Residual protection of steel following suspension of Impressed Current Cathodic Protection system on a wharf structure

Impressed Current Cathodic Protection (ICCP) is an established technique for the remediation of steel reinforced concrete structures. There have been examples of residual protection being afforded to structures where the ICCP system has been de-activated but to date no detailed investigation over the duration of the de-activation period has been undertaken. This study reports the findings of a systematic study in which an ICCP system was suspended for a period of 106 days. The results showed that based on the absolute passive potential criterion of maintaining a potential more positive than -150 mV with respect to a silver silver chloride reference electrode, 10% of the elements studied displayed residual protection. However, analysing the data based on the movement of the instant off potential to more positive values with time showed that 85% displayed evidence of residual protection. The data displayed a good correlation between charge passed and the duration of residual protection.