Preparation of self-consolidating cemented backfill with tailings and alkali activated slurry: Performance evaluation and environmental impact

Development of low-cost and eco-friendly mine backfills is essential for the sustainable mining technology. This study focuses on the design and performance assessment of self-consolidating cemented backfills consisting of iron tailings and alkali-activated slurry (SCBTA). The effects of alkali content, activator modulus, and precursor constituents on SCBTA were clarified by means of investigations including workability and stability at fresh state, mechanical properties, drying shrinkage, and environmental benefits. Moreover, X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were employed to understand the mechanism behind phenomena. The research findings indicate that the alkali activator modulus, alkaline content, and fly ash promote the flowability and stability of fresh SCBTA slurry. When the water-cement ratio is 0.6 and the alkali activator modulus increases from 0 to 1.0, the flow diameter of the fresh SCBTA slurry increases by 40 %. When the alkali activator modulus was 1.0 and the alkali content was 8 %, the addition of fly ash significantly improved the resistance to bleeding and segregation of the slurry. Compared to the alkaline-activated pure slag slurry, the inclusion of fly ash increases these properties by 60 % and 20 %, respectively. However, higher alkaline content and modulus result in a decrease in the resistance to shrinkage strain of hardened slurry. Hardened SCBTA slurry with an alkali activator modulus of 1 and alkaline content of 6 % and 8 % experiences severe shrinkage cracking within 7 days. MIP tests demonstrate that a higher alkali activator modulus promotes structural densification, with gel pores being the primary pore types distributed below 100 nm. Considering the mechanical properties, fluidity, workability, shrinkage, and environmental indicators, the recommended backfill slurry for mining operations is a slag/fly ash mixture with an alkaline content of 6 %, an alkali activator modulus of 0.5, and a water-cement ratio of 0.6.