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DiscusstheconstructiontemperatureandcrackoftheconcretelightlyByG.K.Kululanga,W.Kuotcha,R.McCaffer,Member,ASCE,andF.Edum-Fotwe,TheAmericanSocietyofCivilEngineersThesummary,Inordertopreventtheownersoftheconcreteworkofclaims,wemustdoagoodjobintheconstructionprocessinthetemperatureandcrackcontrol,throughobservationliveformanyyears,throughconsultingthemonographaboutstresswithintheconcrete,explaintoconcretetemperaturereason,on-the-spotconcretecontrolandmeasure,preventionofcrackoftemperaturethatcrackproduce.KeywordConcreteTemperaturestressCrackControl1.Theconcreteoccupiestheimportantpositioninmodernengineeringconstruction.Buttoday,thecrackoftheconcreteiscomparativelygeneral,thecracksarenearlyomnipresentinthescienceofbridgebuilding.Thoughwetakevariouskindsofmeasuresinconstructing,careful,butthecrackstilloccursnowandthen.Tracingittoitscause,itisoneofthemincompletelythatourchangetoconcretetemperaturestresspaysattentionto.Inthelargevolumeconcrete,temperaturestressandtemperaturecontrolaresignificant.Thisismainlybecauseofthereasonoftworespects.Firstofall,concreteoftenappearthetemperaturecrackinnotconstructing,influencetheglobalityanddurabilityofthestructure.Secondly,inthecourseofoperating,thetemperaturechangehasremarkableinfluencethatcantbeignoredonthestressstateofthestructure.Wemeettoconstructtemperaturecrackinmainly,soonlytoorigincauseofformationandtreatmentmeasure,concreteofcrackmakeadiscussioninconstructingthistext.ReasonofacrackHavemanykindsofreasonstoproducethecrackintheconcrete,itismainlythechangesoftemperatureandhumidity,fragilityanddisparityoftheconcrete,andthestructureisunreasonable,therawmaterialsisnotuptostandard(ifthealkaliaggregatereact),thetemplateisoutofshape,thefoundationdoesnotsubsideetc.evenly.Thecementemitsalargeamountofheatofhydrationwhentheconcreteishardenned,insidetemperatureisrisingconstantly,causethestressofdrawingonthesurface.Inthecourseofloweringthetemperature,isitcongealfoundationpayrestraintomixalwayslaterstage,willpresentthestressofdrawingwithintheconcrete.Reducingoftemperaturecansurfacecauseheavystressofdrawingveryinconcretetoo.Whenthesedrawthestressandgobeyondresistingtheabilityofsplittingofconcrete,namelywillpresentthecrack.Alotofinsidehumidityofconcretechangeverylightorchangerelativelyslow,surfacehumiditymightchangeheavytheviolentchangetakesplacing.Suchasmaintainingthoroughly,whengettingwetterwhennotdoing,contractsurfacetherearentdeformationdoing,oftencausethecracktoo.Theconcreteisakindoffragilitymaterial,tensilestrengthisabout1/10ofthecompressionstrength,isitcarryononesshoulderorbacklimitwhendrawoutofshapetohave*104only,isitcarryononesshoulderorbacklimitlocationwhenstretchoutofshapetothereis*104toaddforalongtimetoaddashorttime.Becauserawmaterialseven,waterdustthanunstable,transportandbuildphenomenonofemanatingofcourse,itstensilestrengthisnoteveninthesameconcrete,alotofresisttheabilityofdrawingverylow,itisapttopresenttheweakpositionofthecrack.Amongarmoredconcrete,drawstresstoundertakebyreinforcingbarmainly,concretebearstressofkeepingjust.Orreinforcingbarmixifedgepositiongonetotocongealpresentthestressofdrawinginthestructureinplainconcrete,mustrelyontheconcreteoneselftobear.Requiretoavoidthestressofdrawingoronlyverysmallstressofdrawingappearsofthethegeneraldesign.Buttheconcreteiscooledfrommaximumtemperaturetothesteadytemperatureofoperatingperiodinconstructing,oftencausesizabletodrawthestresswithintheconcrete.Thetemperaturestresscanexceedotheroutsidesandloadthestressescausedsometimes,knowchangelaw,temperatureofstressforcarryonreasonablestructuraldesignandconstructextremelyimportant.Analysisof2temperaturestressesCanbedividedintofollowingthreestagesaccordingtotheformingprocessofthetemperaturestress:(1) Itisearly:Buildconcreteisitisitoverbasicallytosendoutheattocementtobegin,generallyoneonedaybyoneself.Twocharacteristicsatthisstage,first,thecementemitsalargeamountofheatofhydration,second,mixandcongealthechangingsharplyofelasticmodelquantity.Becauseofthechangeofelasticmodelquantity,formtheremainingstressintheconcreteinthisperiod.(2) Middleperiod:Uptilltheconcreteiscooleduntilstabilitytemperaturefromcementsendoutheatfunctionbasicallywhenexpiring,inthisperiod,thetemperaturestressismainlybecausethecoolingoftheconcreteandexternaltemperaturechangecause,thesestressesandremnantsstressesthatisformedinearlydaysaresuperposed,mixandcongealtheelasticmouldamountthatgoestoanddoesnotchangemuchduringthisperiod.(3) Laterperiod:Operationperiodafterthecompletecoolingofconcrete.Temperaturestresswhetherexternaltemperaturechangecausemainly,thesestressesandfirsttwokindsofremnantsstressesesarechangedandadded.Canbedividedintotwokindsaccordingtothereasonwhythetemperaturestresscauses:(1) Spontaneousstress:Therearenotanyrestraintortotallystaticstructureattheborder,ifinsidetemperatureisnon-lineardistribution,temperaturestressappearingbecausestructurerestrainsfromeachother.Forexample,thebodyofmoundofthebridge,thephysicaldimensionisrelativelylarge,surfacetemperatureislowwhentheconcreteiscooled,insidetemperatureishigh,presentthestressofdrawingonthesurface,presentthestressofpressinginthemiddle.(2) Restrainthestress:Allofthestructureonesoritrestrainexternalonesomeborder,cantoutofshapeandstressnotcausenotfree.Suchascaseroofbeamroofconcreteandguardrailconcrete.Thistwokindsoftemperaturestressesdrawbackstressescausedtoactonwiththedoingofconcretetogetherfrequently.Itisamorecomplicatedjobtowanttoanalysethedistribution,sizeofthetemperaturestressaccuratelyaccordingtoknowntemperature.Incaseofgreatmajority,needtorelyonthemodeltestorthenumbervaluetocalculate.Toisitmaketemperaturestresshavesizablelimptocreepconcrete,atthestressaccountingtemperature,mustconsidertheinfluencethatcreep,calculateconcretlythatnolongerstatesthinlyhere.Controlandpreventingthemeasureofthecrackof3temperatureForpreventcrack,lightentemperaturestresscanfromcontroltemperatureandisitisitsetabouttorestraintermsfromtwotoimprove.Themeasureofcontrollingtemperatureisasfollows:(1) Isitimproveaggregategrademix,isitdorigidconcretetospend,mixmixturetoadopt,isitguideangrypharmaceuticalorplastificationpharmaceutical,etc.measureinordertoreducecementconsumptionofconcretetoadd;(2) Addwaterorthewatertocoolthebrokenstoneinordertoreducethetemperatureofbuildingoftheconcretewhilemixingandshuttingtheconcrete;(3) Reducethethicknessofbuildingwhilebuildingtheconcreteonhotday,utilizeandbuildtheaspecttodispeltheheat;(4) Burythewaterpipeundergroundintheconcrete,enterthecoldwatertolowerthetemperatureopenly;(5) Stipulaterationalformremovaltime,thetemperaturekeepswarmthesurfacewhileloweringsuddenly,incasethattherapidtemperaturegradienttakesplaceintheconcretesurface;(6) Theconcretewithmediumandlong-termandexposedconstructionbuildsapieceofsurfaceorthinwallstructure,takethemeasureofkeepingwarmincoldseason;Themeasureofimprovingconditionofrestrainingis:(1) Divideandsewanddivideonerationally;(2) Preventthefoundationfromrisingandfallingtoobig;(3) Rationalarrangementconstructionprocess,preventthetoobigdiscrepancyinelevationandsidefromexposingforalongtime;Inaddition,improvetheperformanceoftheconcreteandimproveandresisttheabilityofsplitting,strengthenmaintenance,preventthesurfacefrombeingdoneandcontracted,especiallyguaranteethequalityoftheconcreteisveryimportanttopreventingthecrack,shouldpayspecialattentiontoavoidingproducingandrunningthroughthecrack,theglobalityresumeditsstructureafterappearingisverydifficult,soshouldrelymainlyonpreventingtheemergenceoftherunningthroughcrackwhileconstructing.Inconstructionofconcrete,forraiseturnoverrateoftemplate,demandconcreteformremovalassoonaspossiblethatbuildnewlyoften.Shouldconsiderformremovaltimeproperlywhenconcretetemperatureishigherthanthetemperature,soasnottocausethesuperficialearlycrackofconcrete.Buildingtheearlyformremovalnewly,causeverylargestressofdrawingonthesurface,thephenomenonthattemperatureisassaultedappears.Buildinitialstageinconcrete,becauseheatofhydrationissentout,thesurfacecausessizabletodrawthestress,surfacetemperatureisalsohigherthantemperatureatthismoment,removethetemplateatthismoment,surfacetemperatureisloweredsuddenly,mustcausetemperaturegradient,thusaddanddrawthestressonthesurface,changeandaddwiththeheatofhydrationstress,inaddition,theconcretedriesandcontracts,thesuperficialstressofdrawingreachesverygreatnumbervalue,havedangerofcausingthecrack,butcoveralight-dutyheatinsulatorwithonthesurfaceintimeafterremovingthetemplate,forinstancefoamsponge,etc.,forpreventconcretesurfacefromproducethetoobigstressofdrawing,haveremarkableresults.Addmuscleinfluencetolargevolumetemperaturestressofconcreteverylight,becauselargevolumeconcreteincludemuscletoberateverymuchlow.Justhaveinfluenceonthegeneralarmoredconcrete.Ontermsthattemperatureisnotveryhighandthestressislessthanlimitofsurrendering,everyperformanceofthesteelissteady,andhavenothingtodowithstressstate,timeandtemperature.Linebloatedcoefficientofsteelandconcretelinebloatedcoefficientdifferenceverylight,takeplacelittleinternalstressveryonlybetweenthetwowhilechangingintemperature.Becauseelasticmouldamountofsteelconcreteelasticmould715ofquantity,reachasinteriorconcretestresstensilestrengthandwhenfracturing,thestressofthereinforcingbarwillnotexceed10000kg/cm2.Soisitisitpreventtinyappearancedifficultyverymuchofcrackfromtomakeuseofreinforcingbartowantamongconcrete.Butthecrackinthestructuregenerallybecomesnumerous,theintervalislittle,thewidthanddeptharesmallerafteraddingthemuscle.Andifdiameterofreinforcingbardetailedandwhenintervaldense,toimproveconcreteresistresultofpersonwhosplitbetter.Concreteandsurface,armoredconcreteofstructurecantakeplacedetailedandshallowcrackoften,amongthemthegreatmajoritybelongtoanddoanddrawbackthecrack.Thoughthiskindofcrackisgenerallyallrelativelylight,itstillshavecertaininfluenceontheintensityanddurabilityofthestructure.Inordertoguaranteeconcreteprojectquality,preventfracturing,improvethedurabilityoftheconcrete,usetheadmixturetoreduceoneofthemeasuresthatfracturescorrectly.Whetherisitreducewaterisitsplitpharmaceuticaltodefend,Isummarizehismainfunctioninpracticetouse.