Chloride-induced reinforcement corrosion in blended cement concretes exposed to chloride-sulphate environments

This paper reports the results of a study conducted to investigate the influence of sulphate concentration and associated cation type on chloride-induced reinforcement corrosion in blended cement concretes. Reinforced concrete specimens were exposed to chloride plus sulphate solutions for a period of 1200 days. The exposure solutions contained a fixed concentration of 5% sodium chloride and the sulphate concentration was varied from 0 to 4% SO₄²⁻. The effect of cation type associated with sulphate ions, namely Na⁺ and Mg⁺⁺, on chloride-induced reinforcement corrosion was also evaluated. Reinforcement corrosion was assessed by measuring corrosion potentials and corrosion current density at regular intervals. The results indicated that the presence of sulphate ions in the chloride solution increased the corrosion current density, but no significant effect on the time to initiation of reinforcement corrosion was noted. Further, the corrosion current density increased with increasing sulphate concentration and the period of exposure. The corrosion current density on steel in the blended cement concrete specimens was much less than that in the plain cement concrete specimens, indicating that the corrosion resistance of blended cements was much better than that of plain cements. The cation type associated with sulphate ions did not significantly influence either the initiation or rate of reinforcement corrosion.