Effect of sulfate ions and associated cation type on the pore solution chemistry in chloride-contaminated plain and blended cements

This paper presents the results of a study conducted to evaluate the effect of chloride and sulfate contamination on the pore solution chemistry in plain and blended cements. The cement paste specimens were admixed with a fixed quantity of sodium chloride and varying quantities of sodium sulfate or magnesium sulfate. The pore solution was extracted from these specimens and analyzed to determine OH-, Cl- and SO42- concentrations. The OH- concentration of the pore solution in both the plain and blended cements increased with increasing concentration of sodium sulfate while no increase was noted in the specimens admixed with sodium chloride plus magnesium sulfate. The chloride concentration in the pore solution in plain and blended cements increased with increasing sodium sulfate concentration. In the specimens admixed with magnesium sulfate, the increase was noted up to 1% SO42- beyond which no change was noted. The SO42- concentration also increased with increasing quantity of sulfate contamination in the specimens admixed with both sodium and magnesium sulfate. The sulfate concentration in the cements admixed with sodium chloride plus sodium sulfate was more than that in the specimens admixed with sodium chloride or sodium chloride plus magnesium sulfate. The alkalinity of the pore solution influenced both chloride- and sulfate-binding capacity of cements. (C) 2002 Elsevier Science Ltd. All rights reserved.