Investigating the sulfate resistance of mortars with multiple mineral admixtures in ammonium-magnesium sulfate solution

This study aims to evaluate the sulfate resistant of mortars containing sulfate-resistant cementitious materials (SRCMs) developed by mixing ground granulated blast furnace slag, fly ash, silica fume, and desulfurization gypsum. Compressive strength test, XRD, DTA, and MIP were carried out in this work. The results showed that the sulfate resistance of mortars mixed with SRCMs at replacement percentage of 74 wt.% was superior to that of mortars with 30 wt.% fly ash when they were exposed to drying-wetting cycle in sodium sulfate solution, which was because adding SRCMs decreased Ca(OH)2 content, causing a reduction in gypsum formation. Moreover, reducing W/B from 0.50 to 0.35 increased the loss of compressive strength ratio (Lf) of mortars with SRCMs immersed in ammonium-magnesium sulfate complex solution. Specifically, Lf values of mortars with W/B of 0.50 and 0.35 were 42.7% and 36.0% after 100 days of immersion, respectively. Furthermore, the main components of samples subjected to complex solution were identified as gypsum. Further, both Lf and porosity presented a strong linear positive correlation with W/B. At last, the findings of this study confirmed that optimizing the composition of cementitious materials and lowering W/B could improve the sulfate resistance of concretes used for sulfate-rich sewage environment.