ABSTRACT

Chloride ingress is a much more rapid phenomenon than carbonation. Reviewing the results of an extensive programme of work in connection with offshore concrete oil production structures, Leeming [3] noted that chlorides penetrated rapidly down narrow cracks, of the order of 0.1 mm. (This suggests that limiting crack widths to this level in marine structures, as required by current design codes, serves no practical purpose.) Significant corrosion of the reinforcement was observed at the end of the 5-year exposure period. This rapid ingress was confirmed by Brown (2] who found significant levels of chlorides in the majority of the bridges he studied, particularly those on motorways that had been subjected to higher amounts of de-icing salts. The rate at which the corrosion occurs will depend on the availability of the oxygen and water, and is thus a function of the permeability of the concrete. In addition the environmental regime plays a major role, with alternative wetting and drying being the most severe. Thus, marine and coastal structures are particularly at risk with high levels of chloride present in the environment and a ready supply of oxygen and water.