外文翻译完整版CORROSION AND PRESTRESSED CONCRETE BRIDGES.

1、CORROSIONANDPRESTRESSEDCONCRETEBRIDGESAdrianT.Ciolko,P.E.1腐蚀和预应力混凝土桥梁阿德里安 T.Ciolko P.E.1AbstractTheimpactonbridgereliability,ofprestressingsteeldeteriorationandtendonrupturecreatedbycorrosionmechanisms,ismuchmorecriticalandrapidthanthatofanyothercomponentofaprestressedconcretebridge.Additionally,det

2、eriorationofembeddedprestressingreinforcementinthesestructuresmaynotnecessarilybemadevisiblethroughmanifestationofexternaldistressintheConcrete.摘要腐蚀机制引起预应力钢筋的恶化和断裂，进而对桥梁的可靠性产生影响，这比对预应力混凝土桥的其他部分的影响更加严重，也更加迅速。 此外，在这些结构中，有粘结预应力钢筋的恶化也不必要通过混凝土外部糟糕的状况表现出来。Initiatingmechanismsandparticularformsofcorrosiona

3、ffectingprestressedconcretestructuresaredescribedbasedontheauthorsexperience.Thesedegradationmechanismsinclude:ChloridesandCorrosionConcreteCarbonationEffectsInfluenceofConcreteCrackingElectrochemical(Macrocell)andPittingCorrosionStressCorrosionCrackingandSteelEmbrittlementFrettingCorrosionCorrosion

4、andFatigue关于腐蚀影响预应力混凝土结构的最初机制和特定形式的描述是基于作者的经验。这些退化机制包括： 氯化物和腐蚀 混凝土碳化影响 混凝土裂缝的影响 电化学 (小区) 和孔蚀 应力腐蚀开裂和钢的脆断 微动腐蚀 腐蚀和疲劳Recently,prestressed,post-tensionedconcretestructureshavebeenthoughttobethreatenedbycertainprematureperformanceimpairmentsworldwide,predominatelywhendefectswerepresent.Theseproblemsmayc

5、ontinuetomanifestthemselves.Therefore,corrosionpreventativemethodsandneedforscrutinyduringconstructionandmaintenanceneedswillbedescribed.Forexistingstructuresexperiencingevidenceofprematuredistress,theauthordiscussescase-studybasedinvestigativetechniquesandavailablerehabilitationStrategies.最近，世界各地的预

6、应力、 后张法预应力混凝土结构已经被认为受到某些早期性能破坏的威胁，尤其是已经存在的缺陷。这些问题可能继续危害结构。因此，我将对预防腐蚀的方法和施工与维护期间的检测进行介绍。对于遭受早期破坏的现有结构，作者讨论案例研究是基于探测技术和有效的修复手段。1VicePresident,ConstructionTechnologyLaboratories,Inc.,5400OldOrchardRoad,Skokie,IL60077.1CopyrightASCE2005Structures2005StructuresCongress2005IntroductionThefirstprestressedc

7、oncretebridgeintheUSwasconstructedin1950;thepaceofacceptanceforthisconstructiontechnologyacceleratedrapidly;mostallconcretebridgesuperstructuresinexistencetodaywerebuiltinthatfashion.Assuringsuccessinnewconstructionandextendingservicelifeofprestressedandpost-tensionedconcretebridgesrequiresattentive

8、nesstothedistinctive characteristicsandbehaviorsinherenttothisparticularconstructiontechnology.介绍美国的第一个预应力混凝土桥建于1950年；接受这种施工技术的步伐迅速加快;在这个时尚潮流中建造了当今大多数的混凝土桥梁上部结构。确保成功应用于新型结构和延长预应力和后张法预应力混凝土桥梁的使用寿命需要专注于这种特殊施工技术的显著特点和固有特征。Thispaperdiscussesconsiderationsnecessaryforachievingthepotentiallowmaintenancese

