The Effects of Calcination Process Parameters on RHA Reactivity and Mortar Mechanical Properties

The insufficient optimization of calcination process parameters severely restricts the enhancement of rice husk ash (RHA) volcanic ash activity. In this study, an intelligent muffle furnace was used for multi-parameter coupled regulation, combined with microscopic characterization techniques, to elucidate the effects of temperature, cooling mode, heating rate, and holding time on the reactivity of RHA. The results showed that the effect of calcination temperature on the volcanic ash activity of RHA was dominant. RHA calcined at 600-700 °C showed a honeycomb porous structure, displayed broad amorphous SiO₂ diffraction peaks and up to 95% content of SiO₂, and exhibited the best volcanic ash activity. The increased crystallinity of RHA calcined at 800 °C led to a decrease in its activity. The subcooling treatment with distilled water effectively rebuilt the lamellar structure, reduced the crystallinity, and enhanced the reactivity. The samples incorporated with 600 °C calcined RHA showed higher compressive strength at 3 days compared to 800 °C calcined RHA.