Detecting invisible corrosion in concrete

Durable concrete, properly designed, ordinarily provides the necessary protection for reinforcing steel by minimizing the penetration of oxygen, moisture, and salts. But either through errors or inadequacies of the original construction or through changes during service of the structure, the reinforcing steel can rust. Corrosion of reinforcing steel is an electrochemical process: that is, both a flow of electricity and a chemical change are involved. The difference in electrical potential at various points on the steel generates a flow of current from one point (anode) to another (the cathode), forming galvanic cells and leading to corrosion. Any salt solution in the concrete in contact with the steel aggravates the process by acting as an electrolyte through which ions migrate and the electric current flows. Detecting and measuring this current flow helps us assess the degree of unseen corrosion activity. To record this information, half cell procedures standardized in ASTM C 876 have been developed. This concrete reinforcement corrosion detection method is described.