DOC

Probabilistic Lifetime Assessment of Marine Reinforced Concrete with Steel Corrosion and Cover Cracking

By Ramon Webb,2014-11-19 11:01
9 views 0
Probabilistic Lifetime Assessment of Marine Reinforced Concrete with Steel Corrosion and Cover Cracking

    Probabilistic Lifetime Assessment of Marine Reinforced Concrete with Steel Corrosion

    and Cover Cracking

    ChinaOceanEng,Vo1.25,No.2,PP.305318

    20l1ChineseOceanEngineeringSocietyandSpringer-VerlagBerlinHeidelberg D0I10.1007/sl33440l100256.ISSN08905487

    PrObabilisticLifetimeAssessmentofMarineReinforcedConcretewithSteel CorrosionandCoverCracking

    LUChun.hua(陆春华),,JINWei.1iang(金伟良)

    andLIURonggui(刘荣桂)

    instituteofStructuralEngineering,ZhejiangUniversity,Hangzhou310058,China DepartmentofCivilEngineering,JiangsuUniversity,Zhenjiang212013,China (Received11August2010;receivedrevisedform6January2011;accepted1March2010) ABSTRACT

    Inordertostudythedurabilitybehaviorofmarinereinforcedconcretestructuresufieringfromchlorideaaack,the

    structuralservicelifeisassumedtobedividedintothreecriticalstages.whichcanbecharacterizedbystee1corrosion

    andcovercracking.Foreachstage.acalculatedmodelusedtopredictthe1iretimeisdeveloped.Basedonthedefinition

    ofdurabilitylimitstate,aprobabilisticlifetimemodelanditstime

    dependentreliabilityanalyticalmethodareproposed

    consideringtherandomnaturesofinfluencingfactors.Then,theprobabilisticlifetimepredictionmodelsareappliedtoa

    bridgepierlocatedintheHangzhouBaywithMonteCarlosimulation.Itisfoundthatthetimetocorrosioninitiationto

    followsalognormaldistribution.whilethatthetimefromcorrosioninitiationtocovercracking^andthetimeforcrack

    todevelopfromhairlinecracktoa1imitcrackwidtht2canbedescribedbyWeibulldistfibutions.Withthepermitted

    failureprobabilityof5.0%.itisalsoobservedthatthestructuraldurability1ifetimemainlydependsonthedurabilitylife

    toandthatthepercentageofpanicipationofthelifetotothetotalservice1ifegrowsfrom61.5%to83.6%whenthecover

    thicknessincreasesfrom40mmto80mmTherefore.foranypartofthemarineRCbridge.thelifetimepredictionsand

    maintenanceeffortsshouldalsobedirectedtowardcontrollingthestageofcorrosioninitiationinducedbychlorideion.

    Keywords:marinereinforcedconcrete;chlorideingress;steelcorrosion;covet"cracking;probabilisticlifetime

    1.IntrOducti0n

    Inrecentdecades,thenumberofmarinereinforeedconcretefRC)structureshasbeenincreasing

    duetotherequirementoflargeinfrastructure,suchasfreightports,bridges,tunnels,offshoreplatforms,

    etc.Fortheseconcretestructures.chloride.inducedreinforcementcorrosionisthemostcommonformof

    structuraldeterioration.whichmayeventuallyresultinthedamagetothestructuresinthefo1"t/1of

    cracking,spallinganddelaminationofconcretecoverandlOSSofbondbetweenconcreteand reinforcement(Bazant,1979;LiuandWeyers,1998;ApostolopoulosandPapadakis,2008;Yangeta1.,

    2009).Usually,corrosion.inducedstructuraldeteriorationisaslowtime.dependentprocess.Chloride

    ioncomingfromseawatergraduallytransportsintoconcreteandmovestowardsthesurfaceof reinforcement.Whentheamountofchlorideaccumulatedaroundsteelreachesthecriticalco

ncentration.

