Flowability, microstructure, early and long-term strength modification of cemented ultrafine tailings backfill using artificial lightweight aggregates

Ultrafine tailings (UFT) characterized by the average particle size <19 mu m are increasingly discharged from mining process. Due to the large specific surface area and high content of clay components for UFT, cemented ultrafine tailings backfill (CUFTB) usually exhibits the poor flowability and strength, which poses an obstacle to the practical application in mine filling. Therefore, this study aims to explore the feasibility of modifying CUFTB through incorporating cold-bonded tailings lightweight aggregates (CBTLWAs). A series of mini slump cone, unconfined compressive strength (UCS), digital image correlation (DIC), microanalysis tests were conducted to investigate the effects of CBTLWAs with uniform particle sizes ( d =2, 4, 6, 8 mm) and full particle gradations (Talbot coefficients n =0.2, 0.4, 0.6, 0.8) on slump flow (SF), UCS, microstructure, and deformation behaviour of CUFTB. Results indicate that adding CBTLWAs as a partial substitute for UFT effectively improves the flowability and strength of CUFTB. With CBTLWAs dosage increases from 15 to 40 wt%, the SF values increase steadily, and the highest values are observed when d =2 mm and n =0.6. After curing of 3 -180 days, the UCS values exceed 1.0 MPa, and the highest values are found in CUFTB when d =8 mm and n =0.4 or 0.6. There is an optimal dosage (20 -30 wt%) for CBTLWAs depending on the particle sizes and gradations. Hydration reactions of IWRs-based binder generated C-S-H, calcite, and ettringite. CBTLWAs bonded with CUFTB matrix to form a skeleton structure, hindering the propagation of cracks and enhancing the ductility. CUFTB incorporating CBTLWAs exhibits a hybrid mode of shear and tensile failure. The utilization of CBTLWAs shows a promising solution to address the challenges associated with performance modification for CUFTB. This provides a more environmentally responsible approach to solid wastes management and contributes to the sustainability of mining industry.