9、rvicelifethesebridgescanoffer.Theseobservationsarederivedfromtheauthorsexperienceininvestigatingandevaluatingprestressed,post-tensionedconcretebridges,anddevelopinginvestigativeandrehabilitationsolutionsattheCTLStructuralEngineeringLaboratorysince1988.Whilethedurabilityofprestressedconcretecanbeinfl

10、uencedbybehaviorsofboththeconcreteandreinforcement,recentconstructiontrendsandposttensionedconcretebridgeperformanceobservationshavefocusedmoreattentiononpreservingtheconditionofprestressingsteel.Consequencesofprestressingsteeldeteriorationaremostserious.Awarenessofthesefeaturesisakeyelementtoconstr

11、uctionoflonglastingprestressedbridgesandextendinglifeofolder,serviceablestructures.本文讨论了实现这些桥梁潜在的低维护使用寿命所需的考虑。自1988 年以来，作者在 CTL 结构工程实验室调查和评估预应力、后张法预应力混凝土桥梁、开发检测和加固解决方案，这些观测结论就源于这期间的经验。混凝土和钢筋两者的性能都影响预应力混凝土的耐久性，但是当近的建设趋势和后张预应力混凝土桥梁性能检测都更多地集中于预应力钢筋的维护。预应力钢筋恶化的后果是最严重的。对这些特点的认识是对建设持久的预应力桥梁和延长旧的可用结构寿命的一个关

12、键因素。FunctionofPrestressingReinforcementinBridgeDesignandConstructionMostconcretehighwaybridgesarecomprisedofprestressedconcreteintwopredominantfabrication/constructioncategories;namelypretensionedandpost-tensioned,withmorethan90%representingpretensioned.Thegeometriccrosssectionsanddesign/constructio

13、nproceduresusedrepresentabroadrangeofpossiblestructuraldesignconfigurations,bothprecastandcast-in-place;theinterestedreaderisencouragedtoobtaininformationfromorganizationssuchasthePrestressed/PrecastConcreteInstitute,thePostTensioningInstituteandtheAmericanSegmentalBridgeInstituteforin-depthdesignan

14、dconstructionguidanceforthistechnology,sinceexploringitscomplexityisbeyondthescopeofthispaper.预应力加固桥梁设计和施工中的作用最具体的公路桥梁是由组成的预应力混凝土在两个主要制造/建筑类别 ；即先张法和后张法，有 90%以上表示先张法预应力。几何截面和使用的设计/施工程序代表的范围广泛的可能结构设计配置、 预制和强制转换的地方 ；有兴趣的读者应该鼓励从预应力/预制混凝土研究所、 后张法研究所和美国节段桥梁研究所深入设计和施工指导对这一技术，等组织获得的信息，因为探索它的复杂性是超出了本文的范围。Pre

15、stressed(lesscommonlyknownaspretensioned)concreteismadebystressingthereinforcementbetweenfixedbulkheadsandcastingconcretearoundthesteelelements.Followingconcretecuring,thesteelstrandisreleasedatthebulkhead,transferringcompressivestressandaddedstiffnessintotheconcrete.Mostallpretensionedconcretebridg

16、ecomponentsareprecastinspecializedfabricationyards,thenshippedanderectedon-site.Post-tensionedconcreteforbridgespredominatelycontainsmultiplestrandorbartendons.Tendonsarestressedagainstbuilt-inmulti-pointanchorages;andtendonforcesareinternallyresistedbytheconcretemassincompression.Tendonsareinstalle

17、dinsheathingorductspreplacedintheformworkpriortocasting.Tensileforcesinstressedtendonsaretransferredtoconcretethroughspecializedanchoragehardware,creatingcompressionintheconcrete,makingthestructuralelementstiffer.Inbridges,bothbondedandunbondedtendonconstructionisused.Inbondedtendonconstruction,2Cop

18、yrightASCE2005Structures2005StructuresCongress2005cementitiousgroutisinjectedintotheductsafterstressing;protectingagainstcorrosionandenhancingthestrengthcapacityofthebridgeelement,sincegroutbondsthetensileelementtothesurroundingconcretemassalongitslength.Bondedtendonsarepositionedwithinthethicknesso

