钢筋对裂缝宽度的影响外文翻译文献.docx
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钢筋对裂缝宽度的影响外文翻译文献.docx
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钢筋对裂缝宽度的影响外文翻译文献
文献信息:
文献标题:
Impactofcrackwidthonbond:
Confinedandunconfinedreba(约束和无约束的钢筋对裂缝宽度的影响)
国外作者:
DavidW.Law,DengleiTang,ThomasK.C.Molyneaux,Rebecca Gravina
文献出处:
《MaterialsandStructures》,2011,44(7):
1287-1296
字数统计:
英文3707单词,18870字符;中文5545汉字
外文文献:
Impactofcrackwidthonbond:
Confinedandunconfinedreba
AbstractThispaperreportstheresultsofaresearchprojectcomparingtheeffectofsurfacecrackwidthanddegreeofcorrosiononthebondstrengthofconfinedandunconfineddeformed12and16 mmmildsteelreinforcingbars.ThecorrosionwasinducedbychloridecontaminationoftheconcreteandanappliedDCcurrent.Theprincipalparametersinvestigatedwereconfinementofthereinforcement,thecoverdepth,bardiameter,degreeofcorrosionandthesurfacecrackwidth.Theresultsindicatedthatpotentialrelationshipbetweenthecrackwidthandthebondstrength.Theresultsalsoshowedanincreaseinbondstrengthatthepointwhereinitialsurfacecrackingwasobservedforbarswithconfiningstirrups.Nosuchincreasewasobservedwithunconfinedspecimens.
Keywords:
bond ;corrosion ; rebar ; cover ; crackwidth ; concrete
1.Introduction
Thecorrosionofsteelreinforcementisamajorcauseofthedeteriorationofreinforcedconcretestructuresthroughouttheworld.Inuncorrodedstructuresthebondbetweenthesteelreinforcementandtheconcreteensuresthatreinforcedconcreteactsinacompositemanner.However,whencorrosionofthesteeloccursthiscompositeperformanceisadverselyaffected.Thisisduetotheformationofcorrosionproductsonthesteelsurface,whichaffectthebondbetweenthesteelandtheconcrete.
Thedeteriorationofreinforcedconcreteischaracterizedbyageneralorlocalizedlossofsectiononthereinforcingbarsandtheformationofexpansivecorrosionproducts.Thisdeteriorationcanaffectstructuresinanumberofways;theproductionofexpansiveproductscreatestensilestresseswithintheconcrete,whichcanresultincrackingandspallingoftheconcretecover.Thiscrackingcanleadtoacceleratedingressoftheaggressiveagentscausingfurthercorrosion.Itcanalsoresultinalossofstrengthandstiffnessoftheconcretecover.Thecorrosionproductscanalsoaffectthebondstrengthbetweentheconcreteandthereinforcingsteel.Finallythecorrosionreducesthecrosssectionofthereinforcingsteel,whichcanaffecttheductilityofthesteelandtheloadbearingcapacity,whichcanultimatelyimpactupontheserviceabilityofthestructureandthestructuralcapacity.
Previousresearchhasinvestigatedtheimpactofcorrosiononbond,withanumberofmodelsbeingproposed.Themajorityofthisresearchhasfocusedontherelationshipbetweenthelevelofcorrosion(masslossofsteel)orthecurrentdensitydegree(corrosioncurrentappliedinacceleratedtesting)andcrackwidth,orontherelationshipbetweenbondstrengthandlevelofcorrosion.Otherresearchhasinvestigatedthemechanicalbehaviourofcorrodedsteelandthefrictioncharacteristics.However,littleresearchhasfocusedontherelationshipbetweencrackwidthandbond,aparameterthatcanbemeasuredwithrelativeeaseonactualstructures.
Thecorrosionofthereinforcingsteelresultsintheformationofironoxideswhichoccupyalargervolumethanthatoftheparentmetal.Thisexpansioncreatestensilestresseswithinthesurroundingconcrete,eventuallyleadingtocrackingofthecoverconcrete.Oncecrackingoccursthereisalossofconfiningforcefromtheconcrete.Thissuggeststhatthelossofbondcapacitycouldberelatedtothelongitudinalcrackwidth.However,theuseofconfinementwithintheconcretecancounteractthislossofbondcapacitytoacertaindegree.Researchtodatehasprimarilyinvolvedspecimenswithconfinement.Thispaperreportsastudycomparingthelossofbondofspecimenswithandwithoutconfinement.
2.Experimentalinvestigation
2.1Specimens
Beamendspecimenswereselectedforthisstudy.Thistypeofeccentricpulloutor‘beamend’typespecimenusesabondedlengthrepresentativeoftheanchoragezoneofatypicalsimplysupportedbeam.Specimensofrectangularcrosssectionwerecastwithalongitudinalreinforcingbarineachcorner,Fig. 1.An80 mmplastictubewasprovidedatthebarunderneaththetransversereactiontoensurethatthebondstrengthwasnotenhancedduetoa(transverse)compressiveforceactingonthebaroverthislength.
Fig. 1 Beamendspecimen
Deformedrebarof12and16 mmdiameterwithcoverofthreetimesbardiameterwereinvestigated.Duplicatesetsofconfinedandunconfinedspecimensweretested.Theconfinedspecimenshadthreesetsof6 mmstainlesssteelstirrupsequallyspacedfromtheplastictube,at75 mmcentres.
