Effect of sulphate contamination on chloride-binding capacity of plain and blended cements

This paper presents the results of a study conducted to assess the effect of sulphate contamination on the chloride-binding capacity of plain and blended cements. Cement paste specimens admixed with a fixed quantity of sodium chloride and varying dosages of sodium sulphate or magnesium sulphate were prepared. The pore solution was extracted from these specimens and analysed to determine OH⁻and Cl⁻concentrations. The chloride concentration increased with increasing quantity of sodium sulphate contamination. In the specimens admixed with magnesium sulphate, a marginal increase in the Cl⁻concentration was noted up to 1% SO₄²⁻. The increase in the Cl⁻concentration in the specimens admixed with more than 1% SO₄²⁻ was minimal. In plain cements the chloride binding was influenced by the C₃A content of cement. The Cl⁻/OH⁻values in plain cements admixed with sodium chloride and sodium sulphate increased marginally with increasing sodium sulphate concentration. However, the Cl⁻/OH⁻ratio in plain and blended cements admixed with sodium chloride and magnesium sulphate increased with increasing quantity of magnesium sulphate up to 1% SO₄²⁻. For SO₄²⁻ concentrations of more than 1%, a decrease in the Cl⁻/OH⁻was noted.