Influence of the external solution in the electroosmotic flux induced by realkalisation

Abstract

Electrochemical repair methods are based on the application of an impressed direct current between the reinforcement and an auxiliary electrode placed at the concrete surface. In the case of realkalisation, the aim of the treatment consists in restoring the alkalinity of the concrete around the rebar to repassivate it. The realkalisation seems to be primarily provided by the generation of OH^- at the rebar which is acting as cathode, through the reaction of water hydrolysis. It had been claimed that also carbonate ions penetrate towards the rebar by the electroosmosis; however it was not until very recently that the authors were able to demonstrate and quantify it through hardened carbonated concrete. In the present paper, laboratory trials are reported showing the influence of the external solution in the electroosmotic flux. The experiments have been carried out on normalised carbonated OPC mortars and 4 different solutions have been tested, ranging from 0.1 to 2M in Na₂CO₃. As a result, it has been proved that the electroosmotic flux is not constant during the experiment. The pH in the anolyte is the determining parameter on the zeta potential and consequently in the electroosmotic flux, reaching its maximum, for the experiments of this research, at the pH of the buffer carbonate/'bicarbonate.