外文翻译-高性能混凝土的耐久性特点-一综述

本科毕业设计英文翻译院（系部）土木工程学院专业名称土木工程专业年级班级道桥4班学生姓名指导老师河南理工大学土木工程学院二○年六月十日Thedurabilitycharacteristicsofhighperformanceconcrete:areviewAbstractDurabilityproblemsofordinaryconcretecanbeassociatedwiththeseverityoftheenvironmentandtheuseofinappropriatehighwater/binderratios.High-performanceconcretethathaveawater/binderratiobetween0.30and0.40areusuallymoredurablethanordinaryconcretenotonlybecausetheyarelessporous,butalsobecausetheircapillaryandporenetworksaresomewhatdisconnectedduetothedevelopmentofself-desiccation.Inhigh-performanceconcrete(HPC),thepenetrationofaggressiveagentsisquitedifficultandonlysuperficial.However,self-desiccationcanbeveryharmfulifitisnotcontrolledduringtheearlyphaseofthedevelopmentofhydrationreaction,therefore,HPCmustbecuredquitedifferentlyfromordinaryconcrete.FieldexperienceintheNorthSeaandinCanadahasshownthatHPCs,whentheyareproperlydesignedandcured,performsatisfactorilyinveryharshenvironments.However,thefireresistanceofHPCisnotasgoodasthatofordinaryconcretebutnotasbadasissometimeswritteninafewpessimisticreports.Concrete,whateveritstype,remainsasafematerial,fromafireresistancepointofview,whencomparedtootherbuildingmaterials.AuthorKeywords:

Curing;Durability;Fire-resistance;Freezingandthawing;HighperformanceconcreteArticleOutline1.Introduction2.Volumetricchanges3.Curingconcrete4.Durability4.1.Generalmatters4.2.Durabilityinamarineenvironment4.2.1.Natureoftheaggressiveaction4.2.2.Chemicalattackonconcrete4.2.3.Abrasionresistance4.3.Freeze–thawresistance5.FireresistanceofHPC5.1.Thechanneltunnelfire5.2.TheDüsseldorfairportfire5.3.Spallingofconcreteunderfireconditions5.4.TheBrite–EuramHITECOBE-1158researchproject6.ConcludingremarksReferences1.IntroductionTherecentdevelopmentsinthefieldofhigh-performanceconcrete(HPC)representagiantsteptowardmakingconcreteahigh-techmaterialwithenhancedcharacteristicsanddurability.Thesedevelopmentshaveevenledtoitbeingamoreecologicalmaterialinthesensethatthecomponents––admixtures,aggregates,andwater––areusedtotheirfullpotentialtoproduceamaterialwithalongerlifecycle.Bethatasitmay,weknowthatconcretewillneverbeaneternalmaterialwhenmeasuredagainstageologicaltimeframe.Anyconcrete,ifwelookfarenoughintothefuture,willenditslifecycleaslimestone,clay,andsilicasand,whicharethemoststablemineralformsofcalcium,silica,iron,andaluminumintheearth’senvironment.Therefore,allwecandoasengineersorscientistsistoextendthelifecycleofthisartificialrockasmuchaspossible.Theconcretethatwasknownashigh-strengthconcreteinthelate1970sisnowreferredtoasHPCbecauseithasbeenfoundtobemuchmorethanjuststronger:itdisplaysenhancedperformancesinsuchareasasdurabilityandabrasionresistance.Althoughwidelyused,theexpression“HPC”isveryoftencriticizedasbeingtoovague,evenashavingnomeaningatall.SincethereisnosinglebestdefinitionforthematerialknownasHPC,itispreferabletodefineitasalowwater/binderconcretewhichreceivesanadequatewatercuring.HPCcanbemadewithcementaloneoranycombinationofcementandmineralcomponents,suchas,blastfurnaceslag,flyash,silicafume,metakaolin,ricehuskash,andfillers,suchaslimestonepowder.Ternarysystemsareincreasinglyusedtotakeadvantageofthesynergyofsomemineralcomponentstoimproveconcretepropertiesinthefreshandhardenedstates,andtomakehighperformanceconcretemoreeconomicalandecological.Fig.1

representsschematicallythefundamentalmicrostructuraldifferencebetweencementpasteshavinga0.65and0.25water/cementratio.Ina0.25

