Effect of chloride in mix ingredients on sulphate resistance of concrete

Abstract

The sulphate resistance of concretes containing various levels of chloride introduced in the mixing water was assessed by immersion in sodium sulphate and magnesium sulphate solutions. Mortar and concrete cubes were made using ordinary Portland cement (OPC) and sulphate-resisting Portland cement (SRPC) with chloride contents of 0–4·5%; the chloride was introduced in a salt of either sodium or calcium. Deterioration was monitored by comparing the strength of cubes in sulphate solutions with that of similar cubes stored in water over a period of 7 years for concrete and of 1 year for mortar. The 100 mm concrete cubes (which were also assessed visually at 3 and 7 years) were made with two levels of cement content (225 and 335 kg/m3). A 1:3 cement/sand mix was used for the 12·5 mm mortar cubes. The results over 1 year for the mortar cubes showed that chloride had either a negligible or a generally beneficial effect on the resistance to sulphate attack for both OPC and SRPC. A similar overall trend was observed for the concrete cubes after 7 years, with the apparent exception of some concretes containing calcium chloride and immersed in strong sulphate solutions, for which sulphate resistance was considerably reduced.