports, pp. 21-24.

10.66. Hollister, S.C., “Urgent Need for Research inHigh-Strength Concrete,” ACI JOURNAL, Proceedings V.73, No. 3, Mar. 1976, pp. 136-137.

10.67. “How Super are Superplasticizers?,” ConcreteConstruction, V. 27, No. 5, May 1982, pp. 409-415.

10.68. Hughes, B.P., “Temperature Rises in Low-HeatCement Concrete,” Proceedings, ASCE, V. 97, ST12, Dec.1971, pp. 2807-2823.

10.69. Ikenaga, Hirotake, and Oshima, Hisaji, “Studyon the Relation between an Age of Concrete and Shrink-age, Creep, and Strength--Study of Mixing Design of

Site Concrete Preventing from Cracking Due to Shrink-age and Creep,” Transactions, Architectural Institute ofJapan (Tokyo), V. 215, Jan. 1974, pp. 13-30. (in Japanesewith English abstract)

10.70. “Innovation in Concrete,” Progressive Arch-itecture, V. 59, No. 5, May 1978, pp. 100-109.

10.71. “In Sub-Freezing Weather: Bridge DeckRepaired with Quick-Set Gunned Concrete,” BetterRoads, V. 45, No. 5, May 1975, p. 44.

10.72. James, Robert M., “High-Strength ConcreteDoes Have Its Problems,” ACI JOURNAL, Proceedings, V.75, No. 2, Feb. 1978, p. N8.

10.73. Johnston, Colin D., “Fifty-Year Developmentsin High Strength Concrete,” Proceedings, ASCE, V. 101,C04, Dec. 1975, pp. 801-818.

10.74. Kageyama, H.; Nakagawa, K.; and Nagafuchi,T., “High-Strength Concrete Made With Special CementAdmixture,” Zairyo, V. 29, No. 318, Mar. 1980, pp. 220-225. Also, abstract in Chemical Abstracts, V. 93, No. 3,Aug. 11, 1980, p. 371.

10.75. Kar, Anil K., “Underwater Structures,” Bulletin,International Association for Shell and Spatial Structures(Madrid), No. 50, Dec. 1972, pp. 49-56.

10.76. Karlsson, Inge, “High-Strength Concrete (Hog-hallfast Betong),” Nordisk Betong (Stockholm), No. 4,1977, pp. 19-22. (in Swedish)

10.77. Kemi, Toroa, et al., ‘Experiment of Grouting bySpecial Super High Early Strength Cement Paste,” Reviewof the 31st General Meeting-Technical Session, CementAssociation of Japan, Tokyo, May 1977, pp. 218-221.

10.78. Kennedy, Henry, “High Strength Concrete,” Pro-ceedings, 1st United States Conference on PrestressedConcrete, Massachusetts Institute of Technology, Cam-bridge, 1951, pp. 126-135.

10.79. Klieger, Paul, “High Strength Concrete,” pre-sented at the 3rd Symposium on Modern Concrete Tech-nology, Caracas, Nov. 1976, 29 pp.

10.80. Kobayashi, Masaki, and Tanaka, Hiroshi, “OnFrost Resistance of High-Strength Concrete,” Review ofthe 28th General Meeting- Technical Session, Cement Asso-ciation of Japan, Tokyo, 1974, pp. 173-174.

10.81. Krishna, Raju N., “Compressibility and Modulusof Rupture of High-Strength Concrete,” Journal of the In-stitute of Engineering (India), Civil Engineering Division,V. 52, No. 3, Part C12, Nov. 1971, pp. 98-101.

10.82. Law, Sheldon M., and Rasoulian, Masood, “De-sign and Evaluation of High Strength Concrete for Gir-ders,” Report No. FHWA/LA-80/138, Louisiana Depart-ment of Transportation, Baton Rouge, 1980, 50 pp. Also,PB81-151 623, National Technical Information Service.

10.83. Lawrence, C.D., “The Properties of CementPaste Compacted Under High Pressure,” Research ReportNo. 19, Cement and Concrete Association, WexhamSprings, June 1969, pp. 1-20.

10.84. Lobanov, A.T., et al., “Practice of Prefabricationof High-Strength Concrete Columns for Buildings (OpytIzgotovleniya Kolonn Iz Vysokoprochnyky Betonov DlyaZhilykh Domov),” Beton i Zhelezobeton (MOSCOW), No.

