Non-saturated ion diffusion in concrete – A new approach to evaluate conductivity measurements

Abstract

Non-saturated ion diffusion properties of cementitious materials were evaluated in an experimental study. To assess these properties, resistivity measurements have been performed on mortars with different binders (ordinary Portland cement – OPC, OPC with 5% silica fume, 40% slag and 70% slag, respectively) and different water-to-binder ratios (w/b, 0.38 and 0.53). Specimens have been conditioned to eight different climates with relative humidity (RH) from 100% to 33% RH in order to assess an effective diffusion coefficient. The results from the resistivity measurements have been corrected for changes of the conductivity of the pore solution when drying to different degrees of saturation.The diffusion coefficients for Portland cement binders within the range 100–59% RH are presented. They showed that the diffusion coefficient of the mortar with high w/b ratio was higher at high RH, but at low RH the opposite trend was found. By comparing these results with the corresponding desorption isotherms, it is shown that the diffusion coefficient for the two w/b ratios have the same dependency on the degree of saturation.