Shortcomings of geometrical approach in multi-species modelling of chloride migration in cement-based materials

Abstract

Chloride migration tests and chronoamperometries were carried out on three cement mortars with different water/cement (w/c) ratios. The electrical current of the chloride migration is simulated with a multi-species model, which takes into account the geometrical properties of the pore structure throughout the diffusibility ratio. The comparison between the measured and the simulated currents shows a significant difference: systematically, simulated currents evolve faster than those measured. From these results, it appears that the purely geometrical approach alone is insufficient correctly to describe the transport of ionic species in cement-based materials. Finally, it is shown that the introduction of a ‘viscoelectric effect’, which conveys the electrical double-layer effect (EDL), improves the results of the model. As a first approach the EDL is taken into account empirically by considering a reducing factor 1/rD applied to the effective diffusion coefficients of the cations. This factor is deduced from Truc's work.