Corrosion and Protection of Reinforced Concrete


: Steel-reinforced concrete characteristicsConcrete and reinforced concreteThe structure of concreteCements and the cementing actionGeneralHeat of hydrationRate of strength developmentSupplementary cementitious materials – blended cementsGeneralFly ashSlagSilica fumeTriple blendsAggregatesGeneralThe design of a concrete mixEstimation of fine aggregate content and mechanical propertiesMixing and curing waterAdmixturesAir entraining admixturesSet retarding admixturesSet accelerating admixturesWater reducing and set retarding admixturesWater reducing and set accelerating admixturesHigh range water reducing admixturesWaterproofing agentsOtherSteel reinforcementBackgroundConventional steel reinforcementPrestressing steel reinforcementFibre-reinforced concreteReferences: Concrete deterioration mechanisms (A)Reinforced concrete deteriorationCrackingGeneralPlastic settlement crackingPlastic shrinkage crackingEarly thermal contraction crackingDrying shrinkage crackingCrazingAlkali aggregate reaction crackingPenetrabilityChemical deteriorationGeneralAlkali aggregate reactionDelayed ettringite formationSulphate attackAcid sulphate soilsThaumasite sulphate attackAcid attackAggressive (Dissolved) carbon dioxide attackSeawater attackLeaching and efflorescencePhysical salt attackOther chemical attackReferences: Concrete deterioration mechanisms (B)Biological deteriorationBacteriaFungiAlgaeSlimesBiofilmsPhysical deteriorationFreeze-thawFireMechanical deteriorationAbrasionErosionCavitationImpactStructural deteriorationOverloadingSettlementFatigueOtherFire damaged concreteGeneralEffects on concreteVisual concrete fire damage classificationEffect on reinforcement and prestressing steelExamination of sitesReferences: Corrosion of reinforcement (A)BackgroundPortland cement and blended cement bindersAlkaline environment in concretePhysical barrier provided by concretePassivity and the passive filmBackgroundThermodynamicsKineticsFilm formationFilm compositionFilm thicknessModels and theoriesReinforcement corrosionLoss of passivity and corrosion of steel in concreteUniform (Microcell) corrosion and pitting (Macrocell) corrosionCorrosion products composition – chloride-induced corrosionCorrosion products composition – carbonation-induced corrosionCorrosion products development – visible damageCorrosion products development – no visible damageChloride-induced corrosionGeneralPassive film breakdown/pit initiationMetastable pittingPit growth/pit propagationGeneralChemical conditions within propagating pitsReinforcing steel qualityMetallurgyDefectsChloride threshold concentrationsChloride/hydroxyl ratioCarbonation-induced corrosionLeaching-induced corrosionStray and interference current-induced corrosionGeneralGround currentsInterference currentsLocal corrosion due to stray or interference currentsReferences: Corrosion of reinforcement (B)Thermodynamics of corrosionBackgroundThe driving potential – the Nernst equationThe potential – pH diagramKinetics of corrosionBackgroundPolarisationInvestigation of the corrosion statePitting corrosionOxygen availabilityPolarisation of the anodic processResistance between anodic and cathodic sitesPotential difference between anodic and cathodic sitesReinforcement corrosion progressModelling chloride-induced corrosion initiationModelling carbonation-induced corrosion initiationModelling corrosion propagationBackgroundCorrosion damage criterionFactors affecting corrosion ratesCorrosion rates – chloride contaminated concreteCorrosion rates – carbonated concreteLength of corrosion propagation periodBackgroundGeneral modelAndrade (2014) modelAndrade (2017) modelDesign life achievementReferences: Condition survey and diagnosis (A) – on-site measurementsPlanning a condition surveyVisual inspectionCracksDelamination detectionConcrete coverElectrochemical measurementsElectrode (half-cell) potential mappingPolarisation resistanceConcrete resistivityOther measurementsRebound hammerUltrasonic pulse velocityUltrasonic pulse echoImpact