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.

This study elucidates the effects of total air content, pore size distribution, and bubble spacing coefficient on mortar frost resistance. It presents a systematic comparison between mortars obtained with different porous structures. Conventional porous mortars and mortars with controlled porosity were prepared using air-entraining agents (SJ2) and hollow polymer microspheres with a controllable particle size (WEA, 20–80 μm), respectively. The study shows that WEA can construct uniformly sized and regularly shaped pores in mortar and can introduce controllable and stable pore sizes compared with SJ2, which are almost independent of mixing, molding, hydration, and hardening factors. Under equivalent air content, WEA mortar exhibits superior mechanical properties and frost resistance compared to SJ2 mortar, showing a negative correlation with WEA particle size. The frost resistance of WEA (40 μm) mortar with 1% volume content is comparable to that of SJ2 air-entrained mortar with 4% air content; i.e., compared to an SJ2 air-entraining agent, to achieve the same frost resistance level, WEA mortar has lower air content and a larger bubble spacing coefficient.