An investigation into impressed current cathodic protection systems in Australian wharves

Over the past forty years a significant number of corroding and at risk reinforced concrete structures have been successfully managed using Impressed Current Cathodic Protection (ICCP). ICCP systems are electrochemical treatments which are capable of arresting the corrosion of steel. A recent study of ten structures in the UK showed steel reinforcement in bridges remained passive up to three years after ICCP was no longer applied. Similar findings were reported in a study conducted in southern Australia. These findings indicate that ICCP can provide a form of lasting residual protection. Whilst the presence of residual protection has been established both the reasons for, and the mechanisms behind it and the duration for which it persists are currently unknown. It is believed that the period of passivity is due to changes in the microenvironment of the concrete adjacent to the steel. The most likely cause for this is prolonged operation of the ICCP system changing the chemistry of the concrete however at this time this is yet to be conclusively shown. This study examined the phenomenon of residual protection by suspending the operation of established ICCP systems in two wharves located in southern Victoria and monitoring the effect on the passivity of the steel via electrochemical testing. The results of the study confirm that the steel in selected elements within these structures remained passive once the ICCP system was interrupted. The primary factor in determining which elements remained passive, and the duration of passivity was the amount of charge injected into the element over the life of the ICCP system. The environment surrounding the element was also observed to influence the residual protection. The study also highlighted that the currently accepted criterion for absolute passivity cannot reliably be applied to the tidal zone