Chloride induced reinforcement corrosion: Electrochemical monitoring of initiation stage and chloride threshold values

Reinforcement steel embedded in six different concrete mixes was exposed to chloride by wetting/drying cycles. Various parameters were continuously monitored during more than 1 year. Cement replacement with fly ash had beneficial long-term effects regarding chloride penetration resistance. Concerning corrosion performance, by far the most dominant influencing parameter was the steel/concrete interface since corrosion initiated on the lower side of the rebar (with respect to casting direction) regardless of binder type and w/b ratio. In many cases, after the first signs of depassivation, a marked increase in chloride content was required to prevent repassivation and to enable stable pit growth.

Research highlights
► Chloride induced reinforcement corrosion was studied under open circuit conditions.
► The most important influencing factor was found to be the steel/concrete interface.
► Transition from a passive to active corrosion state might occur over long time.
► Depassivation/repassivation events were frequently detected.
► Significant increase in chloride content was often needed to sustain stable pitting.