Materials

Fibres can markedly enhance the uniaxial compressive strength (UCS) of cemented paste backfill (CPB). However, previous studies have mainly verified the effectiveness of polypropylene and straw fibres in improving the UCS of CPB experimentally, while systematic multi-factor evaluation remains limited. In this study, laboratory experiments were conducted on polypropylene- and straw fibre-reinforced CPB to construct a reliable dataset. The factors influencing the intensity of uniaxial compressive strength were divided into four aspects (mixture proportions, physical properties of the cement–tailings mixture, chemical characteristics of tailings, and fibre properties), and four intelligent models were developed for effectiveness analysis and UCS prediction. SHapley Additive exPlanations (SHAP) were employed to quantify the contributions of individual features, and the findings were experimentally validated. The GWO–LGBM model outperformed the SVR, ANN, and LGBM models, achieving R² = 0.907, RMSE = 0.78, MAE = 0.515, and MAPE = 0.157 for the training set, and R² = 0.949, RMSE = 0.627, MAE = 0.38, and MAPE = 0.115 for the testing set, respectively. Feature analysis reveals that mixture proportions contribute the most to UCS, followed by the tailings’ physical properties, the fibre properties, and the tailings’ chemical characteristics. This study found that cement content and tailings gradation control CPB structural compactness and fibres enhance bonding between hydration products and tailings aggregates, while the chemical composition of the tailings plays an inert role, functioning mainly as an aggregate.

Improper disposal of granite sawdust from stone processing and heavy metal-containing tailings sand can pose severe threats to the environment and human health. Based on their physicochemical properties, granite sawdust was used to synthesize a zeolite-based stabilizer (GFAS) for immobilizing lead (Pb) and zinc (Zn) in tailings waste. The stabilizer was prepared through an alkali fusion–hydrothermal method, followed by phosphoric acid modification. Characterization by XRD, SEM-EDS, and BET revealed that GFAS possesses a Na-P1 zeolite structure (Na₆Al₆Si₁₀O₃₂) with a micro-mesoporous texture and a specific surface area of 35.00 m²/g, representing a 10-fold increase over raw sawdust. The cation exchange capacity (CEC) of GFAS reached 57.08 cmol⁺/kg, a 116-fold enhancement. The stabilization mechanism involved synergistic physical adsorption, chemical precipitation (e.g., Pb₃(PO₄)₂, Zn(OH)₂), and ion exchange. This study presents a sustainable “waste-treats-waste” strategy for effectively reducing the mobility of heavy metals in tailings waste, thereby contributing to the remediation of seepage from tailings pond foundations.

Ultra-High-Performance Concrete (UHPC) is being increasingly utilized in major engineering projects due to its excellent mechanical properties, strong durability, and superior overall performance. Nevertheless, the widespread use of premium cementitious materials leads to high expenses and a substantial environmental impact. In this work, crushed recycled paste was calcined at 600 °C for two hours to produce calcined recycled fine powder (RFP) with varying hydration reactivity. UHPC was produced using the RFP in place of some of the cement. Chemical activation was accomplished by adding a composite activator system made up of Ca(OH)₂, Na₂SO₄, Na₂SiO₃·9H₂O, and K₂SO₄ in order to further improve the performance of UHPC. Particle size, viscosity, fluidity, mechanical properties, and hydration products were analyzed to establish the best activator type and dosage, as well as the ideal activation procedure for recycled fine powder. By mass replacement of cementitious materials, when 15.0% of the calcined recycled fine powder was added, the compressive strength of UHPC reached 149.1 MPa, a 23.2% increase over reference UHPC without calcined recycled fine powder. The results show that the calcined recycled fine powder ground for 60 min exhibits the highest activity. More hydrated products were formed in UHPC as a result of the addition of Ca(OH)₂. The compressive strength peaked at 162.2 MPa at an incorporation rate of 1.5%, which is 8.8% higher than UHPC without an activator.