In this study, graphite tailings produced in Luobei County, Heilongjiang Province, were used as a sustainable aggregate to replace river sand (0%, 25%, 50%, 75%, 100%) in UHPC for the preparation of ultra-high-performance concrete (UHPC). The experimental results showed that the incorporation of 75% graphite tailings caused a significant increase in the wet bulk density of UHPC mortar. The workability of UHPC decreased monotonically with the increase in graphite tailing substitution rate, and wet bulk density decreased by 28.42% with 100% graphite tailings (compared with no graphite tailings). The incorporation of 75% graphite tailings helped to improve the compressive and flexural strengths as well as the durability of UHPC. Compared with the UHPC without graphite tailings, the 28 d compressive and flexural strengths increased by 8.82% and 7.28%, respectively, and the chloride ion electrical flux decreased by 19.49%. XRD and thermogravimetric analysis data indicate that the incorporation of graphite tailings did not change the type of hydration and that the incorporation of graphite tailings helped to increase the degree of hydration within the UHPC matrix. MIP and SEM showed that 75% graphite tailings helped to reduce the porosity and the number of harmful pores inside the matrix. The 100% graphite tailings treatment replacing river sand decreased the economic cost of UHPC by up to 23.78%.

As an innovative approach to advancing sustainable construction, this study explores the integration of molybdenum tailings as fine aggregate in 3D-printed mortar. The rheological and mechanical properties of the developed mixtures are systematically investigated. Environmental and economic assessments demonstrate that molybdenum tailings sand exhibits negligible global warming potential (GWP), acidification potential (AP), and cumulative energy demand (CED), completely avoiding the environmental impacts associated with natural sand extraction. Economically, full replacement with molybdenum tailings reduces material costs, as the tailings are typically provided without charge by mining enterprises. Furthermore, the template-free 3D printing technology eliminates formwork-related environmental impacts and simplifies construction processes. Experimental results indicate that mortars with cement-to-sand ratios between 1:1 and 1:2 possess favorable printability, with nozzle movement parameters significantly influencing printed dimensions. While increased molybdenum tailings content reduces mechanical strength, the cement-to-sand ratio exerts a more pronounced effect. The compressive strength of mold-printed and free-printed mortar reaches 55–75% and 35–55% of conventional mortar, respectively. Anisotropy analysis reveals minimal directional dependence in flexural strength, whereas compressive strength shows clear anisotropy, with X-direction strength measuring approximately 70% of that in the Y direction. This research provides valuable insights into the sustainable design and performance optimization of 3D-printed mortar using industrial byproducts.