Monitoring the passivation of steel in concrete induced by cathodic protection

This work examines the applicability of mixed potential theory to predict the corrosion rate of steel in concrete using the negative potential shift induced by a known cathodic current density. Under atmospherically exposed conditions the kinetics of the cathodic reaction often exhibit activation controlled behaviour. It is shown that in these conditions the corrosion rates estimated from a large negative potential shift are very similar to those determined using the more widely acceptable polarisation resistance method. This provides the basis for an improved reinforced concrete cathodic protection criterion in which a conservative estimate of the potential shift, given by the potential decay on interrupting the current, is combined with a knowledge of the local applied current density to determine the unpolarised corrosion rate. Such a criterion may be used to monitor the development of steel passivity induced by a cathodic protection system. (C) 1997 Elsevier Science Ltd.