Magnesium sulfate resistance of geopolymer mortar

•The performance of geopolymer mortar in magnesium sulfate solution was evaluated.•Effect of curing temperature, NaOH molarity on sulfate resistance were studied.•Increasing curing temperature up to 90 °C improves strength and durability properties.•Addition GGBS and silica fume yields better properties compared to fly ash only.•Various geopolymer mortars achieved higher sulfate resistance than OPC mortar. Sulfate attack is one of the reasons which cause deterioration and damages of concrete structures throughout the world. Thus, sulfate attack resistance is an important durability and serviceability concern for materials used in construction. Various geopolymer mortars and OPC mortars were manufactured to evaluate magnesium sulfate resistance. This paper studied the effect of curing temperature, sodium hydroxide solution molarity, alkaline solution to binder ratio and binder type on magnesium sulfate resistance of geopolymer mortar and make a comparison between OPC mortar and various geopolymer mortars. Specimens were immersed in 10% magnesium sulfate solution up to 48 weeks. The evaluated properties in this study were water absorption and voids ratio, visual inspection, microstructure of specimens, weight change, compressive strength, flexural strength and expansion strain. Results indicated that increasing curing temperature, sodium hydroxide solution molarity and decreasing alkaline solution to binder ratio enhanced magnesium sulfate resistance of geopolymer mortar. Mixes containing 50% fly ash, 35% ground granulated slag (GGBS) and 15% silica fume achieved the best performance in magnesium sulfate solution. Generally, various geopolymer mortars achieved better performance in magnesium sulfate solution compared to OPC mortars.