HIGH PERFORMANCECONCRETES ANDAPPLICATIONSEdited byS
PShahWalterPMurphyProfessorofCivil
Engineering,andDirectorofNSFCenter
forScienceandTechnologyofAdvancedCementBasedMaterialsNorthWesternUniversity,Evanston,IL,USAS
H AhmadProfessorofCivilEngineeringNorthCarolina
StateUniversityRaleigh, NC,USAEdward ArnoldA member of theHodder
Headline GroupLONDONMELB OU RNEAU CK LAND1994 P Shah and S H
AhmadFirstpublished in GreatB r itain 1994British
LibraryCataloguing in Publication DataHigh Perf ormance
ConcretesandApplicationsI. Shah, Surendra P.II. Ahmad, S. H.691ISB
N 0-340-58922-1All rights reserved.No part of this publication may
be reproducedortransmitted in any f or m or by any means,
electronically ormechanically, including photocopying, recording or
any inf or mationstorage or retrieval system, without either prior
permission in wr itingf r omthe publisher or a licencepermitting
restricted copying. In theU nited K ingdom such licencesare
issuedby the CopyrightLicensingAgency: 90 TottenhamCourtRoad,
LondonWlP9HETypeset in 10/12 Times by Wearset, B oldon, Tyne
andWear.Pr inted in Great B r itain f or Edward Arnol d, a division
ofHodderHeadline PLC, Mill Road, DuntonGreen, Sevenoaks, K entTN13
2YA by St Edmundsbur y Press Ltd, B ur y St Edmunds,Suf f ol k,and
bound by Hartnolls Ltd, B odmin, Cornwall.PrefaceHighper f or
manceconcretes(HPC)representsar
atherrecentdevelop-mentinconcretematerialstechnology.HPCisnotacommoditybutarange
of products, eachspecificallydesignedtosatisf yin themostef f
ectiveway theperf ormancerequirementsf or
theintendedapplication.Concretehaslargenumberof propertiesorattr
ibutes.These attr
ibutescanbegroupedintothreegeneralcategories:(1)attr
ibuteswhichbenef
ittheconstructionprocess;(2)enhancedmechanicalproperties;(3)en-hancednon-mechanicalpropertiessuchasdur
abil ityetc.Forhardenedconcrete,strengthand dur abil ity are thetwo
mostimpor tantattributes.Inthelastthreeorf o u
ryears,severalnational-scaleresearchprogramshavebeenestablishedtostudyvariousaspectsofhighperf
ormanceconcretes.TheseincludethetwointheU
S:CenterforScienceandTechnologyf orAdvancedCement-B
asedMaterials(ACB
M),StrategicHighwayResearchProgram(SHRP);TheCanadianNetwor
kofCentersofExcellence(NCE)ProgramonHighPerf ormanceConcrete;
theRoyalNorwegianCouncilf
orScientificandIndustrialResearchProgram;theSwedishNationalProgramonHPC;theFrenchNational
Programcalled'New Ways f or Concrete' and the JapaneseNew
ConcreteProgram. As theresultsf
romtheseprogramsstarttobedisseminatedanddigestedintheconcreteindustr
y,theconcretetechnologywillexperienceasignif
icantadvancement.Historically, moreattention has beengiven to the
strength attr ibute andconcreteperf
ormancehasbeenspecifiedandevaluatedintermsofcompressivestrength the
higher the compressive strength, the bettertheexpectedperf
ormance.However,experiencehasshownthatdur abil
ityconsiderationsbecomemoreimpor tantf
orstructuresexposedtohostileenvironments(e.g.marinestructuresandsanitarystructures)andf
orstructuressuchasbridgesandpavementswhicharedesignedf
orlongerservicel if e.TheSHRPprogramonHighPerf
ormanceConcretehasdef inedHPCf orhighwayapplicationsintermsofstr
ength anddur abil ityattr
ibutesandwater-cementiousmaterialsratio.HPCisdef
inedascon-cretethatmeetsthef ol l owingcriteria:It shall have one
of the f ollowingstrength characteristics:4-hour strength^25OO
psi(17.5MPa)24-hour strength^50OO psi(35 MPa)28-day str
ength^10,0OO psi(70 MPa)It shall havea durabil ity f actor>80%af
ter300 cycles of f reezingandthawingIt shall have a
water-cementitious materialsratio^0.35Dur
ingthelastdecade,developmentsinmineralandchemical
admix-tureshavemadeitpossibletoproduceconcreteswithrelativelymuchhigherstrengthsthanwasthoughtpossible.Presentlyconcreteswithstrengthsof14,000to16,000
psi(98 to112 MPa)arebeing
commerciallyproducedandusedintheconstructionindustr y inU
SA.OthercountriessuchasEngl and,Canada,Norway,Sweden,France,Ital
y,Japan,HongK ongandSouthK
oreaareaggressivelyemployingthehighstrengthconcretetechnology in
their
constructionpractice.Theaimofthisbookistosummarizethedevelopmentsofthelastdecade
in theareaof materialsdevelopmentfor producing higher
strengthconcrete,productionmethods,mechanicalpropertieseval
uation,nonmechanicalpropertiessuchasdur abil ity,
andtheimplicationofmaterialpropertiesonthestructuraldesignandperf
ormance.Theuseofhigherstrengthconcretesintheconstructionindustr
yhassteadilyincreaseddur ingthelastdecade,andtheref oretwo
chaptershavebeendevotedtosummarizetheapplicationsofhigherstrengthconcretes.Expertsf
r omU SA,Canada,France,Nor
way,SpainandJapanhavecontributedindi-vidual chaptersso as to give
thebooka broadperspectiveof the prevailingstate-of -the-artin dif f
er entparts of the world. Thebookis intended fortheacademics,
engineers,consultants,
contractorsandresearchers.Theelevenchaptersin thebookarearrangedso
thatthereadercan beselective. Chapter1 providesthe background for
the selectionof materialsand proportions.This chapteralso
providesinf ormation on qual ity controlaspectsf or concreteswith
higher
strengths.Chapter2addressestheshorttermmechanicalpropertiessuchascompressivestr
ength,modul us of elasticity,
tensilestrengthetc.Thelongtermmechanicalpropertiessuchascreep,shrinkageandtemper
atur eef f ectsarediscussedinChapter3.Chapter4 providestheinf or
mation onthe bond and f atiguecharacteristics. The impor tant
aspectof the dur abil ityanditsimplicationf ortheperf
ormanceofconcretearediscussedinChapter s.Thef r actur e
mechanicsapproachtotheunder standing of the str uctur alresponseis
outlined in Chapter 6. Thebehavior of thestr uctur al
memberssuchasbeam,columnsandslabsisdetailedinChapter
?.Theductilityissues of thestr uctur al members andthestr uctur al
ductil ity is presentedinChapter 8.Chapter9 addressesstr uctur al
designconsiderationsandthestr uctur alapplications withspecial
emphasis on high-rise buil dings andbridges.Thischapter also
summarizes the special construction considerations neededf
ortheseconcretes.Chapter10isdedicatedtohighstr
engthlightweightaggregate concreteandits applications.Thelast
chapteris devotedtotheapplications of HPCin JapanandSouth
EastAsia.List of ContributorsP AckerHead,Division: 'B etons et
Ciments pour Ouvrages d'Ar t',LaboratoireCentral des Fonts et
Chaussees,Paris,FranceS HAhmadProfessor, Departmentof Civil
Engineering, North Carolina StateU niversity, Raleigh, NC, U SAP
NBalaguruProfessor, Civil Engineering Department,Rutgers U
niversity, Piscataway,N J, U S ATW BremnerProfessor of Civil
Engineering, U niversity of New B runswick,
Fredericton,CanadaFdeLarrardSenior Scientist, Division: 'B etons et
Ciments pour Ouvrages d'Ar t',LaboratoireCentral des Fonts et
Chaussees,Paris,FranceAS EzeldinAssistant Professor,Departmentof
Civil, Environmental andCoastalEngineering, Stevens Institute of
Technology, Hoboken,NJ,U SARGettuSenior Researcher,Technical U
niversity of Catal unya, B arcelona, SpainS K GhoshDirector,
Engineered Structures and Codes, Portland CementAssociation,
Skokie, IL, U SAOEGj0rvProfessor, Division of B uilding Materials,
Norwegian Institute ofTechnology - NTH, Trondheim - NTH,
NorwayTAHolmVice Presidentof Engineering, Solite Corporation,PO B
ox 27211,Richmond, VA, U SAR Le RoyResearchEngineer,Division: 'B
etons et Ciments pour Ouvrages d'Art',LaboratoireCentral des Ponts
et Chaussees,Paris,FranceSMindessProfessor,Departmentof Civil
Engineering, U niversity of B ritishColumbia, Vancouver,
CanadaSNagatakiProfessor of Civil Engineering, Tokyo Institute of
Technology,O-okayama, Meguru-ku, Tokyo152,JapanA H
Nilson(Professor)162 Round Pound Road, HC-60, B ox 162, Medomak,
Maine, U SA(f ormerly of Cornell U niversity)HG RussellVice
President, ConstructionTechnology LaboratoriesInc., 5420
OldOrchardRoad,Skokie, IL, U SAMSaatciogluAssociateProfessorof
Civil Engineering, U niversity of Ottawa, CanadaE SakaiManager,
Special Cement Additives Division, Denki K agaku K ogyo Co.Ltd,
Yuraku-cho, Chiyoda-ku, Tokyo100,JapanSP ShahWalter P Murphy
Professor of Civil Engineering; Director,NSF Center forScience and
Technology of Advanced Cement-B asedMaterials;
andDirector,Centerfor Concrete and Geomaterials,NorthwesternU
niversity, Evanston, IL, U SAThis page has been reformatted by
Knovel to provide easier navigation. v Contents Preface
....................................................................................
ix List of contributors
...................................................................
xi 1.Materials Selection, Proportioning and Quality Control
.............................................................................
1
1.1Introduction.........................................................................
1 1.2Selection of Materials
......................................................... 2 1.3Mix
Proportions for High Strength Concrete....................... 13
1.4Quality Control and
Testing................................................ 17
1.5Conclusions........................................................................
23 References
..................................................................................
24 2.Short Term Mechanical Properties
................................ 27
2.1Introduction.........................................................................
27
2.2Strength..............................................................................
28
2.3Deformation........................................................................
50 2.4Strain Capacity
...................................................................
55 2.5Poisson's
Ratio...................................................................
59 References
..................................................................................
60 3.Shrinkage Creep and Thermal Properties..................... 65
3.1Introduction.........................................................................
65 3.2Shrinkage
...........................................................................
66 3.3Creep
.................................................................................
80 3.4Drying Shrinkage and Drying Creep
.................................. 86 3.5Thermal
Properties.............................................................
97 3.6Structural Effects: Case
Studies......................................... 102 This page has
been reformatted by Knovel to provide easier navigation.vi Contents
3.7Summary and Conclusions
................................................ 108 References
..................................................................................
110 4.Fatigue and Bond Properties
......................................... 115
4.1Introduction.........................................................................
115 4.2Mechanism of
Fatigue........................................................ 120
4.3Cyclic Compression
........................................................... 121
4.4Cyclic Tension
....................................................................
124 4.5Reversed Loading
.............................................................. 126
4.6Effect of Loading
Rate........................................................ 127
4.7Effect of Stress Gradient
.................................................... 127 4.8Effect
of Rest
Periods.........................................................
127 4.9Effect of Loading Waveform
............................................... 128 4.10Effect of
Minimum Stress: Comparison of Normal and High Strength
Concrete...................................................... 128
4.11Effect of Concrete Mixture Properties and Curing..............
128 4.12Biaxial State
.......................................................................
129 4.13Bond Properties
.................................................................
130
4.14Summary............................................................................
134 References
..................................................................................
135 5.Durability
.........................................................................
139
5.1Introduction.........................................................................
139 5.2Permeability
.......................................................................
139 5.3Corrosion Resistance
......................................................... 143
5.4Frost Resistance
................................................................
148 5.5Chemical Resistance
......................................................... 149
5.6Fire Resistance
..................................................................
150 5.7Abrasion-Erosion Resistance
............................................. 153 5.8Concluding
Remarks..........................................................
156 References
..................................................................................
156 This page has been reformatted by Knovel to provide easier
navigation.Contents vii 6.Fracture Mechanics
........................................................ 161
6.1Introduction.........................................................................