W/Cratiocementpaste,therearemorecementgrainsandconsequentlylesswaterperunitvolumesothatcementgrainsaremuchclosertoeachotherthanina0.65

W/C

cementpaste.Thismajordifferenceresultsinacompletelydifferenttypeofhydratedcementpaste.A0.65

W/C

ratiocementpasteisveryporousandrichincrystallizedouterhydrationproductsformedthroughasolution–precipitationprocess,whilea0.25

W/C

ratiocementpasteisverycompactandessentiallycomposedofinnerhydrationproductsresemblingageldevelopedthroughadiffusionprocess.

Fig.2

and

Fig.3

illustratethemajordifferenceexistingbetweenthemicrostructureofahighandlow

W/C

ratiocementpaste.Thisessentialmicrostructuraldifferenceresultsinamajordifferenceinthemechanicalanddurabilitybehaviorofboththecementpasteandthetransitionzonebetweenthepasteandtheaggregates.

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(13K)Fig.1.Schematicalrepresentationofthemicrostructureoftwocementpasteshaving

W/C

ratiosof0.65and0.25.\o"Full-sizeimage(71K)-Opensnewwindow"Full-sizeimage

(71K)Fig.2.Microstructureofhighwater/cementratioconcrete:(a)highporosityandheterogeneityofthematrix,(b)orientatedcrystalofCa(OH)2

onaggregate(AG),(c)CHcrystals.\o"Full-sizeimage(52K)-Opensnewwindow"Full-sizeimage

(52K)Fig.3.MicrostructureofaHPC:lowporosityandhomogeneityofthematrix:(a)absenceoftransitionzonebetweentheaggregateandcementpaste;(b)densecementpasteinanairentrainedhighperformanceconcrete.Inparticular,inHPC,thecoarseaggregatecanbetheweakestlinkinconcretewhenthestrengthofthehydratedcementpasteisdrasticallyincreasedbyloweringitswater/binderratio.Insuchcases,concretefailurecanstarttodevelopwithinthecoarseaggregate.Asaconsequence,therecanbeexceptionstothewater/binderratiolawwhendealingwithHPC.Insomeareas,decreasingthewater/binderratiobelowacertainlevelisnotpracticalfromamechanicalpointofviewbecausethestrengthoftheHPCwillnotsignificantlyexceedthecompressivestrengthoftheaggregate.Whenthecompressivestrengthislimitedbythecoarseaggregate,theonlywaytogethigherstrengthistouseastrongeraggregate.Butalthoughthecompressivestrengthisnotincreasedwhendecreasingthe

W/B

ratio,thecompactnessofthematrixisincreasedandthedurabilityofHPCisimproved.2.VolumetricchangesAswithanyothermaterial,thevolumeofconcretechangesasitstemperaturechanges.Likeanyothermaterialconcretecreeps.Butitisnottheonlyvolumetricvariationsexertingitselfonconcrete.Dependingonitscuringcondition,concretepresentsvolumetricvariations,itusuallyshrinksbutsometimesitswells.Inthispaper,swellingofchemicalorigin,suchassulfateorthaumasiteattackoralkaliaggregatereactionwillnotbeconsidered,theonlyvolumetricvariationtakenintoaccountwillbeplasticshrinkage,autogenousorisothermalshrinkage,anddryingshrinkage[2].Carbonationshrinkagewillnotbeconsideredbecauseitisaveryslowprocessthattakesplacemuchlater.Inallcasesthatwillbeconsideredinthispaper,theoriginofthevolumetricvariationisthesame,theappearanceoftensilestressesinthemeniscicreatedinthefreshconcreteasitisdrying(plasticshrinkage)orinthehardenedconcreteduetoself-desiccation(autogenousshrinkage)andduetodying(dryingshrinkage).Autogenousshrinkageisaconsequenceofthechemicalcontractionoccurringinthecementpastewhenwaterhydratescementparticles.Infact,theabsolutevolumeofthehydratesformedissmallerthanthesumoftheabsolutevolumeofthecementparticlesandthewaterthathavereacted.Hydrationcreatessome8%voids,asfoundbyLeChatelierandPowers[3].Thisveryfineporositydrainswaterfromthecoarsercapillarieswherewaterisnotasstronglybonded.Consequently,ashydrationprogressesitisobservedthatthecoarsecapillariesarebeingemptied(asinthecaseofdryingshrinkage)butwithoutanymassloss.Thisphenomenoniscalledself-desiccation.Self-desiccationisduetothemovementofthewaterthatismovingfromthepreexistingcoarsecapillariestowardstheveryfineporositycreatedbycementhydration.Dryingshrinkageoccurswhenconcretedriesindryair,asconcreteloosessomeofitsinternalwater;menisciappearwithinthecoarsesuperficialcapillaries.Inthecaseofdryingshrinkagethereisamassloss.Inordinaryconcretewith

