Evaluation of sulfate resistance of Portland and high alumina cement mortars using hardness test

Portland cement and high alumina cement mortar specimens were exposed to cycles of drying at 40 °C, cooling at 20 °C and immersion in Na2SO4 and MgSO4 solutions at 20 °C. The resistance of mortars was evaluated by visual inspection and by measuring the change in surface hardness and weight of the specimens. The decrease and increase in surface hardness were observed in both mortars by treating with Na2SO4 and MgSO4 solutions, respectively. The combined effect of the chemical and physical attack by Na2SO4 was attributed to the complete failure of Portland cement mortar, whereas only marginal damage of high alumina cement mortar was believed owing to physical salt crystallization. No damage was observed in both mortars treated with MgSO4 solution.