1.CORROSION AND PROTECTION OF STEELREINFORCED CONCRETE PROVIDED BY: EMAD BEHDAD LECTURER: PROF.SHAMS

2. OUTLINE INTRODUCTION CORROSION PROCESS TYPES OF CORROSION CAUSES OF CORROSION PROTECTION METHODS CONCLUSION 3. ASTM terminology (G 15) defines corrosion as thechemical or electrochemical reaction between a material,usually a metal, and its environment that produces adeterioration of the material and its properties. For steelembedded in concrete, corrosion results in the formationof rust which has two to four times the volume of theoriginal steel and none of the good mechanical properties.Corrosion also produces pits or holes in the surface ofreinforcing steel, reducing strength capacity as a result ofthe reduced cross-sectional area. 4. Electrochemical process of steelcorrosion in concrete 5. Volumetric change 6. Ca, Na, K hydroxides inhydrated cement raise the pHto ~13.5 A dense protective ferricoxide (Fe2O3) passive filmforms around thereinforcement Passive film develops on the bar surface This passive film stops irondissolution, and is stable atpH >10 pH >13 7. Yes if: (a) Concrete is always dry, then there is no H2O to form rust. Also aggressive agents cannot easily diffuse into dry concrete. (b) Concrete is always wet, then there is no oxygen to form rust. (c) Cathodic protection is used to convert all the reinforcement into a cathode using a battery. This is not easy to implement because anodic mesh is expensive, and this technology is not easy to install and maintain 8. (d) A polymeric coating is applied to the concretemember to keep out aggressive agents. These areexpensive and not easy to apply and maintain.(e) A polymeric coating is applied to thereinforcing bars to protect them from moisture andaggressive agents. This is expensive and there issome debate as to its long- term effectiveness.(f) Stainless steel or cladded stainless steel is usedin lieu of conventional black bars. This is muchmore expensive than black bars. 9. Can we avoid corrosion? No, not entirely: Concrete is not usually under water or continuously dry. Aggressive agents such as carbon dioxide, de-icing agents and/or sea water can diffuse into the best of moist concrete, and corrosion will eventually result. 10. COMMON CORROSION TYPES1) Crevice CorrosionCrevice corrosion is a localized form of corrosion usuallyassociated with a stagnant solution on the micro-environmentallevel. Such stagnant microenvironments tend to occur in crevices(shielded areas). Oxygen in the liquid which is deep in the creviceis consumed by reaction with the metal. Oxygen content of liquidat the mouth of the crevice which is exposed to the air is greater,so a local cell develops in which the anode, or area being attacked,is the surface in contact with the oxygen-depleted liquid. 11. Crevice Corrosion of Rebar Has Some Similarities with Filliform CorrosionThe head of the advancing filament becomes anodic, with a low pH and a lack of oxygen, as compared with the cathodic area immediately behind the head where oxygen is available through the semipermeable film. Corrosion proceeds as the cathode follows behind the anodic head (from Corrosion Basics NACE). 12. 2) PittingTheories of passivity fall into two general categories, one based on adsorption andthe other on presence of a thin oxide film. Pitting in the former case arises asdetrimental or activator species, such as Cl-, compete with O2 or OH- at specificsurface sites. By the oxide film theory, detrimental species become incorporatedinto the passive film, leading to its local dissolution or to development ofconductive paths. Once initiated, pits propagate auto-catalytically according to thegeneralized reaction, M+n + nH2O + nCl- M(OH)n + nHCl, resulting in acidificationof the active region and corrosion at an accelerated rate (M+n and M are the ionicand metallic forms of the corroding metal). 13. ChloridesAirborne, marine, industrial, groundwater, cast-inCl can penetrate through the passive filmAt Cl- > threshold, passive film breaks down, corrosion initiatesCl- threshold value is typically 0.05% by wt of concrete (0.02% prestressed concrete)Pitting corrosionChlorides are main cause of reinforcement corrosion 14. CarbonationCa(OH)2 + CO2 CaCO3 + H2O 15. EFFECT OF CARBONATION It can cause soft surface, dusting and colorchange It reduces quality concrete It reduces the concrete ability to protectreinforcement from corrosion (in an exposedenvironment) It will result in additional shrinkage incarbonated region. 