The influence of internal relative humidity on the rate of corrosion of steel embedded in concrete and mortar

Abstract Once corrosion of reinforcing steel has been initiated, the internal relative humidity and electrical resistivity of the concrete cover are two of the factors controlling active corrosion. To determine this influence, simultaneous measurements of corrosion rate, electrical resistivity and internal relative humidity were carried out on mortar and concrete specimens. The corrosion rate was found to be strongly dependent on the electrical resistivity of the mortar or concrete cover. The electrical resistivity is, in turn, determined by the relative humidity and the concentration of chlorides in the pore solution and the experimental results suggest the existence of a threshold limit of the relative humidity below which a significant corrosion current cannot be supported.