Fresh and hardened properties of cemented paste backfill: Links to mixing time

Current technical knowledge is insufficient regarding the influence of mixing time on fresh and hardened properties of cemented paste backfill (CPB). This work focused on experimental studies to gain a deeper understanding of the influence of mixing time on the rheological properties (yield stress, viscosity), self-desiccation, permeability and mechanical properties or behavior (strength, deformation behavior) of CPB. A series of CPB specimens were prepared with various mixing times (1, 2, 4, 7, 10, and 15 min) and cured at different times (1, 2, 4, 7, 10 and 15 min) for rheological property testing. Unconfined compressive strength (UCS), hydraulic conductivity and microstructural tests were performed on CPBs that were made with various mixing times and cured for different times (up to 90 days). Monitoring experiments were also carried out on CPBs prepared with various mixing times. The results obtained indicate that the mixing time significantly affects the rheological, mechanical, hydraulic and microstructural properties of CPB. Moreover, the self-desiccation of CPB is a function of the mixing time. A longer mixing time increased the yield stress and decreased the viscosity. The longer mixing time promoted binder dissolution and hydration in the CPB, which increased the amount of hydration products and decreased the volumetric water. Longer mixing time intensified the CPB self-desiccation, which is beneficial for the early age mechanical strength of CPB. CPB specimens made with longer mixing time experienced a higher strength and elastic modulus due to the generation of more cement hydration products and the reduction of the volume of pores in CPB. A longer mixing time reduced the CPB hydraulic conductivity, due to the refinement of the CPB pore structure. This study provides relevant knowledge and technical information that will contribute to the design of more cost-effective and sustainable CPB structures.