High-temperature properties of fly ash and silica fume composite magnesium potassium phosphate cement

Magnesium potassium phosphate cement (MKPC) is extensively employed in patching materials and fireproof coatings owing to its outstanding properties. This study employs a blend of fly ash and silica fume to substitute a portion of the cementitious materials, aiming to enhance the performance of MKPC under high-temperature conditions. The relative proportions of fly ash and silica fume were considered. MKPC was subjected to cubic compression and three-point flexural tests. Additionally, the phase and microstructure of MKPC were also characterized using XRD and SEM. The compressive strength, flexural strength, visual appearance, and mass loss of MKPC specimens were evaluated before and after exposure to various high temperatures. Following exposure to elevated temperatures, MKPC specimens without fly ash and silica fume doping showed a significant decrease in strength. Conversely, specimens doped with 15% or 10% silica fume exhibited the most remarkable strength enhancement. The dehydration of K-struvite at elevated temperatures was the primary reason for the mass loss and strength reduction of MKPC. Silica fume and fly ash can facilitate the sintering of phases and amorphous particles derived from K-struvite decomposition, leading to the formation of ceramic-like structures. Notably, the contribution of silica fume to the sintering effect exceeds that of fly ash. Therefore, blending fly ash and silica fume proves to be an effective approach to enhancing the high-temperature resistance of MKPC.