The apparent and effective chloride migration coefficients obtained in migration tests

The apparent (Dapp) and effective (Deff) migration coefficients obtained in chloride migration tests are investigated in this study. The presented Dapp profiles in concrete show that the apparent migration coefficient is strongly concentration-dependent. As demonstrated, the binding of chlorides is very low at low free-chloride concentrations and therefore the chloride penetration front progresses throughout the concrete only slightly retarded by the binding. The diffusion flux during migration tests is shown to be insignificant compared to the migration flux. The DRCM coefficients obtained from the Rapid Chloride Migration (RCM) tests are found to be equal to the computed Dapp at the locations of the chloride penetration fronts, which gives evidence that the DRCM represents only the migration coefficient at the front. A very good linear trend is found between the DRCM obtained from the traditional RCM model, and the Deff obtained from the chloride transport model which includes non-linear chloride binding and concentrations in non-equilibrium.