161 6.2Linear Elastic Fracture Mechanics
..................................... 162 6.3The Fracture Process
Zone ............................................... 166 6.4Notch
Sensitivity and Size Effects......................................
169 6.5Fracture Energy from Work-of-Fracture
............................. 172 6.6Nonlinear Fracture Mechanics
of Concrete........................ 175 6.7Material
Characterization
................................................... 187 6.8Other
Aspects of Fracture in Concrete............................... 194
6.9Applications
........................................................................
196 References
..................................................................................
200 7.Structural Members
........................................................ 213
7.1Introduction.........................................................................
213 7.2Axially Loaded
Columns..................................................... 214
7.3Flexure in Beams
............................................................... 219
7.4Beam Deflections
............................................................... 222
7.5Shear in
Beams..................................................................
224 7.6Bond and Anchorage
......................................................... 227
7.7Flexural and Shear
Cracking.............................................. 228
7.8Prestressed Concrete Beams
............................................ 229 7.9Slabs
..................................................................................
229 7.10Eccentrically Loaded
Columns........................................... 230 7.11Summary
and Conclusions ................................................
233 References
..................................................................................
233 8.Ductility and Seismic
Behaviour.................................... 237
8.1Introduction.........................................................................
237 8.2Deformability of High-Strength Concrete Beams
............... 239 8.3Deformability of High-Strength Concrete
Columns ............ 274 This page has been reformatted by Knovel
to provide easier navigation.viii Contents 8.4Deformability of
High-Strength Concrete Beam-Column Joints
....................................................................
290 8.5Application of High-Strength Concrete in Regions of High
Seismicity...................................................................
306
8.6Summary............................................................................
310 References
..................................................................................
310 9.Structural Design Considerations and
Applications.....................................................................
313
9.1Introduction.........................................................................
313 9.2Structural Design
Considerations....................................... 314
9.3Construction Considerations
.............................................. 317 9.4Quality
Control....................................................................
320 9.5High Rise Buildings
............................................................ 322
9.6Bridges
...............................................................................
334 9.7Special Applications
........................................................... 337
References
..................................................................................
338 10.High Strength Lightweight Aggregate Concrete .......... 341
10.1Introduction.........................................................................
341 10.2Materials for High Strength Lightweight Aggregate
Concrete.............................................................................
349 10.3High Strength Lightweight Concrete Laboratory Testing
Programs...............................................................
351 10.4Physical Properties of High Strength Lightweight Aggregate
Concrete
........................................................... 352
10.5Constructability of High Strength Lightweight Aggregate
Concretes .........................................................
363 10.6Applications of High Strength Lightweight Aggregate
Concrete.............................................................................
366 References
..................................................................................
371 This page has been reformatted by Knovel to provide easier
navigation.Contents ix 11.Applications in Japan and South East
Asia.................. 375
11.1Introduction.........................................................................
375 11.2Methods of Strength
Development..................................... 376
11.3Applications
........................................................................
379 11.4Summary and Conclusions
................................................ 393 References
..................................................................................
396 Index
.......................................................................................
399 1Materials selection,proportioningand
qualitycontrolSMindess1.1IntroductionHighperformanceconcretes(HPC)areconcreteswithpropertiesorattributes
which satisfytheperformancecriteria.Generally concretes
withhigherstrengthsandattributessuperiortoconventionalconcretesaredesirablein
theconstruction industry. Forthe purposesof this book,HPCis
definedin terms of strengthanddurability.
TheresearchersofStrategicHighway ResearchProgram SHRP-C-205 on High
Performance Concrete1definedthe high performance concretesfor
pavement applications in termsofstrength,durability attributes
andwater-cementitious materials ratioasfollows:It shall have one of
the following strength characteristics:4-hour
compressivestrength^25OO psi (17.5MPa) termedas veryearly
strengthconcrete(VES), or24-hourcompressivestrength^50OO psi(35
MPa)termedas highearly strengthconcrete(HES), or28-day
compressivestrength^10,0OO psi (70 MPa)termedas
veryhighstrengthconcrete(VHS).Itshallhaveadurability
factorgreaterthan80%after300 cycles offreezingand thawing.It shall
have a water-cementitious materials ratio=$0.35.Highstrength
concrete(HSC)couldbeconsideredas high
performanceifotherattributesaresatisfactoryintermsofitsintendedapplication.Generallyconcreteswithhigherstrengthsexhibitsuperiorityofotherattributes.InNorthAmericanpractice,highstrengthconcreteisusuallyconsideredtobea
concretewitha 28-daycompressivestrength of atleast6000
psi(42MPa).InarecentCEB-FIPState-of-the-ArtReportonHighStrengthConcrete2itisdefinedasconcretehavingaminimum28-daycompressivestrengthof8700
psi(6OMPa).Clearlythen,thedefinitionof'high strength concrete' is
relative; it dependsupon boththe periodof timein question,and
thelocation.Theproportioning(ormix design)of
normalstrengthconcretesis basedprimarily onthew/c ratio'law' first
proposedby Abramsin1918.Atleastforconcreteswithstrengthsupto6000
psi(42MPa),itisimplicitlyassumedthatalmostanynormal-weightaggregateswillbestrongerthanthehardenedcementpaste.Thereisthusnoexplicitconsiderationofaggregatestrength(orelasticmodulus)inthecommonlyusedmix
designprocedures,suchas those proposedby
theAmericanConcreteInstitute.3Similarly,theinterfacialregions(orthecement-aggregatebond)arealsonotexplicitlyaddressed.Rather,itisassumedthatthestrengthofthehardenedcementpastewillbethelimiting
factorcontrolling
theconcretestrength.Forhighstrengthconcretes,however,allofthecomponentsoftheconcretemixture
are pushedto their critical limits. High
strengthconcretesmaybemodelledasthree-phasecompositematerials,thethreephasesbeing(i)
thehardenedcementpaste(hep);(ii)
theaggregate;and(iii)theinterfacialzonebetweenthehardenedcementpasteandtheaggregate.These
threephasesmustall beoptimized,which
meansthateachmustbeconsideredexplicitly in thedesign process. In
addition, as has beenpointedoutby Mindessand
Young,4'itisnecessarytopaycarefulattentiontoallaspectsofconcreteproduction(i.e.selectionofmaterials,mixdesign,handlingandplacing).Itcannotbeemphasizedtoostrongly
thatquality
controlisanessentialpartoftheproductionofhigh-strengthconcreteandrequiresfullcooperationamongthematerialsorready-mixedsup-plier,the
engineer,and the
contractor'.Inessencethen,theproportioningofhighstrengthconcretemixturesconsistsof
threeinterrelatedsteps:(1) selectionof
suitableingredients-cement,supplementarycementingmaterials,aggregates,waterandche-micaladmixtures,(2)determinationoftherelativequantitiesofthesematerials
in ordertoproduce,as economicallyas possible,a
concretethathasthedesiredrheologicalproperties,strengthanddurability,
(3)carefulquality controlof every phaseof theconcrete-making
process.1.2SelectionofmaterialsAs indicatedabove, it is necessaryto
get themaximum performance out
ofallofthematerialsinvolvedinproducinghighstrengthconcrete.Forconvenience,
the various materials are discussed separately below.Howev-er, it
must be rememberedthat prediction with any certainty as to how
theywillbehavewhen combinedinaconcretemixture is notfeasible.
Particu-larlywhenattemptingtomakehighstrengthconcrete,anymaterialincompatibilitieswillbehighly
detrimentaltothe finished product.Thus,theculmination of anymix
design process must betheextensive testing oftrial
mixes.Highstrengthconcretewillnormally containnotonly
portlandcement,aggregateand water, butalso superplasticizersand
supplementary
cement-ingmaterials.Itispossibletoachievecompressivestrengthsofupto14,000
psi (98 MPa)using fly ash or ground granulated blast furnaceslag
asthesupplementarycementingmaterial.However,toachievestrengths
inexcess of14,000 psi (100 MPa),theuseof silica
fumehasbeenfoundtobeessential,anditisfrequently
usedforconcretesinthestrengthrangeof9000-14,000 psi (63-98 MPa)as
well.Portland
cementTherearetwodifferentrequirementsthatanycementmustmeet:(i)itmustdeveloptheappropriatestrength;and(ii)itmustexhibittheappropriaterheologicalbehaviour.Highstrengthconcretes
havebeenproducedsuccessfully
usingcementsmeetingtheASTMStandardSpecificationC150forTypesI,IIandIIIportlandcements.Unfortunately,ASTMC150isveryimpreciseinitschemicalandphysicalrequirements,andsocementswhichmeettheseratherloosespecificationscanvaryquitewidelyintheirfinenessandchemical
composition.Consequently,cementsof nominally
thesametypewillhavequitedifferentrheologicalandstrengthcharacteristics,particu-larlywhenusedincombinationwithchemicaladmixturesandsup-plementarycementingmaterials.Therefore,whenchoosingportlandce-mentsforusein
high strengthconcrete,itis necessarytolookcarefullyatthecement
fineness and
chemistry.FinenessIncreasingthefinenessoftheportlandcementwill,ontheonehand,increase
theearly strength of theconcrete,sincethehighersurfacearea
incontactwith water will leadto a morerapid hydration. Ontheother
hand,toohighafinenessmayleadtorheologicalproblems,asthegreateramountofreactionatearlyages,inparticulartheformation
ofettringite,will leadto a higher rate of slump loss. Early work by
Perenchio5 indicatedthat fine cementsproducedhigherearlyage
concretestrengths,thoughatlateragesdifferencesinfinenesswerenotsignificant.MostcementsnowusedtoproducehighstrengthconcretehaveElaine
finenesses thatare intherangeof1467to1957ft2/lb(300to400
m2/kg),though when
TypeIII(highearlystrength)cementsareused,thefinenessesareintherange
of2201 ft2/lb(450 m2/kg).Chemical composition of the cementThe
previously citedwork of Perenchio5 indicates thatcements with
higherC3Acontentsleadstohigherstrengths.However,subsequentwork6hasshownthathighC3Acontentsgenerallyleadstorapidlossof
flow
