6外文翻译双面打印Word文档下载推荐.docx

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Baseduponanalysisofthereasonscausedthecracksofconcretethetemperaturestressofconcreteisstudied.Thecontrolmeasuresoftemperaturestressaswellaspreventivemeasuresofcracksareelaboratedindetailinordertoavoidproductionofcracksinconstructionprocesstoensureconstructionquality.

Keywords:

concrete,temperaturestress,crack,construction

Inthemassconcrete,temperaturestressandtemperaturecontrolsystemhasgreatsignificance.Therearetworeasons:

1）Intheconstructionofconcreteitoftenappeartemperaturecracks,whichaffectstheintegrityanddurabilityofthestructure;

2）Intheoperationprocess,thetemperaturechangeshaveinfluenceonstressstateofstructurewhichcannotbeignored.Sincetemperaturecrackcausedintheconstructionismainlymet,thecausesofcracksandProcessingmeasuresintheconstructionisexploredinthispaper.

1.thecausesofthecracks

Cracksinconcreteareavarietyofreasons,mainlytemperatureandhumiditychanges,brittleandunevenconcrete,aswellasthestructureisirrational,failureofrawmaterials（suchasalkali-aggregatereaction）,templatedeformation,andsoonthebasisofdifferentialsettlement.

Theconcretetohardenoffalargenumberofcementduringthehydrationheat,theinternaltemperaturerisingonthesurfacecausedbytensilestress.Lateinthecoolingprocess,duetocoagulationonthebasisoforbeboundbytheold,willemergeintheconcretetensilestress.Lowertemperaturesintheconcretesurfacewillbealotoftensilestress.Whenthetensilestressbeyondthecapacityofconcretecrack,thecrackswillappear.Anumberofconcretechangesintheinternalhumidityorchangesverylittleslow,butpossiblechangesinsurfacehumidityormoredramaticchanges.Suchasconservation,failedtokeepdrywhenwet,surfaceshrinkagedeformationofconcretesubjecttointernalconstraints,butalsooftenleadstocracks.Short-termloadingatthetimeofultimatetensiledeformationonly（0.6~1.0）×

104,thelimitoflong-termloadingspaceswhentheonlystretchdeformation（1.2~2.0）×

104.Unevenlyasaresultofrawmaterials,water-cementratioofinstability,andtransportationandpouringintheprocessofsegregationphenomena,inthesamepieceofconcreteinthetensilestrengthisuneven,therearemanylowtensilecapacity,easytofractureinaweakposition.Inreinforcedconcrete,thetensilestressismainlybornebythesteel,concreteissubjecttocompressivestress.Inplainconcreteorreinforcedcoagulationontheedgeofthesiteifthestructureofthetensilestressappearstoberelyingonitsownconcretecommitment.

2.thermalstressanalysis

Accordingtotheformationofthermalstresscanbedividedintothefollowingthreestages:

（1）early:

Sincethebeginningofpouringconcretetocementtheendofexothermicbasicgeneralabout30days.Twocharacteristicsofthisstage,first,toreleasealargenumberofcementhydrationheat,andtheotheristheelasticmodulusofcoagulationdramaticchanges.Modulusofelasticityasaresultofchangeswithinthisperiodintheformationofresidualstressintheconcrete.

（2）medium-term:

fromthebasicroleofcementheatuntiltheendofthestabletemperatureoftheconcretecoolingtime,duringthisperiod,thetemperaturestresswasmainlyduetocoolingandtheoutsideconcretecausedbytemperaturechanges,stressandearlyformationoftheseresidualstresssuperpositionphase,duringwhichthecoagulationoftheelasticmoduluschangedlittle.

（3）late:

concretecompletelycoolingperiodaftertheoperation.Thermalstressismainlycausedbyexternaltemperaturechanges,thestressandthefirsttwo-phasesuperpositionofresidualstress.

Underthethermalstresscausedbythereasonscanbedividedintotwocategories:

（1）self-stress:

thereisnoconstraintontheborderorcompletelystaticstructure,iftheinternaltemperaturedistributionisnonlinear,duetostructuralconstraintsarisingfromtheirco-temperaturestress.Forexample,theconversionlayerofitsrelativelylargersize,concretecoolingsurfacetemperaturelow,theinternaltemperaturesarehigh,thesurfacetensilestress,compressivestressappearsinthemiddle.

（2）boundbystress:

thestructureofallorpartoftheboundaryboundbytheoutsideworldcannotbefree-formdeformationcausedbystress.Roofbox,suchasconcreteandconcretebarrier.

Boththetemperatureandtheconcretestressisoftencausedbyshrinkageofthecombinedeffectofstress.

Knowntobeinaccordancewithanaccurateanalysisofthetemperatureofthethermalstressdistribution,sizeisamorecomplextask.Inmostcases,theneedtorelyonmodeltestornumericalcalculation.Creepofconcretesothatthetemperaturethereisconsiderablestressrelaxation,thermalstresscalculation,wemustconsidertheeffectsofcreep,isnolongercalculatedindetailhere.

