New Insights into the NT Build 492 Rapid Chloride Migration Test

In this study a new theoretical model is developed for the popular Rapid Chloride Migration test (NT Build 492). This model can in a proper way predict the transport of chlorides due to application of the electrical field. In order to improve the traditional chloride transport model, the non-linear binding of chlorides and non-equilibrium between free- and bound- chlorides are introduced. The new system of equations is solved numerically and applied to experimental data obtained elsewhere. From these simulations several parameters are obtained, namely: the effective chloride diffusion coefficient, the non-linear binding constants and the chloride mass transfer coefficient. This opens the new possibility of obtaining the effective chloride diffusion coefficient (usually derived from long-term, laborious techniques) from the short-term migration tests. The obtained binding constants are in line with experimental data found in literature. The chloride mass transfer coefficient shows a tendency to decrease in time during the application of electrical field, which can give evidence of changes in the microstructure and/or in the pore solution of concrete.