土木工程外文文献及翻译

（建筑工程管理）土木工程外文文献及翻译外文文献：MaterialsandStructures©RILEM201010.1617/s11527-010-9700-yOriginalArticleImpactofcrackwidthonbond:confinedandunconfine谢谢阅读drebarDavidW.Law1,DengleiTang2,ThomasK.C.Molyneaux3andRebeccaGravina3谢谢阅读(1SchooloftheBuiltEnvironment,HeriotWattUniversity,Edinburgh,EH谢谢阅读)144AS,UK(2VicRoads,Melbourne,VIC,Aust感谢阅读)ralia(3SchoolofCivil,EnvironmentalandChemicalEngineering,RMITUniversi精品文档放心下载)ty,Melbourne,VIC,3000,Australia精品文档放心下载DavidW.LawEmail:D.W.Law@hw.ac.ukReceived:14January2010Accepted:14December2010Publishedon精品文档放心下载line:23December2010AbstractThispaperreportstheresultsofaresearchprojectcomparingthe精品文档放心下载effectofsurfacecrackwidthanddegreeofcorrosiononthebondst感谢阅读rengthofconfinedandunconfineddeformed12and16mmmildsteelr感谢阅读einforcingbars.Thecorrosionwasinducedbychloridecontamina感谢阅读tionoftheconcreteandanappliedDCcurrent.Theprincipalparam精品文档放心下载etersinvestigatedwereconfinementofthereinforcement,theco谢谢阅读verdepth,bardiameter,degreeofcorrosionandthesurfacecrack感谢阅读width.Theresultsindicatedthatpotentialrelationshipbetwee精品文档放心下载nthecrackwidthandthebondstrength.Theresultsalsoshowedani感谢阅读ncreaseinbondstrengthatthepointwhereinitialsurfacecracki感谢阅读ngwasobservedforbarswithconfiningstirrups.Nosuchincrease谢谢阅读wasobservedwithunconfinedspecimens.谢谢阅读Keywords:bond;corrosion;rebar;cover;crackwidth;concrete精品文档放心下载1IntroductionThecorrosionofsteelreinforcementisamajorcauseofthede精品文档放心下载teriorationofreinforcedconcretestructuresthroughoutthewo精品文档放心下载rld.Inuncorrodedstructuresthebondbetweenthesteelreinforc谢谢阅读ementandtheconcreteensuresthatreinforcedconcreteactsinac感谢阅读ompositemanner.However,whencorrosionofthesteeloccursthis精品文档放心下载compositeperformanceisadverselyaffected.Thisisduetothefo谢谢阅读rmationofcorrosionproductsonthesteelsurface,whichaffectt精品文档放心下载hebondbetweenthesteelandtheconcrete.谢谢阅读Thedeteriorationofreinforcedconcreteischaracterizedb感谢阅读yageneralorlocalizedlossofsectiononthereinforcingbarsand感谢阅读theformationofexpansivecorrosionproducts.Thisdeteriorati谢谢阅读oncanaffectstructuresinanumberofways;theproductionofexpa谢谢阅读nsiveproductscreatestensilestresseswithintheconcrete,whi精品文档放心下载chcanresultincrackingandspallingoftheconcretecover.Thisc感谢阅读rackingcanleadtoacceleratedingressoftheaggressiveagentsc感谢阅读ausingfurthercorrosion.Itcanalsoresultinalossofstrengtha感谢阅读ndstiffnessoftheconcretecover.Thecorrosionproductscanals感谢阅读oaffectthebondstrengthbetweentheconcreteandthereinforcin感谢阅读gsteel.Finallythecorrosionreducesthecrosssectionoftherei谢谢阅读nforcingsteel,whichcanaffecttheductilityofthesteelandthe精品文档放心下载loadbearingcapacity,whichcanultimatelyimpactupontheservi精品文档放心下载ceabilityofthestructureandthestructuralcapacity[12,25].精品文档放心下载Previousresearchhasinvestigatedtheimpactofcorrosiono感谢阅读nbond[2–5,7,12,20,23–25,27,29],withanumberofmodelsbein精品文档放心下载gproposed[4,6,9,10,18,19,24,29].Themajorityofthisresearc谢谢阅读hhasfocusedontherelationshipbetweenthelevelofcorrosion(m谢谢阅读asslossofsteel)orthecurrentdensitydegree(corrosioncurren精品文档放心下载tappliedinacceleratedtesting)andcrackwidth,orontherelati精品文档放心下载onshipbetweenbondstrengthandlevelofcorrosion.Otherresear感谢阅读chhasinvestigatedthemechanicalbehaviourofcorrodedsteel[1,1谢谢阅读1]andthefrictioncharacteristics