Heavy-Metal Immobilization Potential and Durability of OPC–MgO–Fly Ash–Blended Concrete Containing Zinc Slag as a Fine Aggregate

Abstract

The use of industrial byproducts as alternatives to natural sand in concrete presents a viable approach to conserving natural resources and minimizing environmental impacts. This study investigates the influence of partial replacement of natural fine sand with zinc slag (ZS) at replacement levels of 0%, 20%, 40%, 60%, 80%, and 100% on the performance of concrete incorporating a ternary binder comprises of 50% ordinary portland cement (OPC), 30% reactive magnesium oxide (MgO), and 20% fly ash also known as OMF. A hydration agent was incorporated in the ternary binder for improving the hydration of MgO. The concrete mixes prepared were tested for compressive strength, water penetration, surface absorption, and abrasion resistance. Zinc slag with up to 60% replacement showed higher compressive strength, lower surface absorption, reduced water penetration, enhanced abrasion resistance, and lower chloride ingress compared with the concrete mixes with 100% natural fine sand. The raw ZS exhibited high leachate concentrations ( Cu = 3.25 , Cd = 1.76 , Fe = 10.84 , Mn = 18.62 , Pb = 31.72 , Zn = 55.2 mg/L), while the OMF-0.75 mix with 100% ZS showed immobilization efficiencies of 97.8% for Cu, 99.4% for Cd, 99.07% for Fe, 97.3% for Mn, 99.6% for Pb, and 98.5% for Zn. These values are well below the prescribed USEPA limits. Immobilization of heavy metals resulted from the formation of dense C-S-H and M-S-H gels, together with melilite and C-F-A-S-H phases derived from zinc slag. These phases refined the pore structure and enhanced heavy metal binding for safe and sustainable valorization of zinc slag.