Electrochemical Chloride Extraction : Influence of Concrete Surface on Treatment

Federal Highway Administration2002PDFTech ReportCleme\uf1a, Gerardo G.Kelly, R. G.Sharp, Stephen R.Virmani, Y. PaulStoner, Glenn E.Kelly, Robert G.Virginia Transportation Research Council (VTRC)United States. Department of Transportation. Federal Highway Administration. Turner-Fairbank Highway Research CenterUniversity of Virginia. Dept. of Materials Science and EngineeringUnited States. Federal Highway Administration. Office of Infrastructure Research and DevelopmentTurner-Fairbank Highway Research CenterUnited States. Federal Highway AdministrationUnited StatesCalcium carbonateCalcium chlorideCathodic protectionChloridesDepositionElectrical resistivityElectrochemical processesRehabilitation (Maintenance)Reinforced concrete bridgesSurfacesWater cement ratioBridgesElectrochemical corrosionIonsRehabilitationReinforced concreteRestorationService lifeSurface treatmentEfficiencyElectrochemical chloride extractionChloride ionsRehabilitation of concrete bridgesRemoval of chlorideSteel corrosion in concreteFHWA-RD-02-107VTRC 02-RInterim ReportOne bridge restoration technique available for reducing corrosion-induced concrete deterioration, which removes chloride ions while simultaneously realkalizing the concrete adjacent to the steel, is electrochemical chloride extraction (ECE). Studies have shown that ECE is capable of removing, in a single application, a significant portion of the chloride ions from a reinforced concrete structure. Prior research has also shown that the quantity of chloride ions removed is dependent on numerous factors including quantity and spacing of reinforcing steel, applied voltage, initial chloride concentration, etc. In addit ion, investigations into chloride binding and competition between other ions as current carriers have helped to clarify the probable mechanisms responsible for decreases in current efficiency with time during chloride removal. This portion of the investigation has focused on the influence of water-to-cement (w/c) ratio. In addition, an investigation was conducted to identify the cause of decrease in efficiency during chloride removal. A clear relationship between the w/c ratio and the chloride extraction rate was not evident. However, the investigation revealed that the resistance of the concrete surface layer increases considerably during ECE, which effectively restricts the current flow, while the resistance of the underlying layer of concrete either decreases or remains constant. It appears that the increased resistance of the surface layer concrete is accompanied by the formation of a tightly adhering residue on the concrete surface. Preliminary analysis of the surface formation indicates it contains calcium carbonate and calcium chloride.120