CATHODIC PROTECTION OF REINFORCEMENT BARS IN CONCRETE

Abstract

This research involved investigation of various aspects of cathodic protection in corrosion prevention of the steel reinforcement in concrete. The performance evaluation of cathodic protection, a very important aspect in its operation was widely dealt with. Various criteria used in the cathodic protection of reinforced concrete were examined. Particular emphasis was placed on the depolarization shift criterion of 100 mV in four hours, which has been commonly used in operating cathodic protection systems in practice. Different magnitudes of current densities were used to ascertain a value which provides adequate protection to the steel. The use of galvanic current in measuring corrosion and in gauging the amount of protection by cathodic means was also investigated.

The research program comprised of three series of specimens. Artificial corrosion, such as concrete doped with chlorides, accelerated carbonation, impressed corrosion current or galvanic corrosion, were used to sustain and promote corrosion of the steel inside the concrete. Cathodic protection was then applied to the corroding specimens, to arrest the corrosion of steel, for several months after which the specimens were broken. The steel bar inside the specimens was cleaned by removing the corrosion products on the surface, and the final weights measured. During cathodic protection of the specimens, various parameters which effect the protection of the steel inside the concrete were recorded. Control specimens without any protection were used as reference. Analysis of the results showed that the criterion of 100 mV depolarization shift in four in four 4 hours consistently correlated well with the weight loss data, in comparison to other criteria, It is suggested that this criteria be primarily used in the operation of cathodic protection systems in reinforced concrete. Depolarization shift of less than 100 mV did not provide adequate protection, while not much additional benefit was derived with higher depolarization shifts. Current densities in the range of 40-50 rnA/m2 of the protected surface area were found to be optimum, in terms of a good degree of protection. The galvanic current was found to provide a good correlation with the weight loss data, and can also be used in evaluating the performance of cathodic protection.