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宁波新城艺术宾馆2#楼结构设计与预算毕业设计外文翻译

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'毕业设计(论文)外文翻译设计(论文)题目:宁波新城艺术宾馆2#楼结构设计与预算学院名称:建筑工程专业:土木工程学生姓名:顾丽敏学号:06404010101指导教师:袁坚敏2010年01月10日 外文原文I:AfundamentalexplanationofthebehaviourofreinforcedconcretebeamsinflexurebasedonthepropertiesofconcreteundermultiaxialstressM.D.KotsovosDepartmentofCivilEngineering,ImperialCollegeofScienceandTechnology,London(U.K.)Thepaperquestionsthevalidityofthegenerallyacceptedviewthatforareinforcedconcretestructuretoexhibit’’ductile”behaviourunderincreasingloaditisnecessaryforthestressstrainrelationshipsofconcretetohaveagraduallydescendingpost-ultimatebranch.Experimentaldataarepresentedforreinforcedconcretebeamsinbendingwhichindicatethepresenceoflongitudinalcompressivestrainsonthecompressivefaceinexcessof0.0035.Itisshownthatthesestrains,whichareessentialfor"ductile”behaviour,arecausedbyacomplexmultiaxialcompressivestateofstressbelowultimatestrengthratherthanpostultimatematerialcharacteristics.Thepresenceofacomplexstresssystemprovidesafundamentalexplanationforbeambehaviourwhichdoesnotaffectexistingdesignprocedures.1.INTRODUCTIONThe"planesections”theorynot,onlyisgenerallyconsideredtodescriberealisticallythedeformationresponseofreinforcedandprestressedconcretebeamsunderflexureandaxialload,butisalsoformulatedsothatitprovidesadesigntoolnotedforbothitseffectivenessandsimplicity[1].Thetheorydescribesanalyticallytherelationshipbetweenload-carryingcapacityandgeometriccharacteristicsofabeambyconsideringtheequilibriumconditionsatcriticalcross-sections.Compatibilityofdeformationissatisfiedbythe”planecross-sectionsremainplane’’assumptionandthelongitudinalconcreteandsteelstressesareevaluatedbythematerialstress-straincharacteristics.Transversestressesandstrainsareignoredforthepurposesofsimplicity.Thestress-straincharacteristicsofconcreteincompressionareconsideredtobeadequatelydescribedbythedeformationalresponseofconcretespecimenssuchasprismsorcylindersunderuniaxialcompressionandthestressdistributioninthecompressionzoneofacross-sectionattheultimatelimitstate,asproposedbycurrentcodesofpracticesuchasCP110[1],exhibitsashapesimilartothatshowninfigure1.Thefigureindicatesthatthelongitudinalstressincreaseswiththedistancefromtheneutralaxisuptoamaximumvalueandthenremainsconstant.Suchashapeofstressdistributionhasbeenarrivedatonthebasisofbothsafetyconsiderationsandthewidelyheldviewthatthestress-strainrelationshipofconcreteincompressionconsistsofbothanascendingandagraduallydescendingportion(seefig.2).Theportionbeyondultimatedefinesthepost-ultimatestresscapacityofthe materialwhich,Typicalstress-strainrelationshipforconcreteincompression,asindicatedinfigure1,isgenerallyconsideredtomakeamajorcontributiontothemaximumload-carryingcapacityofthebeam.Fig.1.