Further insight into the strength development of cemented paste backfill materials containing polycarboxylate ether-based superplasticizer

Abstract

The utilization of water-reducing admixtures has become immensely popular in underground mine backfilling operations not only to enhance the workability of cemented paste backfill (CPB, a mine construction material), but also for their ability to enhance the mechanical strength and long-term durability of CPB. This study aims to evaluate the effect of a polycarboxylate ether-based superplasticizer (PES) on the mechanical strength of CPB made with different mix components (tailings, dosages of PES, cement and solids contents, tailings fineness, and water chemistry), and subjected to various curing conditions (stress-free, under stress, constant temperature, and non-isothermal temperatures). An extensive experimental program has been conducted to investigate the uniaxial compressive strength development, hydraulic (positive pore pressure, suction) and microstructural properties of CPB with PES. The results show that including PES in CPB mixtures significantly increases the unconfined compressive strength (UCS) as well as affects the microstructure and hydraulic properties of CPB. This UCS increase depends on the amount of PES added, type and fineness of the tailings, sulphate content, and curing time. After 7 days of curing, the UCS of the CPB increases as the dosage of the PES is increased. The CPB that contain PES and cured under stress exhibit a higher compressive strength after just 3 days of curing as compared to that without PES and cured under similar stress conditions. It is also found that curing CPB under non-isothermal conditions considerably increases the compressive strength and this increase is more significant with the presence of PES. These findings have significant impacts on the short- and long-term performances of CPB structures with PES and their associated economic implications for underground mine backfilling operations.