Development of low-carbon cement utilizing waste incineration ash: Mechanical properties, hydration behavior, and environmental impact

Developing low-carbon cement from municipal solid waste incineration ash (fly ash (FA) and bottom ash (BA)) is vital for solid waste management and reducing carbon emission. Raw FA was pretreated by ultrasonic accelerated carbonation and ultrasound-assisted carbonated fly ash (UFA) was introduced to create a novel UFA-BA-cement (UBC). The UBC paste demonstrated excellent compressive strength (33.2 MPa) and resistance to chloride penetration due to its refined pore structure. Both UFA and BA exhibited dilution and filling effects, with UFA notably enhancing the early hydration reaction (0–1 hour) of UBC. This significantly increased the polymerization degree of the early curing UBC paste, resulting in a dense microstructure. The addition of gypsum or CaO (2.5 % and 5 %) has a negative effect on the UBC cement system. Reducing the cement clinker ratio from 50 % to 40 % significantly weakened the paste strength. Additionally, the chloride salts in BA reacted with CaCO₃, forming insoluble chloride salt Tunisite (NaCa₂Al₄(CO₃)₄(OH)₈Cl), which further strengthened cement structure. The leaching concentrations of As, Ba, Cr, Cu, Ni, Pb, Se, and Zn are all lower than the Chinese groundwater grade IV standard. According to life cycle assessment, the UBC scenario emits the least CO₂ (322 kg-CO₂ eq.), which is 53.6 % lower than that of plain cement. Therefore, although the compressive strength of UBC is lower than that of plain cement (PC), its significant advantages in carbon emission reduction, environmental performance, and resource recovery make it a promising low-carbon alternative for non-structural and semi-structural applications, supporting the sustainable utilization of FA.