Study of Compressive Strength and Durability of Fly Ash and Trass Based Geopolymer Mortar
Abstract
In this research, the effect of natural pozzolanic trass (NT) content as a partial replacement of sand in fly ash (FA) based geopolymer mortar on setting time, workability, compressive strength, absorption, porosity, resistance in sodium sulfate (Na2SO4)/water solutions with wet-dry cycles and microstructure were studied. The geopolymer mortar mixtures were made with NaOH 10 M, FA/sand ratio of 0.5, Na2SiO3/NaOH ratio of 2.5, alkali activator/FA ratio of 0.5 and indoor curing. NT content of 0%, 10%, 20%, and 30% by weight of sand. The results showed that the setting time was shorter and the mortar flow decreased with increasing NT substitution. Absorption, porosity, and weight loss in Na2SO4 and water solutions showed the minimum values, while the compressive strength showed maximum results in NT substitution of 20%. The geopolymer mortar has better resistance in sodium sulfate solution than in water. The SEM results showed the formation of a denser mortar and fewer micro-cracks with NT substitution. XRD analysis shows that NT substitution increases the content of albite phase Na(Al Si3 O8) or N-A-S-H gel which played an important role in increasing the compressive strength and durability of geopolymer mortar.