Electrochemical noise analysis of cathodically protected steel reinforcement in concrete using carbon fiber sheet as anode

This paper presents an efficiency and mechanism analysis of impressed current cathodic protection (ICCP) for corroded steel reinforcements in concrete by means of electrochemical noise (EN), which is an advanced technique that allows real-time monitoring without any disturbance. The considered variables include protection method (non-protection, ICCP) and current density of ICCP (30 mA/m2, 90 mA/m2). In the cases of ICCP, carbon fiber sheet is adopted as the anode thanks to its good electrochemical properties and durability. Electrochemical potential noise (EPN) and electrochemical current noise (ECN) of steel reinforcement in concrete are measured every 30 d during the 120-d exposure period and analyzed from the perspectives of time and frequency domains. The results show that ICCP treatment with a current density of 30 mA/m2 leads to slighter fluctuations in ECN signals, an improvement in noise resistance Rn, and decreases in the low frequency plateau WL in power density diagram (PSD) of ECN signals. It indicates that the corrosion of steel is alleviated. However, the results of the specimen protected with a current density of 90 mA/m2 are the opposite, which is overprotected and hydrogen corrosion may happen. Compared to the specimen with no protection, the specimen treated with 30 mA/m2 ICCP shows an evident increase in energy proportion of d1-d3 wavelet crystals. Additionally, with increasing the treatment duration, the energy proportion of d1-d3 wavelet crystals increases. This illustrates that ICCP is more effective in inhibiting general corrosion than pitting corrosion. Extra caution should be paid to EPN signals of specimens subjected to ICCP, namely polarization, because EPN signals may anomalously exhibit severer fluctuations as a result of insufficient depolarization. It is suggested to use ECN signals instead of EPN signals to analyze the corrosion behavior of specimens subjected to ICCP.