materiel for high performance concrete

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1 Materials selection,proportioning and qualitycontrolS Mindess

1.1 IntroductionHigh performance concretes (HPC) are concretes with properties orattributes w hich satisfy the performance criteria. Generally concretes withhigher strengths and attributes superior to conventional concretes aredesirable in the con struction indu stry . For the purposes of this book , HP Cis defined in terms of strength and durabili ty. The researchers of StrategicHighway Research Program SHRP-C-205 on High Performan ce Concrete1defined th e high perform ance concretes for pavem ent applications in termsof strength, durabili ty attr ibutes and water-cementitious materials ratio asfollows: It shall have one of the follow ing strength characteristics:4-hour compressive strength ^25OO psi (17.5 MPa) termed as veryearly strength concrete (VES), or24-hour compressive strength ^50OO psi (35 MPa) termed as highearly strength concrete (HES), or28-day compressive strength ^10,0OO psi (70 M Pa) termed as veryhigh strength concrete (VHS). It shall have a durability factor greater than 80% after 300 cycles of

freezing and thawing. It shall hav e a water-cementitious materials ratio =$0.35.High strength concrete (HSC) could be considered as high performanceif other attr ibutes are satisfactory in terms of its intended application.Generally concretes with higher strengths exhibit superiority of otherattributes. In North American practice, high strength concrete is usuallyconsidered to be a concrete with a 28-day com pressive streng th of at least6000 psi ( 42MP a) . In a recent CEB-FIP State-of-the-Art Report on High


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Strength Concrete2 it is defined as concrete having a minimum 28-daycompressive strength of 8700 psi ( 6 O M P a ) . Clearly then, th e definition of'high strength concrete' is relative; it depends upon both the period of timein question, and the location.The proportioning (or mix design) of normal strength concretes is based

primarily on the w/c ratio 'law' first proposed by Abrams in 1918. At leastfo r concretes with strengths up to 6000 psi (42MPa), it is implicitlyassumed that almost any normal-weight aggregates will be stronger thanthe hardened cement paste. There is thus no explicit consideration ofaggregate strength (or elastic modulus) in the commonly used mix designprocedures, such as those proposed by the American Concrete Institute.3Similarly, the interfacial regions (or the cement-aggregate bond) are alsonot explicitly addressed. Rather, it is assumed that the strength of thehardened cement paste will be the limiting factor controlling the concretest rength.For high strength concretes, however, all of the components of theconcrete mixture are pushed to their critical limits. High strength concretesm ay be modelled as three-phase composite materials, the three phasesbeing (i) the hardened cement paste (hep); (ii) the aggregate; and (iii) theinterfacial zone between the hardened cement paste and the aggregate.These three phases must all be optimized, which means that each must beconsidered explicitly in the design process. In addition, as has been pointedout by Mindess and Young,4

'it is necessary to pay careful attention to all aspects of concreteproduction (i.e. selection of materials, m ix design, handling andplacing). It cannot be emphasized too strongly that quality control isan essential part of the production of high-strength concrete andrequires full cooperation among the materials or ready-mixed sup-plier, the engineer, and the contractor'.In essence then, the proportioning of high strength concrete mixturesconsists of three interrelated steps: (1) selection of suitable ingredients -cement, supplementary cementing materials, aggregates, water and che-mical admixtures, (2) determination of the relative quantities of thesematerials in order to produce, as economically as possible, a concrete thathas the desired rheological properties, strength and durability, (3) carefulquality control of every phase of the concrete-making process.

1.2 Selection of materialsAs indicated above, it is necessary to get the maximum performance out ofall of the materials involved in producing high strength concrete. Forconvenience, the various materials are discussed separately below. Howev-er, it must be remembered that prediction with any certainty as to h ow theywill behave when combined in a concrete mixture is not feasible. Particu-


