Corrosion of Steel in Concrete PDF
Preview Corrosion of Steel in Concrete
Luca Bertolini, Bernhard Elsener, Pietro Pedeferri, Rob Polder Corrosion of Steel in Concrete CorrosionofSteelinConcrete. LucaBertolini,BernhardElsener,PietroPedeferri,RobP.Polder Copyright(cid:1)2004WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim ISBN:3-527-30800-8 Related Titles from WILEY-VCH Cahn,R.W.(ed.)/Haasen,P.(ed.)/Kramer,E.J.(ed.) Corrosion and Environmental Degradation ATwo Volume Set of the Materials Science and Technology Series ISBN3-527-29971-8 1110pp.,2000 R.WinstonRevie(Editor) Uhlig’s Corrosion Handbook, 2nd Ed. ISBN0-471-15777-5 1340pp.,2000 DECHEMA Corrosion Handbook: Corrosive Agents and Their Interaction with Materials Volumes 1–12, Index and Suppl. ISBN1126651800 1987–1993 Luca Bertolini, Bernhard Elsener, Pietro Pedeferri, Rob Polder Corrosion of Steel in Concrete Prevention, Diagnosis, Repair Authors Thisbookwascarefullyproduced.Nevertheless, authorsandpublisherdonotwarranttheinformation LucaBertolini containedthereintobefreeoferrors.Readersare PhD,AssociateProfessor advisedtokeepinmindthatstatements,data, DipartimentodiChimica, illustrations,proceduraldetailsorotheritemsmay MaterialieIngegneriaChimica„G.Natta“, inadvertentlybeinaccurate. PolitecnicodiMilano viaMancinelli,7 20131Milano LibraryofCongressCardNo.:appliedfor Italy BritishLibraryCataloguing-in-PublicationData BernhardElsener Acataloguerecordforthisbookisavailablefrom Dr.sc.tech./PhD,AssociateProfessor theBritishLibrary. SwissFederalInstituteofTechnology, InstituteofMaterialsChemistryandCorrosion Bibliographicinformationpublishedby ETHHönggerberg DieDeutscheBibliothek 8093Zürich DieDeutscheBibliothekliststhispublication Switzerland intheDeutscheNationalbibliografie;detailed and bibliographicdataisavailableintheInternetat Dept.ofInorganicandAnalyticalChemistry http://dnb.ddb.de. UniversityofCagliari 09042Cagliari (cid:1)2004WILEY-VCHVerlagGmbH&Co.KGaA, Italy Weinheim PietroPedeferri Allrightsreserved(includingthoseoftranslation FullProfessor inotherlanguages).Nopartofthisbookmaybe DipartimentodiChimica, reproducedinanyform–byphotoprinting,micro- MaterialieIngegneriaChimica„G.Natta“, film,oranyothermeans–nortransmittedor PolitecnicodiMilano translatedintomachinelanguagewithoutwritten viaMancinelli,7 permissionfromthepublishers.Registerednames, 20131Milano trademarks,etc.usedinthisbook,evenwhennot Italy specificallymarkedassuch,arenottobeconsidered unprotectedbylaw. RobB.Polder PhD PrintedintheFederalRepublicofGermany. TNOBuildingandConstructionResearch Printedonacid-freepaper. DepartmentCivilInfrastructure P.O.Box49 Composition HagedornKommunikation, 2600AADelft Viernheim Netherlands Printing straussoffsetdruckGmbH, Mörlenbach Bookbinding Litges&DopfBuchbindereiGmbH, Heppenheim ISBN 3-527-30800-8 Preface V Preface Over the millennia, concrete prepared by the Romans using lime, pozzolana and aggregateshassurvivedtheelements,givingproofofitsdurability.Prestigiouscon- crete works have been handed down to us: buildings such as the Pantheon in Rome, whose current structure was completed in 125 A.D. and also structures inmarineenvironmentshavesurvivedforovertwothousandyears.Thisprovides a clear demonstration that concrete can be as durable as natural stone, provided that specificcauses of degradation, such as acids or sulphates, freeze-thaw cycles, or reactive aggregates, are not present. Today,thankstoprogressmadeoverthepastfewdecadesinthechemistryofce- ment and inthe technology ofconcrete,eventhesecausesofdeteriorationcan be fought effectively. With an appropriate choiceof materials and careful, adequately controlled preparation and placement of the mixture, it is possible to obtain con- crete structures which will last in time, under a wide variety of operative condi- tions. The caseof reinforcedconcreteis somewhat different. These structures are not eternal, or nearly eternal, as was generally supposed up until the 1970s. Instead, their service life is limited precisely because of the corrosion of reinforcement. Actually,concreteprovidestheidealenvironmentforprotectingembeddedsteelbe- causeofitsalkalinity.Ifthedesignofastructure,choiceofmaterials,composition of