Co-utilisation of dredged sludge and zinc–lead mine tailings for sustainable subgrades

The synergistic co-utilisation of dredged sludge (DS) and zinc–lead mine tailings (ZLMT) offers a sustainable pathway for large-scale waste valorisation. To address current environmental challenges, this study developed an eco-friendly stabilisation approach for road subgrades, utilising ZLMT to optimise the physical skeleton alongside a low-carbon red mud (RM) and calcium carbide residue (CCR) binary binder. Systematic evaluation of the stabilised matrices revealed that an optimal 5:5 RM–CCR ratio at a 9%–15% dosage achieved 28-day unconfined compressive strengths of 300.15–399.62 kPa. The material demonstrated robust durability, retaining over 80% of its strength following 28 days of water immersion. Furthermore, toxicity characteristic leaching procedure tests confirmed effective heavy metal immobilisation well below regulatory limits, while life cycle assessment highlighted substantial carbon dioxide emission reductions compared to conventional binders. Microstructural analyses by way of Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy indicated that coupled hydration, carbonation, and pozzolanic reactions drove the precipitation of calcium silicate hydrate, calcium aluminate hydrates, and calcium aluminosilicate hydrate gels, ettringite, and calcite, yielding a highly densified microstructure. Ultimately, this study provides critical mechanistic insights into the physical–chemical stabilisation of multi-source solid wastes, establishing a feasible and sustainable framework for subgrade construction in Northwest China.