Data analysis of the long-term residual effect of cathodic protection on reinforced concrete structures

The application of impressed current cathodic protection (CP) is a well-established technology for the corrosion protection of reinforced concrete structures situated in marine environments. While the protective benefits of cathodic protection are well known, the lasting effects following the discontinuation of CP current are not entirely understood. This paper presents research findings on the residual protective effect which is known to occur following long durations of impressed current cathodic protection. The residual effect was replicated in university laboratories using reinforced concrete test blocks and accelerated CP testing methods. The experimental results depicted a clear improvement in the electrochemical state of the reinforcing steel with a shift of 150 to 300 mV to more positive values following CP application. The research also involved analysis of monitoring data from six in-service cathodic protection systems which were operating in Australia for nearly two decades. The behaviour of the steel potential readings was analysed and the results of the combined research confirmed that the protection provided by cathodic protection systems does not actually cease when the CP current is switched off. Rather, the embedded steel undergoes a significant and sustained shift to more positive values and this phenomenon is documented and discussed in this paper