The Slice-Resistivity method to measure the chloride ion diffusion coefficient of cementitious materials

Abstract

Most of the existing experimental and research methods for the diffusion of chloride ions in cement-based materials use an applied electric field test method with electrodes, which are unable to eliminate the effect of polarization. In this study, the relationship between resistivity and chloride ion diffusion coefficient (CIDC) is established by the Nernst-Einstein equation. Based on the non-contract electrical resistivity measurement technique, the resistivity of cement-based material is measured by the Slice-Resistivity method, in which the chloride ion diffusion coefficient can be obtained with no polarization effect. In the experiments undertaken, the chloride ion diffusion coefficients of samples with 0.3, 0.4, 0.5 water-cement ratios and aggregate volume fractions of 12%, 22% were calculated at 3, 7, 14 and 28 days ages. It was found that the size of the slices has no influence on the results; however a decrease of the water-cement ratio as well as an increase of aggregate volume would lower the chloride ion diffusion coefficient. According to the experimental results and the Bruggeman model, a new general equation describing the relationship between w/c, curing time, aggregate volume and the chloride ion diffusion coefficient is proposed. In addition, simulation based on the homogenization method is applied to predict the equivalent chloride ion diffusion coefficient of the samples added aggregate. The results show that the simulation results are consistent with the experimental results, especially for 14 and 28 days.