Dual utilization of municipal solid waste incineration fly ash as precursor and aggregate in alkali-activated solid-waste composite mortar: Performance and Mechanism

This study investigates a dual-utilization strategy for municipal solid waste incineration fly ash (MSWIFA) in alkali-activated composite solid-waste mortar (AACSWM), where MSWIFA is incorporated either as the precursor replacing ground granulated blast-furnace slag (GGBS)/fly ash (FA) or as the aggregate replacing natural sand. The effects of MSWIFA on fresh behavior, hardened performance, shrinkage, and microstructural evolution were systematically quantified, and the governing mechanisms were resolved using SEM, TG, and MIP methods. Rough and porous MSWIFA particles drastically reduced workability (up to 48.9% loss), yet as aggregate (≤10%) they retarded setting. Shrinkage predominantly occurred within the first 7 days, representing up to about 70% of the total. While higher MSWIFA precursor content slowed early shrinkage, it increased total shrinkage; whereas MSWIFA aggregate mitigated early shrinkage via an internal water-storage effect. Incorporating MSWIFA as precursor (≤16%) resulted in a modest 8.2% reduction in flexural strength; however, further increases in the replacement rate decreased strength. As aggregate, MSWIFA induced a non-monotonic strength response of AACSWM, characterized by an initial increase followed by a decline, peaking at 5.9 MPa. Microstructurally, MSWIFA lowered the available Si/Al supply, suppressing C/N-(A)-S-H formation, but promoted crystalline phases (Friedel’s salt, ettringite) that filled pores. The fractal dimensions of AACSWM all fall within the range of 2.74–2.81, indicating that an appropriate addition of MSWIFA effectively reduces the fractal dimension and improves the pore distribution characteristics. Overall, P16A10 delivered the best balance among strength, compactness, and microstructural optimization. This work establishes a feasible pathway for upcycling MSWIFA into high-value alkali-activated construction materials.
© 2026 Published by Elsevier Ltd.