Performance and implications of cost-effective natural sand substitutes for quartz in ultra-high performance concrete

This study experimentally investigated the use of locally available natural sands as cost-effective substitutes for high-purity quartz sand in ultra-high performance concrete (UHPC). Motivated by the low cost of natural sands, which can be up to 95 % less expensive than quartz sand, four regional sand types (mason, golf, desert, and bunker sand) were evaluated as full or partial replacements. The experimental program assessed the impact of sand selection on particle packing efficiency, fresh workability, compressive strength, fiber pull-out behavior, and composite-scale tensile performance. All alternative sands produced UHPCs with compressive strengths exceeding 150 MPa, with some partial replacements outperforming the reference silica sand mixture. Single-fiber pull-out tests of smooth and striated steel fibers demonstrated that aggregate morphology, particularly angularity and surface texture, substantially enhances the fiber–matrix interfacial bond, with the most pronounced effects observed in bunker and desert sand systems. This improvement led to increased tensile strength and strain-hardening capacity. Additionally, this study demonstrates for the first time the positive effects of sand morphology on the interfacial bond performance of striated steel fibers. These findings indicate that properly selected and proportioned natural sands can reliably replace or supplement quartz sand in UHPC without sacrificing fresh properties or mechanical performance, providing a practical pathway to more cost-effective and sustainable UHPC formulations utilizing abundant regional fine aggregates. • Regional natural sands were evaluated as quartz sand substitutes in UHPC. • All mixtures achieved compressive strength above 150 MPa with good workability. • Desert and bunker sands enhanced fiber–matrix bond and tensile performance. • Aggregate morphology strongly influenced pull-out energy and strain hardening. • Findings support low-cost, sustainable UHPC using locally available fine sands.