W/C

ratiogreaterthan0.50,forexample,thereismorewaterthanrequiredtofullyhydratethecementparticlesandalargeamountofthiswateriscontainedinwellconnectedlargecapillariessothatthemeniscicreatedbyself-desiccationappearinlargecapillarieswheretheygenerateonlyverylowtensilestresses.Therefore,thehydratedcementpastebarelyshrinkswhenself-desiccationdevelops(40–60microstrains)[4].InthecaseofHPCwitha

W/B

ratioof0.35orless,significantlymorecementandlessmixingwaterhavebeenused,sothattheinitialporenetworkisessentiallycomposedofveryfinecapillaries.Whenself-desiccationstartstodevelop,assoonashydrationbegins,meniscirapidlydevelopintosmallcapillariesifnoexternalwaterisadded.SincemanycementgrainsstarttohydratesimultaneouslyinHPC,thedryingoftheveryfinecapillariescangeneratehightensilestressesthatshrinkthehydratedcementpaste.Thisearlyshrinkageisreferredtoasautogenousshrinkage.Ofcourse,autogenousshrinkageisaslargeasdryingshrinkageobservedinordinaryconcretewhenthesetwotypesofdryingdevelopincapillariesofthesamediameter[2].But,whenthereisanexternalsupplyofwater,thecapillariesdonotdryoutaslongastheyareconnectedtothisexternalsourceofwater[5].Theresultisthatnomenisci,notensilestress,andnoautogenousshrinkagedevelopwithinaHPCthinelementhavinga

W/C

ratioof0.35thatisconstantlywatercuredfromthemomentofitssetting.Butwhenthe

W/C

ratioislowerthan0.35oratthecenterofalargeconcreteelementmadewitha0.35

W/C

ratioHPC,concretemicrostructurecanbesodensethatwaterpenetrationcanbestoppedandself-desiccationcandevelopincertainpartsofconcrete.Infact,whencementparticlesarehydratingwithwatercomingfromanexternalsourcethereisanincreaseintheabsolutevolumeofthecementthatleadstothefillingofsomeporesandcapillaries.Inthiscase,itwouldbemoreappropriatetospeakofisothermalshrinkageratherthanautogenous,sinceautogenousshrinkagereferstotheshrinkageofaclosedsystem.Thus,theessentialdifferencebetweenordinaryconcreteandHPCisthatordinaryconcreteexhibitspracticallynoautogenousshrinkage,whetheritiswatercuredornot,whereasHPCcanexperiencesignificantautogenousshrinkageifitisnotwatercuredduringthehydrationprocess.AutogenousshrinkagedoesnotdevelopinHPCaslongastheporesandcapillariesareinterconnectedandhaveaccesstoexternalwater,but,whenthecontinuityoftheporeandcapillarysystemsisbroken,then,andonlythendoesautogenousshrinkagestarttodevelopwithinthehydratedcementpasteofaHPC,asshownin

Fig.4.

