Effect of chloride salt type on chloride binding behavior of concrete

Effect of four cations (Na+, K+, Mg2+ and Ca2+) on the chloride binding mechanism in concrete has been researched. This investigation was carried out by chloride ions concentrations testing, pH testing, XRD and TG-DTG techniques. The results showed that chloride binding capability and the pH value of pore solution were greatly affected by chloride cation type, with binding capability of Ca2+ > Mg2+ > Na+ ≈ K+; Na+ and K+ lead to the rise of the pH value of pore solution, increasing the solubility of Friedel’s salt to release the bound chlorides, and have more content of free chloride ions but less bound and total chloride ions than Mg2+ and Ca2+; Mg2+ leads to the decreasing of the pH through the reaction with hydrated Calcium Silicate Hydrate (C–S–H), consequently having a lower pH and less free chloride ions than Na+ and K+; Ca2+ generates more C–S–H, while C–S–H and Ca(OH)2 would bind more chloride ions than Magnesium Silicate Hydrate (M–S–H) and Mg(OH)2 did, so more bound and total chloride ions exist than Mg2+.