—Stressand«nindktribuiiomproposedbyCP110for•Fig,1—Typical$(re$»^(r3inrvlarioislwpforconcreteincomprwsioacriticalsectionatfailure.However,arecentanalyticalinvestigationofthebehaviourofconcreteunderconcentrationsofloadhasindicatedthatthepost-ultimatestrengthdeformationalresponseofconcreteundercompressivestatesofstresshasnoapparenteffectontheoverallbehaviourofthestructuralformsinvestigated([2],[3]).Ifsuchbehaviouristypicalforanystructure,thenthelargecompressivestrains(inexcessof0.0035)measuredonthetopsurfaceofareinforcedconcretebeamatitsultimatelimitstate(seefig.1),cannotbeattributedtopost-ultimateuniaxialstress-straincharacteristics.Furthermore,sincethecompressivestrainattheultimatestrengthlevelofanyconcreteunderuniaxialcompressionisoftheorderof0.002(seefig.2),itwouldappearthatarealisticpredictionofthebeamresponseunderloadcannotbebasedsolelyontheascendingportionoftheuniaxialstress-strainrelationshipofconcrete.Inviewoftheabove,theworkdescribedinthefollowingappraisesthewidelyheldviewthatauniaxialstress-strainrelationshipconsistingofanascendingandagraduallydescendingportionisessentialfortherealisticdescriptionofthebehaviourofareinforcedconcretebeaminflexure.Resultsobtainedfrombeamssubjectedtoflexureundertwo-pointloadingindicatethatthelargestrainsexhibitedbyconcreteinthecompressionzoneofthebeamsareduetoatriaxialstateofstressratherthantheuniaxialpost-ultimatestress-straincharacteristicsofconcrete.Itisshownthattheassumptionthatthematerialitselfsuffersacompleteandimmediatelossofload-carryingcapacitywhenultimatestrengthisexceedediscompatiblewiththeobserved"ductile”structuralbehaviourasindicatedbyload-deflexionormoment-rotationrelationships.1.EXPERIMENTALDETAILS2.1.SpecimensThreerectangularreinforcedconcretebeamsof915mmspanand102mmheightx51mmwidthcross-sectionweresubjectedtotwo-pointloadwithshearspansof305mm(seefig.3).Thetensionreinforcementconsistedoftwo6mmdiameterbarswithayieldloadof11.8kN.Thebarswerebentbackattheendsofthebeamssoastoprovidecompressionreinforcementalongthewholelengthoftheshearspans.Compressionandtensionreinforcementalongeachshearspanwerelinkedby seven3.2mmdiameterstirrups.Neithercompressionreinforcementnorstirrupswere providedinthecentralportionofthebeams.Duetotheabovereinforcementarrangementallbeamsfailedinflexureratherthanshear,althoughtheshearspantoeffectivedepthratiowas3.Thebeams,togetherwithcontrolspecimens,werecuredunderdamphessianat20〜forsevendaysandthenstoredinthelaboratoryatmosphere(20°C〜and40%R.H.)forabout2months,untiltested.FulldetailsoftheconcretemixusedaregivenintableL2.2.TestingLoadwasappliedthroughahydraulicramandspreaderbeaminincrementsofapproximately0.5kN.Ateachincrementtheloadwasmaintainedconstantforapproximately2minutesinordertomeasuretheloadandthedeformationresponseofthespecimens.Loadwasmeasuredbyusingaloadcellanddeformationresponsebyusingboth20mmlongelectricalresistancestraingaugesanddisplacementtransducers.Thestraingaugeswereplacedonthetopandsidesurfacesofthebeamsinthelongitudfnalandthetransversedirectionsasshowninfigure4.Thefigurealsoindicatesthepositionofthelinearvoltagedisplacementtransducers(LVDTs)whichwereusedtomeasuredeflexionatmid-spanandattheloadedcross-sections.Themeasurementswererecordedbyanautomaticcomputer-baseddata-logger(Solatron)capableofmeasuringstrainsanddisplacementstoasensitivityof±2microstrainand土0.002ram,respectively.1.EXPERIMENTALRESULTSThemainresultsobtainedfromtheexperimentstogetherwithinformationessentialforabetterunderstandingofbeambehaviourareshowninfigures5to14.Figure5showstheuniaxialcompressionstressstrainrelationshipsoftheconcreteusedintheinvestigation,whereasfigures6and7showtherelationshipsbetweenlongitudinalandtransversestrains,measuredonthetopsurfaceofthebeams(a)atthecross-sectionswheretheflexurecrackswhicheventuallycausefailurearesituated(criticalsections)and(b)atcross-sectionswithintheshearspan,respectively.Figures6and7alsoincludethelongitudinalstraintransversestrainrelationshipcorrespondingtothestress-strainrelationshipsoffigure5.+305<1S2,Smmi唪mm■中3-2nrw-r206mm11111竹51什mm2-2crosssectFig.3.—Beamderails.Figure8showsthetypicalchangeinshapeofthetransversedeformationprofileofthetopsurfaceofthebeamswithloadincreasingtofailureandfigure9providesaschematicrepresentationoftheradialforcesandstressesdevelopingwithincreasingloadduetothedeflectedshapeofthebeams.Typicalload-deflexionrelationshipsofthebeamsareshowninfigure10,whereasfigure11depictsthevariationoncriticalsectionsoftheaverageverticalstrainsmeasuredonthesidesurfacesofthebeamswith thetransversestrainsmeasuredonthetopsurface.Figure12indicatesthestrengthanddeformationresponseofatypicalconcreteundervariousstatesoftriaxialstressandfigure13presentsthetypicalcrackpatternofthebeamsatthemomentofcollapse.Finally,figure14showstheshapeofthelongitudinalstressdistributiononthecompressivezoneofacriticalsectionatfailurepredictedonthebasisoftheconceptsdiscussedinthefollowingsection. 中文翻译I:在多向应力作用下从混凝土的特性看受弯钢筋混凝土梁变化的一个基本试验M.D.Kotsovos伦敦皇家科学与技术学院土木工程系本文所探讨的问题是通常认为在荷载递增下钢筋混凝土结构呈现弹性状态,这必须是因为混凝土的应力-应变关系有一个逐渐递减的临界部分的真实性。试验数据显示受弯钢筋混凝土梁会在受压面的纵向压应变超出0.0035。这表明这些应变是钢筋混凝土结构的本质,它是由于一个比极限强度小的复杂多向的应力状态而不是塑性材料的特性引起的。一个复杂应力系统的存在为梁的状态提供了一个基本试验,而不是想象的一个现有设计过程。1引言“剖面”理论不仅是通常认为能很真实地描述钢筋混凝土梁和预应力混凝土梁在弯矩和轴向荷载下的变形,而且能确切地阐述,所以它提供了一个设计工具,因为它的有效和简单而闻名[1]。假设在临界横截面伤是均衡的,这个理论分析地描述了一个梁的承载能力和几何特性之间的关系。