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(12K)Fig.4.Influenceofcuringconditionsontheoccurenceofautogenousshrinkage.Dryingshrinkageofthehydratedcementpastebeginsatthesurfaceoftheconcreteandprogressesmoreorlessrapidlythroughtheconcrete,dependingontherelativehumidityoftheambientairandthesizeofcapillaries.Dryingshrinkageofordinaryconcreteisthereforerapidbecausethecapillarynetworkiswellconnectedandcontainsopencapillariesatthesurfaceoftheconcrete.DryingshrinkageinHPCisslowbecausecapillariesareveryfineandsoongetdisconnected.Anothermajordifferencebetweendryingshrinkageandautogenousshrinkageisthatdryingshrinkagedevelopsfromthesurfaceinwards,whileautogenousshrinkageishomogeneousandisotropic,insofarasthecementparticlesandwaterarewelldispersedwithintheconcrete.Thus,thereareconsiderabledifferencesbetweenordinaryconcreteandHPCwithrespecttotheirshrinkagebehavior.Thecementpasteofanordinaryconcreteexhibitsrapiddryingshrinkageprogressingfromthesurfaceinwards,whereasHPCcementpastecandevelopasignificantisotropicautogenousshrinkagewhennotwatercured.Thisdifferenceintheshrinkagebehaviorofthecementpastehasveryimportantconsequencesforconcretecuringandconcretedurability.Althoughtheshrinkageofahydratedcementpasteisaveryimportantparameterwithrespecttoconcretevolumetricstability,itisnottheonlyone.Akeyparameteristheamountofaggregate,and,morespecifically,thequantityofcoarseaggregate.Toooftenitisforgottenthataggregatesdomorethansimplyactasfillersinconcrete.Infact,theyactivelyparticipateinthevolumetricstabilityofconcretewhentheyrestraintheshrinkageofthehydratedcementpaste:concreteshrinkageisalwaysmuchlowerthanthatofacementpastehavingthesame

W/C

ratio.Itiscommonknowledgethatconcreteshrinkagecanbeeasilyreducedbyincreasingthecoarseaggregatecontent;butitmustnotbeforgottenthattheshrinkageofthehydratedcementpastestaysthesame,itissimplymorerestrainedandthereislesscementpaste,sothatthevolumetricstabilityoftheconcreteisincreased.Restrainingtheshrinkageofhydratedcementpastebymodifyingthecoarseaggregateskeletonmayormaynotproduceanetworkofmicrocracks,dependingontheintensityofthetensilestressesdevelopedbythisprocesswithrespecttothetensilestrengthofthehydratedcementpaste.3.CuringconcreteHPCmustbecuredquitedifferentlyfromordinaryconcretebecauseofthedifferenceinshrinkagebehaviordescribedabove,asemphasizedin

Fig.5.IfHPCisnotwatercuredimmediatelyfollowingplacementorfinishing,itispronetodevelopsevereplasticshrinkagebecauseitisnotprotectedbybleedwater,andlaterondevelopssevereautogenousshrinkageduetoitsrapidhydration.Whilecuringmembranesprovideadequateprotectiontoordinaryconcrete(whichisinsensitivetoautogenousshrinkage),theycanonlyhelppreventthedevelopmentofplasticshrinkageinHPCbuthavenovalueininhibitingautogenousshrinkage.

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(14K)Fig.5.Themostappropriatecuringregimesduringthecourseofthehydrationreaction.ThecriticalcuringperiodforanyHPCrunsfromplacementorfinishing,upto2or3dayslater,andthemostcriticalperiodisusuallybetween12and36h.Infact,theshorttimeduringwhichefficientwatercuringmustbeappliedtoHPCcanbeconsideredasignificantadvantageoverordinaryconcrete.ThosewhospecifyanduseHPCmustbeawareofthedramaticconsequencesofmissingearlywatercuring.Initiatingwatercuringafter24histoolate,becausemostofthetime,agreatdealofplasticandautogenousshrinkagehavealreadyoccurredand,bythistime,thecapillaryandporenetworkaredisconnectedinmanyplacesandthemicrostructureisalreadysocompactthatexternalwaterhaslittlechanceofpenetratingverydeepintotheconcrete.WaterpondingorfoggingisthebestwaytocureHPC;oneofthesetwomethodsmustbeappliedassoonaspossible,immediatelyfollowingplacementorfinishing.Anevaporationretardercanbeappliedtemporarilytopreventthedevelopmentofplasticshrinkage.If,foranyreason,waterpondingorfoggingcannotbeimplementedfor7days,thentheconcretesurfaceshouldbecoveredwithwetburlap(hessian)orpreferablyaprewettedgeotextile.Theburlaporthegeotextilemustbekeptconstantlywetwithasoakerhoseandprotectedfromdryingbyapolyethylenesheetinordertoensurethatatnotimeduringthecuringperiodistheconcreteallowedtodryandexperienceanyautogenousshrinkage[6].Moreover,itisobservedthatwhenanyconcreteiswatercuredduringsettingitdoesnotshrinkbutratherswell.