the mixture, and placement, compaction and curing are carried out in compli- ance with current standards, then concrete is, under most environmental condi- tions, capable of providing protection beyond the 50 years typical of the required service life of many ordinary structures, at least in temperate regions. In fact, casesofcorrosionthathavebeenidentifiedinnumerousstructureswithinperiods muchshorterthanthosejustmentioned,canalmostalwaysbetracedtoafailureto comply to current standards or to trivial errors in manufacturing of the concrete. However, under environmental conditions of high aggressiveness (generally re- latedtothepresenceofchlorides),evenconcretewhichhasbeenproperlyprepared andplacedmayloseitsprotectivepropertiesandallowcorrosionofreinforcement long before 50 years have elapsed, sometimes resulting in very serious conse- quences. Theproblemofcorrosioninreinforcedconcretestructuresisthusaveryrealone and must be given special consideration. It is, in fact, only since the early 1980s CorrosionofSteelinConcrete. LucaBertolini,BernhardElsener,PietroPedeferri,RobP.Polder Copyright(cid:1)2004WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim ISBN:3-527-30800-8 VI Preface that research has devoted much attention to this problem. From those years on mainphysiologicalaspectsrelatedtobehaviourofsteelinconcrete,suchasthena- tureoftheaqueousporeliquidpresentinthehardenedconcrete,theelectrochem- istryofsteelinthisenvironment,themechanismofprotectionofsteelbyanoxide film, etc. have been established. Passing to the pathological side, research has ex- plained the phenomenology and mechanisms of corrosion,established the condi- tionswhichgiverisetoitandthelawsgoverningitsevolution,anddevelopedtech- niques fordiagnosing and controlling it. In particular, it has beenshown that the only circumstancesthat can give riseto corrosionare those when both depassiva- tion occurs (e.g. due to carbonation or chlorides) and oxygen and humidity are present. Several points still need to be clarified. For example: the atlas of pathological anatomy has been defined clearly with regard to corroding reinforcement, but onlysketchilyinrelationtothesurroundingconcrete;thebodyofdiagnosticsallows thestateofcorrosioninastructuretobeevaluatedforthemorecommonformsof corrosion, but is still incomplete in the case of hydrogen embrittlement in high strength steels of prestressed structures or corrosion caused by stray current; the handbook of anticorrosionistic pharmacology includes a long list of methodologies of prevention (from inhibitors to coatings, to corrosion resistant reinforcement, to electrochemical techniques), however their long-term effects or their possible negative side-effects are not always clearly known. Probably, the greatest short- comings have to do with the basic aspects of corrosion. For instance, in the area of physiopathology: the species around the passive reinforcement in concrete are known,butthosearoundcorrodingreinforcementarenot;theinfluenceofspecies on the passivity or corrosion of steel is known in qualitative terms, but very little is known of the entity of their interaction with the constituents of cement paste, and thus of their mobility in electrical fields or in various concentration gradients, in relation to the type of cement or to the characteristics of the con- crete, etc. Inthefieldofconstruction,notableprogresshasalsobeenachieved:theproblem ofcorrosion,andmoreingeneralofthedurabilityofstructuresinreinforcedcon- crete, is very seriously taken into consideration; new laws are in place and new technologies and products are available. Buttheabovemustnotlull usintoafalsesenseofsecurity.Itistruethattoday thereisgreatersensitivityto thisproblem,oftenbeingthe subjectofconferences, seminars,andpublications.Newrulesandstandardsdoexist,thoughtheyareper- ceivedascompulsory,beingtheresultoflegislation.Finally,newtechnologiesand sophisticatedproductsarebeingadopted,forexampleinthefieldofrepairofstruc- turesdamagedbycorrosion.Alltheseaspectsdonot,however,inthemselveselim- inate the errors,oftentrivial, that areat the basisofmostfailurestoday, andeven lessaretheyabletosolvethosecaseswherestructuresoperateunderconditionsof