Effect of partial replacement of volcanic ash with slag on the performance of sustainable alkali-activated materials for lead-contaminated soil remediation

Lead-contaminated soils pose critical environmental and ecological risks due to the persistence, mobility, and toxicity of Pb in terrestrial systems. This study investigates the use of alkali-activated binders derived from volcanic ash (VA) with partial replacement by ground granulated blast-furnace slag (GGBFS) for the stabilization/solidification of Pb-contaminated soil. The influence of slag content (0-40 wt%) under both oven and ambient curing regimes was systematically evaluated in terms of unconfined compressive strength (UCS), Pb immobilization efficiency, and environmental performance. A combination of leaching tests (TCLP), spectroscopic and microstructural analyses (XRD, FE-SEM, EDS, FTIR), and life cycle assessment (LCA) was employed. Results demonstrate that slag incorporation markedly enhances matrix densification through the synergistic formation of NASH and C(A)SH gels, leading to up to 75% higher UCS and more than 99% reduction in Pb leachability compared with VA-only binders. Microstructural evidence confirmed Pb incorporation into stable gel phases, while LCA revealed modest climate change benefits (∼5% reduction in CO₂ emissions) alongside trade-offs in ecotoxicity and resource depletion categories. Overall, the findings highlight the novelty and potential of VA-slag hybrid binders as eco-efficient and sustainable stabilizers for long-term remediation of heavy metal-contaminated soils.