Reactivity enhancement of municipal solid waste gasification slag as a low-carbon binder via mechanical and alkaline activation engineering.

Abstract

As cement production is a dominant carbon emission source in construction industry, the development of alternative binders to partially or fully replace ordinary Portland cement (OPC) has been widely motivated. Municipal solid waste gasification slag (MSWGS), generated from a high-temperature slagging gasifier of waste treatment, contains the same key elements as ground granulated blast-furnace slag (GGBS), a common alkali-activated materials (AAMs) binder. However, differences in elemental content, particle size distribution, and mineral phases may affect its reactivity limiting its use as AAMs. This study systematically investigates the effects of mechanical and alkaline activation on the reaction, microstructure and strength development of MSWGS by varying particle size, NaOH molarity and SiO2/Na2O molar ratio. Mechanical activation enhances the early reactivity and strength of MSWGS by promoting Si and Al dissolution but provides limited benefit for 28-day strength. Alkaline activation with 6 M NaOH and SiO2/Na2O molar ratio of 2.56 produced the highest strength, with NMR revealing the coexistence of chain-like and highly polymerized aluminosilicate environments. Increased calcite formation is also observed, potentially providing an additional filler contribution. Optimized paste mixture achieves a compressive strength of 112.6 ± 9.8 MPa at 28 days, approaching that of GGBS based paste and exceeding that of cement paste, while exhibiting a lowest carbon footprint. The mortar system is also evaluated. These findings demonstrate that combined mechanical and alkaline activation can enable MSWGS to function as an independent AAM binder, highlighting its potential for high strength applications with low carbon emissions and the valorization of MSW residues.