highaggressiveness.Substantialprogresswillbemade,alsowithregardtodurabil- ity, only when our current technology, based on empiricism and common sense, evolvesintoatechnologybasedonathoroughknowledgeofdegradationprocesses and of methods for their control. Preface VII Education,andthusteachinginparticular,hasaveryimportantroletoplay,not onlybymakingprofessionalssensitivetothedurabilityproblem,butalsobygiving them the tools necessary to solve it. Wehopethatthistextmaybeusefulforthosewhoworkinthefieldofciviland constructionengineering,aswellasforthoseinvolvedintheareaofmaintenance andmanagementofreinforcedconcretestructures.Itsaimistoprovidetheknowl- edge,toolsandmethodstounderstandthephenomenaofdeteriorationandtopre- vent or control them. In some sections of the text, because of our professional background,we havegone into details ofsomeelectrochemicalaspects.Theseex- planationsgobeyondwhatisstrictlyrequiredincivilandconstructionengineering and are not essential to an understanding of the other sections. Finally,wewishtothank the Europeancommissionsthat, bypromotingtheco- operative actions COST 509, 521 and recently 534, gave to several European re- searchers the opportunity to meet, collaborate and exchange views in the field of corrosionofsteelinconcrete.Thisbookwasbornfromthatcooperation.Wegrate- fully acknowledge all friends and colleagues on COSTActions, RILEM technical committees,andEuropeanFederationofCorrosionworkinggroups,forproviding data, papers and, most of all, for stimulating discussion. The Authors, November 2003 Foreword IX Foreword Steel reinforced concrete structures form an important part of our infrastructure. Thecombinationofhigh compressionstrengthofconcreteandhigh tensileprop- ertiesofreinforcingsteelgivesanidealcompositematerialwhichoffers,compared to other materials, a wide range of applications in structural engineering. Build- ings, slabs, beams, bridge decks, piles, tanks and pipes, all these structures can be executioned with steel reinforced concrete. Inthedesignprocessforstructuresarchitectsandcivilengineersareequallyin- volved and usually a distinction is made between the circumstances which affect the building’s safety and those which do not constitute an immediate hazard but may make the building unusable. This later condition is referred to as the structure’s limit state of serviceability. Traditionally the structuraland non-structuralfactorsaffecting the serviceability ofbuildings have beentreatedas separateissuesby designersand alsohave been dealt with in different circles of engineers. For an architect the aesthetics of the structurestandsinthefocusduringthedesignprocesswhereasthestructuralen- gineer sees his responsability in delivering a structure which is safe and reliable under all loading conditions. But, it is not only mechanical loading that has to be considered: every structure is exposed to an environment which may have an enormous influence on durability. Usually this interaction between the material of the structure and the environ- ment is called corrosion. Studying the history of steel reinforced concrete we find very rare cases where a structure failed due to mechanical loadings which have not been considered at the design stage. Technical standards provide suffi- cient information in giving guidance to civil engineers in designing a structure adequate to withstand all mechanical loading. The problem, instead, arises due tolackofsensitivityandknowledgeofcivilengineerswhendealingwithquestions of corrosion. As pointed out previously seldom failures of structures due to me- chanical overloading are reported but we know of high numbers of structures wherecorrosionandespeciallysteelreinforcementcorrosionhasledtopremature failuresandcostlyrestoration.Socorrosionofsteelreinforcementinstructuresis now a feature which figures heavily in the maintenance of existing buildings and has contributed to a number of structural collapses. CorrosionofSteelinConcrete. LucaBertolini,BernhardElsener,PietroPedeferri,RobP.Polder Copyright(cid:1)2004WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim ISBN:3-527-30800-8 X Foreword Even after about 50 years of experience with corrosion problems in