[13].However,littleresear谢谢阅读chhasfocusedontherelationshipbetweencrackwidthandbond[23,2谢谢阅读6,28],aparameterthatcanbemeasuredwithrelativeeaseonactua感谢阅读lstructures.Thecorrosionofthereinforcingsteelresultsintheformati精品文档放心下载onofironoxideswhichoccupyalargervolumethanthatoftheparen谢谢阅读tmetal.Thisexpansioncreatestensilestresseswithinthesurro感谢阅读undingconcrete,eventuallyleadingtocrackingofthecoverconc感谢阅读rete.Oncecrackingoccursthereisalossofconfiningforcefromt谢谢阅读heconcrete.Thissuggeststhatthelossofbondcapacitycouldber精品文档放心下载elatedtothelongitudinalcrackwidth[12].However,theuseofco谢谢阅读nfinementwithintheconcretecancounteractthislossofbondcap精品文档放心下载acitytoacertaindegree.Researchtodatehasprimarilyinvolved精品文档放心下载specimenswithconfinement.Thispaperreportsastudycomparing感谢阅读thelossofbondofspecimenswithandwithoutconfinement.感谢阅读2Experimentalinvestigation感谢阅读2.1SpecimensBeamendspecimens[28]wereselectedforthisstudy.Thistyp谢谢阅读eofeccentricpulloutor‘beamend’typespecimenusesabondedl感谢阅读engthrepresentativeoftheanchoragezoneofatypicalsimplysup谢谢阅读portedbeam.Specimensofrectangularcrosssectionwerecastwit感谢阅读halongitudinalreinforcingbarineachcorner,Fig.1.An80mmpla感谢阅读stictubewasprovidedatthebarunderneaththetransversereacti谢谢阅读ontoensurethatthebondstrengthwasnotenhancedduetoa(transv谢谢阅读erse)compressiveforceactingonthebaroverthislength.感谢阅读Fig.1BeamendspecimenDeformedrebarof12and16mmdiameterwithcoverofthreetime精品文档放心下载sbardiameterwereinvestigated.Duplicatesetsofconfinedandu感谢阅读nconfinedspecimensweretested.Theconfinedspecimenshadthre精品文档放心下载esetsof6mmstainlesssteelstirrupsequallyspacedfromtheplas精品文档放心下载tictube,at75mmcentres.Thisrepresentsfourgroupsofspecimenswithacombinationo谢谢阅读fdifferentbardiameterandwith/withoutconfinement.Thespeci感谢阅读menswereselectedinordertoinvestigatetheinfluenceofbarsiz谢谢阅读e,confinementandcrackwidthonbondstrength.感谢阅读2.2MaterialsThemixdesignisshown,Table1.ThecementwasTypeIPortland谢谢阅读cement,theaggregatewasbasaltwithspecificgravity2.99.Thec精品文档放心下载oarseandfineaggregatewerepreparedinaccordancewithAS1141-感谢阅读2000.MixingwasundertakeninaccordancewithAS1012.2-1994.Sp谢谢阅读ecimenswerecuredfor28daysunderwethessianbeforetesting.精品文档放心下载Table1Concretemixdesign10mmwas7mmwashMateriCementw/cSandhedaggredaggreSaltSlumpal精品文档放心下载egategate10mmwas7mmwashMateriCementw/cSandhedaggredaggreSaltSlumpal谢谢阅读egategateQuanti0.418.84kg/m

381kg/m3517kg/m3463kg/m3463kg/m3140±25mm

ty9精品文档放心下载3Inordertocomparebondstrengthforthedifferentconcretec精品文档放心下载ompressivestrengths,Eq.1isusedtonormalizebondstrengthfor谢谢阅读non-corrodedspecimensashasbeenusedbyotherresearcher[8].谢谢阅读(1)whereisthebondstrengthforgrade40concrete,τexptlisth谢谢阅读eexperimentalbondstrengthandfcistheexperimentalcompressi精品文档放心下载vestrength.ThetensilestrengthoftheΦ12andΦ16mmsteelbarswasnomi精品文档放心下载nally500MPa,whichequatestoafailureloadof56.5and100.5kN,r感谢阅读espectively.2.3ExperimentmethodologyAcceleratedcorrosionhasbeenusedbyanumberofauthorstor精品文档放心下载eplicatethecorrosionofthereinforcingsteelhappeninginthen谢谢阅读aturalenvironment[2,3,5,6,10,18,20,24,27,28,30].Thesehav感谢阅读einvolvedexperimentsusingimpressedcurrentsorartificialwe感谢阅读atheringwithwet/drycyclesandelevatedtemperaturestoreduce感谢阅读thetimeuntilcorrosion,whilemaintainingdeteriorationmecha谢谢阅读nismsrepresentativeofnaturalexposure.Studiesusingimpress感谢阅读edcurrentshaveusedcurrentdensitiesbetween100μA/cm2and50感谢阅读0mA/cm2[20].Researchhassuggestedthatcurrentdensitiesupto精品文档放心下载200μA/cm2resultinsimilarstressesduringtheearlystagesofc感谢阅读orrosionwhencomparedto100μA/cm2[21].Assuchanappliedcurr感谢阅读entdensityof200μA/cm2wasselectedforthisstudy—represent谢谢阅读ativeofthelowerendofthespectrumofsuchcurrentdensitiesado精品文档放心下载ptedinpreviousresearch.However,cautionshouldbeappliedwhe感谢阅读nacceleratingthecorrosionusingimpressedcurrentastheaccel感谢阅读erationprocessdoesnotexactlyreplicatethemechanismsinvolv谢谢阅读edinactualstructures.Inacceleratedteststhepitsarenotallo谢谢阅读wedtoprogressnaturally,andtheremaybeamoreuniformcorrosio感谢阅读nonthesurface.Alsotherateofcorrosionmayimpactonthecorros精品文档放心下载ionproducts,suchthatdifferentoxidationstateproductsmaybe感谢阅读formed,whichcouldimpactonbond.谢谢阅读Thesteelbarsservedastheanodeandfourmildsteelmetalpla精品文档放心下载teswerefixedonthesurfacetoserveascathodes.Sponges(spraye感谢阅读dwithsaltwater)wereplacedbetweenthemetalplatesandconcret谢谢阅读etoprovideanadequatecontact,Fig.2.精品文档放心下载Fig.2Acceleratedcorrosionsystem谢谢阅读Whentherequiredcrackwidthwasachievedforaparticularba精品文档放心下载r,theimpressedcurrentwasdiscontinuedforthatbar.Thespecim感谢阅读enwasremovedforpullouttestingwhenallfourlocationsexhibit精品文档放心下载edthetargetcrackwidth.Averagesurfacecrackwidthsof0.05,0.精品文档放心下载5,1and1.5mmwereadoptedasthetargetcrackwidths.Thesurfacec谢谢阅读rackwidthwasmeasuredat20mmintervalsalongthelengthoftheba感谢阅读r,beginning20mmfromtheendofthe(plastictube)bondbreakerus感谢阅读inganopticalmicroscope.Thelevelofaccuracyinthemeasuremen精品文档放心下载tswas±0.02mm.Measurementsofcrackwidthweretakenonthesurfa精品文档放心下载cenormaltothebardirectionregardlessoftheactualcrackorien精品文档放心下载tationatthatlocation.Bondstrengthtestswereconductedbymeansofahandoperated谢谢阅读hydraulicjackandacustom-builttestrigasshowninFig.3.Thelo精品文档放心下载adingschemeisillustratedinFig.4.Aplastictubeoflength80mm精品文档放心下载wasprovidedattheendoftheconcretesectionunderneaththetran精品文档放心下载sversereactiontoensurethatthebondstrengthwasnotenhancedb感谢阅读ythereactive(compressive)force(actingnormaltothebar).The感谢阅读specimenwaspositionedsothatanaxialforcewasappliedtotheba精品文档放心下载rbeingtested.Therestraintsweresufficientlyrigidtoensurem谢谢阅读inimalrotationortwistingofthespecimenduringloading.精品文档放心下载Fig.3Pull-outtest,16mmbarunconfined感谢阅读Fig.4Schematicofloading.Note:onlytestbarshownforclarity谢谢阅读3Experimentalresultsanddiscussion感谢阅读3.1VisualinspectionFollowingtheacceleratedcorrosionphaseeachspecimenwas精品文档放心下载visuallyinspectedforthelocationofcracks,meancrackwidthan谢谢阅读dmaximumcrackwidth(Sect.2.3).谢谢阅读Whileeachspecimenhadameantargetcrackwidthforeachbar,精品文档放心下载variationsinthiscrackwidthwereobservedpriortopullouttest精品文档放心下载ing.Thisisduetocorrosionandcrackingbeingadynamicprocessw感谢阅读ithcrackspropagatingatdifferentrates.Thus,whileindividua谢谢阅读lbarsweredisconnected,oncethetargetcrackwidthhadbeenachi谢谢阅读eved,corrosionandcrackpropagationcontinued(tosomeextent)感谢阅读untilallbarshadachievedthetargetcrackwidthandpullouttest感谢阅读sconducted.Thisresultedinarangeofdataforthemaximumandmea感谢阅读ncrackwidthsforthepullouttests.