搜索
1DiscusstheconstructiontemperatureandcrackoftheconcretelightlyByG.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,thetemperaturechangehasremarkableinfluencethatcan'tbeignoredonthestressstateofthestructure.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,contractsurfacetherearen'tdeformationdoing,oftencausethecracktoo.Theconcreteisakindoffragilitymaterial,tensilestrengthisabout1/10ofthecompressionstrength,isitcarryonone'sshoulderorbacklimitwhendrawoutofshapetohave*104only,isitcarryonone'sshoulderorback2limitlocationwhenstretchoutofshapetothereis*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,pre