变形协调必须满足“水平横截面荏苒水平”的假定和纵向混凝土和钢筋的应力是通过材料的应力-应变的特性来估算的。为了简化计算,忽略横向的应力和应变。受压混凝土的应力-应变特性认为能够被混凝土试块的变形充分地描述,例如在极限的有限状态下,棱柱体或圆柱体在横截面的受压区受单轴压力和应力,就像现行规范所建议的CP110[l],显示出一个与图1相似的形状。图1表明纵向应力随着与屮和轴的距离增加而增加至最大值,然后保持不变。这个分布图已经达到安全性和受压混凝土的应力-应变关系的广泛观点,由上升和逐渐下降的两部分组成(如图2所示)。超出极限的部分,材料的塑性应力能力如图1所示,被认为对梁的最大承载能力有较大的作用。6—HorkJforces图1.临界面破坏建议CP为110的应力和应变分布图2.受压混凝土结构的标准应力-应变关系然而,最近关于在集中力作用下的混凝土的变化的一个分析性调查表明,在压应力作用下混凝土的极限强度变形没有对所有被调查的结果形式的变化产生明显的影响G21J31)。如果这个变化对任何结果都是典型的,那么在钢筋混凝土梁的顶面被测的很大的压应变(超出量0.0035)在它的极限冇限状态下(如图1),不能对极限单轴应力-应变特性产生作用。因此,因为压应变在单轴压力下的任何混凝土的极限强度等级下为e=0.002(如阁2所示),在混凝土的单轴应力-应变关系下降部分,将出现一个在荷载作用下梁变化的现在可行的预测。根据以上的观点,木文的描述都在以下的评价中,广泛的支持观点的一个单轴应力-应变关系由一个上升的和一个逐渐下降的部分组成,对受弯的根据混凝 土梁的变化的真实描述是非常必耍的。这个结果是从梁在两点荷载作用下弯曲得到,表明很大的应变的通过梁受压的混凝土呈现的,由于三维应力而不是一味的混凝土极限应力-应变特性。这表明材料木身受到一个完整和直接的承载能力损失,当极限强度被超过的假定与弹性结构的变化并存的,通过偏心荷载或瞬间旋转关系表明的。2.试验细节1试块三根矩形钢筋混凝土梁,跨度915mm,横截面为102mmx51mm,受剪区跨度为305mm(如图2所示)。受力筋由两个直径为6mm,屈服荷载为11.8kN的钢筋组成。在梁端部钢筋弯起,就能为整个受剪跨度提供抗力。整个受剪跨度内压缩张拉的加强筋布置了七个直径为3.2mm的箍筋。在梁的中间部分没有压缩加强筋和箍筋。根据上面所述的钢筋布罝,所有的梁都是受弯破坏而不是受剪破坏,尽管剪跨比为3。所有的梁与受控的试块一起放在20°C的湿麻袋下七天,然后贮存在实验室条件下(20°C,40%湿度)2个月,直到试验结束。所有混凝土配料都在表格T中。2.2试验过程通过液压锤和分布梁加载,每次大约增加0.5kN。为了测量荷载和试块的形变,每次持荷约2分钟。荷载用一个荷载单元来测量,形变由20mm长的电阻应变片和位移转换器测得。应变片贴在梁纵向和横向的顶面和侧面(如阁4所示)。图4也表明了直流电压位移转换器(LVDT’S)的位罝,它是用来测量跨中和加载横截面的形变。测量数据记录在计算机自动数据记录仪中,能够测量应变和形变的灵敏度分别为±2微应变和±0.002mm。3.试验结果主要的试验结果是从试验中得到的,能更好地了解梁的变化,所示图5至图14的信息是必不可少的。图5表明结果的单轴压应力-应变关系应用于调查中,而图6和图7表明纵向应变与横向应变的关系,分别位于(a)弯曲裂缝最终导致破坏横截面出和(b)受剪区跨内的横截面出。图6和图7也包含了纵向应变-横向应变与阁5的应力-应变关系是一致的。图8中标准的改变在梁顶面的横向形变轮廓图中和图9提供一个轴力和应力随着荷载的增加而增大,导致梁向下变形的图框表示方法。梁的标准偏心荷载关系如图10所示,而图11描述了测得平均竖向应变的梁侧面的临界截面变形和横向应变在顶面测得。图12屮标准结果的强度和形变在各种状态的十三轴应力不河阁13所呈现的梁标准裂缝阁样在破坏的瞬间。最后阁14表明在临界截面的受压区伤纵向应力的分布形状,可根据概念来预测破坏,在以下部分将被讨论。图3.梁的细节1-12-2cross 外文原文H:Somequestionsonthecorrosionofsteelinconcrete.PartII:Corrosionmechanismandmonitoring,servicelifepredictionandprotectionmethodsJ.A.Gonzdlez,S.Felifd,P.Rodffguez,W.Lfpez,E.Ramirez,C.Alonso,C.AndradeABSTRACTThissecondpartaddressessomeimportantissuesthatremaincontroversialdespitethevastamountsofworkdevotedtoinvestigatingcorrosioninconcrete-embeddedsteel.Specifically,thesereferto:1)therelativesignificanceofgalvanicmacrocouplesandcorrosionmicrocellsinreinforcedconcretestructures;2)themechanismbywhichreinforcementscorrodeinanactivestate;3)thebestprotectivemethodsforpreventingorstoppingreinforcementcorrosion;4)thepossibilityofareliablepredictionoftheservicelifeofareinforcedconcretestructure;and5)thebestcorrosionmeasurementandcontrolmethods.Theresponsesprovidedaresupportedbyexperimentalresults,mostofwhichwereobtainedbytheauthorsthemselves.INTRODUCTIONConcrete-embeddedsteelisknowntoremaininapassivestateundernormalconditionsasaresultofthehighlyalkalinepHofconcrete