Thisrepresentsfourgroupsofspecimenswithacombinationofdifferentbardiameterandwith/withoutconfinement.Thespecimenswereselectedinordertoinvestigatetheinfluenceofbarsize,confinementandcrackwidthonbondstrength.
2.2Materials
Themixdesignisshown,Table 1.ThecementwasTypeIPortlandcement,theaggregatewasbasaltwithspecificgravity2.99.ThecoarseandfineaggregatewerepreparedinaccordancewithAS1141-2000.MixingwasundertakeninaccordancewithAS1012.2-1994.Specimenswerecuredfor28 daysunderwethessianbeforetesting.
Inordertocomparebondstrengthforthedifferentconcretecompressivestrengths,Eq. 1isusedtonormalizebondstrengthfornon-corrodedspecimensashasbeenusedbyotherresearcher.
(1)
where
isthebondstrengthforgrade40concrete,τexptlistheexperimentalbondstrengthandfcistheexperimentalcompressivestrength.
ThetensilestrengthoftheΦ12andΦ16 mmsteelbarswasnominally500 MPa,whichequatestoafailureloadof56.5and100.5 kN,respectively.
2.3Experimentmethodology
Acceleratedcorrosionhasbeenusedbyanumberofauthorstoreplicatethecorrosionofthereinforcingsteelhappeninginthenaturalenvironment.Thesehaveinvolvedexperimentsusingimpressedcurrentsorartificialweatheringwithwet/drycyclesandelevatedtemperaturestoreducethetimeuntilcorrosion,whilemaintainingdeteriorationmechanismsrepresentativeofnaturalexposure.Studiesusingimpressedcurrentshaveusedcurrentdensitiesbetween100 μA/cm2and500 mA/cm2.Researchhassuggestedthatcurrentdensitiesupto200 μA/cm2resultinsimilarstressesduringtheearlystagesofcorrosionwhencomparedto100 μA/cm2.Assuchanappliedcurrentdensityof200 μA/cm2wasselectedforthisstudy—representativeofthelowerendofthespectrumofsuchcurrentdensitiesadoptedinpreviousresearch.However,cautionshouldbeappliedwhenacceleratingthecorrosionusingimpressedcurrentastheaccelerationprocessdoesnotexactlyreplicatethemechanismsinvolvedinactualstructures.Inacceleratedteststhepitsarenotallowedtoprogressnaturally,andtheremaybeamoreuniformcorrosiononthesurface.Alsotherateofcorrosionmayimpactonthecorrosionproducts,suchthatdifferentoxidationstateproductsmaybeformed,whichcouldimpactonbond.
Thesteelbarsservedastheanodeandfourmildsteelmetalplateswerefixedonthesurfacetoserveascathodes.Sponges(sprayedwithsaltwater)wereplacedbetweenthemetalplatesandconcretetoprovideanadequatecontact,Fig. 2.
Fig. 2 Acceleratedcorrosionsystem
Whentherequiredcrackwidthwasachievedforaparticularbar,theimpressedcurrentwasdiscontinuedforthatbar.Thespecimenwasremovedforpullouttestingwhenallfourlocationsexhibitedthetargetcrackwidth.Averagesurfacecrackwidthsof0.05,0.5,1and1.5 mmwereadoptedasthetargetcrackwidths.Thesurfacecrackwidthwasmeasuredat20 mmintervalsalongthelengthofthebar,beginning20 mmfromtheendofthe(plastictube)bondbreakerusinganopticalmicroscope.Thelevelofaccuracyinthemeasurementswas±0.02 mm.Measurementsofcrackwidthweretakenonthesurfacenormaltothebardirectionregardlessoftheactualcrackorientationatthatlocation.
Bondstrengthtestswereconductedbymeansofahandoperatedhydraulicjackandacustom-builttestrigasshowninFig. 3.TheloadingschemeisillustratedinFig. 4.Aplastictubeoflength80 mmwasprovidedattheendoftheconcretesectionunderneaththetransversereactiontoensurethatthebondstrengthwasnotenhancedbythereactive(compressive)force(actingnormaltothebar).Thespecimenwaspositionedsothatanaxialforcewasappliedtothebarbeingtested.Therestraintsweresufficientlyrigidtoensureminimalrotationortwistingofthespecimenduringloading.
Fig. 3 Pull-outtest,16 mmbarunconfined
Fig. 4 Schematicofloading.Note:
onlytestbarshownforclarity
3.Experimentalresultsanddiscussion
3.1Visualinspection
Followingtheacceleratedcorrosionphaseeachspecimenwasvisuallyinspectedforthelocationofcracks,meancrackwidthandmaximumcrackwidth(Sect. 2.3).
Whileeachspecimenhadameantargetcrackwidthforeachbar,variationsinthiscrackwidthwereobservedpriortopullouttesting.Thisisduetocorrosionandcrackingbeingadynamicprocesswithcrackspropagatingatdifferentrates.Thus,whileindividualbarsweredisconnected,oncethetargetcrackwidthhadbeenachieved,corrosionandcrackpropagationcontinued(tosomeextent)untilallbarshadachievedthetargetcrackwidthandpullouttestsconducted.Thisresultedinarangeofdataforthemaximumandmeancrackwidthsforthepullouttests.
Thevisualinspectionofthespecimensshowedthreestagestothecrackingprocess.Theinitialcracksoccurredinaveryshortperiod,usuallygeneratedwithinafewdays.Afterthat,mostcracksgrew
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