Electrochemical aspects of the accelerated test of chloride ions permeability

This paper describes the electrochemical aspects of the accelerated test of chloride permeability. It underlines the role of the voltage and that of the concrete electrical resistance. These two parameters determine the potentials of the electrodes and the electrochemical reactions which ave likely to develop during the test. Under the common operating conditions of the test, water electrolysis is the main reaction which supports the migration process. It gives oxygen to the anode and hydrogen to the cathode. However, when the anodic potential is raised, the water electrolysis is accompanied by chloride oxidation and this gives chlorine or hypochlorite. In practice, the anodic potential varies throughout the test even if the voltage applied to the cell is kept constant. It is mainly due to the fact that migrant ions accumulate in the porous solution and cause the modification of the concrete electrical resistance. As a result of this variation and according to the Pourbaix diagram, the chlorine species concentrations (Cl-, ClO- and Cl-2) vary during the test and need accurate determination if chloride mass balance is required. Finally, a suitable interpretation of the chloride permeability test supposes the combination of several measurements: pH, conductivity, electrical resistance, potential measurement and chloride content.