.Thepassivityofreinforcementsensuresunlimiteddurabilityofreinforcedconcrete(1KC)structures.However,therearesomeexceptionalconditionsthatdisruptsteelpassivityandcausereinforcementstobecorrodedinanactivestate.Thishasraisedcontroversialinterpretations,someofwhichwerediscussedinPartIofthisseries[1].ThisPartIIanalysesthoughfarfromexhaustively,other-totheauthorsmindsatleast-equallyinterestingissuesonwhichnogeneralconsensushasbeenreached.MATERIALSANDMETHODSThereaderisreferredtoPartIforadetaileddescriptionofthematerialsandmethodsusedinthiswork.Mostoftheexperimentalresultsdiscussedhereinwereobtainedwiththesametypesofspecimensandslabs.Galvaniccouplesweredeterminedonspeciallydesignedspecimens,suchasthoseshowninFigs.1and2.Near-realconditionsweresimulatedbyusingabeamthatwas160cmlongand7x10cmincross-section.Thebeamwasmadefrom350kgcement/m3,halfofwhichcontainednoadditives,whiletheotherhalfincluded3%CaC12bycementweight[2],(Fig.1).InordertostudytheeffectoftheSanod/Scathoaratioongalvanicmacrocouples,theyweremodelledbysurroundingasmallcarbonsteelanodewithastainlesssteel(AISI304)cathodeandviceversa (Fig.2).Inthisway,theratio’sconsistensywasassured.Inaddition,thepotentialandicorrofstainlessstealandthoseofthepassivestructureswereverysimilar.concretewithandwithoutchloridesandtoillustratethesignificanceofpassivesteel/activesteelmacrocouples.Fig.2-Schemeofgalvanicmacrocouplesembeddedinchloride-containingmortarusedtostudytheeffectoftheSanod/Scathodratioandtheirrelativesignificancetocorrosionmicrocells.2.RESULTSANDDISCUSSION2.1WhatistherelativesignificanceofgalvanicmacrocouplesandcorrosionmicrocellsinRCstructures?Accordingtoseveralauthors[3,5],thepolarizationresistancemethodprovidesaneffectivemeansforestimatingthecorrosionrateofsteelinP,C;themethodisquiterapid,convenient,non-destructive,quantitativeandreasonablyprecise.However,itisuncertainwhetheritmaygiverisetoseriouserrorswithhighly-polarizedelectrodesbytheeffectofpassive/activeareagalvanicmacrocouplesinthereinforcements[6].Basedontheauthors1ownexperiencewiththebehaviourofgalvanicmacrocouplesinPC,thecontributionofthesemacrocouplestooverallcorrosionisverymodestrehtivetothatofthecorrosionmicrocellsformedintheactiveareasofreinforcementsinthepresenceofsufficientoxygenandmoisture[2,7,8]•Thus,ithasbeenexperimentallycheckedthat:Galvanicmacrocoupleshaveaslightpolarizingeffectonanodicareasinwetconcrete,whosepotentialistherebyinfluencedinonlyafewmillivolts.Ontheotherhand,macrocoupleshaveastrongpolarizingeffectonpassiveareasdespitethelowgalvaniccurrentsinvolvedrelativetotheoverallcorrosioncurrent.Asaresult,galvaniccurrentscanresultingrosslyunderestimatedicorrvaluesfortheactiveareassincetheyareoftensmallerthan10%oftheico=