3.temperaturecontrolandmeasurestopreventthecracks

Inordertopreventcracking,reducethethermalstresscancontroltheconditionsoftemperatureandtoimprovethebindingoftwoaspects.

Temperaturecontrolmeasuresareasfollows:

（1）usedtoimprovetheaggregategradation,dryhardconcrete,mixedmixture,addair-entrainingagentorplasticizer,etc.measurestoreducetheamountofcementconcrete;

（2）mixingconcretebyaddingwaterorcoolingwaterwillbegravelandpouringconcretetoreducethetemperature;

（3）pouringhotdaystoreducethepouringofconcretethickness,theuseofpouringheatlevels;

（4）laidinconcretewaterpipes,accesstocoldwatertocool;

（5）theprovisionsofreasonabletime,thetemperaturedropwhenthesurfaceinsulation,concretesurfaceinordertoavoidasharptemperaturegradient;

（6）Constructionoflong-termexposuretoblockthesurfaceoftheconcretepouring,orthin-walledstructures,thermalinsulationinthecoldseasontotakemeasures;

Measurestoimprovetheconstraintsare:

（1）areasonablesub-blockjoints;

（2）basistoavoidtoomuchupsanddowns;

（3）reasonablearrangementsfortheconstructionprocess,toavoidexcessivesideelevationandlong-termexposure;

Inaddition,toimprovetheperformanceofconcretetoimprovetheanti-crackingability,tostrengthentheconservation,topreventsurfacedrying,inparticular,istoensurethequalityofconcreteisveryimportanttopreventcracks,shouldpayspecialattentiontoavoidcross-cracksappearstorestoretheintegrityofitsstructureitisverydifficult,sotheconstructionshouldbetopreventtheoccurrenceofcross-cuttingthemaincrack.

Inconcreteconstruction,inordertoincreasetheturnoverrateofthetemplate,oftenrequirenewpouringconcreteassoonaspossible.Whentheconcretetemperatureishigherthanthetemperatureshouldbeappropriatetoconsidertime,soastoavoidtheearlycracksintheconcretesurface.Newpouringearly,alotofthesurfacetensilestress,a"

temperatureshock"

phenomenon.Concretepouringintheearlyheatofhydrationasaresultofthedisseminationofthesurfacecausedbyalargetensilestress,whenthesurfacetemperatureishigherthanthetemperatureatthistimetoremovethetemplate,asharpfallinsurfacetemperatureisboundtoleadtotemperaturegradient,soanadditionaloneonthesurfacetensilestress,thermalstresssuperpositionandhydration,coupledwiththeshrinkageofconcrete,

Tensilestresstoreachthesurfaceofgreatvalue,thereisthedangerofleadtocracks,butifinatimelymanneraftertheremovalofthetemplateonthesurfacecoverageofalightinsulatingmaterial,suchasfoamspongeandsoon,haveaconcretesurfacetopreventexcessivetensilestress,withsignificantresults.

Reinforcedconcreteonthelargevolumeofthermalstresshaslittleeffectbecausethelargevolumeofconcretereinforcedwithaverylowrate.Onlyonthegeneralimpactofreinforcedconcrete.Nottoohighintemperatureandstressbelowtheyieldlimitundertheconditionofthepropertiesofsteelisstable,andwiththestress,timeandtemperaturehasnothingtodo.Linearexpansioncoefficientofsteelandconcretelinearexpansioncoefficientdifferencebetweenthesmallchangesintemperaturebetweenthetwowithonlyaverysmallstress.Sincethemodulusofelasticityofsteeltoconcreteelasticmodulusof7~15-fold,whenthestressreachedthetensilestrengthofconcreteandcracking,thesteelstresswillnotexceed100~200kg/cm2..So

Wanttouseinreinforcedconcretetopreventtheemergenceofsmallcracksisdifficult.However,afterthereinforcedstructureofthenumberofcracksingeneralhasbecomemorethanasmalldistance,asmallerwidthanddepth.Andifthediameterofsteelthinandclosespacing,thecrackresistanceofconcretetoenhancetheeffectofbetter.Concreteandreinforcedconcretestructureofthesurfaceoftenoccurcracksinthinandshallow,mostofthembelongingtoshrinkagecracks.Whilethisisgenerallyshallowcracks,butitsstrengthanddurabilityofthestructureisstillacertainimpact.

Inordertoensurethequalityofconcretetopreventcrackingandimprovethedurabilityofconcrete,theproperuseofadmixturesisalsooneofthemeasurestoreducecracking.Suchastheuseofanti-crackingagentandwater,inpractice,itsmajorroleinconcludingasfollows:

（1）theexistenceofalargenumberofporesintheconcretethat,afterevaporationofwatergeneratedbycapillarycapillarytension,deformationoftheconcreteshrinkage.Poresincreasedcapillarydiametercanreducethesurfacetension,butwouldreducethestrengthofconcrete.

（2）theimpactofwater-cementrat