Fig.6

illustratestheeffectofearlywatercuringonthevolumetricchangeofconcrete.

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(6K)Fig.6.Lengthchangesaccordingtodifferentcuringregimesforthe0.35

W/C

ratioconcrete.Watercuringcanbestoppedafter7daysbecausemostofthecementatthesurfaceofconcretehashydratedandanyfurtherwatercuringhaslittleeffectonthedevelopmentofshrinkage.After7daysofwatercuring,HPCexperiencesslowdryingshrinkageduetothecompactnessofitsmicrostructure,andthatautogenousshrinkagehasalreadydriedoutthecoarsecapillariespores.Eventhen,theoreticallythebestthingtodoistopaintHPCortouseasealingagentsothatthelastwaterthatremainsinconcretecanberetainedtocontributetohydration.Thereisnorealadvantageofpaintingorsealingaveryporousconcretebecauseitisimpossibletoobtainanabsolutelywaterproofcoating;paintingorsealingHPC,however,canbeeasyandeffective.Partialreplacementofcoarseaggregatebyanequivalentvolumeofsaturatedlightweightaggregatehasbeenusedtocounteractautogenousshrinkageinternally[7].Thesaturatedlightweightaggregateparticlesactassmallwaterreservoirsthroughoutthemassofconcrete;theycanfilltheveryfineporescreatedbyhydrationreactions.Therefore,thewaterofthelightweightaggregateparticlesisdrainedalongwiththatcontainedinthefinecapillariesoftheHPC.Themenisciwithinthecementpastearenotdevelopedinsmallcapillaries,whichmeanslowertensilestressandlowerautogenousshrinkage.Lightweightaggregatealsoreducescompressivestrengthandelasticmodulus.Shrinkagereducingadmixturecanalsobeused[8].Itiswellknownthatconcreteisnevercuredproperlyinthefield,despitethefactthatitisalwayswritteninthespecificationsthatcontractorshavetocureconcrete.Contractorsarenotcuringconcreteforaverysimplereason:theyarenotspecificallypaidforit,therefore,concretecuringisalwaysperceivedbythemasanunprofitableactivityorevenasourceofexpenseandthereforeawasteoftime.But,whencontractorsarespecificallypaidtowatercureconcretetheydoitastheywouldforanyotheritemthatispaidfor.Forthreeyearsnow,theCityofMontrealandtheQuébecMinistryofTransportationhaverequestedunitpricesforeachitemdirectlyrelatedtoearlywatercuring.Sincetheinitiationofthisnewpolicyontheearlywatercuringofconcrete,itisamazingtoseehowzealouscontractorscanbecomeinthematterofwatercuring.Forthemwatercuringisnowseenasasourceofprofit.Fromthefirstexperiencesinthatmatterithasbeenfoundthatthecostofanearlywatercuringisaboutonetenthof1%,averymodestpricewhenconsideringtheimproveddurabilityoftheconcretestructuresthatarebuiltthisway.Therefore,thebestwaytobesurethatHPCsareproperlyandefficientlycuredinthefieldistospecificallypaycontractorstocureconcrete[6].Thisverylongintroductoryremarksweremadetoemphasizethattwoimportantkeyparameterscontrolthepenetrationofanyaggressiveagentsinconcrete:thewater/cementorthewater/binderratio,andthecuringofconcrete.Specifyingalowwater/binderratioconcreteisanecessarycondition,butnotasufficientone..高性能混凝土的耐久性特点：一综述摘要普通混凝土的耐久性问题，与环境的严重程度和不适当的高水灰比相联系。具有水灰比在0.30和0.40之间的高性能混凝土通常比普通混凝土更耐用，不仅因为他们气孔少，而且还因为他们的毛细管和毛孔网状物有点不连通而导致自我干燥的发展。在高性能混凝土（HPC），入侵性因子的渗透是相当困难的，只有表面的渗透。然而，自干燥非常有害，如果它不是在水化反应的早期发展阶段的控制，因此，高性能混凝土的养护必须完全不同于普通混凝土。远在北海和加拿大的经验表明，当混凝土得到适当设计和养护，即使在非常恶劣的环境中也令人满意。然而，高性能的耐火不如普通混凝土，但有时并不像一些悲观的报告中那样写的不好。混凝土，无论其类型，相对于其他建筑材料而言，仍然是一个安全的材料。作者关键词：固化；耐久性；耐火性；冷冻和解冻；高性能混凝土文章概要1．介绍2．体积变化3．混凝土养护4．耐久性4.1．一般内容4.2．在海洋环境中的耐久性4.2.1．更强硬措施的性质4.2.2．化学对混凝土侵蚀4.2.3．耐磨性4.3．耐冻融性5．高性能混凝土的耐火性5.1．英吉利海峡隧道内火灾5.2．杜塞尔多夫机场的火灾5.3．火灾条件下的混凝土剥落5.4．Brite-EuramHITECOBE-1158的研究项目6．结束语参考文献1、简介在高性能混凝土领域的最新发展（HPC）代表一个巨大的进步，并增加其耐久性与特性，使混凝土成为高科技材料。这些事态发展，甚至导致它是一个在意义上更加生态材料的组件——外加剂，骨料，水——是用来实现其全部潜力，生产具有较长的生命周期材料。虽然如此，可我们知道，从对地质测量时间来说，混凝土绝不会是一个永恒的材料。如果我们放眼未来足够远，任何混凝土，将结束其生命周期，像石灰石，粘土和石英砂，这是钙，硅，铁，和铝在地球环境中最稳定的矿物形式。因此，作为工程师或科学家，我们所能做的就是将尽可能多的延续这些人工岩石的生命周期。在70年代末被认为是高强度混凝土现在被称为高性能混凝土，因为它被发现不仅仅是强度大：它显示为增强耐久性和耐磨性等方面性能。