valuesestimatedfrompolarizationresistancemeasurements.ThecorrosiveeffectofcoplanarmacrocouplesonRCstructuresonlyprovesdangerouswithinasmalldistancefromtheboundaryofactiveandpassiveareas.Fig.3comparestheestimatedicorrandigvalues,inmortarcontaining3o〜ACaC12,peranodesurfaceunitforanumberofanode/cathodesurfaceratiosforAISI304stainlesssteel/carbonsteelmacrocouplesinsupportoftheaboveconclusions[9].2.2Bywhatmechanismdoreinforcementscorrodeinanactivestate?Whenthepassivestateislost,therateofreinforcementcorrosionininversely 2.RESULTSANDDISCUSSION2.1WhatistherelativesignificanceofgalvanicmacrocouplesandcorrosionmicrocellsinRCstructures?Accordingtoseveralauthors[3,5],thepolarizationresistancemethodprovidesaneffectivemeansforestimatingthecorrosionrateofsteelinP,C;themethodisquiterapid,convenient,non-destructive,quantitativeandreasonablyprecise.However,itisuncertainwhetheritmaygiverisetoseriouserrorswithhighly-polarizedelectrodesbytheeffectofpassive/activeareagalvanicmacrocouplesinthereinforcements[6].Basedontheauthors1ownexperiencewiththebehaviourofgalvanicmacrocouplesinPC,thecontributionofthesemacrocouplestooverallcorrosionisverymodestrehtivetothatofthecorrosionmicrocellsformedintheactiveareasofreinforcementsinthepresenceofsufficientoxygenandmoisture[2,7,8]•Thus,ithasbeenexperimentallycheckedthat:Galvanicmacrocoupleshaveaslightpolarizingeffectonanodicareasinwetconcrete,whosepotentialistherebyinfluencedinonlyafewmillivolts.Ontheotherhand,macrocoupleshaveastrongpolarizingeffectonpassiveareasdespitethelowgalvaniccurrentsinvolvedrelativetotheoverallcorrosioncurrent.Asaresult,galvaniccurrentscanresultingrosslyunderestimatedicorrvaluesfortheactiveareassincetheyareoftensmallerthan10%oftheico=valuesestimatedfrompolarizationresistancemeasurements.ThecorrosiveeffectofcoplanarmacrocouplesonRCstructuresonlyprovesdangerouswithinasmalldistancefromtheboundaryofactiveandpassiveareas.Fig.3comparestheestimatedicorrandigvalues,inmortarcontaining3o〜ACaC12,peranodesurfaceunitforanumberofanode/cathodesurfaceratiosforAISI304stainlesssteel/carbonsteelmacrocouplesinsupportoftheaboveconclusions[9].2.2Bywhatmechanismdoreinforcementscorrodeinanactivestate?Whenthepassivestateislost,therateofreinforcementcorrosionininversely proportionaltotheresistivityofconcreteoverawideresistivityrange[10].Becauseooci|10^—1—1—1—1—20406080100•/•PORESATURATIONFig.6-Influenceofthedegreeofporesaturationonthecorrosionrateofreinforcements.t£3zv5nsj 中文翻译II:混凝土中钢腐蚀的有关问题II:腐蚀机理和监督、使用年限的预测和保护方法J.A.Gonzdlez,S.Felifd,P.Rodffguez.,W.Lfpez,E.Ramirez,C.Alonso,C.AndradejWM:第二部分阐述几个仍然存在争议的重要问题,尽管已经在混凝土中钢腐蚀的调查研宄投入了大量的工作。特别是这几方面:1)在钢筋混凝土结构中的大电偶和腐蚀微电池对的和对重要性;2)激活状态的钢筋腐蚀机理;3)阻止或停止钢筋腐蚀最好的保护方法;4)-个钢筋混凝土结构使用年限的可靠预测的可能性探索;5)最好的防腐措施和控制方法。