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larly when attempting to make high strength concrete, any materialincompatibilities will be highly detrimental to the finished product. Thus,the culmination of any mix design process must be the extensive testing oftrial mixes.High strength concrete will normally contain not only portland cement,aggregate and water, but also superplasticizers and supplementary cement-in g materials. It is possible to achieve compressive strengths of up to14,000 psi (98 MPa) using fly ash or ground granulated blast furnace slag asthe supplementary cementing material. However, to achieve strengths inexcess of 14,000 psi (100 MPa), the use of silica fume has been found to beessential, and it is frequently used for concretes in the strength range of9000-14,000 psi (63-98 MPa) as well.Portland cementThere are two different requirements that any cement must meet: (i) itmus t develop the appropriate strength; and (ii) it must exhibit theappropriate rheological behaviour.High strength concretes have been produced successfully using cementsmeeting the ASTM Standard Specification C150 for Types I, II and IIIportland cements. Unfortunately, ASTM C150 is very imprecise in itschemical and physical requirements, and so cements which meet theserather loose specifications can vary quite widely in their fineness andchemical composition. Consequently, cements of nominally the same typewill have quite different rheological and strength characteristics, particu-larly when used in combination with chemical admixtures and sup-plementa ry cementing materials. Therefore, when choosing portland ce-ments for use in high strength concrete, it is necessary to look carefully atthe cement fineness and chemistry.FinenessIncreasing the fineness of the portland cement will, on the one hand,increase the early strength of the concrete, since the higher surface area incontact with water will lead to a more rapid hydration. O n the other hand,too high a fineness may lead to rheological problems, as the greateramount o f reaction at early ages, in particular the formation of et t r ingi te ,will lead to a higher rate of slump loss. Early work by Perenchio5 indicatedthat fine cements produced higher early age concrete strengths, though atlater ages differences in fineness were not significant. Most cements nowused to produce high strength concrete have Elaine finenesses that are inthe range of 1467 to 1957 ft2/lb (300 to 400 m 2 /kg) , though when Type III(high early strength) cements are used, the finenesses are in the range of2201 ft2/lb (450 m 2/kg).


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Chemical composition of the cementThe previously cited work of Perenchio5 indicates that cements with higherC3A contents leads to higher strengths. However, subsequent work6 hasshown that high C3A contents generally leads to rapid loss of flow in thefresh concrete, and as a result high C3A contents should be avoided incements used for high strength concrete. Aitcin7 has shown that the C3Ashould be primarily in its cubic, rather than its orthorhombic, form.Further, Aitcin7 suggests that attention must be paid not only to the totalamount of SO3 in the cement, but also to the amount of soluble sulfates.Thus, the degree of sulfurization of the clinker is an important parameter.

In addition to commercially available cements conforming to ASTMTypes I, II and III, a number of cements have been formulated specificallyfor high strength concrete. For instance, in Norway, Norcem Cement hasdeveloped two special cements for high strength concrete, in addition totheir ordinary portland cement. The characteristics of these cements aregiven in Table 1.1.s Note that for the two special cements (SP30-4A andSP30-4A MOD), the C3A contents were held to 5.5%.Table 1.1 Compositionof special cementsfor high strength concrete (developedby NorcemCement8)

* Ordinary portland cement, fo r comparisonI m 2 / kg = 4.89ft2/ lb

Supplementary cementing materialsAs indicated above, most modern high strength concretes contain at leastone supplementary cementing material: fly ash, blast-furnace slag, or silicafume . Very often, the fly ash or slag is used in conjunction with silica fume.These materials are all specified in the Canadian CSA Standard A23.5.9 Inthe United States, fly ash is specified in ASTM C618,10 and blast furnaceslag in ASTM C98911; there is, as yet, no U.S. standard for silica f u m e .These materials are described in detail in Supplementary CementingMaterials for Concrete.12

Using a somewhat different approach, a high silica modulus portland

C2S (%)C3S (%)C3A (%)C4AF (%)MgO (%)S03(%)Na2O equivalent (%)Elaine fineness (m 2/kg)heat of hydra t ion (kcal/kg)setting time (min): initialfinal

SP30*18558933.31.130071

120180

SP30-4A28505.591.5-2.02-30.631056

140200

SP30-4A MOD28505.591.5-2.02-30.640070

120170


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Table 1 .2 Bogue composition and other propertiesof H TS cement (after Aitcin et al.13)

cement (referred to as HTS, or Haute Teneur en Silica, or high silicacontent) was developed,

13with the composition shown in Table 1.2. Notethat, compared to more conventional cements (such as the SP-30 ofTable 1.1), there is a very high total silicate content (84%), and C3Acontent of only 3.6%. T he cement is rather coarsely ground (Elainefineness of 1565 ft2/lb (320 m2/kg)). It is made from a clinker composed ofsmall alite and belite crystals, and minute C3A crystals. It is capable ofproducing concretes with excellent 28-day compressive strengths, as indi-cated in Table 1.3, when used in conjunction with 10% silica fume.