虽然广泛使用，但是“高性能混凝土”还是很经常被过于模糊的批评，甚至有没有意义。

由于高性能混凝土没有一个最佳的材料定义，更适合将其定义为一低水灰比并接收充足的水分固化的混凝土。高性能混凝土，可单独与水泥或与水泥和任何矿物成分结合，如高炉矿渣，粉煤灰，硅粉，偏高岭土，稻壳灰，石灰石粉填料。三元系统越来越多地用于采取一些矿物成分的协同作用，以改善混凝土在新鲜和硬化方面的性能，使高性能混凝土更经济和生态。图1代表最根本的微观结构，在水灰比为0.65和0.25的水泥浆体之间的区别。在水灰比为0.25的水泥浆中的单位体积内有更多的水泥颗粒和较少的水，使其水泥颗粒比水灰比为0.65水泥浆中的更紧密。这个主要的不同结果在于水泥浆水化的类型完全不同。水灰比为0.65的水泥浆会有很多孔和通过降解水的过程形成富含结晶的外部水化产物，而一个水灰比为0.25的水泥浆非常紧凑，在本质上水泥水化产物组成的是一种凝胶中发展类似的扩散过程。图2和图3说明了在高和低水灰比的水泥浆之间的主要显微结构的差异。在这个根本的微观结构差异的一个主要差异是水泥浆和过渡区的糊状物和骨料的机械和耐久性。

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(13K)图1.表示的是水灰比为0.25和0.65的水泥浆体的显微结构。\o"Full-sizeimage(71K)-Opensnewwindow"Full-sizeimage

(71K)图2微观结构的高水灰比的混凝土:(a)高孔隙度和储层非均质性的基质(b)朝向晶体的Ca(OH)2的骨料(AG),(c)CH晶体。\o"Full-sizeimage(52K)-Opensnewwindow"Full-sizeimage

