Effect of intermittent cathodic protection on chloride and hydroxyl concentration profiles in reinforced concrete

Abstract

This work quantifies the changes induced by intermittent cathodic protection (CP) in the pore solution composition of cement paste and concrete specimens exposed to sea water. In most cases the pulsed current resulted in a significant reduction in the Cl^-/OH^-ratio of the pore solution in the vicinity of the cathode. Although the increase in the hydroxyl concentration at the cathode was limited at low currents, the current was still important in maintaining a high pH value and has a similar effect to the presence of precipitated Ca(OH)₂ . Significant differences were noted between the concrete and the cement paste specimens. The cement paste specimens had a higher initial pH value, a lower resistivity, and a greater free chloride content corresponding to the greater volume of pore solution at a higher cement content. Thus, more significant protective effects were induced in the concrete specimens treated with the same applied charge. A beneficial increase in resistivity, resulting in an increase in the voltage drop across the specimens, occurred with increasing duration of treatment. Possible reasons for this include the generation of gas at the cathode and the precipitation of deposits on the concrete surface.