steel rein- forced concrete structures there is still need for structural and architectural de- signers to acquire a greater understanding of factors and parameters influencing reinforcement corrosionand developing or improving standards or codes of prac- ticetoplacemoreemphasisontheneedfordesignfordurability.Ofcourse,there is not only the technical side of the problem. Serviceability implications are re- flected mainly in the economic losses which may be incurred through temporary or complete loss of use, cost of repairs and monitoring, or in the worst case the need for premature demolition and replacement. These issues together form a valid argument for greater awareness of the need for designers to consider expli- citly the implication of their requirements for durability. Thisbookisspecificallyaimedatgivingsupporttoengineersinupgradingtheir knowledgeonsteelreinforcementcorrosiontothehighestlevel.Acarefulcompil- ing and collecting of information for publishing a book is important, but the pri- maryrequirementistohaveauthorswhichintheirpersonholdalongtermrecord indealingwiththesubjecttheywanttowriteabout.Hereallauthorsinvolvedguar- anteethehighestlevelofqualificationforwritingaboutsteelreinforcementcorro- sion.Theirexpertiseresultsprimarilyfromtheirownscientificworkonthesubject ofreinforcementcorrosionbutinadditioneachofthemisinvolvedintheworkof severalinternationalbodieswhereinformationisnotonlygatheredanddiscussed but also transferred into publications, standards, regulations or codes of practice. This high level of knowledge and expertise is proved by the systematic concept of the book. For the benefit of the reader as well as for scientific structuring the book is divided into 5 parts and several chapters in each part. Forinitiatingcorrosionofsteelinconcretethecementitiousmaterialsandtheir transportpropertiesplayanimportantrole.Thereforepart1givesagoodoverview onpropertiesofcementitiousmaterialsandtheirinfluenceontransportproperties includingasectionondegradationofconcrete.Inpart2themechanismsofcorro- sion of steel reinforcement are completely described and in addition to ordinary reinforcementalsotheproblemofhydrogeninducedstresscorrosionforprestres- singsteeliscovered.Part3dealswithpreventativemeasuresandspecificallywith additionalmeasureswhichshouldstabilisepassiveconditionsforthesteelreinfor- cement even under highly aggressive conditions. Part 4 is dedicated to diagnosis, including chapters on most recent electrochemical monitoring techniques. Part 5 is dedicated to repair measures. Summarising the content of the book it can be concluded that all interesting aspects of reinforcement corrosion are covered ranging from the mechanism of corrosiontorepairmeasures.In factnothing ismissingandthebookofferscom- prehensive state-of-the-art knowledge and information. Scientists and engineers will equally benefit from the book and, hopefully, the bridge between theory and practicewhichisofferedwithinthisbookwillbeusedandcrossedbyahighnum- ber of readers. Bernd Isecke, Berlin November 2003 Contents XI Contents Preface V Foreword IX Part I Properties of Cementitious Materials 1 1 Cements and Cement Paste 3 1.1 Cement Types and Hydration Reaction 3 1.2 Porosity and Transport Processes 5 1.2.1 Water/cement Ratio and Curing 6 1.2.2 Porosity, Permeability and Percolation 8 1.3 Blended Cements 10 1.3.1 Pozzolanic Materials 10 1.3.2 Ground Granulated Blast Furnace Slag 12 1.3.3 Properties of Blended Cements 12 1.4 Common Cements 14 1.5 Other Types of Cement 17 2 Transport Processes in Concrete 21 2.1 Composition of Pore Solution and Water Content 22 2.1.1 Composition of Pore Solution 23 2.1.2 Water in Concrete 23 2.1.3 Water Content and Transport Processes 26 2.2 Diffusion 28 2.2.1 Stationary Diffusion 28 2.2.2 Non-stationary Diffusion 29 2.2.3 Diffusion and Binding 32 2.3 Capillary Suction 32 2.4 Permeation 34 2.4.1 Water Permeability Coefficient 34 2.4.2 Gas Permeability Coefficient 35 2.5 Migration 36 CorrosionofSteelinConcrete. LucaBertolini,BernhardElsener,PietroPedeferri,RobP.Polder Copyright(cid:1)2004WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim ISBN:3-527-30800-8
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