(52K)图3高性能混凝土的微观结构和孔隙度低均匀的基质:(a)在水泥浆和骨料之间缺乏的过渡区;(b)浓厚的水泥浆在一个空气中产生高性能混凝土。在高性能混凝土中，特别是粗骨料在混凝土中最薄弱的环节时，通过降低其水灰比，使水泥浆的强度大幅增加。在这种情况下，混凝土破坏就可以开始在粗骨料发展。因此，在高性能混凝土处理的时候，可以有例外水灰比。在一些地区，减少了水灰比且低于一定水平的比例，实际上并不是从机械角度，因为高性能混凝土的强度不会明显超过了混凝土骨料的抗压强度。当其抗压强度被粗骨料限制，唯一的方法只有增加骨料的强度，才能获得较高的强度。不过，减少水灰比时虽然没有增加抗压强度，但基质密压实度的增大，也提高高性能混凝土的耐久性。2、体积变化与任何其他材料一样，混凝土体积随温度变化而变化。像任何其他材料一样具体的蠕动。但它不是混凝土本身发生变化的唯一体积。根据其固化条件，混凝土出现体积变化，它通常会缩小，但有时它膨胀。在本文中，化学制品膨胀的来源，如硫酸盐或碳硫硅钙石攻击或碱骨料反应等引起的膨胀将不予考虑，只有考虑塑性收缩，自体或等温收缩，干燥收缩等引起的体积变化。碳化收缩将不会被考虑，因为这是一个非常缓慢的过程，发生的晚得多。在所有被本文所考虑的情况下，体积变化的来源是相同的，拉应力出现在新拌混凝土制造中，因为它是干燥（塑料收缩）或在硬化混凝土中因为自干燥（自收缩）和死亡（干燥收缩）而引起的。自收缩是一种发生在水泥水化物水泥颗粒化学收缩的结果。事实上，固化剂的绝对体积小于水泥颗粒和参加反应的水总和绝对体积。水化能产生8％空隙，被LeChatelier和Powers发现。这很细的孔隙从较粗的毛细管那里吸水。因此，水化的进展已观察到，粗毛细管的水被掏空（如在干燥收缩的情况），但没有任何质量损失。这种现象被称为自干燥。自干燥是由于水的运动正在从既存的粗毛细血管向很细的孔隙度由水泥水化。当混凝土干燥收缩在干燥空气中，混凝土会输送一些内部水，半月板在粗糙毛细管表面出现。在干燥收缩的情况是有质量的损失。在普通混凝土中水灰比比值大于0.50，例如，有更多的水要被水泥颗粒充分水化，大量的水都包含在与其保持良好关系,以便状大微血管由自干燥出现于大毛细管的地方,他们只生成非常低的拉应力。因此，水泥的水化时几乎缩自干燥的发展。在高性能混凝土中水灰比为0.35或低于的情况下，显然更多的水泥和少量水已被使用，因此，初始孔隙网络基本上是由很细的毛细血管组成。当自我干燥开始发展，一旦水化开始，如果没有外部加水则将迅速发展成为小毛细管。由于许多水泥颗粒开始在高性能混凝土中与水化合，非常细的干燥毛细管可以产生高拉应力。这种早期收缩被称为自收缩。当然，这两种类型的干燥发展在相同直径的毛细管中，在普通混凝土中可以看到自收缩和干燥收缩的收缩率是一样大的。但是，当有外部提供的水，只要它们连接到这个水源，毛细管就不会干燥。结果是，没有半月板就无拉应力，并且没有自收缩发展在一个水灰比为0.35且有不断的水来养护的高性能混凝土中。但是，当水灰比低于0.35或在该中心有一些大的混凝土构件水灰比为0.35的高性能混凝土时，混凝土微观结构是如此密集，可以阻止水的渗透，和在混凝土自我干燥。事实上，当水泥颗粒和有外加水源的水水化，水泥绝对体积的增加，导致了充填的一些小孔和毛细管。在这种情况下，有个更为合适说法那是等温收缩而