The time to commencement of reinforcement corrosion in marine environments

This paper presents an overview of the considerable differences in the time taken before the commencement of reinforcement corrosion for real concrete structures exposed to various marine environments. Usually the disparity is attributed to differences in the rate at which chlorides can reach the reinforcement. However, actual field data do not consistently support this notion. Cases exist where the chloride contents are well above the normally accepted threshold level without obvious exterior evidence of corrosion. Based on recently reported observations for many identical elements exposed for some 65 years to the North Sea it is proposed that a high level of calcium carbonate in the concrete may be beneficial for long term durability, provided this is not compromised by poor workmanship, porous aggregates and alkali aggregate reactions. The hypothesis is discussed in terms of the current conventional wisdom for the corrosion of reinforcing steel in concrete structures.