HIGH STRENGTH CONCRETE 3S3R-53

12, Dec. 1976, pp. 14-15. (in Russian)10.85. Machida, F.; Nakahara, S.; Hirose, T.;

Kumonda, T.; Miyasaka, T.; and Ishikawa, H., “Designand Execution of Prestressed Concrete Girder UsingHigh Strength Concrete,” Journal, Japan PrestressedConcrete Engineering Association (Tokyo), V. 16, No. 4,1974, pp. 30-36, and No. 5, 1974, pp. 36-45. (in Japanese)

10.86. MacInnis, Cameron, and Kosteniuk, Paul W.,“Effectiveness of Revibration and High-Speed SlurryMixing for Producing High-Strength Concrete,” ACIJOURNAL, Proceedings V. 76, No. 12, Dec. 1979, pp.1255-1265.

10.87. MacInnis, Cameron, and Thomas, Donald V.,“Special Techniques for Producing High Strength Con-crete,” ACI JOURNAL, Proceedings V. 67, No. 12, Dec.1970, pp. 996-1002.

10.88. Malhotra, V.M., “Development of Sulphur-ln-filtrated High-Strength Concrete,” ACI JOURNAL, Pro-ceedings V. 72, No. 9, Sept. 1975, pp. 466-473.

10.89. Malhotra, V.M., “Superplasticizers in Concrete,”Modern Concrete, V. 41, No. 12, Apr. 1978, pp. 38-43.

10.90. Malhotra, V.M.; Painter, K.E.; and Soles, J.A.,“Development of High-Strength Concrete at Early StatesUsing a Sulphur Infiltration Technique,” Mines BranchInternal Report No. MPI (A) 74-4, CANMET, Depart-ment of Energy, Mines and Resources, Ottawa, July1974, 13 pp.

10.91. Mather, Bryant, “High-Compressive-StrengthConcrete, A Review of the State of the Art,” TechnicalDocumentary Report No. AFSWC-TDR-62-56, Air ForceSpecial Weapons Center, Kirtland Air Force Base, Aug.1962, 90 pp.

10.92. Mather, Bryant, “High Strength Concrete,”Seminar on Control of Quality of Concrete and Construc-tion Practice, ACI Canadian Capital Chapter, Ottawa,1968, 56 pp.

10.93. Mather, Bryant, “Tests of High-Range Water-Reducing Admixtures,” Superplasticizers in Concrete,SP-62, American Concrete Institute, Detroit, 1979, pp.157-166.

10.94. Mather, Katharine, “High Strength, High Den-sity Concrete,” ACI JOURNAL, Proceedings V. 62, No. 8,Aug. 1965, pp. 951-962.

10.95. Matsumoto, Y., et al., “Precast PrestressedConcrete Truss Railway Bridge Using Extremely HighStrength Concrete,” Final Report, 10th IABSE Congress(Tokyo, 1976), International Association for Bridge andStructural Engineering, Zurich, 1976, pp. 433-438.

10.96. Matsushita, H., “Studies on High-Strength Con-crete with Superplasticizer,” Abstract of 31st GeneralMeeting, Cement Association of Japan, Tokyo, 1977, pp.191-192. (in Japanese)

10.97. Mattison, E.N., and Beresford, F.D., “Studies ofthe Production of High Strength Concrete,” 4th Symposi-um on Concrete Research and Development 1970-1973,National Conference Publication No. 73/6, Institution ofEngineers, Australia, Sydney, 1973, pp. 5-10.

10.98. Maxson, Orwin G., and Achenbach, Gary D.,

“Properties of Concrete with Pressured Hydrocarbonsand Seawater,” Proceedings, 8th Annual Offshore Tech-nology Conference, Houston, May 1976, paper OTC2662,V. 3, pp. 507-512.

10.99. McBee, William C., and Sullivan, Thomas A.,“Development of Specialized Sulphur Concretes,” ReportNo. 8346, U.S. Bureau of Mines, Washington, D.C., 1979,21 pp.

