外文翻譯-高性能混凝土的耐久性特點-一綜述

本科畢業(yè)設(shè)計英文翻譯院（系部）土木工程學院專業(yè)名稱土木工程專業(yè)年級班級道橋4班學生姓名指導老師河南理工大學土木工程學院二○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點：一綜述摘要普通混凝土的耐久性問題，與環(huán)境的嚴重程度和不適當?shù)母咚冶认嗦?lián)系。具有水灰比在0.30和0.40之間的高性能混凝土通常比普通混凝土更耐用，不僅因為他們氣孔少，而且還因為他們的毛細管和毛孔網(wǎng)狀物有點不連通而導致自我干燥的發(fā)展。在高性能混凝土（HPC），入侵性因子的滲透是相當困難的，只有表面的滲透。然而，自干燥非常有害，如果它不是在水化反應的早期發(fā)展階段的控制，因此，高性能混凝土的養(yǎng)護必須完全不同于普通混凝土。遠在北海和加拿大的經(jīng)驗表明，當混凝土得到適當設(shè)計和養(yǎng)護，即使在非常惡劣的環(huán)境中也令人滿意。然而，高性能的耐火不如普通混凝土，但有時并不像一些悲觀的報告中那樣寫的不好?；炷粒瑹o論其類型，相對于其他建筑材料而言，仍然是一個安全的材料。作者關(guān)鍵詞：固化；耐久性；耐火性；冷凍和解凍；高性能混凝土文章概要1．介紹2．體積變化3．混凝土養(yǎng)護4．耐久性4.1．一般內(nèi)容4.2．在海洋環(huán)境中的耐久性4.2.1．更強硬措施的性質(zhì)4.2.2．化學對混凝土侵蝕4.2.3．耐磨性4.3．耐凍融性5．高性能混凝土的耐火性5.1．英吉利海峽隧道內(nèi)火災5.2．杜塞爾多夫機場的火災5.3．火災條件下的混凝土剝落5.4．Brite-EuramHITECOBE-1158的研究項目6．結(jié)束語參考文獻1、簡介在高性能混凝土領(lǐng)域的最新發(fā)展（HPC）代表一個巨大的進步，并增加其耐久性與特性，使混凝土成為高科技材料。這些事態(tài)發(fā)展，甚至導致它是一個在意義上更加生態(tài)材料的組件——外加劑，骨料，水——是用來實現(xiàn)其全部潛力，生產(chǎn)具有較長的生命周期材料。雖然如此，可我們知道，從對地質(zhì)測量時間來說，混凝土絕不會是一個永恒的材料。如果我們放眼未來足夠遠，任何混凝土，將結(jié)束其生命周期，像石灰石，粘土和石英砂，這是鈣，硅，鐵，和鋁在地球環(huán)境中最穩(wěn)定的礦物形式。因此，作為工程師或科學家，我們所能做的就是將盡可能多的延續(xù)這些人工巖石的生命周期。在70年代末被認為是高強度混凝土現(xiàn)在被稱為高性能混凝土，因為它被發(fā)現(xiàn)不僅僅是強度大：它顯示為增強耐久性和耐磨性等方面性能。

雖然廣泛使用，但是“高性能混凝土”還是很經(jīng)常被過于模糊的批評，甚至有沒有意義。

由于高性能混凝土沒有一個最佳的材料定義，更適合將其定義為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，可單獨與水泥或與水泥和任何礦物成分結(jié)合，如高爐礦渣，粉煤灰，硅粉，偏高嶺土，稻殼灰，石灰石粉填料。三元系統(tǒng)越來越多地用于采取一些礦物成分的協(xié)同作用，以改善混凝土在新鮮和硬化方面的性能，使高性能混凝土更經(jīng)濟和生態(tài)。圖1代表最根本的微觀結(jié)構(gòu)，在水灰比為0.65和0.25的水泥漿體之間的區(qū)別。在水灰比為0.25的水泥漿中的單位體積內(nèi)有更多的水泥顆粒和較少的水，使其水泥顆粒比水灰比為0.65水泥漿中的更緊密。這個主要的不同結(jié)果在于水泥漿水化的類型完全不同。水灰比為0.65的水泥漿會有很多孔和通過降解水的過程形成富含結(jié)晶的外部水化產(chǎn)物，而一個水灰比為0.25的水泥漿非常緊湊，在本質(zhì)上水泥水化產(chǎn)物組成的是一種凝膠中發(fā)展類似的擴散過程。圖2和圖3說明了在高和低水灰比的水泥漿之間的主要顯微結(jié)構(gòu)的差異。在這個根本的微觀結(jié)構(gòu)差異的一個主要差異是水泥漿和過渡區(qū)的糊狀物和骨料的機械和耐久性。

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(13K)圖1.表示的是水灰比為0.25和0.65的水泥漿體的顯微結(jié)構(gòu)。\o"Full-sizeimage(71K)-Opensnewwindow"Full-sizeimage

