Effects of electrochemical chloride extraction on chemical and mechanical properties of hydrated cement paste

Abstract

To simulate the effects of applying electrochemical chloride extraction to reinforced concrete, rectangular prism specimens of hydrated cement paste containing sodium chloride were subjected to electrolysis between centrally embedded steel cathodes and external anodes of activated titanium. The cathodic current density was galvanostatically controlled at values in the range 1-5 A/m2 for periods of 4-12 weeks. Control specimens in which the steel was subjected to a modest level of cathodic protection at a current density of 5 mA/m2 were also prepared. After treatment, the specimens were sectioned and analysed to determine changes in the distribution of ions within the pore solution phase and in the total chloride content. Microhardness profiles were also measured. It was found that, as well as causing the free and bound chloride content of the specimens to decrease with time, the higher current densities also produced major increases in the pore solution alkali concentrations near the embedded steel. Associated with this local increase in pH value, there was an increase in soluble sulphate ion concentration which appeared to be controlled by solubility equilibria. For the limited range of specimens studied, no significant changes in microhardness profiles were observed.