In situ monitoring of the efficiency of the cathodic protection of reinforced concrete by electrochemical impedance spectroscopy

In the course of applying cathodic protection on concrete structures exposed to chloride contamination (sea-water or de-icing salt), characterization of the effectiveness of the protection procedure is a most important point. This effectiveness is related with the removal of aggressive ions and with the rebuilding of the passive layer on the steel surface. The measuring-procedure applied until now is based on the measurement of the change with time of the potential difference between the reinforcement and (normally embedded) reference electrodes after switching off the protection current. The criterion defined by NACE (National Association of Corrosion Engineers) for a sufficient working of a cathodic protection installation is based on empirically evaluated values. The workability of an improved cathodic protection equipment, using recently developed anodic materials, was monitored by impedance spectroscopic techniques. A strong dependence of the charge transfer resistance (R sub ct ) values of the corrosion reaction on the cathodic charge consumed during the protection procedure was found. Results from linear polarization and corrosion potential measurements are well comparable with the impedance data. The main advantage of the impedance technique is the capability of a fast and automatic measuring procedure and of the possibility of on-line monitoring.