(71K)圖2微觀結(jié)構(gòu)的高水灰比的混凝土:(a)高孔隙度和儲層非均質(zhì)性的基質(zhì)(b)朝向晶體的Ca(OH)2的骨料(AG),(c)CH晶體。\o"Full-sizeimage(52K)-Opensnewwindow"Full-sizeimage

(52K)圖3高性能混凝土的微觀結(jié)構(gòu)和孔隙度低均勻的基質(zhì):(a)在水泥漿和骨料之間缺乏的過渡區(qū);(b)濃厚的水泥漿在一個空氣中產(chǎn)生高性能混凝土。在高性能混凝土中，特別是粗骨料在混凝土中最薄弱的環(huán)節(jié)時，通過降低其水灰比，使水泥漿的強度大幅增加。在這種情況下，混凝土破壞就可以開始在粗骨料發(fā)展。因此，在高性能混凝土處理的時候，可以有例外水灰比。在一些地區(qū)，減少了水灰比且低于一定水平的比例，實際上并不是從機械角度，因為高性能混凝土的強度不會明顯超過了混凝土骨料的抗壓強度。當其抗壓強度被粗骨料限制，唯一的方法只有增加骨料的強度，才能獲得較高的強度。不過，減少水灰比時雖然沒有增加抗壓強度，但基質(zhì)密壓實度的增大，也提高高性能混凝土的耐久性。2、體積變化與任何其他材料一樣，混凝土體積隨溫度變化而變化。像任何其他材料一樣具體的蠕動。但它不是混凝土本身發(fā)生變化的唯一體積。根據(jù)其固化條件，混凝土出現(xiàn)體積變化，它通常會縮小，但有時它膨脹。在本文中，化學制品膨脹的來源，如硫酸鹽或碳硫硅鈣石攻擊或堿骨料反應等引起的膨脹將不予考慮，只有考慮塑性收縮，自體或等溫收縮，干燥收縮等引起的體積變化。碳化收縮將不會被考慮，因為這是一個非常緩慢的過程，發(fā)生的晚得多。在所有被本文所考慮的情況下，體積變化的來源是相同的，拉應力出現(xiàn)在新拌混凝土制造中，因為它是干燥（塑料收縮）或在硬化混凝土中因為自干燥（自收縮）和死亡（干燥收縮）而引起的。自收縮是一種發(fā)生在水泥水化物水泥顆?；瘜W收縮的結(jié)果。事實上，固化劑的絕對體積小于水泥顆粒和參加反應的水總和絕對體積。水化能產(chǎn)生8％空隙，被LeChatelier和Powers發(fā)現(xiàn)。這很細的孔隙從較粗的毛細管那里吸水。因此，水化的進展已觀察到，粗毛細管的水被掏空（如在干燥收縮的情況），但沒有任何質(zhì)量損失。這種現(xiàn)象被稱為自干燥。自干燥是由于水的運動正在從既存的粗毛細血管向很細的孔隙度由水泥水化。當混凝土干燥收縮在干燥空氣中，混凝土會輸送一些內(nèi)部水，半月板在粗糙毛細管表面出現(xiàn)。在干燥收縮的情況是有質(zhì)量的損失。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顆粒充分水化，大量的水都包含在與其保持良好關(guān)系,以便狀大微血管由自干燥出現(xiàn)于大毛細管的地方,他們只生成非常低的拉應力。因此，水泥的水化時幾乎縮自干燥的發(fā)展。在高性能混凝土中水灰比為0.35或低于的情況下，顯然更多的水泥和少量水已被使用，因此，初始孔隙網(wǎng)絡基本上是由很細的毛細血管組成。當自我干燥開始發(fā)展，一旦水化開始，如果沒有外部加水則將迅速發(fā)展成為小毛細管。由于許多水泥顆粒開始在高性能混凝土中與水化合，非常細的干燥毛細管可以產(chǎn)生高拉應力。這種早期收縮被稱為自收縮。當然，這兩種類型的干燥發(fā)展在相同直徑的毛細管中，在普通混凝土中可以看到自收縮和干燥收縮的收縮率是一樣大的。但是，當有外部提供的水，只要它們連接到這個水源，毛細管就不會干燥。結(jié)果是，沒有半月板就無拉應力，并且沒有自收縮發(fā)展在一個水灰比為0.35且有不斷的水來養(yǎng)護的高性能混凝土中。但是，當水灰比低于0.35或在該中心有一些大的混凝土構(gòu)件水灰比為0.35的高性能混凝土時，混凝土微觀結(jié)構(gòu)是如此密集，可以阻止水的滲透，和在混凝土自我干燥。事實上，當水泥顆粒和有外加水源的水水化，水泥絕對體積的增加，導致了充填的一些小孔和毛細管。在這種情況下，有個更為合適說法那是等溫收縮而