Table 1.3 28 day compressive strengths of concretemade with H TS cement and 10% silica fume13

Silica fumeIt is possible to make high strength concrete without silica fume, atcompressive strengths of up to about 14,000psi (98MPa). Beyond thatstrength level, however, silica fume becomes essential, and even at lowerstrengths 9000-14,000 psi (63-98 MPa), it is easier to make HSC with silicafume than without it . Thus, when it is available at a reasonable price, itshould generally be a component of the HSC mix.Silica fume14 is a waste by-product of the production of silicon andsilicon alloys, and is thus not a very well-defined material. Consequently, itis important to characterize any new source of silica f ume , by determiningthe specific surface area by nitrogen adsorption, and the silica, alkali andcarbon contents. In addition, it is desirable to minimize the content of

C2S(%)C3S (%)C3A (%)C4AF(%)Na2O equivalent (%)lime saturation factorsilica modulusElaine fineness, m 2/kgIm2/kg = 4.89ft2/ lb

22623.66.90.3892.74.8320

vv/c0.310.230.200.171 ksi = 6.89 MPalMPa = 0.145ksi

f c(MPd)74106115124


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the mixes shown in Table 1.9, Burg and Ost19 found that, when specimensthat had been moist cured for 28 days were then subjected to air curing,their strengths at 91 days exceeded those of continuously moist-curedspecimens; however, by 426 days, the continuously moist-cured specimenswere from about 3% to 10% higher in strength than the air-cured ones.On the other hand, several investigators have reported that, as long as aweek or so of moist curing is provided, subsequent curing under ambientconditions is not particularly detrimental to strength development. Peter-m an and Carrasquillo16 have stated that 'the 28-day compressive strengthof high strength concrete which has been cured under ideal conditions for 7days after casting is not seriously affected by curing in hot o r dry conditionsfrom 7 to 28 days after casting.'Finally, contrary results were reported by Moreno30 w ho indicated that

air-cured specimens were about 10% stronger than moist-cured specimensat all ages up to 91 days.Type of mold for casting cylindrical specimensASTM C470: Molds for Forming Concrete Test Cylinders Vertically,describes the requirements for both reusable and single-use molds, andASTM C31: Making and Curing Concrete Test Specimens on the Fieldpermits both types of mold to be used. However, it has long been knowntha t different molds conforming to ASTM C470 will result in specimenswith different measured strengths. This is true for both normal strengthand high strength concretes. In general, more flexible molds will yieldlower strengths than very rigid molds, because the deformation of theflexible molds during rodding or vibration leads to less efficient compactionthan when using rigid molds. The experimental data largely bear this out.It should be noted that, whatever the mold materials, the molds must beproperly sealed to prevent leakage of the mix water. If any significantleakage does occurs, the apparent strength will generally increase, becauseof th e lower effective w /c ratio, and increased densification of thespecimens.

For the standard 6x12 in. (150x300 mm) molds, Carrasquillo andCarrasquillo29 found that steel molds gave strengths about 5% higher thanplastic molds, while Hester31 found about a 10% difference. Similar resultswere reported by Howard and Leatham.32 Peterman and Carrasquillo16reported that steel molds gave strengths about 10% higher than thoseobtained with cardboard molds, and Hester31 showed that steel molds gavest rengths about 6% higher than tin molds.

On the other hand, Cook15 reported that 'good success was experiencedon the use of single-use rigid plastic molds', while Aitcin33 reportsincreasing use of rigid, reusable plastic molds. In addition, Carrasquilloand Carrasquillo29 have reported that for the smaller 4x8in .(100 x 200 mm) molds, there were no strength differences between steel,plastic or cardboard molds.