(1)ThereisporeDaoofalargenumberofmaointheconcrete,producecapillarytensioninthecapillaryafterwaterisevaporated,makeconcreteisitcontractoutofshapetodo.Increasingthethinapertureofhaircanreducethecapillarysurfacetension,butwillmaketheintensityofconcretereduce.Thissurfacetensiontheoryhasalreadybeenconfirmedintheworldasfarbackasthesixties.(2)Waterdustthaninfluenceimportantfactorthatconcreteshrink,isitreducewaterisitsplitpharmaceuticalcanmakeconcretewaterconsumptionreduceby25%todefendtouse.(3) Cementconsumptionimportantfactor,concreteofpersonwhoshrinktoo,isitaddandsubtractwaterisitsplitconcretereducible15%ofthecementconsumptionontermsthatkeeptheintensityofconcreteofpharmaceuticaltodefendtomix,itsvolumeissupplementedbyincreasingaggregateconsumption.(4) Reducewaterisitsplitpharmaceuticalcanimproveconsistencyofgrout,reduceconcretesecreteinktodefend,reduceandsinkanddrawbackdeforming.(5) Improveglueingthestrengthofformingofthegroutandaggregate,theconcreteimprovedresiststheperformanceofsplitting.(6) Concreteisitproducestressofdrawingtorestrainfromwhileshrinking,crackwhendrawingthestressandisgreaterthanconcretetensilestrengthcanproduce.Reducewaterisitsplitpharmaceuticaleffectiveconcretetensilestrengthofimprovementverytodefend,improveresistingtheperformanceofsplittingofconcretebyawidemargin.(7) Itcanmaketheconcretedensitygoodtoaddtheadmixturetomix,canimproveresistingcarbonizationofconcreteeffectively,reducecarbonizationtoshrink.(8) Isitreducewaterisitsplitslowcoagulationtimeproperconcreteunderpharmaceuticaltodefend,onthebasisofpreventingthefastwaterofcementfromsendingoutheateffectivelytomix,preventtheplasticityshrinkthatbringsbecausethecementisnotcongealedforalongtimefromincreasing.(9) Mixadmixtureconcreteandgettingeasyandkind,surfaceeasytofeelflat,formlittlemembrane,reducethemoisturetoevaporate,reducedrilyandshrink.Alotofadmixtureallhavethefunctionsofslowcoagulation,increasingandapt,improvementplasticity,theexperimentthatweshouldcarryoninthisrespectmoreintheprojectpracticeiscomparedwithandstudied,thanleanagainstnotimprovingtermsmoresimple,maygettingsimpleandmoredirect,economy.Earlymaintenanceof4concretePracticehasproved,thecommoncrackofconcrete,mostisthesurfacecrackofdifferentdepth,mainreasonitswhethertemperaturegradientcausecoldtemperatureofarealowertooeasytoformcracksuddenly.Sosaythewarm-keepingoftheconcreteisespeciallyimportanttopreventingtheearlycrackofsurface.Fromtheviewpointoftemperaturestress,shouldreachandrequiretokeepwarmfollowingly:1) Preventconcreteinternalandexternaltemperaturepoorandconcretesurfacegradientfrom,preventthesurfacecrack.2) Preventconcretefromtobeultraandcold,shouldisitisitmaketheminimumtemperatureisnotlowerthanthesteadytemperatureofconcreteservicetimeconstructiontimeinconcretetotrytotryonesbest.3) Preventtheoldconcretesubcooling,inordertoreducetherestraintamongtheoldandnewconcrete.Theearlymaintenanceoftheconcrete,themainpurposeliesinkeepingthesuitablewarmandhumidcondition,inordertogettheresultoftworespects,ontheotherhandmaketheconcreteavoidtheinvasionandattackoftheunfavorableandwarm,humidityoutofshape,theonesthatpreventfromharmfullyarecoldtocontractanddotocontract.Ononehandmakecementwaterfunctiongoonsmoothly,isinthehopeofreachingtheintensitydesignedandresistingtheabilityofsplitting.Thesuitablewarmdampconditionisinterrelated.Mixwarm-keepingmeasurepaidtocongealoftenprotectwetresultstoo.Analyse,waterconcreteincludemoisturecanmeetdemand,cementofwaterhaveenoughandtosparenewlytheoretically.Butbecausethereasonofevaporatingetc.oftencauseslossesofthemoisture,thuspostponeorhinderwaterofthecementfrom,thesurfaceconcretereceivesthiskindofadverseeffecteasiestlyanddirectly.Keyperiodwhenmaintainedininitialafewdaysaftersotheconcreteisbuilt,shouldpayattentiontoconscientiouslyinconstructing.ConclusionsConstructiontemperatureandrelationofcrackinconcretetheabovecarryonpreliminarydiscussionoftheoryandpractice,thoughtheacademiahasdifferenttheoriestoorigincauseofformationandcomputingtechnologyoftheconcretecrack,buttoconcretepreventionandimprovingthemeasuresuggestiontorelativelyunify,applicationinpracticeresultfinetooatthesametime,concretetoisitobserve,comparemoremorebyustowantinconstructing,analysemore,summarizemoreaftergoingwrong,combinemanykindsofpreventionanddealwiththemeasure,thecrackoftheconcretecanbeavoided.2.QualitycontrolofwaterproofconcreteconstructionCombinedwithexperienee,fromformworkdesign,fabricationandinstallation,assembingreinforoement,pouringandcuringofconcreteandotheraspectsconstructiontechnologyoffair-facedconcreteisintroducedaswellasqualitycontrolmeasuresandstandardsinordertoreduceengineeringcosttoacquiresatisfiedeconomicandsocialbenefits.Thefactorsofinflueningwaterproof-concretequalityareverymanyAnylinksdoesnotpayattentiontothewater-proofconcreteoffieldlosshindersthewaterfunctionwithoutexceptionjointlywithdegree.Engineeringconstructioninthebasementadoptssecondaryformboardfabricationandinstallation,reinforcedbarfabricationandbind,concretestirringandmixingsystemandtransport,concreteconcretecovibrationbeatwithastick,constructionjointpractice,concretecuringanddismantlemodelandbeingreadyforbackfillandsoonaspects.Theseareverycriticaltoqualitymethodtoensurethatwater-proofconcreteselfwater-proof,andthewayofpracticehaswanout.Methodbeingunderconstruction2.1 FabricationandInstallationAccordingtotheconcrettofcloselyknit,demandofreasonwhytoformboardsincethewater-proofalsoconcretehavemadeandhaveassembledcorrespondingriseisspecial,betorequirethatnotleavingoutthickfluid,firmcloselyknitblockofwooddeformation,waterabsorptionCharactershouldbesmallandoughttogiveprioritytoselectandusingbambooslabrubberformboardorthesteelform.Strictcontrolformboardroomgapsize,necessaryexceeding2mmsusesfoamrubberorplastictosqueezeacrackin,porousformboardnonutilitywithoutexceptiontoboardfaceBereadyforwallpostatthesametimerottingthepreventionandcurejobAdoptthecementmortarpouringsame,indiciainbeforetherootsegmentstickingthefoamrubberorplasticstrip,thebottomputsonacementmortar,concreteaconcrete,first5cm10cm.Sincewater-proof,concretestructurewallthicknessismostlymoreinfertile.Betoensurethatcomponentgeometrydimension,Changadopttheinsideandoutsidebolttopullthemeasuremeetingattentionto,respondstoonplayreceiveboltcentreinterposestopwaterironplate,topreventwaterfromformingpilotagepassagealongboltleakage.2.2 