Possibilities to Recycle Thermal Power Plant By-Products in Refractory Castables

The current research focuses on the analysis of fly ash cenospheres (FACs), a waste generated in coal-fired power plants, and the possibilities of using them in refractory castables. Cenospheres are micro-scale (~50–400 µm) spherical structures derived from fly ash, predominantly composed of silica and alumina oxides (86.7%). Their distinctive morphology and characteristics make them highly advantageous for a diverse array of applications, notably as lightweight fillers and nondegradable pore-forming agents. Furthermore, cenospheres have the potential to contribute significantly to the performance of refractory castables when incorporated into compositions with calcium aluminate cement (CAC). FAC XRD analysis revealed that FACs mainly consist of mullite along with cristobalite, which forms at higher temperatures. Furthermore, the study examined the impact of FACs on the properties of medium cement castable (MCC), especially durability, when 3%, 5%, and 7% of fine fireclay were replaced by FACs; 5% of FACs were found to reduce the density of refractory castables and decrease the cold crushing strength by approximately 6%, but it increased the resistance to thermal shock by approximately 75% and 43%, depending on the thermal treatment temperature, 950 °C and 1100 °C, respectively, and improved resistance to alkali corrosion. A higher FAC content (7%) does not have any positive effect on the MCC properties tested.