Electrochemical chloride removal from reinforced concrete structures and its ability to repassivate prerusted steel surfaces

Abstract

Gravimetric and electrochemical measurements were used to expose the relationship between the degree of prerusting of reinforcements embedded in chloride-contaminated mortar or concrete and the efficiency with which they are repassivated once depassivating ions are removed. The results show that, above a certain, ill-defined rusting threshold, the electrochemical chloride removal does not ensure effective repassivation of reinforcements in the steel/concrete system. Once the passivity of reinforcements embedded in reinforced concrete structures (RCS) is overcome, the typical corrosion rates of the active state seemingly suffice to maintain an acid pH at the metal/rust interface in the bulk of such a strongly alkaline material as concrete. After this local acidification, the metal inside pits probably behaves similarly as it would in an acid solution. As a result, it does not suffice to remove the rusting agent in RCS in order to stop corrosion; rather, the agent must be removed before the first visible signs of deterioration appear. © WILEY-VCH Verlag GmbH, 2001.