inthefreshconcrete,andasaresulthighC3Acontentsshouldbeavoidedincementsusedforhighstrengthconcrete.Aitcin7hasshownthattheC3Ashouldbeprimarilyinitscubic,ratherthanitsorthorhombic,form.Further,Aitcin7suggeststhatattentionmust
be paidnotonly tothetotalamountofSO3
inthecement,butalsototheamountofsolublesulfates.Thus, thedegreeof
sulfurization of theclinker is
animportantparameter.InadditiontocommerciallyavailablecementsconformingtoASTMTypesI,
IIand III, a number of cementshave been formulated
specificallyforhighstrengthconcrete.Forinstance,in Norway,
NorcemCementhasdevelopedtwospecialcementsforhighstrengthconcrete,inadditiontotheirordinaryportlandcement.ThecharacteristicsofthesecementsaregiveninTable1.1.sNotethatforthetwospecialcements(SP30-4AandSP30-4AMOD),theC3A
contentswereheldto 5.5%.Table 1.1Composition of special cements for
high strength concrete (developedby Norcem Cement8)* Ordinary
portland cement, for comparisonIm2/kg=4.89ft2/lbSupplementary
cementing
materialsAsindicatedabove,mostmodernhighstrengthconcretescontainatleastone
supplementary cementing material: fly ash, blast-furnace slag, or
silicafume.Very often, the fly ash or slag is usedin
conjunctionwith silica fume.These materials areall specified in
theCanadianCSA Standard A23.5.9 IntheUnitedStates,flyashis
specified inASTMC618,10andblast
furnaceslaginASTMC98911;thereis,asyet,noU.S.standardforsilicafume.ThesematerialsaredescribedindetailinSupplementaryCementingMaterials
forConcrete.12Usingasomewhatdifferentapproach,ahighsilicamodulusportlandC2S
(%)C3S (%)C3A (%)C4AF (%)MgO (%)S03(%)Na2O equivalent (%)Elaine
fineness (m2/kg)heat of hydration (kcal/kg)setting time (min):
initialfinalSP30*18558933.31.130071120180SP30-4A28505.591.5-2.02-30.631056140200SP30-4AMOD28505.591.5-2.02-30.640070120170Table
1.2Bogue compositionandotherpropertiesofHTScement(afterAitcin et
al.13)cement(referredtoasHTS,orHauteTeneurenSilica,orhighsilicacontent)was
developed,13 with thecompositionshown in
Table1.2.Notethat,comparedtomoreconventionalcements(suchastheSP-30ofTable1.1),thereisaveryhightotalsilicatecontent(84%),andC3Acontentofonly3.6%.Thecementisrathercoarselyground(Elainefinenessof1565ft2/lb(320
m2/kg)).Itis madefroma clinker
composedofsmallaliteandbelitecrystals,andminuteC3Acrystals.Itiscapableofproducingconcreteswithexcellent28-daycompressivestrengths,as
indi-catedin Table1.3,when usedin conjunction with 10%
silicafume.Table 1.328 day compressive strengths of concretemade
with HTS cementand10% silicafume13Silica
fumeItispossibletomakehighstrengthconcretewithoutsilicafume,atcompressivestrengthsofuptoabout14,000psi(98MPa).Beyondthatstrengthlevel,however,silicafumebecomesessential,andevenatlowerstrengths
9000-14,000 psi (63-98 MPa), it is easier to make HSC with
silicafumethanwithoutit.Thus,whenitisavailableatareasonableprice,itshould
generally bea componentof theHSC
mix.Silicafume14isawasteby-productoftheproductionofsiliconandsilicon
alloys, and is thus nota very well-definedmaterial.Consequently,
itis importanttocharacterizeanynewsourceof silica fume,by
determiningthespecific surfaceareaby
nitrogenadsorption,andthesilica,alkali
andcarboncontents.Inaddition,itisdesirabletominimizethecontentofC2S(%)C3S
(%)C3A (%)C4AF(%)Na2O equivalent (%)lime saturation factorsilica
modulusElaine fineness, m2/kgIm2/kg
=4.89ft2/lb22623.66.90.3892.74.8320vv/c0.310.230.200.171 ksi =6.89
MPalMPa = 0.145ksif
c(MPd)74106115124Table1.4SomeCanadianspecifications
forsilicafume(taken fromCSAStandard
A23.59)crystallinematerial.Theacceptancelimitsforsilicafume,takenfromCSA-A23.59
aregiven in Table1.4.Silicafumeis available in severalforms.Inits
bulk form, its unit weightis in therangeof118 to147.5 pcf(200-250
kg/m3), which makes handlingdifficult.Morecommonly now,silicafumeis
available
inadensifiedform,inwhichthebulkdensitiesareabouttwiceasgreatasthoseofthebulkform(i.e.400-500kg/m3).Ingeneral,thismakesiteasiertohandle.Inaddition,silicafumeis
availableinslurry form(ofteninconjunction
withsuperplasticizersintheliquid phase),with
asolidscontentofabout50%.Thisformofsilicafumerequiresspecialequipmentforitsuse.Finally,silicafumeisavailablealreadyblendedwith
portlandcement(atpercen-tages of thetotal mass of cementitious
material in therange of 6.7
to9.3%)inCanada,FranceandIceland.Inspiteofthisapparentlywideselection,however,
in any onelocationthechoiceof silica fumeswill be very
limited,andonemust use whatis locally available.Fly
ashFlyashhas,ofcourse,beenusedveryextensivelyinconcreteformanyyears.Flyashesare,unfortunately,
muchmorevariablethansilicafumesin both their physical and chemical
characteristics. Any fly ash which
workswellinordinaryconcretemixesislikelytoworkwellinhighstrengthconcreteaswell.However,mostflyasheswillresultinstrengthsofnotmuch
more than10,000 psi (70 MPa), though there have beena few
reportsofhighstrengthconcreteswithstrengthsofupto14,000
psi(98MPa)inwhich fly ash has beenused.Forhigher strengths,silica
fumemust beusedin conjunction with the fly ash,thoughthis
practicehas notbeencommonin thepast.Chemical requirementsSi 02, mi
n(%)SO3, max(%)Loss in ignition, max (%)Physical
requirementsAcceleratedpozzolanic activity index, min, (%) of
controlFineness, max, (%) retainedon 45 jxm sieveSoundness
-autoclave expansion or contraction (%)Relative density, max
variation fromaverage(%)Fineness, max variation
fromaverage(%)Optional physical requirementsIncreaseof drying
shrinkage, max (%) of controlReactivity with cementalkalis: min
reduction(%)851.06.085100.2550.0380Ingeneral,forhighstrengthconcreteapplications,flyashisusedatdosageratesofabout15%ofthecementcontent.Becauseofthevariabilityoftheflyashproducedevenfromasingleplant,however,qualitycontrolisparticularlyimportant.Thisinvolvesdeterminations
oftheElainespecific
surfacearea,aswellasthechemicalcomposition(inparticularthecontentsofSiO2,Al2O3,Fe2O3,CaO,alkali,carbonandsulfates).And,aswith
silicafume,itis importanttocheckthedegreeofcrystallinity;
themoreglassy the fly ash, thebetter.Blast furnace
slagInNorthAmerica,slag is notas widely available as in
Europe,andhencethereisnotmuchinformationavailableastoitsperformanceinhighstrengthconcrete.However,theindications
arethat,as with fly ash,slagsthat performwell in ordinary
concretearesuitable for use in high
strengthconcrete,atdosageratesbetween15%
and30%.Thelowerdosageratesshould be used in the winter, so that
theconcretedevelopsstrength
rapidlyenoughforefficientformremoval.Forveryhighstrengths,inexcessof14,000psi(98
MPa),itwill likelybenecessarytousetheslag in conjunc-tion with
silicafume.Thechemicalcompositionofslagsdoesnotgenerally vary very
much.Therefore,routinequalitycontrolis generallyconfined toElaine
specificsurfaceareatests,andX-raydiffractionstudiestocheckonthedegreeofcrystallinity(which
shouldbelow).Limitation on the use of silica fume, fly ash or
slagThereappeartobenoparticulardeleteriouseffectswhensilicafumeisusedinconcrete.However,theuseof
fly ashandslag
mayleadtosomeproblems:(i)TheearlystrengthdevelopmentofmixesinwhichsomeofthePortland
cement has beenreplacedby slag or fly ash is less rapid
thanthatwhenonlyportlandcementisused,andthismayadverselyaffectthetime
at which theforms can be stripped,particularly at
lowtemperatures.Onewayofdealingwiththisproblemisbyfurtherreductionsin
the w/c ratio, through theuse of even
moresuperplasti-cizer.Clearly,thisisnoteconomicallyveryattractive;ifhighearlystrengthis
needed,it may well benecessarytoreducethe fly
ashorslagcontent.(ii)Theexistingtestdataareratherambiguouswithregardtothefree-thawdurabilityofhighstrengthconcretemadewithsup-plementarycementitiousmaterials.Thisistruebothforair-entrainedandnon-air-entrainedmixes.Therefore,until
moredataareavailable,designersshouldbe cautious when using high
strengthconcrete in an environment in which the concretewill be
subjected tomany freeze-thaw cycles in a
saturatedstate.(iii)Atthesubstitutionlevelsused(15-30%),flyashorslagwillhaveverylittleeffectonthemaximumtemperature
developmentinmassconcretepours.SuperplasticizersInmodernconcretepractice,itisessentiallyimpossibletomakehighstrengthconcreteatadequateworkabilityinthefieldwithouttheuse
ofSuperplasticizers.Unfortunately,differentSuperplasticizerswillbehavequitedifferentlywithdifferentcements(evencementsofnominallythesame
type). This is due in part to the variability in the minor
components ofthecement(which arenotgenerally specified), andin
parttothefactthattheacceptancestandardsforSuperplasticizersthemselvesarenotverytightlywritten.Thus,somecementswillsimply
befound tobeincompati-ble with certain
Superplasticizers.Thereare,basically,threeprincipaltypesofsuperplasticizer:(i)ligno-sulfonate-based\(ii)polycondensateofformaldehydeandmelaminesul-fonate(oftenreferredtosimplyas
melaminesulfonate;and(iii)polycon-densateof
formaldehydeandnaphthalenesulfonate,(oftenreferredtoasnaphthalenesulfonate).Inaddition,avarietyofothermoleculesmightbemixedinwiththesebasicformulations.ItmaythusbeverydifficulttodeterminetheprecisechemicalcompositionofmostSuperplasticizers;certainlymanufacturerstrytokeep
theirformulations as
closelyguardedsecrets.ItshouldbenotedthatmuchofwhatweknowaboutSuperplasticizerscomes
fromtests carriedout on normal strength concretes, at relatively
lowsuperplasticizercontents.Thisdoesnotnecessarilyreflecttheirperform-anceat
very low w/c ratiosandvery high
superplasticizeradditionrates.Lignosulfonate-based
SuperplasticizersInhighstrengthconcrete,lignosulfonateSuperplasticizersaregenerallyused
in conjunction with eithermelamine or
naphthaleneSuperplasticizers.Theytendnottobeefficientenoughfortheeconomicproductionof
veryhighstrengthconcreteson theirown.Sometimes,lignosulfonates
areusedforinitialslumpcontrol,withthemelaminesornaphthalenesusedsubsequently
forslump controlin thefield.Melamine sulfonate
SuperplasticizersUntilrecently,onlyonemelaminesuperplastizerwasavailable(trade-nameMelment),butnowothermelamine-basedSuperplasticizersarelikely
tobecomecommerciallyavailable.MelamineSuperplasticizersareclearliquids,
containing
about22%solidparticles;theyaregenerallyintheformoftheirsodiumsalt.Thesesuperplasticizers
have been used for many years now with goodresults, andso they
remain popularwith high strengthconcreteproducers.Naphthalene
sulfonate
superplasticizersNaphthelenesuperplasticizershavebeeninuselongerthananyoftheothers,
and are available under a greaternumber of brand names. They
areavailableasbothapowderandabrownliquid;intheliquidformtheytypicallyhavea
solidscontentofabout40%.Theyaregenerally
availableaseithercalciumsalts,ormorecommonly,sodiumsalts.(Calciumsaltsshould
be used in case where a potentially alkali-reactive aggregate is
tobeused.)Theparticularadvantagesofnaphthalenesuperplasticizers,apartfromtheirbeing
slightly lessexpensivethantheothertypes,appearstobe
thattheymakeiteasiertocontroltherheologicalpropertiesofhigh
strengthconcrete, becauseof theirslight
retardingaction.Superplasticizer
dosageThereisnoaprioriwayofdeterminingtherequiredSuperplasticizerdosage;itmustbedetermined,in
theend,by somesortof trialanderrorprocedure.Basically,if strengthis
theprimarycriterion,thenoneshouldwork with the lowest w/c ratio
possible, and thus the highest
Superplasticiz-erdosagerate.However,if therheologicalproperties of
thehigh strengthconcretearevery important,thenthehighest w/c
ratioconsistent with
therequiredstrengthshouldbeused,withtheSuperplasticizerdosagethenadjustedtogetthedesiredworkability.Ingeneral,ofcourse,someintermediatepositionmustbefound,so
thatthecombinationof
strengthandrheologicalpropertiescanbeoptimized.TypicalSuperplasticizerdosagesforanumberofhigh
strengthconcretemixesaregiven below, inTables1.5 to1.10.Table
1.5Mix proportions for InterfirstPlaza, Dallas
