Influence of silicate ratio and additives on the sulphate resistance of Portland cement

The role of the silicate ratio in determining the content of calcium hydroxide liberated in the hydration process and the effect of additives on sulphate attack was evaluated. The resistance of Portland cements with varying silicate ratios and blended cements with ground granulated blast-furnace slag (GGBFS) or fly ash (FA) to sulphate attack was assessed by determining the deterioration factor (DF) and length change caused in mortar specimens with immersion to a 5% sodium sulphate solution. Additionally, microstructural investigations were performed by instrumental analysis (XRD, ESEM, EDS, MIP and DTA). Results of this study indicate that the silicate ratio is more influential than C3A content on sulphate attack resistance. The performance of blended cements was better than that of parent cements and is attributed to the lower calcium hydroxide content of blended cements resultant from pozzolanic reaction.