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Causesandcontrolmeasuresofconcretecracksstudytheproblem
Keywords:
Causespreventionofconcretecracks
Abstract:
Atpresent,paidcloseattentiontotheproblemofconcretecracks,thiscrackintheconcreteonthebasisofclassification,analysisofthecausesofdifferentcracks,andproposedmeasurestocrackpreventionandtreatment.
1.Introduction
Isthemaximumamountofconcreteasabuildingmaterial,widelyusedinindustrialandcivilconstruction,agricultureandforestrywithurbanconstruction,waterconservancyworksintheharbor.However,manyconcretestructuresoccursduringtheconstructionanduseofdifferentdegreesanddifferentformsoffracture.Thisnotonlyaffectstheappearanceofthebuilding,butalsoendangerthenormaluseofbuildingsandstructuresdurability.Therefore,thecracksbecomepeopleconcerns.Inrecentyears,withtheready-mixedconcreteandvigorouslypromotetheuseandstructurebecomeincreasinglylarge,complex,makingtheproblemevenmoreprominent.However,cracksinconcretestructuresisafairlycommonphenomenon,largenumberofengineeringpracticeandmodernscienceontheconcretestrengthofmicrostudiesshowthatthestructuresofthecrackisinevitable,whichisapropertyofthematerial.Therefore,thescientifictreatmentofcracksinthecrackproblemistoclassifyonthebasis,adopteffectivemeasurestoharmfullevelsofcrackcontroltotheextentpermitted.Thisconcretestructurewillcausecracksincommon,controlmeasuresandtherepairmethodtoanalyzesomelight.
2.Classificationofconcretecracks
2.1DividedbyCrackAccordingtothecausesofconcretecracks,structuralcracksandcanbedividedintotwomajorcategoriesofnon-structuralcracks.
(1)StructuralcracksCausedbyavarietyofexternalloadscracks,alsocalledloadcracks.Itincludestheexternalloadscausedbythedirectstresscracksandthestructureunderexternalloadscausedbysecondarystresscracks.
(2)Non-structuralcracksDeformationcausedbythechangefromavarietyofcracks.Itincludestemperature,shrinkageandswellingcausedbyfactorssuchasdifferentialsettlementcracks.Suchcracksinthestructurewhenthedeformationisrestrictedduetothestresscaused.Researchdatafromabroadandalargenumberofengineeringpractice,non-structuralcracksintheworksinthemajority,about80%,whichledtoshrinkagecracks.
2.2Dividedbythetimethecracks
(1)CracksduringconstructionIncludingplasticshrinkagecracks,settlementshrinkagecracking,dryingshrinkagecracks,shrinkagecracksitself,thetemperaturecracks,thecrackswereimproperconstructionoperations,theroleofearlyfrost,andsomeirregularcrackscausedbycracks.
(2)UseofcrackduringIncludingtheexpansionofsteelcorrosioncracksgenerated,saltandaciderosiontypeliquidmediumcausedbycracks,thecrackscausedbyfreezingandthawing,alkaliaggregatereaction,andcrackscausedbycyclicloadingcumulativedamagecausedbycracks.
2.3Classificationoffracturedbycracksintheshapeoftheshapecanbedividedby:
(1)Longitudinalcracksparalleltothebottomcomponent,thedistributionalongtendons,mainlycausedbytheroleofsteelcorrosion
(2)Transversecracksperpendiculartothebottomcomponentmainlybytheloading,temperatureeffectscaused
(3)Shearcracksduetodisplacementcausedbyverticalloadorvibration
(4)Diagonalcrackseightshapedorherringbonecracks,commoninthewallofconcretebeams,mainlyduetotheunevenfoundationsettlement,andthermaleffectscausedby
(5)X-shapedcrackscommonintheframeworkofbeams,columnsandwallsontheends,duetotheimpacteffect,ormomentloadscausedbyearthquake
(6)Allkindsofirregularcrackssuchasrepeatedfreezingandthawing,orfirescausedbycracks
Inaddition,concretemixingandtransporttimeforlongcracksduetomesh,squareappearsfloorslaborplatesurfaceradialcracksappearinthecrosscracksandsoon.
2.4Thedevelopmentofthestatedividedbycracks
Accordingtofracturethemovementinwhichthestateanddevelopmenttrends,canbedividedintothefollowingcategories:
(1)StablecrackThiscrackdoesnotaffectthepersistenceofapplications,includingtwotypes.Oneisinmotiontheprocessofself-healingoffracturescouldbecommoninanumberofnewwaterprojects,thisisbecausethecrackofcementparticlesintheleakageofwaterfurthercompoundstheprocess,precipitateCa(OH)2crystalandpartoftheCa(OH)2hasdissolvedinthewaterwithCO2carbonationreactiontoformCaCO3crystallizationoccurs,boththeformationofcracksinthegelmaterialwillbegluedclosed,andthusstoptheleakage,crackstoheal.Theotherisinastablemovementofthecracks,suchastheperiodicloadgeneratedbythecyclicalexpansionandclosureofcracks.
