Circular Construction Approach Using Fly Ash–Dolomite Geopolymers with Zinc Slag: Strength, Durability, and Environmental Compatibility
The growing demand for sustainable construction materials has intensified efforts to reduce the environmental impact of conventional concrete production and industrial waste disposal. Zinc slag, a by-product of metallurgical industries, poses significant environmental challenges due to large-scale landfilling and the potential for heavy-metal leaching. In this context, the development of ambient-cured geopolymer concrete using industrial by-products offers a promising approach to reduce carbon emissions while enhancing material performance. This study investigates the utilization of zinc slag as a partial to full replacement of natural fine aggregate in fly ash–dolomite-based geopolymer concrete synthesized under ambient curing conditions. Geopolymer concrete mixes were prepared using fly ash and dolomite as aluminosilicate precursors, activated by alkaline solutions of varying molarity. Zinc slag was incorporated at different replacement levels to evaluate its influence on geopolymerization and material performance. Mechanical properties were assessed through compressive strength testing, while phase evolution and microstructural characteristics were analyzed using X-ray diffraction and Fourier transform infrared spectroscopy, confirming the formation of N-A-S-H and C-A-S-H gel phases. Environmental performance was evaluated using the toxicity characteristic leaching procedure to assess the immobilization of heavy metals, such as Pb, Zn, Cr, and Cd. The results demonstrate that moderate zinc slag incorporation enhances compressive strength and promotes matrix densification while effectively immobilizing hazardous elements. The findings highlight the potential of zinc slag–based geopolymer concrete as a sustainable and environmentally safe alternative for construction applications.