Use of municipal solid waste incineration fly ash as a supplementary cementitious material: CO₂ mineralization coupled with mechanochemical pretreatment

The use of municipal solid waste incineration fly ash, commonly referred to as “fly ash”, as a supplementary cementitious material (SCM), has been explored to mitigate the CO₂ emissions resulting from cement production. Nevertheless, the incorporation of fly ash as an SCM in mortar has been shown to weaken its compressive strength and increase the risk of heavy metal leaching. In light of these challenges, this study aims to comprehensively evaluate the influence of CO₂ pressure, temperature, and residual water/binder ratio on the CO₂ uptake and compressive strength of mortar when combined with fly ash. Additionally, this study systematically examines the feasibility of mechanochemical pretreatment, which enhances the homogenization of fly ash and augments the density of the mortar's microstructure. The results indicate that the use of mechanochemical pretreatment leads to a notable 43.6% increase in 28-day compressive strength and diminishes the leaching of As, Ba, Ni, Pb, Se, and Zn by 17.9-77.8%. Finally, a reaction kinetics model is proposed to elucidate the CO₂ sequestration process under varying conditions. These findings offer valuable guidance for incorporating fly ash as an SCM and CO₂ sequestrator in mortar.