精品文档放心下载Thevisualinspectionofthespecimensshowedthreestagesto精品文档放心下载thecrackingprocess.Theinitialcracksoccurredinaveryshortp精品文档放心下载eriod,usuallygeneratedwithinafewdays.Afterthat,mostcrack精品文档放心下载sgrewataconstantrateuntiltheyreached1mm,3–4weeksafterfi精品文档放心下载rstcracking.Aftercrackshadreached1mmtheythengrewveryslow谢谢阅读ly,withsomecracksnotincreasingatall.Fortheconfinedandunc精品文档放心下载onfinedspecimensthesurfacecrackstendedtooccuronthesideof精品文档放心下载thespecimens(asopposedtothetoporbottom)andtofollowthelin精品文档放心下载eofthebars.Inthecaseoftheunconfinedspecimensingeneralthe感谢阅读seweretheonlycrackwhileitwascommoninthecasesofconfinedsp感谢阅读ecimenstoobservecracksthatwerealignedverticallydownthesi感谢阅读de—adjacenttooneofthelinks,Fig.5.感谢阅读Fig.5TypicalcrackpatternsDuringthepull-outtestingthemostcommonfailuremodeforb谢谢阅读othconfinedandunconfinedwassplittingfailure—withtheinit谢谢阅读ial(pre-test)crackscausedbythecorrosionenlargingunderloa精品文档放心下载dandultimatelyleadingtothesectionfailingexhibitingspalli谢谢阅读ngofthetopcorner/edge,Fig.6.Howeverforseveraloftheconfin感谢阅读edspecimens,asecondmodeoffailurealsooccurredwithdiagonal感谢阅读(shearlike)cracksappearinginthesidewalls,Fig.7.Theappear谢谢阅读anceofthesecracksdidnotappeartoberelatedtothepresenceofv谢谢阅读erticalcracksobserved(inspecimenswithstirrups)duringthec精品文档放心下载orrosionphaseasreportedabove.感谢阅读Fig.6Longitudinalcrackingafterpull-out精品文档放心下载Fig.7Diagonalcrackingafterpull-out谢谢阅读Thebarswereinitially(precasting)cleanedwitha12%hydro感谢阅读chloricacidsolution,thenwashedindistilledwaterandneutral感谢阅读izedbyacalciumhydroxidesolutionbeforebeingwashedindistil谢谢阅读ledwateragain.Followingthepull-outtests,thecorrodedbarsw感谢阅读erecleanedinthesamewayandweighedagain.感谢阅读Thecorrosiondegreewasdeterminedusingthefollowingequa感谢阅读tionwhereG0istheinitialweightofthesteelbarbeforecorrosio感谢阅读n,Gisthefinalweightofthesteelbarafterremovalofthepost-te谢谢阅读stcorrosionproducts,g0istheweightperunitlengthofthesteel精品文档放心下载bar(0.888and1.58g/mmforΦ12andΦ16mmbars,respectively),l感谢阅读istheembeddedbondlength.Figures8and9showsteelbarswithvaryingdegreeofcorrosio谢谢阅读n.Themajorityexhibitedvisiblepitting,similartothatobserv精品文档放心下载edonreinforcementinactualstructures,Fig.9.However,asmall感谢阅读numberofothersexhibitedsignificantoverallsectionloss,wit谢谢阅读hamoreuniformlevelofcorrosion,Fig.8,whichmaybeafunctiono感谢阅读ftheaccelerationmethodology.感谢阅读Fig.8Corroded12mmbarwithapproximately30%massloss谢谢阅读Fig.9Corroded16mmbarwithapproximately15%massloss精品文档放心下载3.2Bondstressandcrackwidth精品文档放心下载Figure10showsthevariationofbondstresswithmeancrackwi谢谢阅读dthfor16mmbarsandFig.11forthe12mmbars.Figures12and13show感谢阅读thedataforthemaximumcrackwidth.感谢阅读Fig.10Meancrackwidthversusbondstressfor16mmbars精品文档放心下载Fig.11Meancrackwidthversusbondstressfor12mmbars感谢阅读Fig.12Maximumcrackwidthversusbondstressfor16mmbars精品文档放心下载Fig.13Maximumcrackwidthversusbondstressfor12mmbars感谢阅读Thedatashowaninitialincreaseinbondstrengthforthe12mm谢谢阅读specimenswithstirrups,followedbyasignificantdecreaseinbo精品文档放心下载nd,whichisinagreementwithotherauthors[12,15].Forthe16mms谢谢阅读pecimensanincreaseonthecontrolbondstresswasobservedforsp感谢阅读ecimenswith0.28and0.35mmmeancrackwidths,however,adecreas谢谢阅读einbondstresswasobservedforatthemeancrackwidthof0.05mm.