10.100. Melnik, R.A., and Patsula, A.Y., “Investigationof the Nonlinear Creep of High Strength Concrete (Issle-dovanie Nelineinoi Polzuchesti VysokoprochnykhBetonov),” Beton i Zehelzobeton (Moscow), No. 3, Mar.1973, pp. 39-40. (in Russian)

10.101. “Mix Design for Pre-Mixed Concrete 50-55MPa,” Boral Resources (Vic) Pty Limited, Boral Con-crete, Abbotsford, Australia, 11 pp.

10.102. Moe, Johannes, “Feasibility Study of Pre-stressed Concrete Tanker Ships,” ACI JOURNAL, Proceed-ings V. 71, No. 12, Dec. 1974, pp. 617-626.

10.103. Moreno, Jaime, “Sixteen Years of High-Strength Concrete in the Chicago Area,” presented at theACI Annual Convention, Atlanta, Jan. 1982.

10.104. Morgan, Austin H., “High-Strength Ready-Mixed Concrete,” National Ready Mixed Concrete Asso-ciation, Silver Spring, Jan. 1971, 18 pp.

10.105. Morin, A.L.; Tkachuk, V.M.; and Korytnyuk,Y.V., “Investigation of the Eccentrically CompressedStructural Components Built by Using High-StrengthConcrete (Issledovaniya Vnetsen-trenno Szhatykh Ele-mentov Iz Betonov Vysokikh),” Beton i Zhelezobeton(Moscow), No. 1, Jan. 1974, pp. 39-41. (in Russian)

10.106. Muguruma, Hiroshi, and Tanaka, Shinzo,“Mechanical Properties of High-Strength Concrete,”Review of the 27th General Meeting-Technical Session,Cement Association of Japan, Tokyo, May 1973, pp. 140-143.

10.107. Nagataki, S., “The Properties of High-StrengthConcrete,” Concrete Journal (Tokyo), V. 14, No. 3, 1976,pp. 38-41. (in Japanese)

10.108. Nagataki, S., and Imai, M., “Some Experimentson High-Strength Concrete,” 27th Annual Meeting, JapanSociety of Civil Engineers, Tokyo, 1972, pp. V-187-190.(in Japanese)

10.109. Nasser, George D., “Are We Headed TowardsVery High-Strength Concretes?"Concrete Products, V. 70,Oct. 1967, pp. 53-54.

10.110. Nasser, George D., “Bibliography on HighStrength Concretes,” ACI JOURNAL, Proceedings V. 64,No. 10, Oct. 1967, pp. 690-691.

10.111. Nilson, A.H., and Slate, F.O., “Properties ofHigh Strength Concrete,” presented at the Session onInelastic Response of Normal, Lightweight, and High-Strength Concrete, ASCE Fall Convention, Chicago, Oct.1978.

10.112. Nilson, A.H., and Slate, F.O., “StructuralProperties of High-Strength Concrete,” presented at theACI Annual Convention, Milwaukee, Mar. 1979.

10.113. Nishi, H.: Ohshio, A.: and Fukuzawa, K., -


“Autoclave-Cured High Strength Concrete and Piles,”Cement and Concrete, No. 299, Cement Association ofJapan, Tokyo, 1972, pp. 23-29. (in Japanese)

10.114. Okada, Kiyoshi, and Azimi, M. Azam,“Strength and Ductility of Reinforced High StrengthConcrete Beams,” Memoirs, Faculty of Engineering,Kyoto University, V. 43, Part 2, Apr. 1981, pp. 304-318.

10.115. Okada, Kiyoshi, and Kobayashi, Kazuo, “Ef-fects of Addition of Gypsum and Super Water-ReducingAgent on Mechanical Properties of Blast-Furnace SlagCement Mortar,” Proceedings, 21st Japan Congress onMaterials Research (Tokyo, Oct. 1977), Society ofMaterials Science, Kyoto, 1978, pp. 209-213.

10.116. Parrot, L.J., “High-Strength Concrete,” Con-crete (London), V. 4, No. 2, Feb. 1970, pp. 83-84.

10.117. Parrot, L.J., “The Production and Properties ofHigh-Strength Concrete,” Concrete (London), V. 3, No.11, Nov. 1969, pp. 443-448.

10.118. Parrott, L.J., “The Selection of Constituentsand Proportions for Producing Workable Concrete witha Compressive Cube Strength of 80 to 110 n/mm2 (11,600to 15,900 lbf/in2),” Technical Report No. 416, Cement andConcrete Association, Wexham Springs, 1969, 12 pp.

