The directional regulation and performance enhancement mechanism of composite-activated biomass power plant ash on all-solid-waste eco-friendly supersulfated cement.

To address the low strength and limited precursor supply for supersulfated cement (SSC), and achieve high-value utilization of biomass power plant ash (BPPA), a sustainable strategy of utilizing composite-activated BPPA (CABPPA) to directionally replace granulated blast furnace slag was proposed for developing an all-solid-waste supersulfated cement (BASSC). Combining multi-scale characterization and fractal theory, the directional regulation and performance enhancement mechanism of CABPPA on BASSC was revealed, and a compressive strength prediction model was established. Meanwhile, through multi-criteria comprehensive evaluation and leaching tests, the overall environmental and economic benefits of the system were quantified. The results showed that an optimal CABPPA dosage (20%) accelerated reaction kinetics and improved hydration completeness. Reactive silica and alumina from CABPPA optimized the Ca/Si and Si/Al ratios of the system, which directionally promoted the structural evolution and densification of gels. Combined with its ball-bearing effect and micro-aggregate effect, it eliminated localized microstructural phase-enrichment flaws, optimized the pore structure, thereby enhancing the 28 d compressive strength by 18.8%. However, high dosages triggered a dilution effect and calcium depletion, resulting in severe degradation of macroscopic mechanical properties. Furthermore, the quadratic polynomial model established based on the fractal dimension of region IV pores accurately predicted the compressive strength (R2 = 0.99883). Regarding environmental and safety aspects, BASSC with 20%-40% dosages not only demonstrated excellent heavy metal immobilization capacity (with an immobilization efficiency approaching 100%), but also reduced the CO2 emission index and cost index by over 92% and 44%, respectively, compared with Portland cement. Accordingly, potential application directions in scenarios such as foundation engineering and mine backfilling were envisioned. These findings provided an integrated solution for overcoming the performance shortcomings and material bottlenecks of SSC.