Linear polarisation resistance measurements using a potentiostatically controlled guard ring

Abstract

The use of a sensor controlled guard ring has been developed in recent years to enhance the accuracy of linear polarisation corrosion rate measurements on reinforced concrete structures. The established method of measurement uses a galvanostatically controlled guard ring device. In the method reported in this article the reinforcing steel is polarised potentiostatically by an inner auxiliary electrode and the real time plot of the current response is displayed on a laptop computer which controls the guard ring device. The area of steel polarised is confined by a current applied from an outer guard ring electrode which is controlled by two sensor electrodes positioned between the inner auxiliary and outer guard ring electrode. The potential between the two sensor electrodes is continually monitored, and the current output from the guard ring electrode varied to maintain a constant potential difference between the two sensor electrodes. The method has been validated on an electrical test circuit simulating active and passive reinforcement corrosion. Further testing has been conducted on a reinforced concrete specimen and the results compared with those of commercially available galvanostatically controlled equipment and those of standard unconfined linear polarisation resistance measurements.