Design and performance analysis of ultra-high performance concrete using fully recycled molybdenum tailings waste

This study addresses the issue of carbon emissions and economic costs arising from the high usage of cementitious materials and quartz sand in the production of ultra-high-performance concrete (UHPC). A low-carbon preparation method is proposed by synergistically replacing cementitious materials and fine aggregates with molybdenum tailings waste (MTW). Utilizing the modified Andreasen-Andersen (MAA) model to optimize particle gradation design and incorporating an engineering-applicable high-temperature steam-standard composite curing system, the effects of molybdenum tailings powder (MTP), obtained by mechanical grinding, and molybdenum tailings sand (MTS), obtained by sieving reorganization, on the performance of UHPC are systematically investigated. Experimental results indicate that the appropriate incorporation of MTS and MTP improves the workability and mechanical properties of UHPC while significantly reducing shrinkage and heavy metal leaching. The gradation compensation effect of MTS notably enhances the flowability and packing density of the paste, while MTP increases compressive strength by promoting C-S-H gel formation at lower replacement rates. Microscopic characterization reveals that appropriate use of MTW can improve the pore structure, interface transition zone (ITZ), and carbonation resistance. The optimal mix ratio is P₁₅S₄₀ group, which achieves a compressive strength of 136.62 MPa and a shrinkage value reduced by 25.6 %. Life cycle assessment shows that this system can significantly reduce greenhouse gas emissions, ozone depletion potential, energy consumption, and costs. The study confirms that the gradient utilization of MTW enables the synergistic optimization of UHPC mechanical performance and environmental benefits, providing theoretical support for solid waste resource utilization and the development of green building materials.