Hardened and fired geopolymer mortars fabricated from Cyclone’s waste clay and submicron sand: A comparative study

Abstract

This work focuses on recycling of Cyclone’s waste clay in the existence of various percentages of submicron sand (400–800 nm), i.e. 2.50, 5.00 and 7.50 wt-%, for production of hardened and fired geopolymer mortars. After drying the hardened geopolymer mortars, they were subjected to low rate firing at different temperatures, i.e. 800, 1000, and 1200 °C. The physico-mechanical properties of dried and sintered geopolymer mortars were investigated by various tools. The apparent porosity and bulk density were tested by water-displacement method. The mineralogical composition and reaction products were identified by X-ray diffraction technique and Fourier transform infrared spectroscopy, respectively. The microstructure was investigated by scanning electron microscopy. The compression strength was also evaluated. The results revealed that the addition of submicron sand to geopolymer mortars enhances the physico-mechanical properties of geopolymer mortars. The mortar that contained 7.5 wt-% submicron sand exhibited lower porosity (25%) and the highest compressive strength (27 MPa) as compared to the other mortars. After firing, the mortars fired at 1000 °C exhibited improved properties than that fired at 800 °C, while that fired at 1200 °C was deformed and fused. On the other hand, the mortar that contains 2.50 wt-% submicron sand showed the best physico-mechanical properties as compared to the other ones. It exhibited the lower porosity (2.50 wt-%) and the highest compressive strength (85 MPa) after firing at 1000 °C.