Investigating the effect of Interrupted Cathodic Protection on reinforced concrete structures

Impressed Current Cathodic Protection (ICCP) has been one of the major components of the repair and maintenance strategy on many motorway structures in the U.K. It has helped to prolong the life of more than 700 structures, in a significantly sustainable manner, by reducing the need to remove chloride contaminated (but otherwise sound) concrete. This study was initiated after identifying that some of the ICCP systems were reaching the end of their design life and required a significant level of maintenance (including anode replacement) to operate in accordance with the latest Codes of Practice. In addition, there were a number of structures where the application of ICCP has been interrupted due to severe anode deterioration or vandalism. The objective of this work was to collate evidence from structures to support preliminary laboratory results that the application of ICCP to a reinforced concrete structure over a period of time can transform the environment around the reinforcement, even after the protective current has been interrupted. This experimental field study interrupted the current to ten structures which had been protected with ICCP between 5 and 16 years and corrosion rates were monitored to determine when reinforcement corrosion will initiate again. It was found that after five or more years of ICCP, the steel remained passive for at least 30 months after interrupting the protective current, despite the presence of chloride contamination representing a substantial corrosion risk. In some cases, severe anode deterioration meant that the current was interrupted at an unknown point in time prior to the initiation of the scheme. Four main conclusions are drawn regarding this approach: it can give an indication of when repairs to ICCP systems are likely to be critical; provide new evidence for the design lives attributed to systems using lower cost anodes; reduce the requirement to replace systems at the end of their functional lives; and potentially extend the interval between planned maintenance of existing systems with corresponding reduction in monitoring frequency, cost and disruption.