10.119. Pastor, J.A.; Nilson, A.H.; and Slate, F.O.,“Strength and Deformation of High Strength ReinforcedConcrete Beams,” Research Report, Department of Struc-tural Engineering, Cornell University, Ithaca (in pre-paration).

10.120. Perenchio, W.F.; Whiting, D.A.; and Kantro,D.L., “Water Reduction, Slump Loss, and Entrained AirVoid Systems as Influenced by Superplasticizers,” Super-plasticizers in Concrete, SP-62, American Concrete Insti-tute, Detroit, 1979, pp. 137-155.

10.121. Pollet, Henri M., “Attainment of Very HighStrength Concrete-eater than 1000 kg/cm2 (Reali-sation de Betons a Tres Haute Resistance-Supreiure a1000 kg/cm2),” Annales, Institut Technique du Batimentet des Travaux Publics (Paris), No. 214, Oct. 1965, pp.1425-1426. (in French)

10.122. Popovics, Sandor, “Strength Relationships forFly Ash Concrete,” ACI, JOURNAL, Proceedings V. 79, No.1, Jan.-Feb. 1982, pp. 43-49.

10.123. “Precasting Efficiency Pays Off on LongBridge," Construction Equipment, V. 64, No. 1, Aug. 1981.

10.124. P’yachev, V.A.; P’yachev, G.E.; and Kokhaev,N.F., “Raw Materials in Cement Manufacture for Produc-ing High-Strength Concrete (Tsementy Dlya Vysokopro-chniykh Betonov),” Tsement (Leningrad), No. 1, Jan.1974, pp. 21-22. (in Russian)

10.125. Rayner, Johnathan, “Floating Docks in Van-couver Need Continuous Pour of New High-StrengthConcrete,” Engineering and Contract Record (Don Mills),V. 89, No. 9, Sept. 1976, pp. 22-24.

10.126. Reigstad, Gordon H., “Energy Conservation inBuildings: A Prestressed Concrete System,” ProfessionalEngineer, V. 47, No. 4, Apr. 1977, pp. 27-28.

10.127. Richart, F.E., “A Study of the Economics ofHigh Strength Concrete in Building Construction,” ACI

JOURNAL, Proceedings V. 32, No. 4, Mar.-Apr. 1936, pp.459-472.

10.128. Roy, Della M., and Gouda, G.R., “HighStrength Generation in Cement Pastes,” Cement andConcrete Research, V. 3, No. 6, Nov.-Dec. 1973, pp.807-820.

10.129. Roy, D.M.; Gouda, G.R.; and Bobrowsky, A.,“Very High Strength Cement Pastes Prepared by HotPressing and Other High Pressure Techniques,” Cementand Concrete Research, V. 2, No. 3, May-June 1972, pp.349-366.

10.130. Ryaboshapko, Y.I.; Vaslavskii, V.F.; andOlginskii, A.G., “Experience in the Application of High-Strength Concrete with Acid FIy Ash Admixture (OpytPrimeneniya Vysokomarochnogo Betona S Prisadkoi Kis-loi Zoly-Unosa),” Beton i Zhelezobeton (Moscow), No. 5,May 1974, pp. 12-13. (in Russian)

10.131. Ryell, John, “High Strength Concrete,” TenthAnnual School of Concrete Technology, Ready MixedConcrete Association of Ontario, Toronto, Apr. 1969, 19pp.

10.132. Ryell John, “High Strength Concrete,” Can-adian Pit and Quarry (Don Mills), Jan. 1970, pp. 16-19,and Feb. 1970, pp. 26-28.

10.133. Saito, T.; Ohshio, A.; Goto, Y.; and Omori, Y.,“High Strength Concrete. Part 2, Strength Properties,Durability, and Thermal Characteristics,” Journal ofResearch, Onoda Cement Co., V. 28, 1976, pp. 12-27. (inJapanese)

10.134. Saucier, Kenneth L., “High-Strength Concrete,Past, Present, Future: Concrete International Design &Construction, V. 2, No. 6, June 1980, pp. 46-50.

