Using waste materials in concrete production is a sustainable approach to mitigate carbon emissions, reduce waste and environmental pollution, lower costs, and preserve natural resources. This study investigates the potential of one-part geopolymer concrete (OGPC) produced with ground granulated corex slag and naturally abundant metakaolin as a binder, combined with Polokwane platinum slag (PPS) aggregate as a replacement for natural fine aggregate (Malmesbury sand). The workability, mechanical properties (compressive, flexural, and splitting tensile strengths), and morphology of water-cured OGPC with varying PPS aggregate contents (0%, 25%, 50%, 75%, and 100%) were examined. The results indicate that increasing PPS aggregate content progressively improved workability, with a 23.8% improvement at full replacement. The compressive strength result shows an optimal sand replacement level of 50% having 26.7 MPa and 30.8 MPa, at 7- and 28-day, respectively, with a 4.8% improvement compared to the control at 28 days. However, higher PPS aggregate inclusion (75% and 100%) led to an 8.5% and 8.8% decrease in the compressive strength, respectively. At 7- and 28-day, the splitting tensile strength (STS) remained comparable to the control up to 50% PPS aggregate inclusion but declined by 20.6% with full sand replacement. Flexural strength exhibited a different trend, with a 6.4% reduction at 50% PPS aggregate and further decreases by 13.7% and 21.3% at 75% and 100% PPS inclusion, respectively. In conclusion, PPS aggregate can replace up to 50% of natural sand by volume in one-part metakaolin-based geopolymer concrete, offering potential benefits in reducing aggregate costs and minimising environmental pollution.
