High-temperature behaviour of alkali-activated composites based on fly ash and recycled refractory particles

This study aims to develop innovative and sustainable alkali-activated composites with enhanced performance at high temperatures. To reduce production costs and promote a circular economy model, coal fly ashes are selected as a precursor for the alkali activation and recycled refractory particles are used to develop products with high thermal dimensional stability. Matrices and composites are investigated as a function of two curing conditions (heat curing vs room temperature curing) and amounts of dispersed phase (recycled refractory particles) added to the matrix. Thermal stability is assessed based on thermal exposure in a muffle furnace at 800 and 1000 °C, heating microscope analysis, and dilatometry. In addition, mineralogical quantitative analyses are performed to obtain an insight into phase changing after thermal exposure. Results show that the recycled refractory particles do not hinder the alkali activation process, significantly reduce heat-induced cracking, increase the maximum temperature of dimensional stability of the composites up to 1240 °C, and improve the linear dimensional stability during heating. In addition, the heat curing does not significantly increase the temperature range of dimensional stability, whereas the room temperature curing generates a product less prone to cracking when exposed to high temperature, and therefore it can be preferred.