Cathodic protection with localised galvanic anodes in slender carbonated concrete elements

Abstract

A combined experimental and numerical investigation was carried out with the aim of determining whether few localised galvanic anodes per unit length could protect the reinforcement of slender carbonated concrete elements, exposed to atmospheric conditions, which could not be repaired with traditional methods. Initially, the cathodic behaviour of steel under galvanostatic polarisation was determined on small-size specimens obtained from a real element. A correlation of potential versus applied current was obtained. The current distribution in slender elements was then determined through finite elements simulations, considering various scenarios of carbonation and humidity. Results showed that, in spite of the high electrical resistivity of carbonated concrete, anodes with spacing of 0.45 m are enough to protect corroding reinforcement in most exposure conditions, even in thin parts of element. Estimated anode durations were of the order of several years or even decades; however, it was shown that also reinforcement in dry (carbonated or alkaline) concrete, which does not need to be protected, contributes to anode consumption. Although other aspects play a role on the performance of a cathodic protection system (such as the effectiveness of anode-encasing material and of electrical connection to reinforcement), the results obtained are supportive of a repair strategy based on the use of localised galvanic anodes and can be generalised to slender elements exposed to atmospheric conditions suffering carbonation induced corrosion.