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In view of the above results, it would be prudent to use rigid steel mo ldswhenever practicable, particularly for concrete strengths in excess of about14,000 psi (98 M Pa ), at least until m ore test data becom e available for thesmaller molds.Specimen sizeFor m ost materials, including concrete, it has generally been observed th atthe smaller the test specimen, the higher the strength. For high strengthconcrete, however, though this effect is often observed, there are contra-dictory results reported in the l i terature. The results of a n u m b er of studiesare compared in Table 1.11. I t may be seen that the observed strengthratios of 4x8in. (100x200 m m ) cylinders to 6x12 in . (15Ox300 m m)cy linders range from about 1.1 to 0.93. These contradictory resultsmay be du e to d ifferences in testing procedures am ongst the v ariousinvestigators.It must be noted that while for a given set of materials and testprocedures, i t may be possible to increase th e apparent concrete strengthby decreasing th e specimen size, this does not in any way change th estrength of the concrete in the structure. O ne pa rticular specimen size doesnot give 'truer' results than any other. Thus, one should be careful tospecify a particu lar specimen size for a given project, rath er th an leaving itas a matter of choice.Specimen end conditions

According to ASTM C39: Compressive Strength of Cylindrical ConcreteSpecimens, the ends of the test specimens must be plane within 0.002 in .(0.05 m m ) . This may be achieved either by capping the ends (usually with asulfur mortar) or by sawing or grinding. Unfortunately, different endTable 1.11 Effect of specimen size on the comp ressive strength of high strengthconcreteInvestigatorPeterman and Carrasquillo 16Carrasquillo, Slate and Nilson 34How ard and Leatham 32Cook15Burg and Ost19Aitcin33Moreno 3083 MPa concrete119 MPa concreteCarrasquillo and Ca rrasquillo29

fc (100 x 200 mm cylinder)f c ' (150 x 300 mm cylinder)-1.1-1.1-1.08-1.05-1.01ambiguous results-1.0-0.93-0.93


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conditions can lead to different measured strengths, and so the endpreparation for testing high strength concrete specimens should be spe-cified explicitly for any given project .

The most common method for preparing the ends of normal strengthconcrete is to use sulfur caps; for high strength concrete, high strengthsulfur mortars are commercially available. However, if the strength of thecap is less than the strength of the concrete, the compressive load will notbe transmitted uniformly to the specimen ends, leading to invalid results.Thus, for high strength concrete, in addition to high strength cappingcompounds, a number of other end preparation techniques are beinginvestigated. These include grinding the specimen ends, or using unbondedsystems, consisting of a pad constrained in a confining ring which fits overthe specimen ends.

Most compressive strength tests on high strength concrete are stillcarried out using a high strength capping compound. The materialsavailable in North America will achieve compressive strengths of 12,000 psito 13,000 psi (84MPa to 91 MPa) when tested as 2 in. (50mm) cubes.33Peterman and Carrasquillo21 recommend the use of such capping com-pounds, since they give higher concrete strengths than ordinary cappingcompounds. Cook16 has used such compounds for concrete strengths up to10,000 psi ( 7 O M P a ) , while Moreno30 considers them to be satisfactory atstrengths up to 17,000 psi (119 MPa).Burg and Ost19 report that a high strength capping material may be usedwith concrete strengths of up to 15,000 psi (105MPa); beyond that, themode of failure of the cylinders changed from th e normal cone failure of acolumnar one. They recommend grinding of the cylinder ends for strengthsbeyond 15,000 psi (105MPa). Similarly, Aitcin33 has reported that aboveabout 17,000psi (119MPa), the high strength capping material is pulver-ized as the specimens fail, which might well affect the measured strength.He too recommends grinding of the specimen ends for very high strengthconcretes. (It might be noted that end grinders for concrete cylinders arenow commercially available. In 1992, the cost of such a machine wasapproximately US$12,000.)

