Sulphate resistance of type V cements with limestone filler and natural pozzolana

Sulphate performance of concrete depends primarily on permeability. Under severe conditions of sulphate exposure, low-permeability concrete is prescribed and it must also be made with high sulphate resisting cement. For portland cement, the sulphate resistance depends on the C3A content and the amount of CH produced at early stages of hydration. Some parameters that modify the quantity of early CH in the hardened cement paste are investigated in this paper. Two type V cements with quite different C3S content and blended cements containing natural pozzolana or limestone filler were used. Expansion, flexural and compressive strength of mortar, immersed until 1 yr in sodium sulphate solution, with pH-controlled are presented. Results show that the sulphate performance of portland cement with high C3S content is very poor compared with low C3S portland cement. Addition of natural pozzolana provides the maximum sulphate resistance while the addition of 20% limestone filler declining sulphate performance of low C3A cements. This behaviour can be attributed to the reaction between sulphate ions with CH into the paste that produces an alteration of the predominant mechanism of sulphate attack.