Effects of leaching and chloride migration on the microstructure and pore solution of blended cement pastes during a migration test

Abstract

This paper investigates the influence of the multispecies diffusion and leaching phenomena on the thermodynamic equilibrium and microstructure of cementitious materials containing mineral additions during a chloride migration test. Because of a lack of data on these effects, the aim of this study was to quantify changes in the material’s microstructure during an experimental program based on mercury intrusion porosimetry before and after chloride exposure, scanning electron microscopy and chemical analyses of the materials. The experimental results highlight a modification of pore size distribution and a reduction of up to 60% in total porosity after chloride transfer. This was due to chloride interactions which led to the formation of new compounds in the porosity range of 7–70 nm. These compounds were investigated by elemental analyses and quantified.Moreover, a chloride migration test was performed in order to investigate the leaching of pore solution ions in the two compartments of the migration cell. The results enabled us to: (i) quantify the concentration of ions that diffused into/from the material, and (ii) estimate the kinetics of calcium release and the quantity of portlandite dissolved in the material. The chloride diffusion coefficient of the materials ranged between 2.38 × 10−12 and 5.96 × 10−12 m2/s, the kinetics of calcium, expressed as a flux, were between 1.8 × 10−2 and 1.2 × 10−1 mmol.m−2.s−1.