10.135. Saucier, Kenneth L., “Determination of Prac-tical Ultimate Strength of Concrete,” Miscellaneous PaperNo. C-72-16, U.S. Army Engineer Waterways ExperimentStation, Vicksburg, June 1972, 29 pp.

10.136. Savage, E.S., “Deep-Bed Filtration LengthensFilter Runs, Lowers Backwash Water Needs,” AmericanCity, V. 88, No. 1, Jan. 1973, p. 44.

10.137. Schrader, Ernest K., and Munch, Anthony V.,“Fibrous Concrete Repair of Cavitation Damage,” Pro-ceedings, V. 102, C02, June 1976, pp. 385-399.

10.138. Shah, S.P., and Ahmad, S.H., “Effective Con-finement on High-Strength Concrete,” presented at theACI Annual Convention, Atlanta, Jan. 1982.

10.139. Shah, S.P.; Gokoz, UIker; and Ansari, Farhad,“Experimental Technique for Obtaining Complete Stress-Strain Curves for High Strength Concrete,” Cement,Concrete, and Aggregates, V. 3, No. 1, Summer 1981, pp.21-27.

10.140. Schukla, S.N., and Mittal, M.K., “Short-TermDeflection in Two-Way Reinforced Concrete Slabs AfterCracking,” ACI JOURNAL, Proceedings V. 73, No. 7, July1976, pp. 416-419.

10.141. Slate, F.O., and Nilson, A.H., “High-StrengthConcrete-Preliminary Results on Microcracking andCreep,” presented at the ACI Annual Convention,Milwaukee, Mar. 1979.


10.142. Southworth, George, and Scott, Norman L.,“Special Concretes,” Concrete Construction, V. 26, No. 3,Mar. 1981, pp. 229-233, 275-279.

10.143. “Soviet Concrete Not So Tough?,” EngineeringNews-Record, V. 166, No. 22, June 1, 1961, p. 47.

10.144. Stachiw, J.D., ‘Concrete Deep SubmergenceHollow Shell Structures,” Proceedings, ASCE, V. 95, ST12, Dec. 1969, pp. 2931-2954.

10.145. Stamenkovic, Hrista, “Causes, Mechanisms andControl of Surface Voids,” Concrete (London), V. 7, No.7, July 1973, pp. 45-48.

10.146. “Structural Trends in New York City Build-ings,” Civil Engineering-- ASCE, V. 53, No. 1, Jan. 1983,pp. 30-37.

10.147. Superplasticizers in Concrete, SP-62, AmericanConcrete Institute, Detroit, 1979, 436 pp.

10.148. Swamy, R.N., and Anand, K.L., “Shrinkage andCreep Properties of High Strength Structural Concrete,”Civil Engineering and Public Work Review (London), V.68, No. 807, Oct. 1973, pp. 859-868.

10.149. Swamy, R.N., and Anand, K.L., “Structural Be-havior of High Strength Concrete Beams,” BuildingScience, V. 9, No. 2, June 1974, pp. 131-141.

10.150. Swamy, R.N., and Ibrahim, A.B., “Shrinkageand Creep Properties of High Early Strength StructuralLightweight Concrete, Proceedings, Institution of CivilEngineers (London), V. 55, Sept. 1973, pp. 635-646.

10.151. Swamy, R.N.; Ibrahim, A.B.; and Anand, K.L.,“The Strength and Deformation Characteristics of HighEarly Strength Structural Concrete,” Materials andStructures, Research and Testing (RILEM, Paris), V. 8,No. 48, 1975, pp. 413-423.10.152. Symposium on Concrete for Engineering, En-

gineering for Concrete (Brisbane, Aug. 1977), NationalConference Publication No. 7718, Institution of Engineers,Australia, Brisbane, 1977.

10.153. “Tapping Concrete’s Potentials,” BuildingDesign and Construction, V. 20, No. 10, Oct. 1979, pp.63-93.

10.154. ‘Thaulow, Sven, ‘Tensile Splitting Test andHigh Strength Concrete Test Cylinders,” ACI JOURNAL,Proceedings V. 53, No. 7, Jan. 1957, pp. 699-706.

10.155. “The World’s Tallest Concrete Buildings-Today and Yesterday,” Concrete Construction, V. 28, No.2, Feb. 1983, pp. 91-100.

