On the calculation of chloride diffusion coefficient from the multispecies transference numbers in the standard migration test

Abstract

In order to better exploit the chloride migration test on cementitious materials and the movement of ion in the migration cell and to calculate the ion diffusion coefficients from the measured currents, knowledge of the transference numbers is required. In this paper, calculations of transference numbers of the ions involved in the standard migration test are proposed. This has been achieved from a global mass balance of the ion moving in the three zones of the migration test (catholyte, anolyte and sample). The leached ions from the sample and those generated from the electrode processes were considered. The transference numbers obtained in the catholyte are 0.35; 0.25; 0.05; 0.02; 0.33 for Cl−, Na+, K+, Ca++, OH− and 0.23 for H+ in the anolyte. Those in the sample tested are 0.23; 0.11; 0.41; 0.14 and 0.11 for Cl−, Na+, K+, Ca++ and OH−, respectively. Results of ion diffusion coefficients obtained from the transference numbers varied depending on the interpretation method used; possible causes are discussed.