Ternary synergistic activation of municipal waste incineration bottom ash for high-performance supplementary cementitious materials: Mechanisms, heavy metal immobilization, and sustainability.

The efficient valorization of municipal solid waste incineration bottom ash is fundamentally constrained by its mineralogical inertness and potential environmental toxicity. To address these coupled barriers, this study adopts a three-phase sequential optimization approach, involving mechanical grinding, stoichiometric regulation of Ca/Si/Al molar ratios, and evaluation of four alkali activator types (Ca(OH)2, NaOH, KOH, and water glass) at varying dosages. Accordingly, a mechanical-compositional-alkali ternary synergistic strategy is proposed for the clean upcycling of bottom ash into high-performance supplementary cementitious components within blended binder systems. The activation mechanisms, heavy metal immobilization behavior, and sustainability performance of the proposed strategy are systematically elucidated through comprehensive multiscale characterization (e.g., X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetry-derivative thermogravimetry, and low-field nuclear magnetic resonance) combined with life cycle assessment. Results demonstrate that the ternary synergistic strategy markedly outperforms conventional single-activation approaches, elevating the relative reactivity index of the blended system (30% MSWIBA replacement) to 93% and achieving a structural-grade compressive strength of 42.7 MPa. A self-reinforcing unlock-steer-drive cascading mechanism is proposed to explain this synergy. The dense gel matrix produced under optimal conditions immobilizes over 95% of hazardous heavy metals (Pb and Cd) via a coupled physical-chemical dual-confinement mechanism. Prospective life cycle assessment indicates a potential carbon footprint reduction of 88%-93% relative to Portland cement under laboratory and industrial-symbiosis scenarios, respectively. This work presents a systematic framework for high-performance, environmentally safe, low-carbon valorization of MSWIBA, offering a potentially scalable pathway for advancing circular economy implementation and decarbonization in the construction sector.