Mechanical and microstructural properties of the fly-ash-based geopolymer paste and mortar

Abstract

In this paper we have investigated the influence of synthesis parameters on the mechanical properties of the fly-ash-based geopolymer paste and mortars. Moreover, the influence of an addition of limestone sand on the microstructure of fly-ash-based geopolymers was investigated as well. An addition of limestone sand increased the compressive strength of the fly-ash-based geopolymer mortar, in comparison to the strength of the geopolymer paste, by changing the composition of the gel phase in the geopolymer structure and with the physical strengthening due to the presence of well connected grains of the sand. The results have shown that the compressive strength and Young's modulus of elasticity of the fly-ash-based geopolymer mortar are correlated. The values of these parameters increase as the alkali and silicate dosages increase. At one point, they reach the maximum values and then start to decrease. On the other hand, the parameters that considerably increase the compressive strength slightly decrease the flexural strength of the geopolymer mortar.