Chloride diffusion coefficient: A comparison between impedance spectroscopy and electrokinetic tests

This paper proposes to compare several experimental ways of obtaining the chloride diffusion coefficient through saturated porous materials. The first method is based on the application of the Nernst–Einstein equation for which the conductivity of the saturated sample is measured by impedance spectroscopy for two kinds of materials: inert samples of TiO2, and concretes based on type I and type V cements. The second method is a migration test in which the flux of chloride measured upstream allows calculating the diffusion coefficient by means of the Nernst–Planck equation. In the third case, the diffusion coefficient is calculated by current measurements in an equivalent configuration as the second method. It is shown that the formation factor does not vary neither with the ionic strength of the saturation solution, nor with the change in the pore solution constituents when the material is without mineral additions. The CEM-V concrete exhibits a specific behavior with a strong influence of the addition of chloride in its pore solution on the formation factor. The diffusion coefficients calculated with the three methods are in good agreement provided the metrology of the experiments is carefully controlled.