Hard Rock Mine Waste as a Sustainable Sand Substitute in Cement Concrete Production

The rapid depletion of natural river sand and growing environmental concerns over sand mining have intensified the search for viable alternative fine aggregates in concrete production. Hard rock mining operations, meanwhile, generate substantial waste material that is often discarded without beneficial reuse, contributing to land degradation and disposal challenges. This study investigates the feasibility of utilizing hard rock mine waste as a substitute for natural sand in cement concrete, addressing both resource scarcity and industrial waste management concerns. The mine waste was characterized for its physical, chemical, and mineralogical properties, including particle size distribution, specific gravity, water absorption, and fineness modulus, to assess its suitability as a fine aggregate. Concrete mixes were prepared by replacing natural sand with mine waste at 5%, 10%, 15%, and 20% by weight, maintaining a constant water-cement ratio of 0.45. Fresh properties (workability/slump) and hardened properties, including compressive strength, split tensile strength, and durability parameters (water absorption and sulfate resistance), were evaluated at 7, 28, and 56 days of curing and compared against a control mix using conventional sand. Results show that concrete with 15% mine waste replacement achieved compressive strength higher than the control mix at 28 days. Slump test results indicate an approximate 7% reduction in workability compared to the control specimen, attributed to the angular particle shape and higher fines content of the mine waste. Quantitative results for split tensile strength, water absorption, and sulfate resistance at 28 days are being finalized, with extended-curing results at 56 and 90 days to follow; preliminary trends indicate performance comparable to the control mix, within acceptable ASTM limits. These findings demonstrate that hard rock mine waste is a technically viable and environmentally sustainable substitute for natural sand in concrete production, conserving natural sand resources while providing a productive outlet for mining by-products. This approach aligns with the themes of low-carbon, resource-efficient construction materials.