(adaptedfromCook15)water (kg/m3)cement, Type I (kg/m3)fly ash,
Class C (kg/m3)coarseaggregate (kg/m3)fine aggregate (kg/m3)water
reducer L/m3Superplasticizer L/m3w/cementitious ratiofc28-day
(MPa)- moist curedfc91-day (MPa)- moist cured1 lb/yd3 =0.59
kg/m3or1 in.=25. 4 mmor/ cm
maxsizeaggregate16636015010526831.012.540.3379.589.0lkg/m3
=1.69pcf1 in.=0.0393 mm25 cm
maxsizeaggregate14835714911836041.012.520.2985.892.4Table
1.6Highstrengthconcretemix design
guidelines(afterPetermanandCarrasquillo16)Table 1.7Mix
proportionsfor high strength concreteat Pacific
FirstCenter,Seattle(adaptedfromRandall and Foot17)Table 1.8Five
examplesof commercially producedhigh strength
concretemixdesigns(afterAitcin, Shirlaw and Fines18)water
(kg/m3)cement(kg/m3)fly ash
(kg/m3)coarseagg./fineagg.ratiosuperplasticizerw/cementitious
ratiofc'56-day(MPa)H-H-OO1955582.00.3466H-H-Ol1434742.0yes*0.3072H-H-IO1733911672.00.3169H-H-Il1343351442.0yes*0.2776*
Use highest dosageof superplasticizerwhich will notleadto
segregationorexcessiveretardation.1 lb/yd3 =0.59 kg/m3or1 kg/m3
=1.69 pcfl i n.=25. 4 mmor1 in.=0.0393 mmwater (kg/m3)cement -Type
II (kg/m3)flyash -Type F (kg/m3)silica fume(kg/m3)coarseaggregate
-1 cm max. size(kg/m3)fineaggregate - F. M.=3.2 (kg/m3)water
reducerI(LIm3)water reducerII
(L/m)w/cementitiousratiofc'56-day(MPa)1 lb/yd3 =0.59 kg/m3or1 kg/m3
=1.69 pcf1 in.=25.4 mmor1 in.=0.0393
mm131534594010696231.777.390.21124water (kg/m3)cement (kg/m3)fly
ash (kg/m3)slag (kg/m3)silica fume(kg/m3
)coarseaggregate(kg/m3)fine aggregate(kg/m3)water reducer(L/m3
)retarder(L/m3)superplasticizer(L/m3
)w/cementitiousratiofc'28-day(MPa)fc'91-day(MPa)1955056010306300.9750.3564.878.6165451103074511.250.3779.887.01355003011107004.5140.2742.5106.51453151373611307450.91.85.90.3183.493.413051343108068515.70.251191451
lb/yd3 = 0.59kg/m3or1 kg/m3 =1.69 pcf1 in.=25.4 mmor1 in.=0.0393
mmTable 1.9Highstrength mixtures in theChicagoarea(adaptedfromBurg
andOst19)Table 1.10Mix design for a high strength
concretedesignedfor a low heat ofhydration (adaptedfromBurg and
Ost)RetardersAtonetime retarderswererecommendedfor somehigh
strengthconcreteapplications,tominimize theproblemof overrapidslump
loss.However,itisdifficulttomaintainacompatibilitybetweentheretarderandthesuperplasticizer,i.e.tominimizeslumplosswithoutexcessivelyreducingearlystrengthgain.Inmodernpractice,retardersarerecommendedonlyasalastresort;therheologyisbettercontrolledbytheuseoftheappropriatesupplementarycementingmaterialsdescribedabove.AggregatesTheaggregatepropertiesthataremostimportantwithregardtohighstrength
concreteare:particleshape,particlesize
distribution,mechanicalpropertiesoftheaggregateparticles,andpossiblechemicalreactionsbetweentheaggregateandthepastewhichmayaffectthebond.Unlikewater
(kg/m3 )cement(kg/m3)fly ash (kg/m3)silica fume(kg/m3
)coarseaggregate,SSD 12 mmmax sizefine aggregate,SSD
(kg/m3)superplasticizer -Type F (L/m3)retarder - Type D
(L/m3)w/cementitious ratiofc28-day (MPa) -moistcuredfc'56-day (MPa)
-moistcuredfc91-day (MPa)
-moistcuredMixnumber1158564106864711.611.120.28178.681.486.521604755924106865911.611.040.28788.597.3100.43155487471068:67611.220.970.29191.994.296.0414456489L06859320.121.470.220118.9121.2131.8515147510474106859316.451.510.231107.0112.0119.3water(kg/m3
)cement -Type I (kg/m3 )flyash -Type F (kg/m3)silica fume(kg/m3
)coarseaggregate -25 mm max. size (kg/m3)fine aggregate (kg/m3
)superplasticizer,ASTMTypeF (L/m3)superplasticizer, ASTM TypeG
(L/m)water/cementitious ratiofc28-day (MPa)
-moistcuredfc91-day(MPa)
-moistcured14132787271217426.313.250.323.188.6their use in ordinary
concrete, where we rarely considerthestrength
oftheaggregates,inhigh strengthconcretetheaggregatesmay well
becomethestrengthlimitingfactor.Also,sinceitisnecessarytomaintainalow
w/cratiotoachievehighstrength,theaggregategrading mustbevery
tightlycontrolled.Coarse aggregateIt goes without saying that, for
high strength concrete, the coarseaggregateparticles themselves
must be strong.Anumber of differentrock types
havebeenusedtomakehighstrengthconcrete;theseincludelimestone,dolomite,
granite, andesite,diabase,and so on.It has beensuggested1
thatinmostcasestheaggregatestrengthitself is notusually thelimiting
factorinhighstrength concrete; rather,it is thestrength of
thecement-aggregatebond.Aswithordinaryconcretes,however,aggregatesthatmaybesusceptibletoalkali-aggregatereaction,ortoD-cracking,shouldbeavoidedif
atall possible,eventhoughthelow w/c
ratiosusedwilltendtoreducetheseverity of thesetypesof
reaction.Frombothstrength and rheological considerations,the
coarseaggregateparticlesshouldberoughlyequi-dimensional;eithercrushedrockornatural
gravels, particularly if they areof glacial origin, are suitable.
Flatorelongatedparticlesmust beavoidedat all costs. Theyare
inherently
weak,andleadtoharshmixes.Inaddition,itisimportanttoensurethattheaggregateisclean,sincealayerofsiltorclaywillreducethecement-aggregatebondstrength,inadditiontoincreasingthewaterdemand.Finally,theaggregatesshouldnotbehighly
polished(as is
sometimesthecasewithriver-rungravels),becausethistoowillreducethecement-aggregatebond.Notmuchworkhasbeencarriedoutontheeffectsofaggregatemineralogyonthepropertiesofhighstrengthconcrete.However,adetailedstudybyAitcinandMehta,20involvingfourapparentlyhardstrongaggregates(diabase,limestone,granite,naturalsiliceousgravel)revealedthatthegraniteandthegravelyieldedmuchlowerstrengthsandE-valuesthantheothertwoaggregates.Theseeffectsappearedtoberelatedbothtoaggregatestrengthandtothestrengthofthecement-aggregatetransitionzone.Cook15hasalsopointedouttheeffectofthemodulusofelasticityoftheaggregateonthatoftheconcrete.However,muchwork
remains tobedonetorelatethemechanicaland mineralogicalpropertiesof
theaggregate to thoseof theresulting high strengthconcrete.It is
commonly assumedthat a smaller maximum size of
coarseaggregatewillleadtohigherstrengths,1'2'5'6'21largelybecausesmallersizeswillimprovetheworkability
oftheconcrete.However,thisis
notnecessarilythecase.WhileMehtaandAitcin6recommendamaximumsizeof10-12
mm,they reportthat 20-25 mm maximum size may be usedfor
highstrengthconcrete.Ontheotherhand,usingSouthAfricanmaterials,Addis22foundthatthestrengthofhis
highstrengthconcreteincreasedasthe maximum size of aggregate
increasedfrom13.2 to 26.5 mm. This, then,is anotherareawhich
requiresfurtherstudy.Fine aggregateThe fineaggregateshouldconsistof
smoothroundedparticles,2toreducethe water demand.Normally, the fine
aggregategrading should conform
tothelimitsestablishedbytheAmericanConcreteInstitute3fornormalstrength
concrete.However,it is recommendedthat the gradings should
lieonthecoarsersideoftheselimits;afinenessmodulusof3.0orgreaterisrecommended,1'6
bothto decrease the waterrequirements and to improvetheworkability
of thesepaste-richmixes.Of course,thesandtoomust befreeofsilt
orclay particles.1.3Mix proportions for high strength
concreteOnlyafewformalmixdesignmethodsforhighstrengthconcretehavebeendevelopedtodate.7'22'23Mostcommonly,purelyempiricalproce-duresbasedontrialmixturesareused.Forinstance,accordingtotheCanadianPortlandCementAssociation,'the
trial mix approachis
bestforselectingproportionsforhigh-strengthconcrete'.24Inothercases,mixdesign
'recipes' areprovidedfor differentclassesof high strength
concrete;anexampleof thisapproachis given by
PetermanandCarrasquillo.16Inthissection,itisnottheintentiontoprovideacanonicalmixproportioningmethod.Muchworkremainstobedonebeforeanymixproportioningmethodforhighstrengthconcretebecomesas
universallyaccepted,atleastinNorthAmerica,as hastheACIStandard
211J3
fornormalstrengthconcretes.Rather,theprinciplesonwhichsuchamixdesignmethodshouldbebasedwillbediscussed,andsomegeneralguidelines(andanumberofempiricallyderivedmixesdrawnfromtheliterature)willbepresented.Proportions
of materialsWater/cementitious ratioFor normal strength
concretes,mix proportioningis basedto a large extenton the w/c
ratio'law'.For theseconcretes,in which theaggregate strengthis
generally much greaterthan the pastestrength, the w/c ratio
doesindeeddeterminethestrengthoftheconcreteforanygivensetofrawmaterials.Forhigh
strengthconcretes,however,in which
theaggregatestrength,orthestrengthofthecement-aggregatebond,areoftenthestrength-controllingfactors,theroleofthew/c
ratiois lessclear.Tobesure,it isnecessary to use very low w/c
ratios to manufacture high strength concrete.However, the
relationship between w/c ratio and concretestrength is not
asstraightforwardas it is
fornormalstrengthconcretes.w/cratioFig.1.1Compressivestrengthversus
w/c materialratio:(1) afterAitcin7;(2) after Fiorato25;(3)
afterCook15; (4) normalstrength
concretefromCPCA24Figure1.1showsaseriesofw/cementitiousmaterialvscompressivestrengthcurves
forhigh strengthconcrete.Thesetsof curves
numbered1,2and3showthestrengthrangethatmightbeexpectedforagivenw/cementitiousratio.(Curve1
isfromAitcin7;curve 2isfromFiorato25;curve
3isfromCook.15)Forcomparison,thew/c ratiovs
strengthcurvefornormalstrengthconcreteisshownascurve
4.24Figure1.2showsasimilarseriesofw/cementitiousvsstrengthcurvesobtainedbyotherinvestigators.Curve
1 is fromAddisand Alexander,23 who used high
earlystrengthcement.Curve
2isfromHattori.25Curves3and4arefromSuzuki27;curve
3isforordinaryportlandcement,andcurve 4forhighearly
strengthcement.SeveralconclusionsmaybedrawnfromFigs.1.1and1.2.First,whilestrengthclearly
increasesas thew/cementitiousratiodecreases,thereis
aconsiderablescatteroftheresults,which
mustbeduetovariationsinthematerials,usedinthedifferentinvestigations.Second,andmoreimpor-tant,
the range of strengths for a given w/cementitious ratio increasesas
thew/cementitious ratiodecrease.If onelooksatall of thecurves in
Figs.1.1and1.2,ataw/cementitiousratioof0.45,therangeinstrengthisfrom5400
psi(37MPa)to9500 psi(66MPa);ataratioof0.26,therangeisfrom11,300
psi(78MPa)to17,400 psi(12OMPa).Therefore,the28-day compressive
strength (MPa)w/c ratioFig.1.2Compressive strength versus w/c
material ratio: (1) high early strength cement, afterAddis and
Alexander23; (2) afterHattori26; (3) ordinary Portland cement,
afterSuzuki27; (4)high early strength cement
afterSuzuki24w/cementitiousratiobyitselfisnotaverygoodpredictorofcompressivestrength.Thew/cementitious
vs strengthrelationshipmustthusbedeter-minedforany given setof
rawmaterials.Cementitious materials
contentFornormalstrengthconcretes,cementcontentsaretypically in
therangeof590 to930 pcf (350 to550 kg/m3). Forhigh strength
concretes,however,thecontentof cementitiousmaterials(cement, fly
ash,slag,silica
fume)ishigher,rangingfromabout845to1090pcf(500to650kg/m3).Thequantityofsupplementarycementingmaterialsmayvaryconsiderably,dependinguponworkability,economyandheatofhydrationconsidera-tions.Supplementary
cementing materialsAsindicatedearlier,itis
possibletomakehighstrengthconcretewithout28-day compressive
strength
(MPa)usingflyash,slagorsilicafume.Forhigherstrengths,however,sup-plementary
cementing materialsare generally necessary.In
particular,theuseofsilicafumeisrequiredforstrengthsmuchinexcessof14,000psi(98MPa).Inanyevent,theuseofsilicafume(whichisnowreadilyavailableinmostareas)makestheproductionofhighstrengthconcretemucheasier;itisgenerallyaddedatratesof5%to10%ofthetotalcementitious
materials.SuperplasticizersWithverycarefulmixdesignandaggregategrading,itispossibletoachievestrengthsofabout14,000
psi(98MPa)withoutSuperplasticizers.However,astheyarereadilyavailabletheyarenowalmost
universallyusedinhighstrengthconcrete,sincethey
makeitmucheasiertoachieveadequate workability at very low
w/cementitious ratios.Ratio of coarse to fine
aggregateFornormalstrengthconcretes,theratioof coarseto fine
aggregate(for a0.55