Because of the uncertainty with high strength capping compounds, andthe costs and time involved in end grinding, a considerable amount ofresearch has been carried out on unbonded capping systems. These consistof metal restraining caps into which elastomeric inserts are placed; theassemblies then fit over the ends of the cyl inder. As the elastomeric insertsdeteriorate with repeated use, they are replaced from time to time.Richardson35 used a system of neoprene inserts in aluminium caps fortesting normal strength concretes in the range of 3000 psi to 6000 psi(21 MPa to 42MPa). He found that below 4000 psi (28 MPa), the neoprenepads gave somewhat lower strengths than conventional sulfur caps, whileabove 4000 psi (28MPa) they gave somewhat higher strengths. Overall,however, the mean compressive strengths were not significantly differentbetween the two systems.


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Carrasqui l lo and Carrasquillo 29 compared a high strength sulfur cappingcompound to an unbonded system consis t ing of a polyurethane pad in ana lumin ium rest ra ining r ing. They found that up to about 10,000 psi( 7 O M P a ) , the unbonded system gave strengths that were 97% of thoseobta ined with the capping compound. Beyond 10,000 psi ( 7 O M P a ) ,however, the unbonded system gave much higher s t rengths; they hypothe-sized tha t this m ight be due to greater end restrain t of the cy linders w ithsuch a system. In subsequent work,36 they found tha t up to 10,000 psi( 7 O M P a ) , polyure thane pads in an a lumin ium cap gave results within 5%of those achieved with high strength sulfur caps, while up to 11,000 psi(77MPa), neop rene pads in steel caps gave results w ithin 3% of thoseobta ined w ith the sulfur end caps. Ho wev er, they concluded that the use ofe i ther unbonded sys tem w as quest ionable; substant ia l differences in testresults were obtained when two sets of restraining caps (from the samemanufac tu re r ) were used.

To improve the resul ts obta ined with unbonded systems, Boulay 37developed a system in wh ich, instead of elastomeric inserts, a mixtu re ofdry sand an d w ax is used. I t was foun d 3 8 that the sand m ixtu re gave resultswhich were interm ediate between those o bta ined w ith grou nd ends or withsulfur mortar caps.In summary , then , be low about 14,000psi (98MPa), a thin, highs t rength sulfur m ortar cap m ay be used successful ly . B eyond that s t rengthlevel, it w ould appear that grind ing specimen ends is current ly the only w ayto ensure valid test results.Testing machine characteristicsIn general , for normal strength concrete, the characteristics of the testingmachine itself are assumed to have little or no effect on the peak load.However, for very high s t rength concretes the machine may wel l havesome effect on the response of the specimen to load. From a review of thel i tera ture , Hester31 concluded that the longitudinal stiffness of the testingmachine will not affect th e m aximum load, and this view is shared also byAitcin.3 3 However , if the machine is not stiff enough , the specimens m ayfail explosively, and , of course, a very stiff m achine (with servo-controls) isrequ ired if one w ishes to determ ine the post-peak response of the concrete.On the o ther hand, Hester31 also reports that if the machine is not stiffenough laterally, compressive strengths may be adversely affected.

One must also be concerned about the capacity of the testing machinewhen testing very high strength concretes. Aitcin33 calculated the requiredmachine capacities for different strength levels and specimen sizes, usingthe comm on assum ption that the failur e load sho uld not exceed 2/3 of themachine capacity. Some of his results are reproduced in Table 1.12.Relatively few commercial laboratories are equipped to test high strengthconcrete, since a common capacity of commercial testing machine is292,500 lb s (1.3 M N ) . To test a 6x12 in. (15Ox 300 mm) cyl inder of


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Table 1.12 Machine capacity required for high strength concrete33