精品文档放心下载The12mmbarswithstirrupsdisplayedanincreaseinbondstre精品文档放心下载ssofapproximately25%fromthecontrolvaluestothemaximumbond谢谢阅读stress.Anincreaseofapproximately14%wasobservedforthe16mm精品文档放心下载specimens.Otherresearchers[17,24,25]havereportedenhancem精品文档放心下载entsofbondstressofbetween10and60%duetoconfinement,slight谢谢阅读lyhighertothatobservedintheseexperiment.Howevertheloadin感谢阅读gtechniquesandcoverdepthshavenotallbeenthesame.Variation感谢阅读sinexperimentaltechniquesincludeashorterembeddedlengthan谢谢阅读dalowercover.Thevariationontheproposedempiricalrelations感谢阅读hipbetweenbondstrength,degreeofcorrosion,barsize,cover,l精品文档放心下载inkdetailsandtensilestrengthpredictedbyRodriguez[24]hasb谢谢阅读eendiscussedindetailinTangetal.[28].Theanalysisdemonstra精品文档放心下载testhattherewouldbeanexpectedenhancementofbondstrengthdu谢谢阅读etoconfinementofapproximately25%—correspondingtoachange感谢阅读ofbondstrengthofapproximately0.75MPaforthe16mmbars(asses精品文档放心下载sedata2%sectionloss).Forthe12mmbarsthecorrespondingeffec感谢阅读tofconfinementisfoundtobeapproximately35%correspondingto谢谢阅读a1.0MPadifferenceinbondstress.Theexperimentalresults(14a谢谢阅读nd25%,above)are60–70%ofthesevalues.感谢阅读Bothsetsofdataindicatearelationshipshowingdecreasing谢谢阅读bondstrengthwith(visiblesurface)crackwidth.Aregressionan感谢阅读alysisofthebondstrengthdatarevealsabetterlinearrelations精品文档放心下载hipwiththemaximumcrackwidthasopposedtothemeancrackwidth(精品文档放心下载excludingtheuncrackedconfinedspecimens),Table2.谢谢阅读Table2Bestfitparameters,crackwidthversusbondstrength精品文档放心下载UnconfineConfineUnconfineConfine精品文档放心下载d12mmd12mmd16mmd16mmMeancrackwidthR20.9200.6370.6720.659谢谢阅读Slope(m)−3.997−3.653−2.999−8.848感谢阅读Intercept7.5608.1226.4968.746(b)感谢阅读MaximumcrackwidthR20.9370.8550.7140.616感谢阅读Slope(m)−2.719−2.968−1.815−5.330精品文档放心下载UnconfineConfineUnconfineConfine精品文档放心下载d12mmd12mmd16mmd16mmIntercept7.8058.4036.7079.636(b)感谢阅读Therewasalsoasignificantlybetterfitfortheunconfineds感谢阅读pecimensthantheconfinedspecimens.Thisisconsistentwiththe感谢阅读observationthatintheunconfinedspecimensthebondstrengthwi精品文档放心下载llberelatedtothebondbetweenthebarsandtheconcrete,whichwi感谢阅读llbeaffectedbythelevelofcorrosionpresent,whichitselfwill精品文档放心下载influencethecrackwidth.Inconfinedspecimenstheconfiningst精品文档放心下载eelwillimpactuponboththebondandthecracking.感谢阅读3.3Corrosiondegreeandbondstress谢谢阅读Itisapparentthat(Fig.14)forcorrosiondegreeslessthan5谢谢阅读%thebondstresscorrelatedwell.However,asthedegreeofcorros精品文档放心下载ionincreasedtherewasnoobservablecorrelationatall.Thiscon精品文档放心下载trastswiththerelationshipbetweentheobservedcrackwidthand谢谢阅读bondstress,whichgivesareasonablecorrelation,evenascrackw精品文档放心下载idthsincreaseto2and2.5mm.Apossibleexplanationforthisvari精品文档放心下载ationisthatintheinitialstagesofcorrosionvirtuallyallthed感谢阅读issolvedironionsreacttoformexpansivecorrosionproducts.Th精品文档放心下载isreactionimpactsonboththebondstressandtheformationofcra精品文档放心下载cks.However,oncecrackshavebeenformeditispossiblefortheir谢谢阅读onionstobetransportedalongthecrackandoutoftheconcrete.As精品文档放心下载thebondhasalreadybeeneffectivelylostatthecrackanyironion精品文档放心下载sdissolvingatthecrackandbeingdirectlytransportedoutofthe精品文档放心下载concretewillcauseanincreaseinthedegreeofcorrosion,butnot谢谢阅读affectthesurfacecrackwidth.Thelocation,orientationandche感谢阅读mistrywithinthecrackwillcontroltherelationshipbetweenbon感谢阅读dstressanddegreeofcorrosion,whichwillvaryfromspecimentos谢谢阅读pecimen.Hencethelargevariationsincorrosiondegreeandbonds谢谢阅读tressforhighlevelsofcorrosion.