in.,14mmmaxsizeofaggregate)isintherangeof0.9to1.4.24However,forhighstrengthconcrete,thecoarse/fine
ratiois much
higher.Forinstance,PetermanandCarrasquillo16recommendacoarse/fineratioof
2.0. And,as seenin Tables1.5 to1.10, coarse/fine ratios used in
practicevary in therangeof1.5 to1.8.Examples of high strength
concrete
mixesAsstatedearlier,thereisyetnogenerallyagreeduponmethodofmixproportioning.Mix
designs for high strength concretehave,
hitherto,beendevelopedempirically,dependingontherawmaterialavailableinanylocation.Inthissection,a
numberof typicalmix designs,drawn
fromtherecentliterature,willbepresented.Table1.5showsthemixproportionsforInterfirstPlaza,Dallas,15inwhichtheconcreteachievedcompressivestrengthofabout11,500
psi(8OMPa).Table1.6giveshighstrengthconcretemixdesignguidelinesoriginallydevelopedfortheTexasStateDepartmentofHighwaysandPublicTransportation.16Theexpected56-daystrengthsforthesefourmixes
range from9500 to 11,000 psi (66 to 76 MPa). It should be
notedthatthemix designs in Tables1.5 and1.6 donotinvolve theuse of
silicafume.Table1.7showsthemixproportionsofPacificFirstCenter,Seattle17inwhichtheconcretereacheda56-daycompressivestrengthof18,000
psi(126MPa).Table1.8givesaseriesofmixdesignsforanumberofhighstrengthconcreteprojects,18
while Table1.9 describeshigh
strengthconcretemixescommerciallyavailableinChicago.19InTables1.7,1.8
and1.9,itshouldbenotedthatthehigherstrengthmixesall
containedsilicafume.Finally,Table 1.10 presents a mix designfor a
high strength,low heat ofhydrationconcrete.19FromTables1.5
to1.10,itmaybeseenthatthemix
designs,evenforconcretesofapproximatelythesamestrength,varyconsiderably.Thisreflectsthedifferencesin
thequality of all of theraw materials available
foreachspecificmix.So,whiletheseexamplesmayserveasageneralguidelinefortheproductionofhighstrengthconcrete,copyingamixdesignusedinonelocationisunlikelytoproducethesameconcretepropertiesin
anotherarea.Intheend,aswithconventionalconcrete,mixdesignwillrequiretheproductionofanumberoftrialmixes,thoughtheexamplesgivenabovemay
providereasonableguidance for the first trial batch.In particular,
it
isessentialfirsttoensurethattheavailablerawmaterialsarecapableofproducingthedesiredstrengths,andthattherearenoincompatibilitiesbetweenthecements,theadmixture(s)andthesupplementarycementingmaterials.Withmaterialsforwhichthereis
notmuch field
experience,itmaybenecessarytotrydifferentbrandsofcement,differentbrandsofsuperplasticizers,anddifferentsourcesofflyash,slag,orsilicafume,inorderto
optimizeboth the materials and the concretemixture. This
soundslikealotofwork,andingeneralitis.Atpresent,thereissimplynostraightforwardprocedureforproportioningahighstrengthconcretemixture
withunfamiliarmaterials.1.4Quality control and testingConventional
normal strengthconcreteis a relatively forgivingmaterial;
itcantoleratesmallchangesinmaterials,mix
proportionsorcuringcondi-tionswithoutlargechangesinitsmechanicalproperties.However,highstrength
concrete, in which all of thecomponentsof themix are working
attheir limits, is notatall a
forgivingmaterial.Thus,toensurethequality
ofhighstrengthconcrete,everyaspectoftheconcreteproductionmustbemonitored,fromtheuniformityoftherawmaterialstoproperbatchingand
mixing procedures,to propertransportation,placement, vibration
andcuring, through to propertestingof
thehardenedconcrete.Thequalitycontrolprocedures,suchasthetypesoftestonboththefreshandhardenedconcretes,thefrequencyof
testing,andinterpretationoftestresultsareessentiallythesameasthoseforordinaryconcrete.However,Cook15haspresenteddatawhichindicatethatforhishighstrengthconcrete,thecompressivestrengthresultswerenotnormallydistributed,andthestandarddeviationforagivenmix
wasnotindepen-dentoftestageandstrengthlevel.Thisledhimtoconcludethatthe'qualitycontroltechniquesusedforlowtomoderatestrengthconcretesmaynotnecessarilybeappropriateforveryhighstrengthconcretes.'Tothisdate,however,separatequality
control/qualityassuranceproceduresforhigh strength concretehave
notbeendeveloped.Theremainderof thissectiondealsprimarily with
thedeterminationofthecompressivestrength, /c', sincethis is
thebasis on which high strengthconcreteis designedandspecified.Age
at
testTraditionally,theacceptancestandardsforconcreteinvolvestrengthdeterminationsatanage
of 28 days.Althoughthereis,of course,
nothingmagicalaboutthisparticulartestage,ithasbeenuseduniversally
asthereference time at which concretestrengths are reported.
However,for
highstrengthconcretes,ithasbecomecommontodeterminecompressivestrengthsat56days,oreven90days.Thejustificationforthisisthatconcreteinstructureswillrarely,ifever,beloadedtoanythingapproachingitsdesignstrengthinlessthan3months,giventhepaceofconstruction.
Theincreasein strength between28 and56 or 90 days can
beconsiderable(10%to20%),andthiscanleadtoeconomiesinconstruc-tion.Itis
thus perfectly reasonabletomeasurestrengths
atlaterages,andtospecify theconcrete strengthin termsof these
longercuring
times.Thereare,however,twodrawbackstothisapproach.First,itcanbemisleadingtocomparethecompressivestrengthsofnormalandhighstrengthconcretes,ifthesearemeasuredatdifferenttimes.Ofmoreimportance,
thereis a certain margin of safetywhen
concretestrengthsaremeasuredat28days,sincetheconcretewillgenerallybesubstantiallystrongerwhen
it finally has tocarry its design loads,perhapsattheage ofoneyear
fora typical high-rise concretebuilding. If strengthsare
specifiedatlaterages,this margin is reduced(byanunknown
amount),andhencethere is an implicit reduction in thefactor of
safety.And, of course,
findinghigherstrengthsatlatertestagesdoesnotinanywayimplythattheconcretehas
somehow become'better' than a concretewhose strength wasmeasuredin
theconventional way at28 days.Curing
conditionsIngeneral,thehighestconcretestrengths willbeobtainedwith
specimenscontinuouslymoistcured(at100%relativehumidity)untilthetimeoftesting.Unfortunately,theavailabledataonthispointareambiguous.Carrasquillo,NilsonandSlate28
foundthathigh
strengthconcrete,moist-curedfor7daysandthenallowedtodryat50%relativehumidity
till 28days showed a strength loss of about10% when comparedto
continuouslymoist-curedspecimens.However,insubsequentwork,CarrasquilloandCarrasquillo29
found that up toan age of15 days, specimens treatedwith acuring
compoundand allowed to cure in the field under ambient
conditionsyieldedslightlyhigherstrengthsthanmoist-curedspecimens.At28
days,moist-curedspecimensandfield-curedspecimens(with orwithout
curingcompounds) yielded approximatelythesame results.Only at
laterages (56and91 days) didthestrengths of
themoist-curedspecimenssurpassthoseof the field-cured specimens
treatedwith a curing compound. Similarly, forthemixes shown in
Table1.9,Burg andOst19 foundthat, when
specimensthathadbeenmoistcuredfor28 dayswerethensubjectedtoair
curing,theirstrengthsat91daysexceededthoseofcontinuouslymoist-curedspecimens;however,
by 426 days, thecontinuously moist-cured
specimenswerefromabout3%to10% higher in strengththantheair-cured
ones.Ontheotherhand, several investigators have reportedthat, as
long as aweekorsoofmoistcuring is provided,subsequentcuring under
ambientconditionsis
notparticularlydetrimentaltostrengthdevelopment.Peter-manandCarrasquillo16havestatedthat'the28-daycompressivestrengthof
high strength concretewhich has beencured under ideal conditions
for 7days aftercasting is notseriously affectedby curing in
hotordry conditionsfrom7 to28 days
aftercasting.'Finally,contraryresults werereportedby Moreno30 who
indicated thatair-curedspecimenswereabout10% strongerthan
moist-cured specimensatall ages upto91 days.Type of mold for
casting cylindrical
specimensASTMC470:MoldsforFormingConcreteTestCylindersVertically,describestherequirementsforbothreusableandsingle-usemolds,andASTMC31:MakingandCuringConcreteTestSpecimensontheFieldpermitsbothtypesofmoldtobeused.However,ithaslong
beenknownthatdifferentmoldsconformingtoASTMC470willresultinspecimenswithdifferentmeasuredstrengths.Thisistrueforbothnormalstrengthandhighstrengthconcretes.Ingeneral,moreflexiblemoldswillyieldlowerstrengthsthanveryrigidmolds,becausethedeformationoftheflexible
molds during rodding or vibration leads to less
efficientcompactionthanwhen using rigidmolds.
Theexperimentaldatalargely
bearthisout.Itshouldbenotedthat,whateverthemoldmaterials,themoldsmustbeproperlysealedtopreventleakageofthemixwater.Ifanysignificantleakage
doesoccurs, theapparentstrength will generally
increase,becauseofthelowereffectivew/cratio,andincreaseddensificationofthespecimens.Forthestandard6x12in.(150x300mm)molds,CarrasquilloandCarrasquillo29
foundthatsteelmolds gave strengths about5%higher thanplastic molds,
while Hester31 foundabouta 10% difference.Similar
resultswerereportedbyHowardandLeatham.32PetermanandCarrasquillo16reportedthatsteelmoldsgavestrengthsabout10%higherthanthoseobtained
with cardboardmolds,and Hester31 showed that steelmolds
gavestrengths about6%higher than tinmolds.On theotherhand, Cook15
reportedthat'goodsuccess was
experiencedontheuseofsingle-userigidplasticmolds',whileAitcin33reportsincreasinguseofrigid,reusableplasticmolds.Inaddition,CarrasquilloandCarrasquillo29havereportedthatforthesmaller4x8i
n.(100 x 200
mm)molds,therewerenostrengthdifferencesbetweensteel,plastic or
cardboardmolds.Inview of theaboveresults, it would be prudent touse
rigid steel moldswhenever practicable, particularly for
concretestrengths in excess of about14,000 psi (98
MPa),atleastuntil moretestdatabecomeavailable forthesmaller
molds.Specimen sizeFormost materials, including concrete,it has
generally
beenobservedthatthesmallerthetestspecimen,thehigherthestrength.Forhigh
strengthconcrete,however,thoughthiseffectis
oftenobserved,therearecontra-dictory results reported in
theliterature. Theresults of a number of
studiesarecomparedinTable1.11.Itmaybeseenthattheobservedstrengthratiosof4x8i
n.(100x200 mm)cylindersto6x12 in.(15Ox300 mm)cylinders range
fromabout 1.1 to 0.93. These contradictory
resultsmaybeduetodifferencesintestingproceduresamongstthevariousinvestigators.Itmustbenotedthatwhileforagivensetofmaterialsandtestprocedures,itmay
bepossibletoincreasetheapparentconcretestrengthbydecreasingthespecimensize,thisdoesnotinanywaychangethestrength
of the concretein the structure. One particular specimensize
doesnotgive'truer'resultsthananyother.Thus,oneshouldbecarefultospecifya
particular specimensize fora given project,rather than leaving itas
a matter ofchoice.Specimen end
conditionsAccordingtoASTMC39:CompressiveStrength
ofCylindricalConcreteSpecimens,theendsofthetestspecimensmustbeplanewithin
0.002 in.(0.05 mm). This may be achieved eitherby capping the ends
(usually with
asulfurmortar)orbysawingorgrinding.Unfortunately,differentendTable
1.11Effectof specimen size on thecompressive strength of high
strengthconcreteInvestigatorPeterman and
Carrasquillo16Carrasquillo, Slate and Nilson34Howard and
Leatham32Cook15Burg and Ost19Aitcin33Moreno3083 MPa concrete119
MPaconcreteCarrasquillo and Carrasquillo29fc(100 x 200 mm
cylinder)fc'(150 x 300 mm cylinder)-1.1-1.1-1.08-1.05-1.01ambiguous
results-1.0-0.93-0.93conditionscanleadtodifferentmeasuredstrengths,andsotheendpreparationfortestinghighstrengthconcretespecimensshouldbespe-cifiedexplicitly
foranygiven project.Themostcommonmethodforpreparingtheendsofnormal
strengthconcreteistousesulfurcaps;forhighstrengthconcrete,highstrengthsulfurmortarsarecommercially
available.However,if thestrength ofthecap is lessthanthestrength of
theconcrete,thecompressiveloadwillnotbetransmitteduniformlytothespecimenends,leading
toinvalidresults.Thus,forhighstrengthconcrete,inadditiontohighstrengthcappingcompounds,anumberofotherendpreparationtechniquesarebeinginvestigated.
