Sulphate resistance of silica fume blended mortars exposed to various sulphate solutions

Abstract

The different performances of silica fume blended mortars placed in various sulphate-bearing exposure conditions were investigated. Experimental study was carried out on mortars immersed in 5% sodium sulphate, 5% magnesium sulphate, and mixed 5% sodium sulphate and 5% magnesium sulphate solutions for 270 d of sulphate exposure. Another variable was the replacement ratio of cement with silica fume (0, 5, 10, and 15% of the cement by weight). The results showed conclusively that silica fume should be given serious consideration for use in sulphate environments. In other words, in a sodium sulphate solution, silica fume showed a beneficial effect on mitigating compressive strength reduction and length change of mortars. However, the strength deterioration factor of the mortar specimen with some silica fume content (especially 15% of the cement by weight) was greater than that of the mortar specimen without silica fume under Mg 2+ ion oriented attack. These different sulphate deterioration mechanisms are presented in the study. Microstructural investigations such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDXA), and mercury intrusion porosimetry (MIP) were also used to support the explanation for these mechanisms.Key words: sodium sulphate, magnesium sulphate, silica fume, strength deterioration factor, length change.