10.156. Tognon, G.; Copetti, G.; and Ursella, P., “VeryHigh Strength Concretes for Precasting: ProductionTechnology and Characteristic Properties,” Proceedings,9th International Congress of the Precast ConcreteIndustry (Vienna, Oct. 1978), BIBM, Linz/Donau, 1978,pp. 1-39-I-46.

10.157. Tognon, G.; Ursella, P.; and Copetti, G.,“Design and Properties of Concretes with Strength over1500 kg/cm2,” ACI JOURNAL, Proceedings V. 77, No. 3,May-June 1980, pp. 171-178.

10.158. Towles, Thomas T., “Advantages in the Use ofHigh Strength Concretes,” ACI JOURNAL, Proceedings V.28, No. 9, Apr. 1932, pp. 607-612.

10.159. “Undersea Restaurant Uses 25,500-psi Con-crete,” Engineering News-Record, V. 190, July 13, 1972, p.17.

10.160. Valore, R.C.; Kudrenski, W.; and Gray, D.E.,“Application of High-Range Water Reducing Admixturesin Steam Cured Cement-Fly Ash Concretes,” Superplasti-cizers in Concrete, SP-62, American Concrete Institute,Detroit, 1979, pp. 337-373.

10.161. Vivesaraya, H.C.; Desay, P.; and Babu, ShriK.H., “High Strength Concrete Mix Design, A CaseStudy,” Special Publication No. SP-2, Cement ResearchInstitute of India, New Delhi, Mar. 1970, 28 pp.

10.162. Walz, K., “The Production of High StrengthConcrete,” Translation Tech. No. 2037/R39, Cement andMarketing Company Limited, London, June 1966, p. 7.

10.163. Wang, Pao-Tsan; Shah, Surendra P.; andNaaman, Antoine, “High-Strength Concrete in UltimateStrength Design,” Proceedings, ASCE, V. 104, ST11, Nov.1978, pp. 1761-1773.

10.164. Wantanabe, A., et al., “Fatigue Behavior ofHigh-Strength Concrete,” Abstract of 31st General Meet-ing, Cement Association of Japan, Tokyo, 1977, pp. 221-222. (in Japanese)

10.165. “Water-Tower Place-High-Strength Con-crete,” Concrete Construction, V. 21, No. 3, Mar. 1976,pp. 102-104.

10.166. Wittman, F.H., “Micromechanics of AchievingHigh-Strength and Other Superior Properties,” Proceed-ings, National Science Foundation Workshop on High-Strength Concrete (Dec. 1979), University of Illinois atChicago Circle, 1979, Report A-l, 22 pp.

10.167. Woolgar, G., and Oates, D-B., “Fly Ash andthe Ready-Mixed Concrete Producer,” Concrete Interna-tional: Design & Construction, V. 1, NO. 11, NOV. 1979,pp. 34-40.

10.168. Yamamoto, Y., and Kobayashi, M., “Use ofMineral Fines in High Strength Concrete-Water Re-quirement and Strength,” Concrete International Design& Construction, V. 4, No. 7, July 1982, pp. 33-40.

10.169. Young, J.F.; Berger, R.L.; and Breese, J.,“Accelerated Curing of Compacted Calcium Silicate Mor-tars on Exposure to CO2,” Journal of the American Cer-amic Society, V. 57, No. 9, Sept. 1974, pp. 394-397.

10.170. Zaitsev, Y.B., and Wittman, F.H., “Simulationof Crack Propagation and Failure of Concrete,” Materialsand Structures, Research and Testing (RILEM, Paris), V.14, No. 83, Sept.-Oct. 1981, pp. 357-365.

10.171. Zia, Paul, “Review of ACI Code for Designwith High-Strength Concrete,” Concrete InternationalDesign & Construction, V. 5, No. 8, Aug. 1983, pp. 16-20.

10.172. Zorich, A.S., “Bearing Capacity of Eccentri-cally Tensioned Reinforcing Elements of Ordinary andHigh-Strength Concrete Under Transversal Forces (Ne-sushchaya Sposobnost Vnetsentrenno Rastyanutykh Za-helezobetonnykh Elementov Iz Obychnogo I Vysoko-prochnogo Betonov Pri Deistvii Poperechnykh Sil):Beton i Zhelezobetotn, No. 11, Nov. 1976, pp. 34-37. (inRussian)

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