These include grinding the specimen ends, or using
unbondedsystems,consisting ofa padconstrainedinaconfiningring which
fits
overthespecimenends.Mostcompressivestrengthtestsonhighstrengthconcretearestillcarriedoutusingahighstrengthcappingcompound.Thematerialsavailable
in North Americawill achieve compressive strengths of 12,000
psito13,000 psi(84MPato91 MPa)whentestedas2
in.(50mm)cubes.33PetermanandCarrasquillo21recommendtheuseofsuchcappingcom-pounds,sincetheygivehigherconcretestrengthsthanordinarycappingcompounds.
Cook16 has used such compounds for concretestrengths up to10,000
psi(7OMPa),while Moreno30considersthemtobesatisfactory atstrengths
up to17,000 psi (119MPa).Burg and Ost19 report that a high strength
capping material may be usedwithconcretestrengthsofupto15,000
psi(105MPa);beyondthat,themodeof failureof thecylinders changed
fromthenormal conefailureof acolumnar one. They recommend grinding
of thecylinder ends for strengthsbeyond15,000
psi(105MPa).Similarly,
Aitcin33hasreportedthataboveabout17,000psi(119MPa),thehighstrengthcapping
materialis pulver-izedas thespecimensfail,which might well
affectthemeasuredstrength.Hetoorecommendsgrinding
ofthespecimenendsforvery high strengthconcretes.(Itmight
benotedthatendgrinders forconcretecylinders
arenowcommerciallyavailable.In1992,thecostofsuchamachinewasapproximately
US$12,000.)Becauseof theuncertaintywith high strengthcapping
compounds,andthecostsandtimeinvolvedinendgrinding,aconsiderableamountofresearchhas
beencarriedout on unbondedcapping systems. These
consistofmetalrestrainingcapsintowhichelastomericinsertsareplaced;theassemblies
then fit over theends of thecylinder. As
theelastomericinsertsdeterioratewithrepeateduse,they
arereplacedfromtime to
time.Richardson35usedasystemofneopreneinsertsinaluminium
capsfortestingnormalstrengthconcretesintherangeof3000 psito6000
psi(21 MPa to 42 MPa). Hefoundthat below 4000 psi (28 MPa),
theneoprenepadsgave
somewhatlowerstrengthsthanconventionalsulfurcaps, whileabove4000
psi(28MPa)theygavesomewhathigherstrengths.Overall,however,themeancompressivestrengthswerenotsignificantlydifferentbetween
thetwo systems.Carrasquillo andCarrasquillo29compareda high
strengthsulfurcappingcompoundtoanunbondedsystemconsisting
ofapolyurethanepadinanaluminiumrestrainingring.Theyfoundthatuptoabout10,000
psi(7OMPa),theunbondedsystemgavestrengthsthatwere97%ofthoseobtainedwiththecappingcompound.Beyond10,000
psi(7OMPa),however,theunbonded system gave much higher
strengths;theyhypothe-sizedthatthismight
beduetogreaterendrestraintofthecylinders
withsuchasystem.Insubsequentwork,36theyfoundthatupto10,000
psi(7OMPa),polyurethanepadsinanaluminium capgaveresultswithin
5%ofthoseachievedwithhighstrengthsulfurcaps,whileupto11,000
psi(77MPa),neoprenepadsinsteelcapsgaveresultswithin3%ofthoseobtained
with thesulfurend caps. However,they concluded that theuse
ofeitherunbondedsystemwasquestionable;substantialdifferencesintestresultswereobtainedwhentwosetsofrestrainingcaps(fromthesamemanufacturer)wereused.Toimprovetheresultsobtainedwithunbondedsystems,Boulay37developedasysteminwhich,insteadofelastomericinserts,amixture
ofdrysandandwax is used.Itwas found38thatthesandmixture gave
resultswhich were intermediate betweenthoseobtainedwith ground ends
or
withsulfurmortarcaps.Insummary,then,belowabout14,000psi(98MPa),athin,highstrengthsulfurmortarcapmaybeusedsuccessfully.
Beyondthatstrengthlevel, it would appearthat grinding specimenends
is currently theonly waytoensurevalid testresults.Testing
machinecharacteristicsIngeneral,fornormalstrengthconcrete,thecharacteristicsof
thetestingmachineitselfareassumedtohavelittleornoeffectonthepeakload.However,forveryhighstrengthconcretesthemachinemaywellhavesomeeffectontheresponse
of thespecimentoload.Froma review
oftheliterature,Hester31concludedthatthelongitudinal
stiffnessofthetestingmachinewillnotaffectthemaximum load,andthis
view is sharedalsobyAitcin.33However,if themachineis
notstiffenough,thespecimensmayfailexplosively,and,of course,a very
stiffmachine (with servo-controls)isrequiredif one wishes to
determinethe post-peakresponseof the
concrete.Ontheotherhand,Hester31alsoreportsthatifthemachineisnotstiffenoughlaterally,compressivestrengthsmay
beadversely
affected.Onemustalsobeconcernedaboutthecapacityofthetestingmachinewhentesting
very high strengthconcretes.Aitcin33
calculatedtherequiredmachinecapacitiesfordifferentstrengthlevelsandspecimensizes,usingthe
commonassumptionthat thefailure loadshould not exceed2/3 of
themachinecapacity.SomeofhisresultsarereproducedinTable
1.12.Relativelyfew
commerciallaboratoriesareequippedtotesthighstrengthconcrete,sinceacommoncapacityofcommercialtestingmachineis292,500
lbs(1.3 MN).Totesta6x12 in.(15Ox 300 mm)cylinderofTable1.12Machine
capacity required for high strength
concrete3321,400psi(15OMPa)concreterequiresa900,000Ib(4.0
MN)testingmachine,andrelatively few machines of this
sizeareavailable incommer-cial laboratories.Thisthen,is probably
thedriving forcebehind themoveto thesmaller 4 x 8 in.(100 x 200 mm)
cylinders.Effect of loadingplatensAgain,forordinary
concrete,theeffectsofthespherically
seatedbearingblocks(platens)arenotexplicitlyconsidered,aslongastheymeettherequirements
of ASTMC39:Compressive Strength
ofCylindricalConcreteSpecimens.However,recentworkat
theConstructionTechnologyLabor-atoriesinSkokie,Illinois39hasshownthat,forhighstrengthconcrete,even
this cannot be ignored. Sphericalbearing blocks which deform in
suchaway
thatthestressesarehigheraroundtheperipheryofthespecimenthanatthecentre,yieldhighercompressivestrengthsthanblocks
whichdeformso thatthehigheststressesareatthecentreof
thespecimen,andfallofftowardstheedges(i.e.a'concave'ratherthana'convex'stressdistribution).Measureddifferencescanbeashighas15%forconcreteswithcompressivestrengths
greaterthan16,000 psi (112 MPa).1.5ConclusionsIn conclusion,
then,it has beenshown that theproductionof high
strengthconcreterequirescarefulattentiontodetails.Italsorequiresclosecooperationbetween
the owner, the engineer,the suppliers andproducersoftheraw
materials,thecontractor,andthetesting
laboratory.32Perhapsmostimportant,wemustrememberthatthewell-known'laws'and'rules-of-thumb'thatapply
to normal strength concretemay well notapplyto high strength
concrete, which is a distinctly
differentmaterial.Nonethe-less,wenowknowenoughabouthighstrengthconcretetobeabletoproduce
it consistently, notonly in the laboratory,butalso in the field. It
istobehopedthatcodesof practiceandtesting standardscatchup with
thehighstrengthconcretetechnology,sothattheuseofthisexcitingnewmaterial
can continue toincrease.Specimen size100 x 200 mm150 x 300
mmFailureloadfc'= 100 MPa0.785 MN1.76 MNNote: IMN=225,000
lbffc'=150 MPa1.18 MN2.65 MNMachinecapacityfc'= 100 MPa1.2MN2.65
MNfc'=150 MPa1.75 MN4.0 MNAcknowledgementsThisworkwas supportedby
theCanadian Network ofCentres of Excell-ence on High-Performance
Concrete.References1SHRP-C/FR-91-103(1991)Highperformanceconcretes,astateoftheartreport.StrategicHighwayResearchProgram,NationalResearchCouncil,Washington,DC.2FIP/CEB(1990)Highstrengthconcrete,stateoftheartreport.Bulletind'InformationNo.197.3ACIStandard
211.1 (1989) Recommendedpractice forselecting
proportionsfornormalweight
concrete.AmericanConcreteInstitute,Detroit.4Mindess,S.andYoung,J.F.(1981)Concrete.PrenticeHallInc.,EnglewoodCliffs.5Perenchio,W.F.(1973)Anevaluationofsomeofthefactorsinvolvedinproducingveryhigh-strengthconcrete.ResearchandDevelopmentBulletin,No.RD014-01T,PortlandCementAssociation,Skokie.6Mehta,P.K.andAitcin,P.-C.(1990)Microstructuralbasisofselectionofmaterialsandmixproportionsforhigh-strengthconcrete,inSecondInterna-tionalSymposiumonHigh-StrengthConcrete,SP-121.AmericanConcreteInstitute,Detroit,265-86.7Aitcin,P.-C.(1992)privatecommunication8Ronneburg,H.and
Sandvik, M.(1990)HighStrength Concretefor North
SeaPlatforms,Concrete International,12,1,
29-349CSAStandardA23.5-M86(1986)Supplementarycementingmaterials.Cana-dianStandardsAssociation,Rexdale,Ontario.10ASTMC618Standardspecificationforflyashandraworcalcinednaturalpozzolanforuse
as a mineral admixturein portlandcement concrete.AmericanSocietyfor
TestingandMaterials,Philadelphia,PA.11ASTMC989 Standard
specificationforgroundiron blast-furnaceslag foruse
inconcreteandmortars.AmericanSocietyforTestingandMaterials,Phila-delphia,PA.12Malhotra,V.M.(ed)(1987)Supplementarycementingmaterials
forconcrete.Ministerof Supply
andServices,Canada.13Aitcin,P.-C.,Sarkar,S.L.,Ranc,R.andLevy,C.(1991)AHighSilicaModulusCementforHigh-PerformanceConcrete,inS.Mindess(ed.),Advancesincementitiousmaterials.CeramicTransactions16,
TheAmericanCeramicSocietyInc.,102-21.14Malhotra,V.M.,Ramachandran,V.S.,Feldman,R.F.andAitcin,P.-C.(1987)Condensedsilicafumeinconcrete.CRCPressInc.,BocaRatan,Florida.15Cook,I.E.(1989)10,000
psi Concrete.Concrete International,11, 10, 67-75.16Peter man,M.
B.andCarrasquillo,R. L.(1986)Productionofhighstrengthconcrete.