感谢阅读Fig.14Bondstressversuscorrosiondegree,12mmbars,unconfinedspecimen精品文档放心下载Significantlylargercrackwidthswereobservedfortheunco感谢阅读nfinedspecimens,comparedtotheconfinedspecimenswithsimila谢谢阅读rlevelsofcorrosionandmasslost.Thelargestobservedcrackfor精品文档放心下载unconfinedspecimenswas2.5mmcomparedto1.4mmfortheconfined谢谢阅读specimens.Thisisasexpectedandisadirectresultoftheconfine感谢阅读mentwhichlimitsthedegreeofcracking.精品文档放心下载3.4EffectofconfinementTheunconfinedspecimensforboth16and12mmbarsdidnotdisp感谢阅读laytheinitialincreaseinbondstrengthobservedfortheconfine感谢阅读dbars.Indeedtheunconfinedspecimenswithcracksalldisplayed感谢阅读areducedbondstresscomparedtothecontrolspecimens.Thisisin感谢阅读agreementwithotherauthors[16,24]findingsforcrackedspecim感谢阅读ens.IncrackedcorrodedspecimensFangobservedasubstantialre感谢阅读ductioninbondstrengthfordeformedbarswithoutstirrups,whil精品文档放心下载eRodriguezobservedbondstrengthsofhighlycorrodedcrackedsp精品文档放心下载ecimenswithoutstirrupswereclosetozero,whilehighlycorrode精品文档放心下载dcrackedspecimenswithstirrupsretainedbondstrengthsofbetw精品文档放心下载een3and4MPa.InuncorrodedspecimensChananotedanincreaseinb感谢阅读ondstrengthduetostirrupsofbetween10and20%[14].HoweverRod精品文档放心下载riguezandFangobservednovariationduetothepresenceofconfin精品文档放心下载ementinuncorrodedbars.Thedataisperhapsunexpectedasitcouldbeanticipatedthat精品文档放心下载thecorrosionproductswouldleadtoanincreaseinbondduetothei精品文档放心下载ncreaseininternalpressures,causedbythecorrosionproductsi感谢阅读ncreasingtheconfinementandmechanicalinterlockingaroundth精品文档放心下载ebar,coupledwithincreasedroughnessofthebarresultinginagr感谢阅读eaterfrictionbetweenthebarandthesurroundingconcrete.Howe感谢阅读ver,thesepressureswouldthenrelievedbythesubsequentcracki精品文档放心下载ngoftheconcrete,whichwouldcontributetothedecreaseinthebo谢谢阅读ndstrengthascrackwidthsincrease.Apossiblehypothesisistha精品文档放心下载tduetothelevelofcover,threetimesbardiameter,theeffectofc谢谢阅读onfinementbythestirrupsisreduced,suchthatithaslittleimpa精品文档放心下载ctonthebondstressinuncrackedconcrete.However,oncecrackin精品文档放心下载ghastakenplacetheconfinementdoeshaveabeneficialeffectont精品文档放心下载hebond.Itmayalsobethatthecompressivestrengthoftheconcreteco谢谢阅读mbinedwiththecoverwillhaveaneffectonthebondstressesforun精品文档放心下载corrodedspecimens.Thedatapresentedherehasacoverofthreeti谢谢阅读mesbardiameterandastrengthof40MPa,otherresearchrangesfro感谢阅读m1.5tofourtimescoverwithcompressivestrengthsfrom40to77MP谢谢阅读a.3.5Comparisonof12and16mmrebar精品文档放心下载Themaximumbondstressfor16mmunconfinedbarswasmeasured谢谢阅读at8.06MPaandforthe12mmbarsitwas8.43MPa.Thesebothcorrespo谢谢阅读ndedtothecontrolspecimenswithnocorrosion.Theunconfinedsp感谢阅读ecimensforboththe12and16mmbarsshowednoincreaseinbondstre精品文档放心下载ssduetocorrosion.Fortheconfinedspecimensthemaximumbondst谢谢阅读ressforthecontrolspecimenswere7.29MPaforthe12mmbarsand6.