Combining Chloride Migration and Diffusion Tests to Estimate Freundlich Chloride Binding Parameters and Improve Predictions of Chloride Ingress

Abstract Chloride binding plays a major role with respect to chloride ingress. On one hand, engineering models often rely on “apparent” diffusion coefficients, which account for both the diffusion of chlorides in the pore solution and chloride binding. On the other hand, mechanistic models intend to consider the two phenomena separately. However, the inputs to model chloride binding are quite complex to acquire, because they require dedicated experiments that are usually only conducted for research purposes. In this paper, an approach is proposed to estimate binding parameters from chloride ingress profiles. First, the effective diffusion coefficient is measured with a chloride migration test. Then, a chloride profile from a diffusion test is fitted with a model where transport of free chlorides follows Fick’s second law, and free and bound chlorides are linked by a Freundlich equation. Finally, the surface concentration and the Freundlich parameters are adjusted to obtain the best possible fit. The derived Freundlich parameters are fairly close to the ones measured in dedicated chloride binding experiments. A case study applying this approach to concrete elements exposed to seawater in a Danish harbour is also presented.