19、fgirderwebsandflangesUnbondedtendonconstructionissometimesusedinconcretebridgeswhenexternaltendonsarechosenindesign;thesearepositionedoutsidethemassoftheconcretegirderelements,althoughthesearenearlyalwaysincorporatedwithintheinteriorsofcellularconstruction.Unbondedtendonsarealsogrouted,principallyfo

20、rcorrosionprotectionCommonamongthesebridgecomponentsistheroleoftheprestressingreinforcement,whichcantaketheformofcold-drawnhighstrengthwire,orwirehelicallywoundtoform7-wirestrand,androlledhighstrengththreadedbars.Prestressingstrandforbridgeconstructionispresentlysuppliedwithatensilestrengthof1860MPa

21、,andbarreinforcementin1030to1100Mpatensilestrength.Prestressingwire(parallelwiresystems)hasalsobeenusedforprestressedbridges,thoughnotinthiscountryformorethantwodecades.Inbridges,theprestressingreinforcementelementprovidestheconcretestructureameansforcounteractingtensilestressresultingfromserviceloa

22、ds,andprovidestheneededcapacityforthestrengthlimitstate.Assuch,theprestressingreinforcementmustreliablyandcontinuouslysustain,overthelifeofthestructure,aminimumstresslevelontheorderof60%ofitsnominalstrength.Intherealmofengineeringdesign,thisdemandonmaterialperformanceisverysubstantial.Consequently,t

23、heprestressingreinforcementsqualityanditsprotectionagainstaginganddeteriorationprocessareparamounttoattainingfunctionalandsafetyrequirementsofaconcretebridgestructure.Designofprestressedmembersprovidesdirectlyforseveralformsofdurabilitymeasuressuchasdenseconcretecover,corrosionmitigatinggroutsystems

24、,andinnovative,proprietaryfulllengthcorrosionbarriersintegratedwithanchoragesystemsforpost-tensionedstructures.Additionally,structuraldetailsandstandardshavebeendevelopedandintroducedbyAASHTOandvariousindustryorganizationstomanageeffectsofprestressingreinforcementsheightenedsusceptibilitytoknownagin

25、gmechanismssuchasfatigue,fretting,andtimedependent,inelasticchangesinconcretestructurecomponents.Bridgemanagementstrategypresentlyreliesonfixed-intervalinspectionsandcomputationofbridgeloadratings.Unfortunately,theconditioninspectionsarecomprisedexclusivelyofvisualobservationofthestructuralfeaturesv

26、isibletotheunaidedeye,andfewwidelyacceptedpracticalmeansexistforquantitativelymeasuringconditionoftheprestressingandforintegratingresultsofsuchmeasurementsintothestrengthandserviceabilityratingcomputations.Themostrecent5-yearhistoryofpost-tensionedbridgeconstructionhasevolvedsignificantchangesinperc

27、eptionofthesebridgesperformance.AgingandDegradationMechanismsInfluencePracticesThehistoricperformancerecordofmorethan100,000prestressedconcretebridgestructuresintheUSisgenerallyconsideredsatisfactory;howeversomecorrosion3CopyrightASCE2005Structures2005StructuresCongress2005ofprestressingsteelhadbeen

28、reportedinaminorityofstructures.FHWA-sponsoredsurveysin1987and1992of20majorin-servicestructuresrepresentativeoftheprestressedconcretecomponentofthenationshighwayinfrastructuresupportedandhighlightedneedfordesignforserviceability.Findingsofvisualinspection/corrosionsensing/materialsstudiesbyNovokshch

29、enovandWhitingetal.forpretensionedandpost-tensionedsuperstructuresofvariousconfigurationsthroughoutthefullrangeofUSenvironmentalexposures,foundnoevidenceofseriousprestressingreinforcementcorrosionorothersystemicdegradation.Thesestudiesandothersimilarfindingsofthehighwaytransportationcommunityhaveled

