Chloride removal by intermittent cathodic protection applied to reinforced concrete in the tidal zone

A basis for protecting steel in concrete using intermittent cathodic protection (CP) is provided by the removal of chloride ions from the surface of the steel. The present study reported on parallel, experimental, and theoretical investigations undertaken to study chloride removal effects induced by an intermittent CP current in a tidal zone situation. Factors that affected the short-term chloride removal efficiency included the resistivity of concrete, charge passed, treatment duration, initial chloride content, concrete cover, and chloride diffusion coefficient. Very high extraction efficiencies initially were observed sometimes, possibly as the result of pressure-induced flow of the pore solution resulting from the generation of gas at the cathode. Chloride removal appeared to be limited by the rate of release of bound chloride within the period of treatment if a high charge was applied in a limited period of time. However, in the long term, the chloride profile reached a steady state governed only by the concentration gradients and the average applied electric field determined by the charge passed in a given time and the resistivity. This may be used to select the steady-state design current density.