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

Gravimetric and electrochemical measurements were used to expose the relati onship between the degree of prerusting of reinforcements embedded in chlor ide-contaminated mortar or concrete and the efficiency with which they are repassivated once depassivating ions are removed. The results show that, ab ove a certain, ill-defined rusting threshold, the electrochemical chloride removal does not ensure effective repassivation of reinforcements in the st eel/concrete system. Once the passivity of reinforcements embedded in reinf orced concrete structures (RCS) is overcome, the typical corrosion rates of the active state seemingly suffice to maintain an acid pH at the metal/rus t interface in the bulk of such a strongly alkaline material as concrete. A fter this local acidification, the metal inside pits probably behaves simil arly as it would in an acid solution. As a result, it does not suffice to r emove the rusting agent in RCS in order to stop corrosion; rather, the agen t must be removed before the first visible signs of deterioration appear.