精品文档放心下载34MPaforthe16mmbars.Themaximumbondstressforbothsetsofcon感谢阅读finedspecimenscorrespondedtopointoftheinitialcracking.Th谢谢阅读emaximumbondstresseswereobservedatameancrackwidthof0.01m感谢阅读mforthe12mmbarsand0.28mmforthe16mmbars.Thecorrespondingb精品文档放心下载ondstresseswere,8.45and7.20MPa.Overallthe12mmbarsdisplay感谢阅读edhigherbondstressescomparedtothe16mmbarsatallcrackwidth精品文档放心下载s.Thisisattributedtoadifferentfailuremode.The16mmspecime谢谢阅读nsdemonstratesplittingfailurewhilethe12mmbarsbondfailure感谢阅读.3.6Effectofcastingposition谢谢阅读Therewasnosignificantdifferenceofbondstrengthduetoth谢谢阅读epositionofthebar(toporbottomcast)oncecrackingwasobserve精品文档放心下载d,Fig.15.Forcontrolspecimens,withnocorrosion,however,the谢谢阅读bottomcastbarshadaslightlyhigherbondstressthanthetopcast感谢阅读bars.Theseobservationsareinagreementwithotherauthors[4,1谢谢阅读1,15,22].Itisgenerallyacceptedthatuncorrodedbottomcastba感谢阅读rshavesignificantlyimprovedbondcomparedtotopcastbarsduet谢谢阅读othecorrosionproductsfillingthevoidsthatareoftenpresentu感谢阅读ndertopcastbarsasthecorrosionprogresses[14].Thecorrosion谢谢阅读alsoactsasan‘anchor’,similartotheribsondeformedbars,to感谢阅读increasethebond.Overall,themeanvalueofbondstressforallba精品文档放心下载rs(corrodedanduncorroded)locatedinthetopwerewithin1%ofth谢谢阅读emeanbondstressofallbarslocatedinthebottomofthesection—精品文档放心下载forbothunconfinedandconfinedbars.Thisisprobablyduetothel谢谢阅读evelofcover.Theresultsreportedpreviouslyareonspecimenswi谢谢阅读thonetimescover[14].However,atthreetimescoveritwouldbean感谢阅读ticipatedthatgreatercompactionwouldbeachievedaroundtheto精品文档放心下载pcastbars.Thustheareaofvoidswouldbereducedandthustheeffe精品文档放心下载ctofthecorrosionproductfillingthesevoidsandincreasingthe精品文档放心下载bondstrengthwouldbereduced.感谢阅读Fig.15Bondstressversusmeancrackwidthfor12mmbars,topandbottomcastpos感谢阅读itions,confinedspecimen4ConclusionsArelationshipwasobservedbetweencrackwidthandbondstre感谢阅读ss.Thecorrelationwasbetterformaximumcrackwidthandbondstr精品文档放心下载essthanformeancrackwidthandbondstress.精品文档放心下载Confinedbarsdisplayedahigherbondstressatthepointofin谢谢阅读itialcrackingthanwherenocorrosionhadoccurred.Ascrackwidt精品文档放心下载hincreasethebondstressreducedsignificantly.感谢阅读Unconfinedbarsdisplayedadecreaseinbondstressatinitia谢谢阅读lcracking,followedbyafurtherdecreaseascrackingincreased.感谢阅读Topcastbarsdisplayedahigherbondstressinspecimenswith精品文档放心下载nocorrosion.Oncecrackinghadoccurrednovariationbetweentop精品文档放心下载andbottomcastbarswasobserved.谢谢阅读The12mmbarsdisplayedhigherbondstressvaluesthan16mmwi谢谢阅读thnocorrosion,controlspecimens,andatsimilarcrackwidths.谢谢阅读Agoodcorrelationwasobservedbetweenbondstressanddegre谢谢阅读eofcorrosionwasobservedatlowlevelsofcorrosion(lessthan5%).谢谢阅读However,athigherlevelsofcorrosionnocorrelationwasdiscern精品文档放心下载ed.Overalltheresultsindicatedapotentialrelationshipbetw精品文档放心下载eenthemaximumcrackwidthandthebond.Resultsshownhereinshou谢谢阅读ldbeinterpretedwithcautionasthisvariationmaybenotonlydue谢谢阅读tovariationsbetweenacceleratedcorrosionandnaturalcorrosi感谢阅读onbutalsoduetothecomplexityofthecrackingmechanisminreali感谢阅读ty.中文译文：约束和无约束的钢筋对裂缝宽度的影响收稿日期：2010年1月14纳稿日期：2010年12月14日线谢谢阅读上发表时间：2010年1月23日摘要本报告公布了局限约束和自由的变形对粘结强度1216毫米感谢阅读钢筋的表面腐蚀程度和裂纹影响的比较结果。腐蚀是氯化物污染谢谢阅读的混凝土的诱导和外加直流电流的引起的。调查的主要参数有钢感谢阅读筋剥离，保护层厚度，钢筋直径，腐蚀程度和表面裂缝宽度。结精品文档放心下载果表明了裂缝宽度和粘结强度之间的潜在关系。同时还发现在围精品文档放心下载箍筋处发现表面裂纹的地方粘结强度增加，而无侧限的样本中没精品文档放心下载有观察到粘结强度增加。关键词：粘结；腐蚀；螺纹钢；保护层；裂缝宽度；混凝土精品文档放心下载引言在世界各地，钢筋的腐蚀是钢筋混凝土结构的恶化的重要原感谢阅读因。在未腐蚀的结构中钢筋和混凝土之间的粘结使钢筋混凝土处精品文档放心下载于有利状态。然而，当钢铁的腐蚀发生时，会对这种积极性能产感谢阅读生不利影响。