Preparation of multi-industry solid waste synergistic low-carbon sustainable grouting material: Optimal regulation, diffusion characteristics, synergistic mechanism, and environmental and economic evaluation

To address curtain seepage and multi-industry solid waste disposal, and advance environmental sustainability, a novel multi-industry solid waste synergistic low-carbon sustainable grouting material (MWLGM) was prepared using rice husk ash (RHA) after composite activation, ground granulated blast furnace slag (GGBFS) and steel slag (SS). Its formulation was optimized via response surface methodology combined with performance tests, and heavy metals were solidified. Tests and simulations were conducted to investigated heavy metal solidification efficiency, carbon emissions, phase composition and microstructure of MWLGM, as well as to reveal the synergistic mechanisms of strength formation and heavy metal solidification, and diffusion rules. The results revealed that MWLGM was 10 % RHA, 60 % SS, 30 % GGBFS, 0.4 water-cement ratio and 8 % alkali content, exhibiting 249 mm fluidity, 132min setting time, 22.37 MPa 28d uniaxial compressive strength (UCS), 1.8 MPa seepage pressure and 99.83 % stone formation rate. Raw materials in MWLGM acted synergistically, RHA provided [SiO₄]^4- as silicon source, SS suppled Ca²⁺ and mitigated shrinkage via micro-expansibility, GGBFS rapidly released Ca²⁺ and [AlO₄]^5-. Alkali-activation drove their reaction to form AFt and gels, and promote C(N)–S–H transformation to C(N)-(A)-S-H. These products not only enhanced the mechanical properties (early UCS by AFt, late by gels) and impermeability of MWLGM, but also solidifying heavy metals through physical encapsulation and chemical bonding below limits. Fe achieved 93.6 % solidification, Mn/Cu/Zn were fully solidified. Compared with OPC-based materials, MWLGM reduced carbon emissions by 20.3 % and cost by 9.29 %. It diffused circularly in hydrostatic grouting, and its diffusion shape shifted from ellipse to U-shape in dynamic-water grouting.