The effect of artificial leaching with HCl on chloride binding in ordinary Portland cement paste

Abstract

This study investigates how the pH in the pore solution influences the chloride binding in Portland cement pastes. Cement paste samples were exposed to NaCl, CaCl2 and HCl solutions. The mechanisms of changes in chloride binding were investigated using a wide variety of techniques both for the liquid and solid phase. Lowering the pH from 13 to 12 with CaCl2 or HCl greatly increased chloride binding compared to NaCl, which was associated with increased amounts of chlorides in the AFm-phases. Lowering the pH below 12 lead to reduced chloride binding in part due to dissolution of AFm. Chloride binding approached zero at a pH of 9. The influence of C-S-H on changes in chloride binding could not be conclusively determined. The impact of leaching and low pH on chloride binding is key to explaining the peaking behaviour of chloride profiles in concrete submerged in chloride containing solutions like sea water.