Cracks and Repairs of R.C Structures裂缝与结构维修

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1、CracksandRepairsofR.CStructuresCracksinbuilding•Structuralcracks–duetoincorrectdesign–faultyconstruction–Overloading•NonStructuralcracks–Moisturechanges–Thermalmovement–Elasticdeformation–Creep–Chemicalreaction–Foundationmovementandsettlementofsoil–VegetationNonStructuralcracks:MoistureChanges•Bui

2、ldingmaterialsexpandonabsorbingmoistureandshrinkondrying.Thesearegenerallyreversible.Shrinkageinconcreteormortardependsonanumberoffactors•Cementconcrete:Richerthemixgreateristhedryingshrinkage.•Watercontent:Morewaterinmixinducesgreatershrinkage•Aggregates:Largeaggregateswithgoodgradinghaslessshrin

3、kageforsameworkabilityaslesswaterisused•Curing:Ifpropercuringstartsassoonasinitialsethastakenplaceandcontinuedfor7to10days,shrinkageiscomparativelyless.•Excessivefines:Morefinesinaggregaterequiresmorewaterforsameworkabilityandhencemoreshrinkage.•Temperature:Concretemadeinhotweatherneedsmorewaterfo

4、rsameworkabilityandhenceresultsinmoreshrinkage.SomeMeasuresforcontrollingshrinkage•Shrinkageinplasteringcanbereducedbyensuringproperadhesion.Theplasteredshouldnotbestrongerthanthebackground.•Shrinkagecracksinmasonrycanbeminimizedbyavoidinguseofrichcementmortarandby8delayingplasteringtillmasonryhas

5、driedafterpropercuringandhasundergonemostofitsinitialshrinkage.ThermalMovement•.Thecrackingofatypicalstructureduetothermalmovementisgiveninfigurebelow.•Incaseofframedbuildingsduetothermalmovementframesaredistortedandcracksmayappearasshowninfigurebelow.•8PreventionofThermalCracks•Topreventthermalcr

6、acksexpansionjoints,controljointsandjointsincaseofchangeofshapeanddirectionofwinginastructurearetobeprovided.8Generalguidelinestoprovidemovementjoints  TypeofStructureMovementofJointsaRCroofslabProvide20to25mmwide,jointat10to20Mapartb SupportsforRCslabs4to6MlengthProvideslipjointbetweenslabandbear

7、ingwall.cRCframedstructure,otherloadandbearingstructureProvide25to40mmwideexpansionJointsat30to45MintervaldJunctionbetweenoldandnewstructureProvideverticalslipjoints.eCompoundwallsExpansionjoint5to8mmwideat5to8Mi