Cement-based composite

Introduction

Cement-basedcompositematerialreferstotheuseofPortlandcementasthematrix,alkali-resistantglassfibergeneralsyntheticfiber,variousceramicfibers,carbonandaramidandotherhigh-performancefibers,Metalwire,naturalplantsandfibersasreinforcements,addfillers,chemicaladditivesandwatertoformacompositematerialthroughacompositeprocess.

Materialpreparation

Basically,accordingtothetypesofreinforcementused,cement-basedcompositematerialshaveimprovedperformancecomparedtoordinaryconcrete.Taketheshort-cutalkali-resistantglassfibercompositematerialwithacontentofabout3~10%asanexample.Itsdensityis1600~2500kg/m³,theimpactstrengthis8.0~21.5N.mm/mm²,thecompressivestrengthis48~83MPa,andthethermalexpansioncoefficientis11-16X10¯⁶K¯ᴵ.Theperformancevarieswiththerawmaterialsused,theratio,theprocessandthecuringconditions.Themoldingprocessofthiscompositematerialbasicallyincludesmethodssuchasstirring,spraying,extrusionwindingandlaying.Aftermolding,acertainmaintenanceprocessisrequiredtopreventdistortionandperformancedegradation.Cement-basedcompositematerialsarebasicallyusedtomanufacturebuildingcomponents,suchasinteriorandexteriorwallpanels,ceilings,etc.Attemptshavebeenmadetoreplacetraditionalsteelbarswithcompositematerialscomposedofhigh-performancefibersandresinsintheconcreteload-bearingframesofsuperhigh-risebuildings.

Overviewofconcrete

Cement-basedcompositematerialsrefertothecombinationofhardenedcementpasteformedbythehydrationandhardeningofcementandwaterasthematrixandvariousotherinorganic,metal,andorganicmaterials.Theresultingmaterialhasnewproperties.Severalmajorchangeshavetakenplaceinconcretematerials,threeofwhicharethemostprominent.ReinforcedconcretefirstappearedinFranceinthemiddleofthe19thcentury,prestressedreinforcedconcretewasinventedbyFrancein1928,andpolymercompositeconcreteandconcreteadmixturesappearedinthepast30years.

Concretematerialsareclassifiedaccordingtocementingmaterials:inorganiccementingmaterialconcrete,organiccementingmaterialconcrete,inorganicandorganiccompositecementingmaterialconcrete.Classifiedbybulkdensity:extra-heavyconcrete,heavyconcrete,lightconcrete,extra-lightconcrete.Classifiedbyconcretestructure:ordinarystructuralconcrete,fine-grainedconcrete,macroporousconcrete,porousconcrete.Accordingtothepurposeofclassification,structuralconcrete,thermalinsulationconcrete,decorativeconcrete,acid-resistantconcrete,etc.

Thepropertiesofconcrete:Theconcretemixturemusthavegoodworkabilitytoensuregoodpouringquality.

①Fluidity:referstothenatureofthemixturethatflowsorslumpsunderitsownweightortheexternalforceofmechanicalvibrationtofillthetemplateuniformlyanddensely.

②Cohesiveness:Itmeansthatthemixturehasacertaincohesiveforceintheprocessoftransportationorpouring,sothattheconcretewillmaintaintheoveralluniformperformancewithoutstratificationandsegregation.

③Waterretention:Itmeansthatthemixturehaswaterretentioncapacityandgoodwaterretentionduringtheconstructionprocess,anditisnoteasytoproduceseriousbleeding.

High-performanceconcrete

Concrete:acompositematerialmadeofcement,coarseandfineaggregatestonesandsandinanappropriateproportionanduniformlymixedandvibratedtoformandcuredundercertainconditions.Themaindifferencebetweenhigh-strengthconcrete(HSC)andhigh-performanceconcreteisthatthelatteremphasizesdurability.High-performanceconcretemustnotonlyhavehighstrengthbutalsohighcompactnessandhighvolumestability.Thecharacteristicsofhigh-performanceconcreteintermsofmicrostructure:duetothepresenceofalargenumberofunhydratedcementparticles,theproportionofslurryisreduced.Thetotalporosityoftheslurryissmall,theporesizeissmall,andonlythesmallestporesarewater-saturatedslurry-aggregates.Thereisnoobviousdifferencebetweentheinterfaceandtheslurrybody,whicheliminatesthelowfreecalciumoxidecontentintheweakarea.Thecharacteristicsofhigh-performanceconcrete:self-compacting;goodvolumestability;highstrength,itscompressivestrengthhasexceeded200MPa;waterashisrelativelylow,thehydrationreactionisterminatedearlier,andthetotalheatofhydrationiscorrespondinglyreduced;Afteralongerduration,thetotalshrinkagestrainofhighperformanceconcreteisinverselyproportionaltoitsstrength,andtheearlyshrinkagerateincreaseswiththeincreaseinstrength;thecreepdeformationissignificantlylowerthanthatofordinaryconcrete;theCl-permeabilityislowerthanthatofordinarycement.Itmeetsenvironmentalprotectionrequirements;ithashighcompactnessandimpermeability,anditschemicalresistanceissignificantlybetterthanordinarystrengthconcrete;itwillburstandpeelundertheactionofhightemperature.

