Diffusive transport of chloride into and out of soil-cement mixtures

Abstract

This study investigates the diffusive transport behaviour of chloride in cement-based solidified/stabilised (s/s) soil mixtures, focusing on the differences between inward diffusion (into previously uncontaminated specimens) and outward diffusion (from pre-mixed specimens). Two sets of laboratory diffusion experiments were conducted on identically prepared soil-cement specimens: Set A specimens were exposed to external chloride sources, while Set B specimens were pre-mixed with chloride. Experimental results were interpreted using one-dimensional contaminant transport modelling via POLLUTE to back-calculate effective diffusion coefficients (De) and effective porosities (ne). The value of ne was 0.24 and De ranged from 1.0 × 10-10 to 1.5 × 10-10 m2/s for the Set A specimens. Results indicate that, when normalising experimental results to concentration gradient, the flux of chloride exiting pre-mixed specimens (Set B) is three times lower than that for chloride entering uncontaminated specimens (Set A). It was also shown that the effective porosity method of interpretation of the experimental results provides only a marginal improvement over the total porosity method of interpretation. Sorption was found to be of negligible importance in this study.