A comparative study of chlorides and longer-term reinforcement corrosion

High concentrations of chlorides in reinforced concretes usually are held responsible for reinforcement corrosion. However, this conflicts with many practical examples of actual concrete structures that show little reinforcement corrosion even with very high chloride concentrations. Herein a series of tests is described for reinforced concrete specimens made with fresh water, seawater, and with seawater with additional sodium chloride and exposed for 10years in a moisture-rich environment. All concretes retained concrete pH values well above 9, and particularly for dense high strength concretes, pH around 12. The overall amount of reinforcement corrosion was zero or almost negligible, irrespective of concrete mix proportions or concrete chloride content. These results are in strong contrast with significant corrosion reported in 1959 after only 2-3years exposure in a parallel experiment. The difference is attributed to poor compaction of those concretes inhibiting their inability to maintain sufficiently alkaline conditions and thus protection of the reinforcing bars. Overall the present controlled experiments support practical experience that reinforced concrete structures, properly made, can survive for long periods of time in chloride-rich environments without the occurrence of serious reinforcement corrosion.