21,400psi (15OMPa) concrete requires a 900,000 Ib (4.0 M N) testingmachine, and relatively few machines of this size are available in commer-cial laboratories. This then, is probably th e driving force be hind th e moveto the smaller 4 x 8 in. (100 x 200 mm ) cylinders.Effect of loading platensAgain , for ordinary concrete, the effects of the spherically seated bearingblocks (platens) are not explicitly considered, as long as they meet th erequirements of ASTM C39: Com pressive S trength of Cylindrical ConcreteSpecimens. However, recent work at the Construction Technology Labor-atories in Skokie, Illinois39 has shown that, for high strength concrete,even this cannot be ignored. Spherical bearing blocks w hich deform in sucha w ay that th e stresses are higher around th e periphery of the specimenthan at the centre, yield higher compressive strengths than blocks whichdeform so that th e highest stresses are at the centre of the specimen, andfall off towards the edges (i.e. a 'concave' rather than a 'convex' stressdistribution). Measured differences can be as high as 15% for concreteswith compressive strengths greater than 16,000 psi (112 MPa).1.5 ConclusionsIn conclusion, then, it has been shown that th e production of high strengthconcrete requires careful attention to details. It also requires closecooperation between the owner, the engineer, the suppliers and producersof the raw materials, the contractor, and the testing laboratory.32 Perhapsmost important, we must remember that the well-known ' laws' and'rules-of-thumb' that apply to norm al strength concrete ma y well not applyto high strength concrete, which is a distinctly different material . Nonethe-less, we now know enough about high strength concrete to be able toprod uce it consistently , not only in the labo ratory , b ut also in the field. It isto be hoped that codes of practice and testing standard s catch up w ith thehigh strength concrete technology, so that the use of this exciting newmaterial can continue to increase.

Specimen size100x 200 mm150x 300 mm

Failure loadfc ' = 100 MPa0.785 MN1.76 MN

Note: IMN = 225,000 lbf

fc' = 150 MPa1.18 MN2.65 MN

Machine capacityfc' = 100 MPa1.2MN2.65 MN

fc' = 150 MPa1.75 MN4.0 M N


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AcknowledgementsThis work was supported by the Canadian N etwork of Centres of Excell-ence on High -Performance C oncrete.References

1 SHRP-C/FR-91-103 (1991) High performan ce con cretes, a state of the artreport. Strategic Highw ay Research Program , National Research Coun cil,Washington, DC.2 FIP/CEB (1990) High strength concrete, state of the art report. Bullet ind' Information No. 197.3 ACI Standard 211.1 (1989) Recommended pract ice for selecting proportions fornormal weight conc rete. American Concrete Inst i tute , Detroi t .4 Mindess , S. and Young , J.F. (1981) Concrete. Prentice Hall Inc. , EnglewoodCliffs.5 Perenchio, W.F. (1973) An evaluation of some of the factors involved inproducing very high-strength concrete. Research and Development Bulletin,No. RD014-01T, Portland Cement Association, Skokie.6 Mehta, P. K. and Aitcin, P.-C. (1990) Microstructural basis of selection ofmaterials and mix proportions for high-strength concrete, in Second Interna-tional Symposium on High-Strength Concrete, SP-121. American ConcreteInstitute, Detroit , 265-86.7 Aitcin, P.-C. (1992) private communication8 Ronneburg , H. and Sandvik , M. (1990) High Strength Concrete for Nor th SeaPlatforms, Concrete International, 12, 1, 29-349 CSA Standard A23.5-M86 (1986) Supplementary cementing materials. Cana-dian Standards Association, Rexdale, Ontario.10 ASTM C618 Standard specification for fly ash and raw or calcined naturalpozzolanfor use as a mineral adm ixture in portland cem ent con crete. AmericanSociety for Testing and Materials, Philadelphia, PA.11 ASTM C989 Standard specification for ground iron blast-furnace slag for use inconcrete and mortars. American Society for Testing and Materials, Phila-de lphia , PA.12 Malhot ra , V.M. (ed) (1987) Supplementary cementing materials for concrete.Minister of Supply and Services, Canada.13 Aitcin, P.-C., Sarkar , S.L., Ranc , R. and Levy , C. (1991) A High SilicaModulus Cement for High-Performance Concrete, in S. Mindess (ed.),Advances in cementitious materials. Ceramic Transactions 16, The AmericanCeramic Society Inc., 102-21.14 Malhotra, V.M., Ramachandran, V.S. , Feldman, R.F. and Aitcin, P.-C.(1987) Cond ensed sil ica fume in concrete. CRC Press Inc. , Boca Ratan,Florida.15 Cook, I.E. (1989) 10,000 psi Concrete. Concrete International, 11, 10, 67-75.16 Peterm a n , M.B. and Carrasquillo, R.L. (1986) Product ion of high strengthconcrete. Noyes Publications, Park Ridge.17 Randal l , V .R. and Foot, K . B . (1989) High strength concrete for Pacific FirstCenter . Concrete International: Design and Construction, 11, 4, 14-16.18 Aitcin, P.-C., Shirlaw, M. and Fines, E. (1992) High performance concrete:removing the myths, in Concrescere, New sletter of the H igh-Performan ceConcrete Network of Centres of Excellence (Canada), 6, March.19 B u r g , R.G. and Ost , B.W. (1992) Engineering properties of commerciallyavailable high-strength concretes. Research and Development Bullet inRD104T, Portland Cement Association, Skokie.


