Study of residual protection following interruption of impressed current cathodic protection in concrete

Impressed Current Cathodic Protection (ICCP) is a well-established technique to rehabilitate and protect corroding steel reinforcement in concrete. Recent studies have demonstrated that the protective effects of ICCP do not cease immediately after the system is interrupted, but can persist for a period of time before corrosion re-initiates. The residual effect is attributed to the beneficial effects of ICCP, where chlorides are repelled from the steel and re-alkalisation of the concrete around it occurs, thereby re-establishing passivity. This paper looks into this phenomenon of this residual effect and investigates how long it lasts and how it varies with current densities and duration of ICCP application. A number of parameters including steel potentials, depolarisation values, corrosion rates and concrete resistance were monitored for salt-contaminated reinforced concrete specimens that were subjected to ICCP and subsequently interrupted. Overall the results show that residual protection can be achieved by the application of ICCP to reinforced concrete structures. The duration and current density of the applied current both affect the duration for which this protection will remain.