    }ThepaperwasfinanciallysupposedbytheNationalNaturalScienceFoundationofChina(GrantNos50538087,50908103and

    50878098)

    1CorrespondingauthorEmail:luch79@zjuedu.eii

    306LUChunhuaeta1./ChinaOceanEng.,25(2),2011,305318

    passivefilmofrebarisbrokenandcorrosioncanproceedunimpededinthepresenceofmoistureand

    oxygen.Owingtovolumeexpansionofrustproducts,whichisabout2to6timesthevolumeofsteel

    consumed.thehooptensilestresswillbeinducedincoverconcreteandultimatelyleadtocovercracking

    (LiuandWeyers,1998;PantazopoulouandPapoulia,2o01).Oncethesecracksincoverconcreteappear,

    apathforaquickingressofaggressiveelementstothesteelbarsmaybeprovided,whichmayleadtoa

    speedupincorrosionrateand/orreductionofbond

    leadingtoserviceabilityfailureand/ora1OSSof

    structuralintegrity(VuandStewart,2005).Therefore,forseaRCstructures,theassessmentofstructural

    durabilityanddurability.basedservicelifeshouldfocusonthephenomenaofreinforcementcorrosion

    andcorrosioninducedcovercracking(VuandStewart,2005;StewartandMullard,2007). Owingtotheuncertaintiesinbothparametersandmodels,whichdeterminethechloride

    induced

    steelcorrosionandcovercrackingprocesses,itisreasonabletouseprobabilisticapproachtoassess

    structura1life.cyclereliability.VuandStewartr2oo5)developedatwo

    dimensiona1spatialtime

    dependentreliabilitymodeltopredictthelikelihoodandextentofcorrosion-inducedcovercr

acking.

    Melcherseta1.(2008)usedtheprobabilisticmethodtoestimatethecorrosioninduceddeteriorationof

    structuralcarryingcapacityandfoundthattheestimationprovidedbyproposedprobabilisticmodelwas

    generallyconsistentwiththeexperimentalresults.KwonetaL(2009)consideredtheearly-agecrack

    effectonchloridepenetrationinconcreteandpredictedtheserviceliretocorrosioninitiationin

    probabilisticframeworkofMonteCarlosimulation.Insuchstudies,however,theprobabilistic1ifetime

    assessmentofstructuraldeteriorationdealtwithonlyoneportionofthediffusioncorrosion

    cracking

    process,suchaslifetimetocorrosioninitiationcausedbychloridediffusion,timeforcracktodevelop

    fromfirstcrackingtoalimitcrackwidth.Therefore,thetotalprobabilisticlifetimeassessment,including

    corrosioninitiation,corrosion.inducedcoverfirstcrackingandcrackdevelopmenttoa1imitwidth,was

    relativelyfew.

    TheobjectiveofthispaperistodevelopaprobabilisticlifetimepredictionprocedureformarineRC

    structuressufferingfromchlorideingression,reinforcementcorrosionandcovercracking.Itassessesthe

    totallifetimeasthesumofthreecriticalstages:(1)chloridediffusionintoconcreteuntilcorrosion

    initiation,(2)coverfirstcrackingcausedbycorrosion,and(3)crackgrowthtoalimitwidth.The

    probabilisticmodelsforthreecharacteristictimesareproposedandthecomparisonamongthemisalso

performedwiththeapplicationtoaRCbaybridge.

    2.ServiceLifePredictionDnetoReinforcementCorrosion

    Intheviewofthecorrosionofreinforcement.thestructuralservicelifecanbedividedintotwo phases;(1)chlorideingressuntilcorrosioninitiationphase,and(2)corrosionpropagationphase,as

    showninFig.1.Thetimetocorrosioninitiation,to,isdefinedasthetimeatwhichthechloridecontentat

    thesteelsurfacereachesacriticalvalue.Inthesecondphase,threephenomenacalledfirstcracking,

    crackpropagationtoalimitwidthandspallingofcoverconcretearepresented.Thetimefromcorrosion

    initiationtocovercrackingwithahairlinecrackof0.05mmiscalledtimetofirstcracking,(Vuand

