In this paper a new theoretical model for the Rapid Chloride Migration test is presented. This model accounts for the non-linear chloride binding isotherm and the non-equilibrium conditions between the free- and bound-chloride concentrations in concrete. The new system of equations is solved numerically and compared to a simplified analytical solution, revealing a good agreement. Subsequently, numerical simulations are applied to experimental data on chloride concentration profiles in concrete obtained elsewhere. The binding parameters, the chloride mass transfer coefficient and the effective diffusion coefficient of chloride are estimated with these simulations. The non-linear binding coefficients correspond well to experimental data found in literature. The chloride mass transfer coefficient reveals a tendency to decrease in time during the application of electrical field across a concrete sample. The effective chloride diffusion coefficient (Deff) obtained in the present study is found to be in line with data obtained elsewhere. Finally, it is demonstrated that the values of the diffusion coefficient computed from the Rapid Chloride Migration test in the traditional way are overestimated.