The mechanism controlling corrosion of steel in carbonated cementitious materials in wetting and drying exposure

Experiments were performed to study the mechanism of corrosion of steel in carbonated concrete in cyclic wetting/drying exposure. It was found that the corrosion rate increased during wetting, followed by a decrease during drying. The increase and decrease of the corrosion rate can be explained by changes in electrochemically active steel area as a function of the moisture state of the mortar and its porosity. The corrosion rate achieved in the wet phase stabilizes during the first few wetting and drying cycles. The mechanism of the electrochemical process is discussed on the basis of theoretical considerations. It is concluded that the corrosion kinetics are under activation control. The availability of oxygen does not seem to be a limiting parameter for the corrosion process in cyclic wetting/drying exposure.