    Stewart2005).Thetimetocriticalcrackwidth,t2,isthetimeforcracktodevelopfromhairlinecrackto

    alimitcrackwidth,w(e.g.,w1im=0.5

    1.0mm)(VuandStewart,2005).The1asttime,t3,isdefinedas

    LUChunhuaeta1./ChinaOceanEng.,25(2),2011,305318307

    thetimefromcriticalcrackingtocoverconcretespalling.Duringtheperiodoftimet3,theloadbearing

    abilityofRCelementdeclinesandstructuralsafetysignificantlyreducesduetothelossofbondstrength

    anddegradationofmechanicalpropertyofsteelbar(Torres-AcostaetaL,2007;Apostolopoulosand

    Papadakis,2008).

    Fig.1.Servicelifemodelofcorrodedstructure

    anditstime-dependentreliability.

    Dcgeeof

    COlTOsion

ReliiI

    index

    lph.2Pbase:

    Chlorideins~ssic..|;on即嘲舢

    IIon}=pI.eJ'~rv

    .

    i

    DL:-']

    D

    :

    I

    ===

    :

    =:

    ,………'r………..r.=r'三点:p ,::;

    Withstructuraldeteriorationandagingofmateria1.thestructuralreliabilitybecomesatime- dependentdescendingprocess,asalsoshowninFig.1.Inconsiderationoftherequirementsofstructural

    safetyandserviceability,theconditionofcoverdelaminationandspallingisunacceptableandshouldbe

    avoidedthroughpriorrehabilitationorrepair(StewardandMullard,2007).Moreover,theallowable

    extenttosteelcorrosionmaybedifferentduetothestructuralimportanceandthecorrosionpropertyOf

    steelbar.Therefore,thedefinitionofdurabilitylimitstates(DLS)formarineRCstructurescanbe

    describedwiththefollowingthreelevels(seeFig.1).

    1.DLSl-thestateofcorrosioninitiationofreinforcement;

    2.DLS2thestateofappearanceofhairlinecrack,and

    3.DL$3-thestateofcritica1crackwidth.

ForthreeDLSs,therelevantdurabilitylife,,canbeexpressedas:

    i-1

    re=?,,,(1)

    j=0

    wherei=1,2and3,whichcorrespondstoDLSl,DLS2andDLS3,respectively.

    2.1TheoreticalModelofTimeto

    Chlorideingressinstructuralconcretehasbeenwidelystudiedanditsprocessisconsideredasa

    coupledactionofdiffusion,capillarysuction,convection,electromigration,andSOon.Forthesaturated

    concrete,thediffusionprocessiSassumedtobethemainactionforchlorideingress.While.formarine

    concretessufferingfromdry

    wetcycles,thecapillarysuctionandconvectionwillaffecttheingressof

    chlorideion.Basedonfieldinspections,JinandJin(2009)foundthatapartfrompartsurfaceregionof

    concretecover,thediffusionprocessiSalsovalidinthedeepcoverformarineconcretes.Therefore.the

    chlorideingressinconcretecanbemainlyexpressedbydiffusionprocess,whichisassumedtocomply

    withFick'S2ndLawofone-dimensionalsteadystate,givenas:

    =

    .(,),(2)

    whereCisthechlorideioncontentatthedistancexfortheperiodf;D(t)isthetime

    dependentdiffusion

    308LUChunhuaetal/ChinaOceanEng,

    25(2),2011305318

    coefficientofchloride,whichisusuallyaffectedbyconcreteage,stresslevel,environmental temperatureandrelativehumidity,andexpressedas:

((3)

    whereefisthereferencetime,usuallytref=28d(0.0767year);Drefisthediffusioncoefficientattimetref;

    mistheageexponent,whichcanbeinfluencedbycementitiousmaterial(DuraCrete,2000;Thomasand

    Bentz,2002);tistheconcreteageandD(t)isassumedtobeconstantwhent>30year(ThomasandBentz,

    2002);kr,kRHandk,areinfluencingfactorsofT,RHandappliedstresslevelinconcrete(Samsonand

    Marchand,2007;Ababneheta1.,2003;Lueta1.,2008),whichcanbegivenbyEq.(4),Eq.(5)andEq.

