土木工程外文文献及翻译.docx

土木工程外文文献及翻译.docx

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土木工程外文文献及翻译

外文文献：

MaterialsandStructures

?

?

RILEM?

2010

10.1617/s11527-010-9700-y

OriginalArticle

Impactofcrackwidthonbond:

confinedandunconfinedrebar

David?

W.?

Law1?

Denglei?

Tang2,Thomas?

K.?

C.?

Molyneaux3andRebecca?

Gravina3

（1）?

SchooloftheBuiltEnvironment,HeriotWattUniversity,Edinburgh,EH144AS,UK

（2）?

VicRoads,Melbourne,VIC,Australia

（3）?

SchoolofCivil,EnvironmentalandChemicalEngineering,RMITUniversity,Melbourne,VIC,3000,Australia

David?

W.?

Law

Email:

Received:

14?

January?

2010?

?

Accepted:

14?

December?

2010?

?

Publishedonline:

23?

December?

2010

Abstract

Thispaperreportstheresultsofaresearchprojectcomparingtheeffectofsurfacecrackwidthanddegreeofcorrosiononthebondstrengthofconfinedandunconfineddeformed12and16?

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[12,25].

Previousresearchhasinvestigatedtheimpactofcorrosiononbond[2–5,7,12,20,23–25,27,29],withanumberofmodelsbeingproposed[4,6,9,10,18,19,24,29].Themajorityofthisresearchhasfocusedontherelationshipbetweenthelevelofcorrosion（masslossofsteel）orthecurrentdensitydegree（corrosioncurrentappliedinacceleratedtesting）andcrackwidth,orontherelationshipbetweenbondstrengthandlevelofcorrosion.Otherresearchhasinvestigatedthemechanicalbehaviourofcorrodedsteel[1,11]andthefrictioncharacteristics[13].However,littleresearchhasfocusedontherelationshipbetweencrackwidthandbond[23,26,28],aparameterthatcanbemeasuredwithrelativeeaseonactualstructures.

Thecorrosionofthereinforcingsteelresultsintheformationofironoxideswhichoccupyalargervolumethanthatoftheparentmetal.Thisexpansioncreatestensilestresseswithinthesurroundingconcrete,eventuallyleadingtocrackingofthecoverconcrete.Oncecrackingoccursthereisalossofconfiningforcefromtheconcrete.Thissuggeststhatthelossofbondcapacitycouldberelatedtothelongitudinalcrackwidth[12].However,theuseofconfinementwithintheconcretecancounteractthislossofbondcapacitytoacertaindegree.Researchtodatehasprimarilyinvolvedspecimenswithconfinement.Thispaperreportsastudycomparingthelossofbondofspecimenswithandwithoutconfinement.

2?

Experimentalinvestigation

2.1?

Specimens

Beamendspecimens[28]wereselectedforthisstudy.Thistypeofeccentricpulloutor‘beamend’typespecimenusesabondedlengthrepresentativeoftheanchoragezoneofatypicalsimplysupportedbeam.Specimensofrectangularcrosssectionwerecastwithalongitudinalreinforcingbarineachcorner,Fig.?

1.An80?

mmplastictubewasprovidedatthebarunderneaththetransversereactiontoensurethatthebondstrengthwasnotenhancedduetoa（transverse）compressiveforceactingonthebaroverthislength.

Fig.?

1?

Beamendspecimen

Deformedrebarof12and16?

mmdiameterwithcoverofthreetimesbardiameterwereinvestigated.Duplicatesetsofconfinedandunconfinedspecimensweretested.Theconfinedspecimenshadthreesetsof6?

mmstainlesssteelstirrupsequallyspacedfromtheplastictube,at75?

mmcentres.

Thisrepresentsfourgroupsofspecimenswithacombinationofdifferentbardiameterandwith/withoutconfinement.Thespecimenswereselectedinordertoinvestigatetheinfluenceofbarsize,confinementandcrackwidthonbondstrength.

2.2?

Materials

Themixdesignisshown,Table?

1.ThecementwasTypeIPortlandcement,theaggregatewasbasaltwithspecificgravity2.99.ThecoarseandfineaggregatewerepreparedinaccordancewithAS1141-2000.MixingwasundertakeninaccordancewithAS1012.2-1994.Specimenswerecuredfor28?

daysunderwethessianbeforetesting.

Table?

1?

Concretemixdesign

Material

Cement

w/c

Sand

10?

mmwashedaggregate

7?

mmwashedaggregate

Salt

Slump

Quantity

381?

kg/m3

0.49

517?

kg/m3

463?

kg/m3

463?

kg/m3

18.84?

kg/m3

140?

±?

25?

mm

Inordertocomparebondstrengthforthedifferentconcretecompressivestrengths,Eq.?

1isusedtonormalizebondstrengthfornon-corrodedspecimensashasbeenusedbyotherresearcher[8].

（1）

where

isthebondstrengthforgrade40concrete,τexptlistheexperimentalbondstrengthandfcistheexperimentalcompressivestrength.

ThetensilestrengthoftheΦ12andΦ16?

mmsteelbarswasnominally500?

MPa,whichequatestoafailureloadof56.5and100.5?

kN,respectively.

2.3?

Experimentmethodology

Acceleratedcorrosionhasbeenusedbyanumberofauthorstoreplicatethecorrosionofthereinforcingsteelhappeninginthenaturalenvironment[2,3,5,6,10,18,20,24,27,28,30].Thesehaveinvolvedexperimentsusingimpressedcurrentsorartificialweatheringwithwet/drycyclesandelevatedtemperaturestoreducethetimeuntilcorrosion,whilemaintainingdeteriorationmechanismsrepresentativeofnaturalexposure.Studiesusingimpressedcurrentshaveusedcurrentdensitiesbetween100?

μA/cm2and500?

mA/cm2[20].Researchhassuggestedthatcurrentdensitiesupto200?

μA/cm2resultinsimilarstressesduringtheearlystagesofcorrosionwhencomparedto100?

μA/cm2[21].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

3.1?

Visualinspection

Followingtheacceleratedcorrosionphaseeachspecimenwasvisuallyinspectedforthelocationofcracks,meancrackwidthandmaximumcrackwidth（Sect.?

2.3）.

Whileeachspecimenhadameantargetcrackwidthforeachbar,variationsinthiscrackwidth