AssembingreinforoementWater-proofconcretestructurehasdemandingasfollowstothereinforcedbar1) reinforcedbarshouldadopttwistedsteelasfaraspossible,increasesbyholdwrapaforcecomposinginreplyawaterability2) reinforcedbarsconnectshouldtryonesbesttoadopttosolderconnection,stopusingandbeingneedlesstobindconnectiontothefull3) whenbindingareinforcedbar,theironwireheadrespondstoinnerbending.4) strictcontrolreinforcedbarsprotectivelayerthickness.Minimalthicknessofwater-proofconcretereinforcedbarprotectivelayerisnotsmallerthan25mms,theprotectivelayerwelcomingwatersurfaceespeciallyinadmissibilitytodisappointerror,.Theironwireandreinforcedbarthatapplicationburiesinadvancewithinmortarpiecewhileusingmortarheelblockasprotectivelayer,areboundsolid.Whenthecavalryputsupthefixedreinforcedbarifadoptareinforcedbar,YingJiaalsosolderswaterironplateorfixationjustgoesahead,tostrengthenwater-proofeffectintheheelblock.Thisprojectusesnewmaterialsnylontohavefixedthereisaneffectshadguardedagainstreinforcedbarprotectivelayerdeviationpiecebigmasscommonfailings.TheconcretestirringandmixingmakesandtransportsSincethewater-proofconcreterequiresthathighercloselyknit,reasonwhystirandmixsystemalsoneedtohavethefairlygoodhomogeneity,shouldbereadyforburningasfollowsalmostforthispurpose1) ensuresthatmixingtime,mixingateverytimearesecondaryjumpintoaexpectthegeneralejectionofcompactblockofwoodlessthan2mins.2) shouldusetheappositionagent,thesolutionqueenwhoshouldmanufacturecertainthicknessfromappositionagentaddsthemixerinner,thedriedpowderorhighconcentrationsolutionwilladdanagentextranottoaddsthemixerinnerdirectly,preventfrommixingisunevenbutpartconcentrates,bothlosetheappositionagenteffect,andaffectconcretemass.3) respondstotheassuredsourceoflifedegreehavingaspottestontheadmeasurementconcreteattheregularintervalscollapsingintheprocessbeingunderconstruction,constructionismiddleifYurainsorothercause,respondtotheratiodeterminingwhosewaterratio,andadjustingthecompositionbeingunderconstructionintimewhenchangehappenedinsandstonemoisturecontent.4) projectusesthecommodityconcrete,hasboundaryhaveraisedaconcretestirringmassandofallkindseffectappositionagentadulteratingfallswhenamounts,thewaterashhavingcontrolledaconcretestrictlycollapsing.5) concretesconcreteadoptapumptohavegivenhandicraft,effectiveavoidingaconcreteproducingthephenomenonisolatingMiShuiandleavingoutthickfluidintheprocessoftransportation.2.4 Mattersneedingattentioninbeingunderconstruction1) constructionschoolassignmentsoftandflouryisdivided.Water-proofconcretingshouldstratifystrictlybeinginprogress,andacontinuousconstructioniscompletedThefrontandbackandhighandlowconnectbetweenthetiershouldsubjugatewithinthecementinitialsettingtime，Forthispurpose,withhandlingaworkerdividingintoseveral,atthesametimeeachother,schoolassignmentgroupfacesoritisallrightforeachother,carryontheback.2) AchievestrictlyfixedpointdeterminestheamountsofthecomponentsofasubstancematerialdownAccordingtothevehiclecapacitiesstratifyingconcretealtitudeandthemeansoftransport,thequantifycarryingoutfixedpointstrictlyisabletogodownoneimportantringexpectingthatthisistoimprovewater-proofconcretingmass.3) insistthatyougodownmaterialopeningthedoororusestringtoexpectthatunderbarrel(chute)Betopreventacementpastefrompartingfromaggregatefor,toexpectthatlibertyshouldnotexceed1.5msnowandthenhighlyunderwater-proofconcrete。Thewater-proofstructurereinforcedbarisconcentratedShouldconcretealtitudewhenhigher,respondtoaccordingtothematerialstipulatingthatyougodownmaterialopeningthedooronformboardorusingstringofbarrels(chute)tofall,preventacemen
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