Manufacture of alkali-activated cementitious materials using municipal solid waste incineration fly ash (MSWIFA): The effect of the Si/Al molar ratio on fresh and hardened properties

Due to the escalating production of municipal solid waste and the widespread adoption of incineration technology, there is a substantial demand for secure disposal of municipal solid waste incineration fly ash (MSWIFA). In this research, alkali-activated MSWIFA via combination with metakaolin (MK) and cement was used to produce an eco-friendly composite. The influence of Na2O content and modulus (Ms) of alkali activator on the early compressive strength and setting time of the composites was investigated, and 4 wt% Na2O content was found to be the most appropriate alkali content. Then, the influence of the Si/Al ratio (2.35–3.18) on the fresh properties (initial setting time, rheology properties, and hydration heat) and hardened properties (compressive strength and shrinkage performance) of composite materials was studied. The microscopic mechanism of the effect of the Si/Al ratio on material properties was explained by XRD, TG, and SEM-EDX. The results showed that the compressive strength of the composite can reach 16.4 MPa at 28 days, which met the quality standard of MU15 (GB/T 25779–2010) of load-bearing concrete perforated brick. With the increase of the Si/Al ratio, the setting time of the slurry is prolonged and the rheological property has deteriorated. The composites with a lower Si/Al ratio (2.35) have the densest structure and the lowest degree of drying shrinkage, which leads to a higher strength. This study provides a potential solution for MSWIFA solidification in low-carbon construction applications.