这是由于钢表面形成了腐蚀产物，从而影响了钢和谢谢阅读混凝土之间的粘结。钢筋混凝土恶化是由钢筋和形成的膨胀腐蚀产物造成的局部感谢阅读;膨胀产品的产生造成谢谢阅读混凝土的拉应力，这可能会导致混凝土保护层开裂和剥落的。这感谢阅读种开裂可导致更严重的恶化和进一步的腐蚀。它也可以导致在混感谢阅读凝土保护层的强度和刚度的损失。腐蚀产物也可以影响混凝土与谢谢阅读钢筋之间的粘结强度。最终腐蚀减少钢筋截面面积，影响钢筋的感谢阅读延展性和承载能力，从而最终影响结构适用性和结构承载力[12，感谢阅读25]。以往的研究调查腐蚀对粘结的影响[2-57122023-25，感谢阅读27，29]，提出了数据模型[4，6，9，10，18，1924，29]。本研谢谢阅读究主要研究腐蚀（钢材质量损失）水平或电流密度程度（腐蚀电感谢阅读流在加速测试中的应用）和裂缝宽度之间的关系，或粘结强度和谢谢阅读[111]和谢谢阅读摩擦特性[13]。然而，很少有人研究都集中在裂缝宽度与粘结[23，精品文档放心下载26，28]之间的关系上，此参数易与实际结构相联系。谢谢阅读加强钢筋的腐蚀导致生成铁氧化物，它的体积大于原钢材。谢谢阅读这种扩张造成周围的混凝土内的拉应力，最终导致混凝土保护层感谢阅读开裂。一旦开裂发生，混凝土紧箍力就会损失。这表明粘结能力感谢阅读的损失可能与纵向裂缝宽度有关[12]。然而，以混凝土的剥离可精品文档放心下载以在一定程度上抵消粘结力的损失。最新研究主要与剥离样本有精品文档放心下载关。本文报道的一项研究比较了有侧限和无侧限样本的粘结力损精品文档放心下载失。2.实验研究2.1样本梁端样本[28]被选定为这项研究的研究对象。这种撤去偏心谢谢阅读模式样本以一个典型的简支梁锚固区的粘结长度支撑。谢谢阅读1感谢阅读80感谢阅读度（横向）压缩力超过这个长度的钢筋。图1梁端试样试验调查了由3倍直径厚的保护层保护的12和16毫米直径谢谢阅读3套6精品文档放心下载毫米的不锈钢箍筋从其间穿过，在75毫米中心。这代表了四组不同钢筋直径和有侧限/谢谢阅读钢筋规格，混凝土剥离和裂缝宽度对粘结强度的影响。2.2材料配合比设计，如表1所示。水泥是I型硅酸盐水泥，骨料为精品文档放心下载玄武岩，容重2.99。根据AS1141—2000进行粗、细集料的制备。谢谢阅读拌合根据AS1141—1994进行。测试前水浴养护28天。精品文档放心下载表1混凝土配合比设计材料水泥w/c砂10mm集7mm集盐含量塌落度谢谢阅读料料结果381kg/m0.4517kg/kg/m3kg/m3kg/m3140±精品文档放心下载3m325mm为了比较不同的混凝土抗压强度，粘结强度，Eq。公式1已精品文档放心下载被其他研究者用于正常化粘结强度的非腐蚀样本。1为40级混凝土的粘结强度，exptl为实验粘结强度和Fc是实谢谢阅读验抗压强度。Φ12和Φ16毫米钢筋的抗拉强度是500精品文档放心下载个56.5和100.5kN的破坏载荷。2.3实验方法加速腐蚀已被许多作者用于重现在自然环境中发生的腐蚀钢精品文档放心下载筋钢[2，3，5，6，10，18，20，24，27，28，30]。这些相关实感谢阅读验使用外加电流或干湿周期人工风化和升高温度延缓腐蚀时间，感谢阅读同时保持恶化机制处于自然状态。采用外加电流的研究使用的电感谢阅读流密度在100μA/cm2与500mA/cm2之间[20]精品文档放心下载密度200μA/cm2与100μA/cm2相比，200的结果与早期阶段的腐谢谢阅读蚀更相似[21]200μA/cm2被选定为研究使用谢谢阅读电流，这在以前的研究中成为电流密度频谱的低端代表。然而，感谢阅读应谨慎应用外加电流的加速腐蚀，加速过程并不完全复制在实际感谢阅读结构中所涉及的机制。在加速测试中不允许违背自然的发展，并精品文档放心下载有可能在表面上更均匀腐蚀。腐蚀率也可能会影响腐蚀的产品，精品文档放心下载这些产品可能会形成不同的氧化状态，这可能会影响粘结强度。谢谢阅读钢筋作为阳极和四个碳钢金属板固定在表面作为阴极。金属精品文档放心下载板和混凝土之间放置海绵（用盐水喷洒）提供足够的接触，如图谢谢阅读2。图2加速腐蚀系统当裂缝宽度要求需适应特殊钢筋时应该终止施加外加电流。谢谢阅读感谢阅读平均表面裂缝宽度0.05，0.5，1和1.5毫米作为目标裂缝宽度。谢谢阅读表面裂纹宽度沿钢筋长度测量间隔20mm，从约束（塑料管）末端感谢阅读开始20mm用断路器光学显微镜测量。测量精度为±0.02毫米。从精品文档放心下载钢筋表面测量裂缝宽度，不考虑裂缝实际方位在何处。粘结强度测试通过手动操作液压千斤顶和一个定制的试验装感谢阅读置，如图3所示。加载方案见图4。长80毫米的塑料管在末端提感谢阅读精品文档放心下载力）提高而增加。样本定位使轴向力，适用于被测试的钢筋。给谢谢阅读样本足够刚性的约束可以确保在加载过程中最小的旋转或扭曲。谢谢阅读图3拉出测试，16毫米钢筋不承压图4加载示意图。注：只测试显示棒3实验结果与讨论3.1目视检查加速腐蚀阶段后，检查每个样本的裂缝的位置，平均裂缝宽精品文档放心下载度和最大裂缝宽度（第2.3款）。虽然每个钢筋样本都有平均目标裂缝宽度，但是裂缝宽度的谢谢阅读感谢阅读裂缝是以不同的速度传播的。因此，当个别钢筋被拉断的时候，精品文档放心下载精品文档放心下载直到所有的钢筋已达到目标的裂缝宽度，再终止试验进行。这产谢谢阅读生了一系列的最大裂缝和终止测试时的平均裂缝宽度数据。谢谢阅读视觉检测的样本显示了三个阶段的裂解过程。初始裂缝发生谢谢阅读在很短的时间内，通常在几天之内产生。在此之后，大多数裂缝谢谢阅读以一个恒定的速度增长，直到3-4周后首次开裂，他们达到1毫谢谢阅读米。裂缝达到了1毫米后，它们的增长速度非常缓慢，甚至一些谢谢阅读裂缝一点都不增加。侧限和自由的样本表面裂纹往往发生在侧面感谢阅读（如对侧的顶部或底部），并沿钢筋方向发展。一般情况下无侧感谢阅读限的样本只有仅有的一部分裂缝，而自由的样本裂缝的发展却十精品文档放心下载分常见，观察到的裂缝垂直对齐下边，垂直向下侧相邻的链接，感谢阅读如图5。图5典型裂纹模式在拉出测试时最常见的侧限和自由的故障是剥离失败，这是精品文档放心下载/边感谢阅读6感谢阅读7精品文档放心下载察到的垂直裂缝如上面报道的，并不相关。图6拉出后纵向开裂图7角开裂后拉出钢筋最初（预制）由12％的盐酸溶液清洗，然后在蒸馏水清精品文档放心下载洗，另外蒸馏水洗涤之前由氢氧化钙溶液中和。锈蚀钢筋拉出来谢谢阅读测试之后，以同样的方式进行清洗，并再次称重。使用下列公式确定的腐蚀程度其中G0是钢筋腐蚀前的初始重量，G是最终去除腐蚀产物后的测谢谢阅读g012和Φ16毫米精品文档放心下载钢筋分别0.888和1.58g/毫米），l是嵌入式的键长。感谢阅读图8和图9显示有不同程度的腐蚀钢筋。多数表现出可见的感谢阅读9谢谢阅读8感谢阅读方法的功能。图812毫米钢筋腐蚀、约30％的质量损失图916毫米钢筋腐蚀、约15％的质量损失3.2粘结应力和裂缝宽度图10显示了16毫米的钢筋粘结应力与平均裂缝宽度的变化。感谢阅读图11为12毫米的钢筋的。图12和图13显示的最大裂缝宽度的感谢阅读数据。图1016毫米的钢筋平均裂缝宽度、粘结应力图1112毫米的钢筋平均裂缝宽度、粘结应力图1216毫米的钢筋最大裂缝宽度、粘结应力图1312毫米的钢筋最大裂缝宽度、粘结应力数据显示12精品文档放心下载者[1215]16毫米箍筋样本观察到的裂缝宽度谢谢阅读0.28和0.35谢谢阅读均裂缝宽度为0.05毫米。12mm钢筋与箍筋粘结力从控制值到最大粘结应力粘结应力增精品文档放心下载加25%粘结力。16毫米的样本增加约