Chloride threshold values for corrosion in concrete – a myth ?

This paper reviews the established conceptual approach of predicting initiation of chloride induced corrosion of reinforcing steel in concrete. The low predictive power of the current approach is illustrated with help of recent field data for the chloride threshold value. Limitations and particular gaps of knowledge are highlighted, and issues urgently needing further research are identified. This includes the production process and the resulting microstructure of the reinforcing steel. Most of our practical long-term experience from real structures relates to systems, where cold worked steel and Portland cement were used. During the last few decades, however, a transition to thermomechanically strengthened reinforcing steels and to blended cements occurred. There is indication that this drastically affects the corrosion behavior.