30、torecommendationsrelatedprimarilytominimizationofthenumberofdeckjoints,moredurable,protectiveconcretesandcoatingsforanchoragecomponents,improveddeckandjointdrainagesystemstoredirectpassageofaggressivesolutionsfromcorrosion-susceptiblecomponentsneargirderends,andimplementationofmoreeffectivedeckjoint

31、maintenanceprograms.Someprestressedconcretestructureshavedisplayedtroublesomeprematureperformanceimpairmenttrendsworldwide,discriminatingthisstructuralconceptfromotherswhenoneconsidersdevelopmentofarationaleforassessingandmaintainingbridgereliabilityandutilitybeyondthe50-yearagemilestone.Szilard,ina

32、1969surveyperformedonbehalfofFIP,notedthatcorrosionofprestressingreinforcementwasthepredominantformofunexpecteddamagetostructures,whetheraccidentalordeterioration/agingbased.In1971,theAustralianWaterResourcesCouncilpublishedresultsofawide-rangingstudyoftheperformanceofprestressedconcretestructureswo

33、rldwideintendedtoassesstheperformanceofAustralianprestressedstructuresandcompareitwiththatofstructureselsewhere.Theworkwaspromptedbyprematuremultiplefailuresofprestressed,wire-woundpipelinesandtanks,andhelpedestablishimprovedspecificationforprestressingwireandconcrete/mortarandotherprotectivecoating

34、s.Citingthecriticalityofcorrosionprotectionforprestressedconcretepressurevesselsfornuclearreactorcontainments,GriessandNausstudiedcorrosionbehaviorofhigh-strengthprestressingsteelsin1978,reviewingseveralincidentsofprestressingsteelfailuresinnuclearpressurevasselsintheU.S.,France,andUnitedKingdom.Sch

35、upackconductedaperformancesurveycoveringthetimeperiodof1950to1977,concludingthatthenotedfailureincidencerateof200tendonsoutofanestimatedworldwideprestressingsteelconsumptionof30,000,000tonswasnegligible.However,anNCHRPstudyperformedbyaforensicengineeringfirmin1982reportedthat50structureswithtendonco

36、rrosionwerenotedinthetimeperiodbetween1978and1982.Tenofthesereportedlydisplayedbrittlefracturessuggestiveofenvironmentalcrackingphenomena.In1992,CiolkosummarizedstructuralevaluationandfailureanalysisdatafromU.S.prestressedconcretepipelinefailures,estimatingbasedonindustryandwaterutilityrecordsthatmo

37、rethan60suchpressurepipelineshadfailedintheUS,principallyduetoacceleratedcorrosionofpoorlyprotectedprestressingwire.Commontoallasafactorcontributingtoperformanceimpairmentwastheheightenedsusceptibilityofprestressingwiretoacceleratedcorrosionphenomena.4CopyrightASCE2005Structures2005StructuresCongres

38、s2005In1992,Podolnywarneddesignersofthedangerofcomplacencyresultingfromrelianceonthesomeofthefavorableconclusionsfromearlysurveysandreportsoftheconditionofprestressedstructures.Heconcludedthatalthoughthepopulationofprestressedstructureshasgreatlyincreasedinthelasttwodecades,itwasonlyrecentlythatweha

39、vebeguntounderstandtherolethatenvironmentandthemanyformsofcorrosionhaveonreliabilityofprestressingreinforcement.In1998,PostonandWoutersreportedinanNCHRPstudyofdurabilityofprecastsegmental(post-tensioned)bridges,thatnoevidenceofcorrosionorotherdurabilityproblemswiththesebridgesexisted,cautioninghowev

40、er,thatthegatheredinformationwasbasedprincipallyonvisualinspections.Thestudycitedthatlackofimprovednondestructiveevaluationoptionshindersevaluationofthesestructures.Podolnyscautionregardingcomplacencywaswarranted,aswerePostonsconcernsforlackofdiagnosticnondestructivetoolswhichwouldhaveprovidedamorer

