Effect of Early Curing Experiences on Mechanical Properties and Microstructure of ECO-UHPC Prepared by Gold Tailings Sand.

Fine gold tailings particles generated from gold mining and refining have the potential to replace high-cost quartz sand in the preparation of economical ultra-high-performance concrete (ECO-UHPC) due to their large stockpiles, low cost, and elimination of grinding. In this study, ECO-UHPC was prepared by substituting quartz sand with gold tailing sand (GTS) at substitution rates of 0%, 25%, 50%, 75%, and 100%. The mechanical properties of ECO-UHPC, including its cubic compressive strength, elastic modulus, and prismatic compressive strength, as well as its leaching toxicity, were experimentally analyzed under various early curing experiences such as ambient-water curing (WC), hot-water curing (HWC), hot-air curing (HAC), and combined curing (CC). Additionally, scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were employed to interpret the macroscopic behavior of ECO-UHPC. The results indicate that the incorporation of waste GTS slightly reduces the fluidity of fresh ECO-UHPC, decreasing it by approximately 6.1% at a full 100% replacement. As a result of waste GTS substitution, the cubic strength of ECO-UHPC experiencing the WC environment during early curing is reduced by 0.7-12.2%. However, the strength of thermally cured ECO-UHPC is comparable to or even higher than that of pure quartz-based G0, with the maximum value occurring in G-50. Specifically, the strength of G-50 cured with HWC, HAC, and CC varies by +20.0%, +40.2%, and +57.7%, respectively, as compared to that of G-50 cured with WC. The evolution of the elastic modulus and the prismatic strength of ECO-UHPC under different early curing conditions and GTS replacement rates aligns closely with that of its cubic strength. In addition, the implementation of thermal curing conditions also limits the leaching of heavy metals from ECO-UHPC, with the best effect observed under CC. This is because appropriate thermal curing promotes the densification of a cementitious substance and the bonding of GTS-cementitious material. Overall, this study demonstrates the feasibility of utilizing waste GTS as a partial or full replacement for quartz sand in ECO-UHPC while maintaining desirable mechanical performance and environmental safety. The findings provide valuable insights into the influence of GTS substitution and early curing regimes on ECO-UHPC properties, highlighting the potential of thermal curing to enhance strength and mitigate leaching risks. Future research should further explore the long-term durability of GTS-based ECO-UHPC and its broader applicability in sustainable construction practices.