echoGround penetrating radarCarbonation depthConcrete samplingGeneralWet diamond coringDrilled Dust SamplesRepresentativeness of investigations, testings, and samplingReferences: Condition survey and diagnosis (B) – laboratory measurementsGeneralCement (Binder) content and compositionAir contentWater/cement (binder) ratioSCM content and compositionWater absorption, sorption, and permeabilityDepth of chloride penetrationSulphate analysisAlkali aggregate reactionAlkali contentDelayed ettringite formationAcid attackChemical attackMicrobial analysisPhysical deterioration determinationPetrographic examinationCompressive strengthReportingBackgroundCommission/scope of servicesTechnical backgroundSite investigationHypothesisLaboratory testingCommentary on laboratory resultsConclusions and recommendationsReferences: Repair and protection (A) – mechanical methodsIntroductionCrack repairRepair and protection optionsPatch repairStages in the processBreakoutRebar coatingsBonding agentsPatching materialsEquipment and workmanshipSprayed concrete (Shotcrete/Gunite)Recasting with new concreteInhibitorsCoatings and penetrantsAnti-carbonation coatingsChloride-resistant coatingsPenetrantsStructural strengtheningPile jacketingReferences: Repair and protection (B) – cathodic protectionIntroductionHistory of cathodic protectionImpressed current cathodic protectionGalvanic cathodic protectionThe application of cathodic protectionImpressed current anodesHistoricSoil/water anodesMesh anodesRibbon/grid anodesDiscrete anodesArc sprayed zincConductive organic coatingsRemote (soil/water) anodesGalvanic anodesRemote (soil/water) anodesThermally sprayed metalsZinc mesh with fibreglass jacketZinc sheet anodesThe actions of cathodic protectionGeneralThermodynamicsKineticsCriteria for cathodic protectionBackgroundPotential criterionInstantaneous off measurementsmV shift criterionmV potential decay (polarisation) criterionAS 2832.5 criteriaISO 12696 criteriaOther standardsCP criteria are provenSelection and design of cathodic protection systemsGeneral considerationsGeneral design considerationsCurrent densityAnode layoutPower requirementsGeneralAnode resistanceCircuit resistanceCathodic polarisation (back emf)Power supplyStray current and interference corrosionGeneralRegulatory requirementsCommissioningSystem documentationQuality and test recordsInstallation and commissioning reportOperation and maintenance manualOperationalWarranty periodMonitoringSystem registrationCathodic preventionReferences: Repair and protection (C) – electrochemical methodsGalvanic electrochemical treatmentsBackgroundDiscrete zinc anodes in patch repairsDistributed discrete zinc anodesPerformance limitationsPerformance assessmentHybrid electrochemical treatmentsBackgroundFirst generation systemSecond generation systemPerformance assessment and limitationsElectrochemical chloride extractionElectrochemical realkalisationRepair and protection options – costs assessment approachesRepair and protection options – technical assessment approachesGeneral‘Do nothing’ optionScenario analyses approachReferences: Preventative measuresIntroductionConcrete technology aspectsGeneralMix design/mix selectionMix selection processBinder typesWater/cement (water/binder) ratioConcrete strengthConstruction considerationsThe 5 Cs/Pentagon of CsCoatings and penetrantsGeneralOrganic coatingsPenetrantsPore blocking treatmentsCementitious overlaysSheet membranesCOATED AND ALTERNATE REINFORCEMENTGeneralGalvanised reinforcementEpoxy coated reinforcementStainless steel reinforcementMetallic clad reinforcementNon-metallic reinforcementPermanent corrosion monitoringReferences: Durability planning aspectsSignificance of durabilityDurability philosophyPhases in the life of a structureOwner requirementsDesigner requirementsContractor requirementsOperator/maintainer requirementsLimit statesService life designDurability assessment – buried aggressive exposure – 100-year design lifeDurability assessment – marine exposure – 100-, 150-, & 200-year design livesReferences