NoyesPublications,
ParkRidge.17Randall,V.R.andFoot,K.B.(1989)HighstrengthconcreteforPacificFirstCenter.Concrete
International: Design and Construction, 11,
4,14-16.18Aitcin,P.-C.,Shirlaw,M.andFines,E.(1992)Highperformanceconcrete:removingthemyths,inConcrescere,NewsletteroftheHigh-PerformanceConcreteNetworkof
Centresof
Excellence(Canada),6,March.19Burg,R.G.andOst,B.W.(1992)Engineeringpropertiesofcommerciallyavailablehigh-strengthconcretes.ResearchandDevelopmentBulletinRD104T,
PortlandCementAssociation,Skokie.20Aitcin,P.-C.andMehta,P.K.(1990)Effectofcoarseaggregatetypeormechanicalpropertiesofhighstrengthconcrete.ACIMaterialsJournal,AmericanConcreteInstitute,
Detroit,87,
2,103-107.21ACICommittee363(1984)State-of-the-artreportonhighstrength
concrete(ACI363R-84).AmericanConcreteInstitute,Detroit.22Addis,B.H.(1992)PropertiesofHighStrengthConcreteMadewithSouthAfricanMaterials,Ph.D.Thesis,University
of
theWitwatersrand,Johannes-burg,SouthAfrica.23Addis,BJ.andAlexander,M.G.(1990)Amethodofproportioningtrialmixesforhigh-strengthconcrete,inACISp-121,Highstrengthconcrete,SecondInternational
Symposium,AmericanConcreteInstitute,
Detroit,287-308.24CanadianPortlandCementAssociation(1991) Design
and control
ofconcrete.EditionCPCA,Ottawa.25Fiorato,A.E.(1989)PCAresearchonhigh-strengthconcrete.ConcreteInternational,11,
4,4450.26Hattori,K.(1979)Experienceswith mighty superplasticizerin
Japan,inACISP-62,Superplasticizersinconcrete,AmericanConcreteInstitute,Detroit,37-66.27Suzuki,T.(1987)Experimentalstudiesonhigh-strengthsuperplasticizedconcrete,inUtilizationofhighstrengthconcrete,Symposiumproceedings.Stavanger,
Norway: TapisPublishers, Trondheim,
53-4.28Carrasquillo,R.C.,Nilson,A.H.andSlate,P.O.(1981)Propertiesofhighstrengthconcretesubjecttoshort-termloads.JournalofAmericanConcreteInstitute,
78, 3, 171-8.29Carrasquillo,P.M.
andCarrasquillo,R.L.(1988).Evaluationoftheuseofcurrentconcretepracticeintheproductionofhigh-strengthconcrete.ACIMaterialsJournal,85,1,
49-54.30Moreno,J.(1990)225 W.WackerDrive.Concrete International,12,
1,35-9.31Hester, W.T.(1980)Fieldtestinghigh-strength concretes:a
critical review ofthestate-of-the-art.Concrete International, 2,12,
27-38.32Howard,N.L. andLeatham,D.M.(1989)Theproductionanddelivery
ofhigh-strengthconcrete.Concrete International,11, 4,
26-30.33Aitcin,P.-C.
(1989)Lesessaissuelesbetonsatreshautesperformances, inAnnalesde
L'InstitutTechniqueduBatiment et desTravaux Publics,No.
473.Mars-Avril.Serie:Beton263, 167-9.34Carrasquillo,R.L.,
Slate,P.O.andNilson,A.H.(1981)Microcrackingandbehaviour of high
strength concretesubjected to short term loading. AmericanConcrete
Institute Journal,78,
3,179-86.35Richardson,D.N.(1990)Effectsoftestingvariablesonthecomparisonofneoprenepadandsulfurmortar-cappedconcretetestcylinders.
ACIMaterialJournal,87, 5, 489-95.36Carrasquillo,P.M.
andCarrasquillo,R.L.(1988)Effectofusingunbondedcappingsystemsonthecompressivestrengthofconcretecylinders.ACIMaterialsJournal,85,
3,141-7.37Boulay,C.(1989)Laboiteasable,pourbienecraserlesbetonsahautesperformances.BulletindeLiaisondesLaboratoiresdesPontsetChausses,Nov/Dec.38Boulay,C,,Belloc,A.,Torrenti,J.M.andDeLarrard,F.(1989)Miseaupointd'unnouveaumodeoperatoire
d'essai decompression pourles betons ahaute performances.Internal
report,LaboratoireCentraldes
PontsetChaus-sees,Paris,December.39CTLReview(1992)ConstructionTechnologyLaboratories,Inc.,Skokie,Illinois,15,
2.2Short term mechanicalpropertiesS H Ahmad2.1IntroductionChapter1
discussedtheproductionofconcreteandtheeffectsofalargenumberof
constituentmaterials-cement,water, fine
aggregate,coarseaggregate(crushedstoneorgravel),airandotheradmixturesontheproductionprocess.Somequalitycontrolissueswerealsoaddressed.Inthe
presentchapter,the mechanical propertiesof
hardenedconcreteundershorttermconditions orloadings
arediscussed.Concretemustbeproportionedandproducedtocarryimposedloads,resistdeteriorationandbedimensionally
stable. Thequality of
concreteischaracterizedbyitsmechanicalpropertiesandabilitytoresistdeteriora-tion.Themechanicalpropertiesofconcretecanbebroadlyclassifiedasshort-term(essentiallyinstantaneous)andlong-termproperties.Short-termpropertiesincludestrengthincompression,tension,modulusofelasticity
and bondcharacteristics. The long-term propertiesinclude
creep,shrinkage,behaviorunderfatigue,anddurabilitycharacteristicssuchasporosity,
permeability, freeze-thaw resistanceand
abrasionresistance.ThecreepandshrinkagecharacteristicsarediscussedinChapters,thebe-havior
under fatigueand the bond characteristicsis addressedin
Chapter4.Theimportantaspectof durability is
presentedinChapter5.Whileinformationonhighperformanceconcretes(HPC)asdefinedinChapter1isscarce,thereisasubstantialbodyofinformationonthemechanical
propertiesof high strengthconcreteand additional
informationisbeingdevelopedrapidly.Oneclassofhighperformanceconcretesaretheearlystrengthconcretes.Themechanicalpropertiesofthesetypes
ofhighperformanceconcretesarebeinginvestigatedundertheStrategicHighwayResearchProgramSHRPC-205whichisinprogressatNorthCarolina
State University. Since high performanceconcretestypically
havelowwater/cementitiousmaterials(w/c)ratiosandhighpastecontents,characteristicswillinmanycasesbesimilartothoseofhighstrengthconcrete.Much
of thediscussion in this chapterwill thereforeconcentrateonhigh
strengthconcretes.Asignificantdifferenceinbehaviorbetweentheearly
strengthandthehighstrengthconcretesisintherelationshipofcompressivestrengthtomechanicalproperties.Strengthgainincompressionistypicallymuchfasterthanstrengthgaininaggregate-pastebond,forinstance.Thiswillleadtorelativedifferences
in elastic modulusandtensilestrength of
earlystrengthconcretesandhigh strengthconcretes,expressedas a
functionofcompressive strength. The relationships of mechanical
propertiesto
28-daycompressivestrengthdevelopedinotherstudiescannotnecessarilybeexpectedtoapply
toearly strengthconcretes.Theinformationdevelopedunder theSHRP
programwill beusefulto fill this knowledge
gap.2.2StrengthThestrength of concreteis
perhapsthemostimportantoverallmeasure
ofquality,althoughothercharacteristicsmayalsobecritical.Strengthis
animportantindicatorofqualitybecausestrengthisdirectlyrelatedtothestructureofhardenedcementpaste.Althoughstrengthisnotadirectmeasureofconcretedurabilityordimensionalstability,ithasastrongrelationshiptothew/cratiooftheconcrete.Thew/cratio,inturn,influencesdurability,dimensionalstabilityandotherpropertiesoftheconcretebycontrollingporosity.Concretecompressivestrength,inpar-ticular,iswidelyusedinspecifying,controllingandevaluatingconcretequality.Thestrengthofconcretedependsonanumberof
factorsincluding
thepropertiesandproportionsoftheconstituentmaterials,degreeof
hydra-tion, rateof loading,methodof testing andspecimengeometry.The
propertiesof theconstituentmaterialswhich
affectthestrengtharethequalityoffineandcoarseaggregate,thecementpasteandthepaste-aggregatebondcharacteristics(propertiesoftheinterfacial,ortransition,zone).These,inturn,dependonthemacro-andmicroscopicstructuralfeaturesincludingtotalporosity,poresizeandshape,poredistributionandmorphologyofthehydrationproducts,plusthebondbetweenindividualsolidcomponents.Asimplifiedviewofthefactorsaffectingthestrengthof
concreteis shown in Fig. 2.1.Testingconditionsincluding age, rateof
loading, methodof
testing,andspecimengeometrysignificantlyinfluencethemeasuredstrength.Thestrength
of saturatedspecimenscan be15% to20%lower than thatof dryspecimens.
Underimpact loading, strength may be as much as 25% to
35%higherthanunderanormalrateofloading(10to20microstrainspersecond).Cubespecimensgenerallyexhibit20%to25%higherstrengthsthancylindricalspecimens.Largerspecimensexhibitloweraveragestrengths.F
ig.2.1Anoversimplifiedview of thefactorsinfluencing strength of
plain concrete53Constituent materials and mix
proportionsConcretecompositionlimits theultimate strengthwhich
canbeobtainedandsignificantlyaffectsthelevelsofstrengthattainedatearlyages.Amorecompletediscussionoftheeffectsofconstituentmaterialsandmixproportionsis
given in Chapter1.However,a review of thetwo
dominantconstituentmaterialsonstrengthis
usefulatthispoint.Coarseaggregateandpastecharacteristicsaretypicallyconsideredtocontrolmaximumconcretestrength.Coarse
aggregateTheimportantparametersofcoarseaggregateareitsshape,textureandthe
maximum size. Since the aggregateis generally stronger than the
paste,itsstrengthis nota
majorfactorfornormalstrengthconcrete,orinearlystrengthconcrete.However,theaggregatestrengthbecomesimportant
inthecaseofhigher-strengthconcreteorlightweightaggregateconcrete.Surfacetextureandmineralogyaffectthebondbetweentheaggregatesandthepasteandthestresslevelatwhichmicrocrackingbegins.Thesurfacetexture,therefore,mayalsoaffectthemodulusofelasticity,theshapeofthestress-straincurveand,toalesserdegree,thecompressivestrengthofconcrete.Sincebondstrengthincreasesataslowerratethancompressivestrength,theseeffectswillbemorepronouncedinearlystrength
concretes. Tensilestrengths may be very sensitive to differences
inaggregatesurface textureandsurface areaperunit volume.C O N C R E
T E S T R E N G T HSPE C IME NP A R A M E T E R SD im ensionsG e o
m e tryM o is tu re s ta teS tre n g tho fth ecom ponent phasesLO
ADIN GP A R A M E T E R SS tre s st y p eR a teo f s t r e s s a p
p lic a tio nM AT R IXPO R O SIT YW a t e r / c e m e n t ra tioM
in e ra l a d m ix tu r e sD egreeo f h y d ra tio ncu rin g tim e,
te m p .,hum idityA ir c o n te n te n tra p p e d a irentrained
airA g g r e g a t ep o ro s ityT R A N S IT IO NZ O N E P O R O S
IT YW a t e r / c e m e n t ra tioM ineral a d m ix tu r e
sBleeding c h a ra c te ris tic sa g g re g a te g ra d in g ,m a x
.s iz e ,a n dg e o m e tryD egreeo f c o n s o lid a tio nD egreeo
f h y d ra tio nc u rin gtim e ,te m p ., hum idityC hem ical in te
ra c tio n b e tw e e na g g re g a te andcem ent pasteTheeffectof
differenttypes of coarseaggregate on concrete strength
hasbeenreportedinnumerousarticles.Arecentpaper12reportsresultsoffourdifferenttypesofcoarseaggregatesinavery
highstrengthconcretemixture(w/c
=0.27).Theresultsshowedthatthecompressivestrengthwassignificantlyinfluencedbythemineralogicalcharacteristicsoftheaggregates.Crushedaggregatesfromfine-graineddiabaseandlimestonegave
thebestresults.Concretesmadefroma smoothriver gravel andfromcrushed
granite that contained inclusions of a softmineral were found to
berelatively weakerin
strength.Theuseoflargermaximumsizeofaggregateaffectsthestrengthinseveralways.Sincelargeraggregateshavelessspecificsurfacearea,thebondstrengthbetweenaggregatesandpasteislower,thusreducingthecompressive
strength. Largeraggregate results in a smaller volume of
pastethereby providing morerestraint to volume changes of the
paste. This
mayinduceadditionalstressesinthepaste,creatingmicrocrackspriortoapplicationofload,whichmaybeacriticalfactorinveryhighstrengthconcretes.TheeffectofthecoarseaggregatesizeonconcretestrengthwasdiscussedbyCooketal.22Twosizesofaggregateswereinvestigated:a3/8
in.(10 mm)and a1 in.(25 mm) limestone.A superplasticizer was
usedinallthemixes.Ingeneral,thesmallestsizeofthecoarseaggregateproducesthe
highest strength for a given w/c ratio, see Figs 2.2-2.6. It maybe
notedthat compressivestrengths in excess of 10,000 psi (70 MPa) can
beproducedusing a 1 in.(25 mm) maximum size aggregate when
themixtureis properlyproportioned.Althoughthesestudies12'22
provideusefuldataandinsight,
muchmoreresearchisneededontheeffectsofaggregatemineralpropertiesandT
e s t age, d a y sF ig.2.2Effectof aggregate type on strength at
differentages for a constant w/c materialsratio without
superplasticizer22Compressive strength, psiw / c-0 .3 2W a t e r -c
e m e n t it io u sra tioFig.2.3Effectof aggregate type on 56 day
strength for concretefor differentw/c
materialsratio22particleshapeonthestrengthanddurability of higher
strength
concrete.ThiswasrecognizedasoneoftheresearchneedsbytheACI363Committee.3PastecharacteristicsThe
most important parameteraffectingconcretestrength is thew/c ratio,S
u p e rp la s tic iz e rW a t e r -r e d u c e rW a te r-c e m e n
titio u sra tioFig.2.4Relationship of w/c materials ratio with and
without a high rangewater-reducingadmixture for coarseaggregate
size not exceeding |in. (10 mm)22N osuperplasticizer56-day
compression strength, psi56-day compression strength, psiF ly
ashiin . lim e s to n eW a t e r -c e m e n t it io u sra tioF
ig.2.5Relationship of w/c materials ratio with and without a high
range water-reducingadmixture for coarse aggregate size not
exceeding 1 in. (25.4 mm)22sometimes referredtoas thew/b (binder)
ratio.Eventhough the strengthof concrete is dependentlargely on the
capillary porosity or gel/space ratio,thesearenoteasyquantities
tomeasureorpredict.Thecapillary porosityof a properly compacted
concreteis determined by the w/c ratio anddegreeofhydration.
