Environmental stability and leaching behavior of alkali-activated cement mortar with high-temperature sintered MSWI fly ash exposed to extreme environmental conditions

Municipal solid waste incinerator fly ash (MSWI FA), a byproduct of MSW incineration , poses significant environmental challenges due to its complex composition containing heavy metals , chlorides, and organic contaminants . To address these concerns and explore utilization, the performance of alkali–activated cement mortar with sintering–treated MSWI FA and metakaolin (MK) was analyzed under high temperature, acidic, alkaline, and natural drying conditions, compared with pure cement mortar as the blank group. Results showed that the sintered MSWI FA–MK cement mortar maintained structural integrity with a compressive strength of 2.5 MPa at 1000 °C for 90 min and stable, high–temperature–resistant minerals like yugawaralite and riversideite–9 Å, retaining 45 % of its initial compressive strength at 600 °C for 30 min. In acidic environments (pH=4), minor loss of mass and strength was observed, whereas in sulfuric acid (pH=2), sluggish fracture growth and inhibited acid penetration were noted. The alkaline solutions (pH=11 and 13) resulted in a decrease in strength due to the dissolution of mineral phases. However, the natural shrinkage rate was much lower than the blank group, and heavy metal leaching met regulatory standards. This work presents empirical evidence supporting the secure and efficient utilization of MSWI FA in construction materials, hence helping sustainable waste management techniques and advancing the circular economy . • Sintered MSWI FA retains 45 % strength of the alkali-activated mortar at 600°C. • Alkali-activated mortar with sintered MSWI FA had low sensitivity to acidic media. • The mortar shows some degradation at pH 13, but retaining practical usability. • Natural dry shrinkage is reduced by over 30 %, improving durability and longevity.