这些冋答需要试验得出,人部分都由作者们得出。刖目正常条件下强碱混凝土中的钢仍然处于钝化状态。钢筋的钝性能保证钢筋混凝土结构无限的耐久性。然而,有一些能破坏钢的钝性和引起钢筋腐蚀的实验条件。在第I部分中讨论到的一些实验结构己经引起了很多争论[1]。第n部分的分析虽然没有竭尽全力,但至少是作者的意思,就像有趣的问题有不同的意见一样。材料和方法读者指岀在第I部分详细描述了用于这项工作的材料和方法。这里所讨论的大部分实验结果都是从一样的试块和平板中得到的。电偶是由特殊设计的试块确定的,如图1和2所示。用一根长16m,70mmX100mm横截面的梁模拟近真实条件。梁是由每立方米350kg水泥制成,梁的一半含有添加剂,另一半含有水泥的重量的3%的CaCl2[2],(图1)。为了了解的比值对大电偶的影响,用在一个小的碳素钢正极环绕一个不锈钢负极并夹紧来模拟。这样,比值的连贯性是可靠的。此外,与钝化结果的电位和不锈钢的^<^是非常相似的。图1.梁用来分别测量混凝土中含有和不含有氯化物图2.用电耦合牢牢嵌入含有氯化物的砂浆里来研究的Ln•和•来说明钝化钢/活跃钢耦合的意义。SWS錄的作用和腐蚀微电池对的相对意义的方案。结果和讨论3.1什么是在钢筋混凝土结构中大电偶和腐蚀微电池对的相对重要性?根据一些作者[3,51,极化电阻作用为估计钢筋混凝土中腐蚀速度提供了一个有效的方法;这个方法是非常快、方便、非破坏性、适量和相当精确的。然而, 它不确定是否会对高度极化的电极产生严重的错误,通过在钢筋中的大电偶的钝化面积与激活面积的比值的影响。在作者自己对钢筋混凝土中大电偶性质的实验基础上,这些大电偶对所有的腐蚀是非常适度的,与存在充分的氧气和水分条件下腐蚀微电池对形成激活状态的钢筋比较[2,7,8]。因此,它已被实验验证:大电偶对潮湿混凝土中的阳极部分由一个轻微的极化作用,只要几毫伏就可以影响它的电位。在另一方面,大电偶对钝化部分有一个很强的极化作用,尽管低电流的运用相对于所有腐蚀流。(C)因此,电流可能会导致,非常低估在激活部分的的值,因为它们通常比极化电阻值估算的krr值的10%还小。(d)腐蚀剂会引起钢筋混凝土结构上共面的电偶,只能证明从激活面积到钝化面积边缘的一个很短的距离存在危险。图3是估算的‘与值的比较,在砂浆中含有3%的CaCl2,每个正极表面单元体为许多正极/负极表面比值作为美国钢铁学会304不锈钢/碳素钢电偶的一部分支持以上结论。OJOIOJIIO100RatioAaZAcIO"IO°IIO171O1161|£3/<36.§|2040TM£(dov»)60ItIotooco-o1111eoo27.CoClj♦OXCoCbIO2020406080TIME(09^1AEPSM3图3.腐蚀微电池对(fe01T)和电耦合(&)在包裹在不含有氯化物砂浆里的钢腐蚀中的相对意义。图4.暴露在自由氧环境下试块的/。^和E⑽的变化趋势。电流都是相对于而计算得到的(在图2的电耦合中的碳素钢)。2钢筋腐蚀的机理是什么?当钝化状态消失,钢筋的腐蚀速度与混凝土的电m率成反比例,在一个很宽的电阻率范围内[10]。因为环境中的相对湿度和混凝土的离子型外加剂确定混凝土的电阻率,这些因素与氧气一起在钢筋的表面控制着腐蚀速度[11]。饱和水混凝土结构的电阻率是相对非常低的,而且腐蚀速度实际上是溶解氧的扩散控制的,通过混凝土包住钢筋实现。这与在中性和强碱条件下唯一可能的负极反应是氧气的还原作业这个理念是一致的。这个重要性归因于氧气的循环作业,它证明这些作用对确定它在混凝土中的扩散率是正确的[12,13]。各种方法和实验条件用于这个目的,已得出了一定范围的水泥浆中的氧气的扩散率(从10_12到10-8m2/s)[14]o因为水溶液(C02=1(X5cm2/s’中氧气的扩散率是饱和浓度(CO2=2.1X107mol/cm3),不流动环境中(麥0.001cm)扩散层的近似密度,都是众所周知的,这个有限扩散流可以这样计算: llo2■-zrr)O2CO^-8X10-4A/cm^(80gA/cm2)其中z是等价的每摩尔(4)的数值,而F就是法拉第(96,500A«s/eq)。平均孔隙率为15%的1cm厚的砂浆保护层厚度与扩散层厚度一样与在养护期的最后空隙饱和条件下估算得的/胃值是非常一致的,这些砂浆不含氯化物离子而都含有2,4或6%的Cl[16]o另一方面,atlOgA/cm2的U见第I部分图9)[4】已经由一些作者从含氯化物的砂浆或碳酸盐砂浆与氧气冇限的扩散流所允许的速度是不协调的。因此,在一些环境下,替代负极的过程必须有更快的动力。在最近的工作屮,裂缝、氯化物例子和溶解氧并存在钢与混凝土的交界面,可以为质子的还原和替换机理的发生提供热动力条件[11,17]。有很多论据反驳氧气的还原作用作为底面腐蚀的定速步骤,即:-在一些环境下,腐蚀一旦开始,它发展到同一个速度尽管氧气正在从媒介中排除(图4)[11]。一当混凝土空隙饱和作用降低,混凝土的电阻率控制在一个宽泛的电阻率范围内;因此,腐蚀速度的减小好像与氧气进入结构的难易成反比例(图5)[10]。在另一方面,有一些论点支持在饱和Ca(OH)2中或水泥砂浆中的质子还原反应[11]:—PH值由12.6减小到ra.5在暴露的含有CT的饱和Ca(OH)2屮的钢与电解质溶液的交界面上。如果提供充足的氧气,PH值可以降低到1-2。一从在潮湿的空气中含有氯化物的砂浆试块的裂缝和大空隙中暴露的PH值1-5的酸性分泌物,腐蚀速度很快(5-10(iA/cm2)。-在蚀坑处涂上氢氧化铁膜的钢在含冇氯化物的饱和(^(0出2中极化成阳极吋会产生气泡,因为电位的降低需要释放氧气。每一个蚀坑点有一个足够低的PH,因参与质子还原反应就像阴极半反应,它们的腐蚀过程与阳极流互相重叠。当包裹在混凝土中的钢处于腐蚀状态,它的腐蚀动力指数随着空隙饱和作用的上升而升高(图6),就像裸露在大气中的钢的腐蚀,随着环境的相对湿度的上升而增加一样[18]。在钢筋上的一些点,催化循环可能被取代等,这些是由Schikon•提出的钢的大气腐蚀[19],是氯化铁而不是SO42"作为催化剂(阁6)。O.O-1O70701—n•1t£3/v5ts-07.Cl♦IV.Cl10080604020PORESATURATION10oo70d111O3/HSIRESISTIVITY(ohm-cm)31'