Application of EIS to cathodically protected steel: Tests in sodium chloride solution and in chloride contaminated concrete

The efficiency of cathodic protection is usually checked by switching off the current and either by measuring the polarized potential or by recording the evolution of the potential decay. These methods although based on a long experience are not indicating directly on the state of the metal, and the interpretation of the results is not always evident. It remains as an interesting goal for the research on alternative methods to verify the efficiency of the cathodic protection. In this paper, a study made by using linear polarization and EIS is presented based on the behaviour of the two cathodically protected systems. The results indicate that the impedance diagrams show important and consistent changes in shape and associated parameters when the steel is protected or unprotected. Although changes have been noticed before by other authors in the EIS diagrams, this study assumes that the system is a galvanic couple.