The influence of chloride binding on the chloride induced corrosion risk in reinforced concrete

Chloride binding by the cement in concrete may affect the rate of chloride ingress and chloride threshold level which in turn determine the time to chloride induced corrosion initiation. In this work, a theoretical assessment of the influence of binding when chloride ingress results from diffusion, is presented. While chloride binding reduces the free chloride content within the concrete, it may increase or decrease the total chloride content depending on the distance from the concrete surface. The total chloride content at the transition between these effects is independent of the period of diffusion and value of the diffusion coefficient. The time to corrosion initiation of embedded steel is dependent on the corrosion risk presented by bound chloride. Bound chloride may participate in corrosion initiation when the establishment of pH gradients are required to sustain passive film breakdown. This is the result of the effect on the pore solution chemistry of the pH dependent solubilities of solid phases containing bound chloride that are very similar to that of calcium hydroxide. In some circumstances: the time to corrosion initiation may be reduced by an increase in binding because of the possible corrosion risk presented by bound chloride. (C) 2000 Elsevier Science Ltd. All rights reserved.