Fiber-reinforcedcement-basedcompositematerial

Fiber-reinforcedcement-basedcompositematerialisacompositematerialformedbydiscontinuousfibersuniformlydispersedinacementconcretesubstrate.FiberandcementslurryThebondingofthebasematerialisrelativelystrong,formingafibernetworkthroughoutthestructure.Whenthebasicmaterialissubjectedtoexcessivetensionandcracks,thetensioncanbegraduallytransferredtothefibersacrossthecrack,whichincreasesthedeformabilityoftheconcretestructure.Thehighertensilestrengthofthefiberincreasesthetensilestrengthoftheconcretestructure.Thetensile,bending,cracking,fatigue,vibrationandimpactresistanceofcompositematerialshavebeensignificantlyimproved.Themainperformancecharacteristicsoffiber-reinforcedcement-basedcompositematerials:themechanicalpropertiesaresignificantlyimprovedthanordinaryconcrete;theslumpvalueoffreshconcreteislowerthanthatwithoutfiber;theimpermeabilityofconcreteissignificantlyimproved;themixingprocessiseasytoproduceFiberclumpingphenomenon;delaminationsometimesoccursduringtransportationandpouring.Thedevelopmenttrendoffiberreinforcedconcreteis:steelfiberandglassfiberarerecognizedasthemostpromisingreinforcingfibers;alkali-resistantglassfibermaybecomeasubstituteforasbestosinthefuture;syntheticfiberssuchaspolypropyleneandnylonarecompletelyineffectiveinincreasingtensilestrength,Buttheimpactresistanceisverygood;theflexuralstrengthofcarbonfiberisbetweenthatofsteelfiberandalkali-resistantglassfiber.Amongvariousfibers,steelfiberhasthebestabilitytorestraincracksandisalsothemosteffectiveforflexuralandtensilestrength.Thetoughnessofreinforcedconcreteisthebest.

Polymercement-basedcompositematerials

Polymercementconcreteismixedwithacertainamountofpolymerduringthemoldingprocessofcementconcretetoimproveitsqualityofusetomeetthespecialneedsofengineering.Theperformancecharacteristicsofconcrete:highrigidity,lowflexibility,andcompressivestrengthfargreaterthantensilestrength.Thepolymerhasthefunctionsoftoughening,plasticizing,fillingandcuringinthecementmatrix.Comparedwithordinaryconcrete,theperformanceimprovement:compressivestrengthandtensilestrengthcanbeincreasedby3times;modulusofrupturecanbeincreasedbynearly3times;modulusofelasticitycanbeincreasedby1time,andmodulusofflexuralelasticitycanbeincreasedbynearly50%;elasticdeformationThehardnessisreducedby10timesandthehardnessisincreasedbymorethan70%;thewaterpermeabilityisalmost0andthewaterabsorptionratecanbereducedby83-95%.Concreteproperties:Themechanicalpropertiesareimproved,theflexuralstrengthisincreased,andthecompressivestrengthisreduced;therigidityisreduced,andthedeformationcapacityisincreased;thedurabilityandcorrosionresistanceareimproved;theadhesionisgood,suitableforrepairingdamagedcementconcrete;fullyadapttothecurrentsituationThereisamanufacturingprocessofcementconcrete;thecostisrelativelylow.Therearetwomainformsofpolymercement-basedcomposites:polymerimpregnatedconcrete;polymercementconcrete.Applicationofpolymercement-basedcompositematerials:polymerimpregnatedconcreteismainlyusedforstressedconcreteandreinforcedconcretestructuralmembersduetoitsgoodmechanicalproperties,durabilityandcorrosionresistance.Becausetheimpregnationprocessiscomplicatedandthecostishigh,theconcretecomponentsneedtobeprefabricatedandthesizeislimited,sotheyaremainlyusedinspecialsituations.Thecomprehensiveperformanceofpolymercementconcreteisnotasgoodaspolymerimpregnatedconcrete,butitsprocessissimple,easytouse,andlowcost,andithasbeenmoreandmorewidelyused.Ifappliedtogroundandroadengineering,appliedtostructuralengineering.