Theeffectof w/c ratioonthecompressivestrength is shownin Fig. 2.7.
The practical use of very low w/c ratio concretes has been
madepossibleby use of both conventional andhigh range water
reducers, whichpermit productionof workable concretewith very low
water contents.Supplementarycementitiousmaterials(fly
ash,slagandsilicafume)havebeeneffectiveadditionsin theproductionof
high strengthconcrete.Although fly ashis
probablythemostcommonmineraladmixture,onavolumebasis,silicafume(ultra-fineamorphoussilica,derivedfromtheproductionofsiliconorferrosilicaalloys)inparticular,usedincombina-SuperplasticizerW
a te r -r e d u c e rW a te r-c e m e n titio u sra tioF
ig.2.6Effectof aggregate type on strength at differentages for a
constant w/c materialsratio, with superplasticizer22w i t
hsuperplasticizer56-day compression strength, psi56-day compression
strength, psiF lyash1inchlim e sto n eWater-cementitious materials
ratioFig.2.7Summary of strengthdataas a function of w/c materials
ratio29tionwithhigh-rangewaterreducers,hasincreasedachievablestrengthlevels
dramatically (Fig.
2.7).10'51'52Theeffectofcondensedsilicafumeonthestrengthofconcretewasreportedin
a very comprehensivestudy.28 Thebeneficial effectof using upto16%
(by weight of cement) condensedsilica on the compressive strengthis
shown in Fig. 2.8.Thedataindicatethattoachieve10,000 psi (70
MPa)28day4 x4 x4 i n.(100x 100x
100mm)cubestrength,thew/cratiosilicafu m eN otes: T estages2 8 to
105d a y s4x8 o r6x12 -in.(102x2 0 3o r152x3 0 5-m m ) cylin d e
rsMoist curing atleast 1 day A llnon-air-entrained c o n c re te
s1.O k s i =6.895M P a'z e r o 'slum p8%C SFHighp e rfo rm a n c ec
o n c re te16%C SFR eferencec o n c re tew / cFig.2.828-day
compressive strength versus w/c materialsratiofor concrete
withdifferentcondensedsilica fume contents28Compressive strength,
ksiCompressive strength, MPaR e f. 15R et. 13R e f.2R e f.3R e f.4R
e f.9R e f. 16R e f .7R e
f.5requiredisabout0.35ifnosilicafumeisused;however,with8%silicafume,thew/c
neededis about0.50,andwith16% silica
fumecontentthew/cratiorequirementincreasestoabout0.65.Thisindicatesthathighercompressivestrengthcanbeachievedveryeasilywithhighsilicafumecontentat
relatively higher w/c
ratios.Theefficiencyofsilicafumeinproducingconcreteofhigherstrengthdepends
on water/cement + silica fumeratio, dosageof silica fume,age
andcuring conditions.Yogenendramet al.S5 investigated
theefficiencyof silicafumeatlower w/c
ratio.Theirresultsindicatedthattheefficiencyis muchlower at w/c
ratio of 0.28as comparedtotheefficiencyat w/c ratio of
0.48.Theperformanceof chemicaladmixturesis influencedby
theparticularcementandothercementitiousmaterials.Combinationswhich
havebeenshowntobeeffectivein many casesmay notwork in all
situations,duetoadversecementandadmixtureinteraction(seeFig.
2.9).Substantialtestingshouldbeconductedwithanynewcombinationofcements,andmineral
or chemicaladmixtures priorto largescaleuse.T est a g e -d a y sF
ig.2.9Effectof varying dosage rates of normal retarding
water-reducing admixtures onthestrength development of concrete22A
S T MC -494 a d m ixtu reM ix no.84-61 13ozs. T ype F :3ozs.T
ypeA]M ix no.84-60 13ozs.T ype F :6ozs.T ypeA]M ix no.84-59 13o
zs.T ypeF :9o zs.T y p eAlM ix no. 84-5813o z s .T ype F :9ozs.T
ypeD]Compressive strength, psiA g e ,d a y sF ig.
2.10Normalizedstrengthgain with age for limestoneconcretes
moist-cureduntiltesting16Strength development and curing
temperatureThestrengthdevelopmentwithtimeisafunctionoftheconstituentmaterialsandcuringtechniques.Anadequateamountofmoistureisnecessarytoensurethathydrationis
sufficienttoreducetheporositytoalevelnecessarytoattainthedesiredstrength.Althoughcementpastewillnevercompletelyhydrateinpractice,theaimofcuringistoensuresufficienthydration.Inpasteswithlowerw/cratios,self-desiccationcanoccurduring
hydrationandthus preventfurtherhydrationunless water
issuppliedexternally.Thestrengthdevelopmentwith timeupto95 days
fornormal,mediumand high strengthconcretesutilizing
limestoneaggregatesand moistcureduntiltestingareshowninFig.
2.10.Theresultsindicateahigherrateofstrengthgainforhigherstrengthconcreteatearlyages.Atlateragesthedifferenceisnotsignificant.Thecompressivestrengthdevelopmentof9000
psi,11,000 psi,and14,000 psi(62MPa,76MPa,97MPa)concretesuptoa
periodof 400 days is shown inFig. 2.11.Theresultsshown
inthefigureareformixescontainingcementonlyorcementandflyash,withsomemixes
using high range water-reducing agents. Thedata indicate
thatformoist-curedspecimens, strengths at 56 days areabout10%
greater than28 daystrengths.Strengthsat90 days
areabout15%greaterthan28 daystrengths. While it is inappropriateto
generalizefromsuch results, they doindicatethepotentialfor
strengthgain at
laterages.Inarecentstudy45atNorthCarolinaStateUniversity(NCSU),con-cretesutilizing
anumberofdifferentaggregatesandmineraladmixtures,withstrengthsfrom7000
psito12,000 psi(48 MPato83 MPa)at28 daysandfrom10,000 psi
toalmost18,000 psi(69 MPato124 MPa)atoneyearweretested.Onexamining
theabsolutestrengthgainagainstthepercen-tagestrengthgain with
time,it was concludedthatthereappearstobeno4 " x8" (10 2mmx2 0 3m m
)cylinderHighs tre n g thM edium s tre n g thN orm als tre n g
thCompressive strengthCompressive strength at 95 daysA g e , d a y
sF ig. 2.11Compressive strengthdevelopment for concretes with and
withouthigh rangewater
reducers29single,constantfactorwhichcanbeusedtopredictlaterstrengthsaccuratelyfromearlystrengthsexceptinavery
generalsense.Thisisnodoubtduetothecontributionsofnotonlytheultimatestrengthoftheaggregateandthemortar,buttothestrengthof
thetransitionzone.Thetransitionzonestrength,orinterfacial
bondstrengthof
themortartotheaggregate,ofconcretesofhigherstrengths,istypicallyaffectedbythebindercompositionas
well as theultimate strengthof themortar.Resultsforsplitting
tensilestrengthandmodulus of rupturewere similar.Theeffectof
condensedsilica fume(CSF)on concrete strengthdevelop-mentat20 0C
generallytakes placefromabout3 to28 daysaftermixing.Johansen40
measuredstrengthup to 3 years and concludedthatthere
waslittleeffectof CSF oneitherthestrengthgain between28 days and1
yearor between1 and 3 years for water-storedspecimens.Theeffectof
cementtypesonthestrengthdevelopmentis presented inTable
2.1.Atordinarytemperatures,fordifferenttypesofportlandandTable
2.1Approximate relative strength of concreteas affectedby cement
typeR e M I ( I4 1O O O p S i ) R e f . 1 0 ( 1 1 , 0 0 0 p s i )R
e f . 10(9,0 0 0psi)R e f . 5(n o H R W R )R e f . 5 (H R W R )R e
f . 9 , 1 0(9,0 0 0 psi; a irc u r e d a f te r 7d a ys)N o te sM o
ist c u rin g unless n o te d1,0 0 0p si=6.895M P aPercent of
28-day strengthType of portland
cementASTMIIIIIIIVVDescriptionNormal or general purposeModerate
heat of hydrationand moderatesulf ateresistingHigh early
strengthLow heat of hydrationSulfate resistingCompressive
strength(percent of strength of Type I ornormal portland cement
concrete)1 day1007519055657 days10085120657528 days10090110758590
days100100100100100A g eF ig.2.12Compressive strength development
of concrete cured at 20 0C withdifferentdosages of condensed
silicafume48blendedcements,thedegreeof hydrationat90 daysandaboveis
usuallysimilar; therefore,theinfluenceof
cementcompositionontheporosity ofthematrixandstrengthis primarilya
concernatearlyages.Theeffectofcondensedsilica
fumeonthestrengthdevelopmentof concreteswithfourdifferenttypesof
cementwas investigated by
MaageandHammer.48Thefourcementtypeswereordinaryportlandcement,10%and25%pulve-rizedfuelash(fly
ash)blends,anda15%slagblend.Concretemixeswithout CSF and with 0%,
5%, and 10% CSF were made at 5 0C, 20 0C and35
0Candmaintainedatthesetemperaturesin waterforuptooneyear.The
compressive strengths were measuredfrom16 hours up toa period ofone
year. Mixes in three strength classes were made: 2000 psi, 3500 psi
and6500 psi (15 MPa, 25 MPa and 45 MPa).Figure 2.12 shows
thecompressivestrengthdevelopmentofconcretewater-curedat20 0C, with
variousCSFdosagesandutilizingdifferentcementtypes.Inthefigureeachcurverepresentsameanvalueforfourcementtypes,andrelativecompressivestrengthof100%represents28
daystrength foreachmix type.Fromthefigure, it can be seen that at
20 0C curing, regardless of the cement type, theCSF had thesame
influenceon thestrength-age relationship.Figures 2.13and 2.14 show
relative strength developmentat 5 0C with and without 10%CSF for
thefourcementtypes,and similar data for 35 0C curing are
showninFigs.2.15and2.16.At50Ccuring,theblendedcementlagsbehindordinary
portland cement concrete (OPC)up to 28 days; with 10% CSF
thelagincreaseswhichindicatesthatthepozzolanicreactionshavenotcontributedmuchtothestrengthin
the28 day perio