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20 Aitcin, P.-C. and Mehta, P.K. (1990) Effect of coarse aggregate type ormechanical properties of high strength concrete. A C I Materials Journal,American Concrete Institute, Detroit, 87, 2, 103-107.21 ACI Committee 363 (1984) State-of-the-art report on high strength concrete(ACI 363R-84). American Concrete Institute, Detroit.22 Addis, B.H. (1992) Properties of High Strength Concrete Made with SouthAfrican Materials, Ph.D. Thesis, University of the Witwaters rand, Johannes-burg, South Africa.23 Addis, BJ. and Alexander, M.G. (1990) A method of proportioning trialmixes fo r high-strength concrete, in ACI Sp-121, High strength concrete,Second International Symposium, American Concrete Institute, Detroit, 287-308.24 Canadian Portland Cement Association (1991) Design and control of concrete.Edition CPCA, Ottawa.25 Fiorato, A.E. (1989) PCA research on high-strength concrete. ConcreteInternational, 11, 4, 4450.26 Hattori, K. (1979) Experiences with mighty superplasticizer in Japan, in ACISP-62, Superplasticizers in concrete, American Concrete Institute, Detroit,37-66.27 Suzuki, T. (1987) Experimental studies on high-strength superplasticizedconcrete, in Utilization of high strength concrete, Symposium proceedings.Stavanger, Norway: Tapis Publishers, Trondheim, 53-4.28 Carrasquillo, R.C., Nilson, A.H. and Slate, P.O. (1981) Properties of highstrength concrete subject to short-term loads. Journal of American ConcreteInstitute, 78, 3, 171-8.29 Carrasquillo, P.M. and Carrasquillo, R.L. (1988). Evaluation of the use ofcurrent concrete practice in the production of high-strength concrete. ACIMaterials Journal, 85, 1, 49-54.30 Moreno, J. (1990) 225 W. Wacker Drive. Concrete International, 12, 1, 35-9.31 Hester, W.T. (1980) Field testing high-strength concretes: a critical review ofthe state-of-the-art. Concrete International, 2, 12, 27-38.32 Howard, N.L. and Leatham, D.M. (1989) The production and delivery ofhigh-strength concrete. Concrete International, 11, 4, 26-30.33 Aitcin, P.-C. (1989) Les essais sue les betons a tres hautes performances, inAnnales d e L'Institut Technique d u Batiment et des Travaux Publics, No. 473.Mars-Avri l . Serie: Beton 263, 167-9.34 Carrasquillo, R.L., Slate, P.O. and Nilson, A.H. (1981) Microcracking andbehaviour of high strength concrete subjected to short term loading. AmericanConcrete Institute Journal, 78, 3, 179-86.35 Richardson, D.N. (1990) Effects of testing variables on the comparison ofneoprene pad and sulfur mortar-capped concrete test cylinders. A C I MaterialJournal, 87, 5, 489-95.36 Carrasquillo, P.M. and Carrasquillo, R.L. (1988) Effect of using unbondedcapping systems on the compressive strength of concrete cylinders. A C IMaterials Journal, 85, 3, 141-7.

37 Boulay, C. (1989) La boite a sable, pour bien ecraser les betons a hautesperformances. Bulletin d e Liaison d es Laboratoires d es Ponts et Chausses,Nov/Dec.38 Boulay, C,, Belloc, A., Torrenti, J.M. and De Larrard, F. (1989) Mise aupoint d'un nouveau mode operatoire d'essai d e compression pour le s betons ahaute performances. Internal report, Laboratoire Central des Ponts et Chaus-sees, Paris, December.39 CTL Review (1992) Construction Technology Laboratories, Inc., Skokie,

materiel for high performance concrete

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