(2)UnstablecrackThiswillresultininstabilityofcrackextension,affectingthesustainableuseofstructures,shouldbeconsideredpartofitsexpansion,totakecorrespondingmeasures.
3.Causesofcracksinconcreteandcontrolmeasures
3.1ShrinkagecracksShrinkagecracksarecausedbythehumidity,itaccountsfornon-structuralcracksinconcreteinthemainpart.Weknowthatconcreteisacementasthemaincementingmaterialtonaturalsand,stoneaggregatemixingwater,aftercastingmolding,hardensandtheformationofartificialstone.Intheconstruction,inordertoensureitsworkability,oftenaddingcementhydrationthanwaterneededfor4to5timesmorewater.Moreofthesewatertofreestateexists,andthegradualevaporationofthehardeningprocess,resultingintheformationoflargeporesinsidetheconcrete,voidsorholes,resultinginvolumeshrinkageofconcrete.Inaddition,thehardeningprocessofconcretehydrationandcarbonationofconcretevolumewillleadtoshrinkage.Accordingtotheexperimentaldeterminationoftheultimateshrinkageofconcreteisabout0104%~0106%.Showsthatshrinkageistheinherentphysicalpropertiesofconcrete,ingeneral,thelargerwater-cementratio,thehighertheconcretestrength,aggregateless,thehigherthetemperature,surfacewaterlossislarger,thelargerthevalueofitscontract,themoreeasilyshrinkagecracks.Accordingtotheformationofshrinkagecracksandformationmechanismofthetime,worksinthecommonshrinkagecracksaremainlyplasticshrinkagecracks,settlementshrinkagecrackinganddryingshrinkagecracksinthreecategories,inadditiontotheircontract(chemicalshrinkage)cracksandcarbonationshrinkagecracks.
3.1.1PlasticshrinkagecracksPlasticshrinkagecracksinconcreteplasticstage,beforethefinalset.Thecauseofthisisconcretepasteandquicklyevaporatingwaterflowtothesurface,withtheincreaseinwaterloss,capillarynegativepressuregeneratedbycontractionoftheconcretesurfaceofthedrasticvolumeshrinkage.Strengthofconcreteatatimehasnotyetformed,whichresultedincrackingoftheconcretesurface.Thismulti-cracksindryweather,hotandwindy,thefractureshallow,intermediatewidth,bothendsofthefine,ofdifferentlengths,anddisconnected.
3.1.2SettlementshrinkagecrackingSettlementshrinkagecracksinconcretepouringabouthalfanhouraftertheoccurrenceandhardeningstops.ThecauseofthisisoccurringaftertheslurryinthePouringunevensink,sinkingofcoarseaggregate,cementgroutfloat,whenthesettlementwasinhibited(suchassteelorembeddedpartsoftheblock)isduetoshearingandcrackingoftheconcrete.Inaddition,floatingintheplasmalayerformedonthesurfacewillbearesultofbleedingandcracking.Thismulti-cracksintheconcretesurface,andpassalongthelongdirectionofthereinforcement,orthestirrupsthedistributionwidthofbothendsofthenarrowmiddle,isacommonearlycracks,especiallyinthepumpconstructionismorecommon.
3.1.3DryingshrinkagecracksDryingshrinkagecracksintheconcretecuringonlyappearedaftercompletion.Itsformationwasmainlyduetotheconcretetoharden,thewaterevaporationcausedbyshrinkageoftheconcretesurface,whentheshrinkagedeformationofconcretebyinternalconstraint,haveagreatertensilestresstocracktheconcretesurfaceispulled.Shrinkagecracksonthesurfacegenerallyproducesveryshallowlocation,multi-componentalongtheshortdirectionofdistribution,wereparallel,linear,ormesh,canbeseverethroughoutthemembersection.
3.1.4Self-shrinkagecracksShrinkagecracksitselfhasnothingtodowiththeoutsidehumidity,butbecauseofthehydrationreactionofcementclinkerintheprocess,thereactionresultantoftheaveragedensityofsmallervolumeshrinkagecausedbysystem(calledchemicalshrinkage)due.Mainlyduetohydrationproductsoffreewaterintoapartofit39;
sspecificvolumereducedby1/4(ie0125cm3Pg).Therefore,thechemicalshrinkageofthesizeofthereductiondependsonthechemicalcombinationofcementhydrationproductsintheamountofwater.
3.1.5CarbonationshrinkagecrackingCarbonationcarbonationshrinkagecracksarefreeionsgeneratedbywaterevaporation,causingshrinkageintheslurry.CarbonationisatmosphericCO2conditionsinthewaterreactswiththehydrationproductofCaCO3,alumina,silicaandwaterfreestate,thispartofthevolumeshrinkageofconcretecausedbywaterevaporation(knownascarbonationshrinkage),anditsessenceisthecarbonateofthecementcorrosion.GeneralalkalinityofcementhydrationproductsandthehighertheconcentrationofCO2inairandmoderatehumidity(50%),themorepronetocarbonation.Therefore,thiscrackpropagationinalternatingwetanddryenvironment,anddryorwatersaturatedenvironment,thereisnoteasy;
andbe