The significance of mixing time in the development of the engineering properties of cemented fiber-reinforced tailings materials

Fibre-reinforced tailings backfill (FRB) has gradually been introduced in backfill mining to improve the mechanical performance of cemented paste backfill, a construction material used worldwide in underground mines. However, the effect of mixing time on the key engineering properties of FRB is not known. Closing this knowledge gap is essential for the cost-effective application of FRB in mines. Thus, the main research objective is to experimentally investigate the influence of the mixing time on key engineering properties of FRB, such as rheological (yield stress, viscosity), mechanical (strength, deformation behaviour), hydraulic (permeability, pore pressure) and microstructural (e.g., cement hydration products, pore structure) properties. An extensive experimental program was conducted using silica tailings and monofilament polypropylene fibers with Portland cement as the binder. The FRB samples were prepared with six different mixing times (1, 2, 4, 7, 10, and 15 min) and subjected to various curing periods (up to 90 days). These samples were subjected to a series of tests, including vane shear tests for yield stress, Brookfield viscometer tests for viscosity, unconfined compressive strength (UCS) tests, and saturated hydraulic conductivity tests. Additionally, microstructural analyses, such as thermogravimetric analysis (TGA) and mercury intrusion porosimetry (MIP), and an extensive monitoring program were conducted to evaluate the development of hydration products and pore structure, as well as to assess the progression of binder hydration and self-desiccation. The findings reveal a significant correlation between the mixing time and the characteristics of the FRB, spanning from its flow properties in the fresh state to its mechanical behaviour and permeability in the hardened state. Prolonged mixing time correlates with heightened yield stress and reduced viscosity, highlighting its pivotal role in influencing the material's performance. Moreover, a prolonged mixing time increased the reaction rate of binder hydration and accelerated the progression of self-desiccation within the FRB, which contributed to the enhancement of strength of FRB at early age. Furthermore, an extended mixing time resulted in pore structure refinement and lower permeability. The findings presented and discussed in the manuscript will contribute to a more cost-effective design of the FRB and its development. •Mixing time impacts properties of fibre-Reinforced Tailing Backfil