    (6),respectively.InEq.(6),isaconstant;2=0.25fortensilestresslevelot,and0.20for

    compressivestressleve1cc.

    kr=exp,0.028(T-23)~,?0.C;(4)

    =

    [+1-RH;

    =+

    O'cq

    /,.?/fck,.<..8.

    Assumingthatthesurfacechlorideconcentration,Cs,isconstantandinitial concrete,Co,iszero,Eq.(2)canbeexpressedwithEq.(7)usingerrorfunction: lr

    C(x,f)=l1erfflAx

    2]],

    (5)

    (6)

    chloridecontentin

    whereisthetotalchloridecontentatadepthafterexposuretimer;Axisthedepthofthesurface convectionregionofconcretecover,inwhichthechlorideconcentrationisapproximatelyequaltocs

    (JinandJin,2009);andDisaverageddiffusioncoefficienttothetimetanditcanbewrittenas(Kwon

    a1.,2009):

    D,1

    /30year)

    %(+()]3,f8)

    Thecriticalchlorideconcentration,Ccr,isdefinedasthecontentwhichcandestroytherustpassive

    layerofsteelandmakecorrosionreactionbegin.So,whenC(c,=Ccr,thetimetocorrosioninitiation,

    t0(year),canbeobtainedfromEq.(7)as:

    ,0:{

    (c).

    4k30Do[erf()]

    ()].to30year

    

    30.>30year

    1

    (9)

    LUChunhuaeta1./ChinaOceanEng.,25(2),2011,305318

    wherecisthecoverthickness;kandaretwoparameters,k=and:1/c

    309

    2.2TheoretiealModelofTimet

    Thetime,,fromcorrosioninitiationtocoverhairlinecrackingwillbeaffectedbymanyfactors, includingcorrosionrate,coverthickness,mechanicalandphysicalpropertiesofconcrete,diameterof

    reinforcement.spacingbetweenreinforcements,etc.(Bazant,1979).Sincecorrosioninitiation,the

    corrosionproductswithlargevolumewillexpandandinduceexpansionpressureqaroundsurrounding

concretewhichcanproducehooptensilestressinconcrete(seeFig.2).

    Fig.2.Modelofcrackpropagationinconcrete

    Assumingthecorrosionproductsformedaroundthesteelsurfaceisuniform,whichiStypically

    usedwhenthevolumeexpansionbycorrosioniSmodeledfLiuandWeyers,1998;ZhaoandJin,2006;

    MaaddawyandSoudki,2007),Wangeta1.(2008)proposedarelationshipmodelbetweentheuniform

    radialpressure,q,andpercentageofmasslossofcorrodedsteel,PLo=(oss/)×

    loo%],whichdidnot

    takeaccountoftheingressofcorrosionproductsintoopencracks.Basedoncomparativeanalysis,Lugt

    a1.(201l1foundthattheinfluenceofdeformationofcorrosionproductsonradia1pressurecouldbe

    neglectedwhentheYoung'SmodulusofcorrosionproductsiSlargerthan10GPa.Then.therelationship

    modelbetweenqandP1canbesimplifiedas"

    q:(?i-而一一2)L(ro+c)(ro

    +c)+(10)

    whereEcefistheeffectiveelasticmodulusofconcrete,Ecef=Ec/(1.O+),beingthecreepcoefficientof

    concrete(LiuandWeyers,1998);isPoisson'Sratioofconcrete;cisthecoverthickness;disthe diameterofsteelbar;doisthemeanthicknessofporouszoneatthesteel-concreteinterface;ro=d/2+do;

    Plistherequiredpercentageofmasslossofcorrodedsteel;isthemeanratioofvolumeofcorrosion

    productstothatofconsumediron.

    Practically,duringtheperiodofcrackpropagation,afractionofcorrosionproductswillpenetrate

    intotheseradialcracksunderradialpressureuntilcoverentirecracking.Lueta1.f2011)propo

Report this document

For any questions or suggestions please email
cust-service@docsford.com