Effect of low-rate firing on physico-mechanical properties of unfoamed and foamed geopolymers prepared from waste clays

Recycling of industrial solid wastes for fabrication of sintered ceramic bodies (fire-resistant materials) through low-rate firing of geopolymer is the main goal of the present study. Different non-foamed and foamed geopolymers prepared from waste clays were subjected to firing at 900 and 1000 degrees C. The composition and function groups of formed phases were identified by X-ray diffraction technique and FT-IR, respectively. The microstructure was investigated by scanning electron microscope while the physical properties were determined by water displacement method. The compressive strength of fried bodies was also measured. The results displayed that the firing of dried geopolymers led to the formation of new nepheline phase in addition to the originally existed quartz phase. After firing of geopolymers, sintered ceramic bodies with relatively compacted microstructures were obtained. Their porosities were lower than that of dried geopolymers while their densities were higher than that of dried geopolymers. In all cases, the geopolymer fired at 1000 degrees C exhibited improved physical and mechanical properties more than that fired at 900 degrees C. The compressive strengths of non-foamed geopolymers (batches A, B &C) fired at 1000 degrees C were 51, 59, and 68 MPa, respectively while that of foamed geopolymer (batch D) was 21 MPa.