41、eliablemeansforjudgingconditionofposttensionedstructures.In1999,corrosion-relatedfailureofanexternal(unbonded)posttensioningtendoninFloridaDOTs20-yearoldNilesChannelBridgefocusedattentiononpost-tensionedbridges.ThreeotherFloridabridgesincludingtheMid-BayBridgeinDestin,SunshineSkyway(St.Petersburg),a

42、ndI-75/I595SawgrassInterchangeinBrowardCountywerelaterinvestigated.Investigationsofthesestructureshighlightedthecriticalrolethattendongroutingandcomplementarycorrosionbarrierstakeinsuccessfulconstruction.Therootcausesofreinforcementdeteriorationinthesebridgeswereidentifiedasgroutingprocedureineffect

43、ivenessforcontrollingentrapmentofbleedwaterintendons,andpoortendonductdetailingcreatingaccessforaggressivesolutions.Theseincidentspromptedrigorousreviewofthedurabilityissuesrelatedtocorrosionofpost-tensionedconcretestructures.CorrosionMechanismsandThreatsCorrosionisdefinedasthedegradationofametalsin

44、tegrityandstrengthbyinteractionwithitsenvironment.Becausethemetalsusedinconstructionarerefinedfromtheirnaturally-occurringoxides,therefinedmetalislessthermodynamicallystablethanitsoxide.Whencorrosionoccurs,therefinedmetalsstructurerevertstoitsnaturally-occurringstatethroughanelectrochemicalreaction.

45、Initiationandsustenanceofthereactionrequireexistenceofanelectrolyticcell.Eachcorrosioncellrequiresthreeelements;ananode(theregionofmetalwhichcorrodes,orrevertstoanoxide),anelectrolyte(acorrosion-enablingmediumorenvironmentwhichprovidesapathorenvironmentforelectronsorcurrenttoflow,whichmaybeinherentl

46、yaggressiveorbenign),andacathode(thelocationwhereelectronsareconsumedorabsorbed,andthemetalisprotectedfromcorrosion).5CopyrightASCE2005Structures2005StructuresCongress2005Metalsinconcrete,includingmildsteelreinforcement,prestressingsteelencasedinhighqualityconcrete(pretensioned),andprestressingsteel

47、infullygroutedpost-tensioningductsareknowntoberesistanttocorrosionduetothebeneficialeffectsofthehighlyalkalineenvironmentthatcementitiousmaterialscanprovide.Whenthesealkalineconditionsareeffectivelysustainedinanunbroken,continuousstate,themetalssurface,whichwouldotherwisebeunstablethermodynamically,

48、isknowntobepassivated,orprotectedbyathinironoxidefilm.Designofconcretestructuresforserviceabilityispredicatedonthisprinciple,andmorethanahundredthousandUShighwaystructureshaveperformedadequatelybasedonthisdesignphilosophy.However,ifthehighlyalkalineenvironmentprovidedbyconcreteorcementitiousgroutisa

49、bsent(atvoidsandotherdefects);whereverthepassivationisinterruptedorbreached;orwhereverthepassivatingenvironmentisalteredchemically,corrosionwilloccur.Itisveryimportanttonoteinanydiscussiononthissubjectmatterthatcorrosionisneveruniformlydistributed.Thatkindofdeteriorationwouldideallyrequirethateachat

50、omonthemetalssurfacebeequallysensitivetothecorrosionmedium(electrolyte)andthatthemediumhaveuniformaccesstoallsurfaceatoms.Thevariousformsandtypesofcorrosionobservedinreinforcedandprestressedconcretearethereforemanifestationsofthenon-uniformitiesinherentinmaterials,manufacturingdefects,alterationoftheconcreteschemistry,andmechanicaldamagearisinginmanufacture,constructionorduringservice.Initiatingmechanismsandparticularformsofcorrosionaffectingprestressedconcretestructuresaredescribedinthefollowingsections;considerationofeachasaninflue