16. DETECTING CARBONATION Depth of carbonation can be detected usingan indicator. A chemical such as Phenolphthalein sprayedon to freshly broken concrete. Areas remaining alkaline will turn in a brightpurply-pink color. Carbonated areas of concrete will remainunchanged in color. 17. Cl- Cl- +ve Ions+ve Ionse- Fe Fe++e-e-e-RebarRebar 18. Reinforcing steel corrosion Migration of chlorides, H20 Corrosion of the steeland O2 into the concrete, noreinforcement andcorrosion and no damage to cracking and/or spallingconcreteof concreteDegree of CorrosionInitiation Propagation (corrosion) Critical chloride threshold I Time 19. Cl-Cl- . Cl-. .- . Cl- .- Cl-.Cl- . Cl Cl. - . Cl- . Cl- Cl- . -. Cl Cl-Cl-.. . .pH >~10 .. .Cl.Cl-.. .. Cl-. - . - .- ..-. .. ... .Cl -Cl Cl . Cl Cl- Cl e e - -Cathode .Cathode...Anode . . . ... .. .ClElectrolyte - . Cl- .Cl-.. Cl . -Cl- . Cl- Cl-Cl.-.Cl- .Cl-Cl-Cl-Iron Oxygen Moisture Corrosion = Iron + Oxygen + MoistureEither the pH falls due to carbonation or other chemicals chlorides reach the steel above the threshold concentration an electrical charge destroys the natural protection of the steel Electrons flow and ions migrate Rust expansion causes cracking Rapid deterioration Spalling 20. RebarSpallinglossCrackswithRust DelaminationStaining 21. Abandoned Electric Pole 22. KISH ISLAND 23. BANDAR ABBAS 24. chloride inducedreinforcement corrosionin concrete exposed toseawaterCorroded rebar from cracked concrete of aparking structure exposed to deicing salts 25. Reinforced steel in concrete cracking 26. CORROSION PREVENTION METHODS REBAR COATING SCARIFIED & PATCHED DECK AWAITS ANODE MESH FLY ASH HOT-DIP GALVANIZING WIRELESS SENSOR FOR MONITORING CHLORIDE INCONCRETE INHIBITORS 27. REBAR COATING 28. EPOXY COATING PREVIEW MODEL 29. EPOXYCOATED BARSAnode Cathode Reduces anode areaReduces cathodic area Increases threshold*REDUCED CORROSIONElectrical Connection Ionic path Electrical path between anode and cathode Makes ionic pathway longer 30. thermally sprayed coatings of Zn and Al, combat corrosion For atmospheric, buried, and marine environment corrosion protection, Zn(TSZ), Al (TSA), and their alloys have proven that they provide long termcorrosion protection and outperform most all other methods. Anodic (TSZ/TSA) metal coatings applied to steel cathodes (more noble thanZn or Al), are referred to as cathodic or sacrificial protection coatingsystems. These thermal spray coatings provide corrosion protection by excluding theenvironment (or electrolyte) and acting as a barrier coating (like paints,polymers, and epoxies), but unlike typical barrier coatings they also providesacrificial anodic protection. 31. Zinc and zinc alloys are also sprayed directly onto concrete to protect thesteel rebar withinArc spraying of zinc on a concrete bridge pierin the Florida Keys. In this case the zinc acts assacrificial anode, although it is more frequentlyused in impressed-current systems. Threeimpressed-current zinc systems have alreadybeen installed by the Ministry ofTransportation of Ontario in TorontoSacrificial cathodic protection of steel inconcrete by thermal zinc spraying 32. FLY ASH using a Fly Ash concrete with very low permeability, which will delay thearrival of carbonation and chlorides at the level of the steel reinforcement. Fly Ash is a finely divided silica rich powder that, in itself, gives no benefitwhen added to a concrete mixture, unless it can react with the calciumhydroxide formed in the first few days of hydration. Together they form acalcium silica hydrate (CSH) compound that over time effectively reducesconcrete diffusivity to oxygen, carbon dioxide, water and chloride ions. Byreducing ion diffusion, the electrical resistance of the concrete alsoincreases 33. CATHODIC PROTECTIONImpressed current (active)Sacrificial anode (passive) 34. TITANIUM ANODE MESHA. TYPICALLY ATTACHED TO THE CONCRETE SURFACE ANDTHEN ENCAPSULATED IN CEMENTITIOUS MATERIALS.B- EASILY CONFORMS TO THE STRUCTURE GEOMETRY.C- MOST USED IMPRESSED CURRENT ANODE FOR CONCRETE. 35. Mixed Metal Oxide activated Titanium Anodes in the form of a ribbonmesh can be installed in close proximity and parallel to thereinforcement bars (rebar).MMO Ribbon Mesh 36. 1. Simple to Install.2. No Power Supply Needed.3. No Wiring or Conduit.4. No Long-Term Monitoring or Maintenance 37. Conventional Patch Repair 38. Embedded Zinc Anode for Patch Repair 39. CATHODIC PROTECTION SACRIFICIAL ANODE 40. REFRENCES Concrete Society Technical Reports TR 36 and 37 41. www.corrocell.co.uk