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

A basis for protecting steel in concrete using intermittent cathodic protec tion (CP) is provided by the removal of chloride ions from the surface of t he steel. The present study reported on parallel, experimental, and theoret ical investigations undertaken to study chloride removal effects induced by an intermittent CP current in a tidal zone situation. Factors that affecte d the short-term chloride removal efficiency included the resistivity of co ncrete, charge passed, treatment duration, initial chloride content, concre te cover, and chloride diffusion coefficient. Very high extraction efficien cies initially were observed sometimes, possibly as the result of pressure- induced flow of the pore solution resulting from the generation of gas at t he 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 appli ed in a limited period of time. However, in the long term, the chloride pro file reached a steady state governed only by the concentration gradients an d the average applied electric field determined by the charge passed in a g iven time and the resistivity. This may be used to select the steady-state design current density.