Electrochemical injection of organic corrosion inhibitors into concrete

Two organic bases (ethanolamine and guanidine) that are known to act as corrosion inhibitors for steel in aqueous media were introduced into saturated specimens of carbonated and non-carbonated concrete from external electrolytes under the influence of an electrical field applied between embedded steel cathodes and external anodes. The cathodic current density was galvanostatically controlled at values in the range 1-5 A/m² for periods of 3-14 days. Control experiments, in which the corrosion inhibitors were applied to similar saturated concrete surfaces from external electrolyte without current, were also conducted. After treatment, the specimens were sectioned and analysed to determine the concentration profiles of the corrosion inhibitors within the concrete. It was found that the efficiency of injection of both ethanolamine and guanidine under the applied field was far higher in carbonated concrete than in non-carbonated concrete and that, in the carbonated specimens, the inhibitors became concentrated near the embedded steel. In non-carbonated concrete, guanidine penetration was accelerated to a modest extent by the applied field but ethanolamine penetration was not significantly enhanced by the field. These findings were explicable in terms of the influence of the pH values of the pore solutions in the various specimens on the degrees of ionisation of the organic bases concerned and hence on their tendencies to migrate and neutralise cathodically-generated hydroxyl ions.