EFFECTS OF MAGNESIUM-SULFATE AND SODIUM-SULFATE ON THE DURABILITY PERFORMANCE OF PLAIN AND BLENDED CEMENTS

In this investigation, mortar specimens made with two plain cements, Type I and V, and blended cements, made with fly ash, silica fume, and blast furnace slag, were exposed to sodium-sulfate and magnesium-sulfate solutions. The performance of these cements, in both the environments, was evaluated by measuring expansion and determining reduction in compressive strength. The data indicate that while the performance of all blended cements, particularly those made with silica fume, was generally excellent in the Na2SO4 (NSBAR) environment, their performance in the MgSO4 (MSBAR) environment was not satisfactory. A similar trend was observed in mortar specimens made with a water-cement ratio of 0.35. The type of cement did not have any significant influence on the performance of either plain or blended cements in both environments. The deterioration of plain and blended cements in NSBAR and MSBAR environments is attributed to the initial reaction of NSBAR and MSBAR with calcium hydroxide (CH). The reduction of CH in blended cements provides an opportunity to MSBAR to react more directly with the primary and secondary calcium silicate hydrate (C-S-H) due to the de-stabilization of these phases by magnesium hydroxide (MH). Comparatively, lower deterioration of blended cements exposed to the NSBAR environment is attributed to the reduced CH, which significantly mitigates the sulfate attack in these cements.