The role of municipal solid waste incineration fly ash in sustainable cementitious system: A waste-derived alkaline activator

Municipal solid waste incineration fly ash (MSWIFA) presents both an environmental hazard and an opportunity for sustainable valorization. However, the inherent high alkalinity of MSWIFA is often overlooked in traditional disposal methods. This study investigates the potential of MSWIFA as a fully waste-derived alkaline activator in a sustainable cementitious system. A binary system incorporating 20 wt% MSWIFA and 80 wt% granulated blast furnace slag (GBFS) achieved a 28-day compressive strength of 36.4 MPa, without the conventional chemical activators. The elevated pH provided by MSWIFA effectively triggered GBFS dissolution and promoted the formation of key hydration products, including calcium (alumino) silicate hydrate (C-(A)-S-H), ettringite, and Friedel’s salt. Notably, MSWIFA contributed not only to mechanical performance through sustained C-(A)-S-H gel accumulation, but also to environmental performance by enabling in situ immobilization of heavy metals through hydroxide precipitation and encapsulation. Higher MSWIFA dosages enhanced early hydration kinetics and promoted ettringite crystallization, yet reduced Friedel’s salt formation due to competitive ion interactions and increased porosity caused by MSWIFA particle morphology. Leaching tests confirmed that all heavy metal concentrations remained well below regulatory thresholds. These findings highlight the potential of MSWIFA as a sustainable, multifunctional activator, offering both chemical reactivity and environmental stabilization in alkali-activated materials. This approach not only valorizes incineration residues but also reduces reliance on commercial alkaline reagents, aligning with circular economic principles.