Studies of the corrosion of mild steel in alkali-activated slag cement mortars with sodium chloride admixtures by a galvanostatic pulse method

Corrosion of mild steel reinforcement in an alkali-activated slag (AAS) cement mortar containing NaCl admixtures has been investigated using an improved galvanostatic pulse technique. Corrosion rates were monitored at 90% relative humidity over a period of several months. On first exposure highest corrosion rates are seen with the lowest chloride levels, but over time different behaviours are seen for different chloride levels. The complex pattern of current and potential variation has been analysed using Tafel plots. Tentative conclusions are put forward to account for the behaviour seen, based on a model where oxidation of sulphide anions to sulphur prevents potential rising into the pitting regime and leads to inhibition of the oxygen cathode reaction.