Assessment of the flowability and compressive strength of cemented paste backfills composed of muscovite-rich tailings: impact of admixtures

The increased prevalence of phyllosilicates such as muscovite in mine tailings and their adverse effects on the compressive strength of cemented paste backfills (CPBs) have recently attracted significant attention. This issue presents challenges for underground backfilling operations, underscoring the necessity for a comprehensive understanding and effective solutions. Admixtures can mitigate the increased water demand and loss of uniaxial compressive strength (UCS) by influencing the binder hydration process and the microstructure of the CPB, which are critical for determining the type and quantity of hydrates formed. This study examines the compatibility of selected admixtures in CPB containing different proportions of muscovite (0, 3, 8 and 18%) and evaluates their effectiveness in enhancing fluidity and compressive strength. The experimental program aims to reveal significant alterations in the mechanical properties of CPB with admixture (A1) at varying dosages (up to 3% by weight of cement). The investigation utilises one type of binder – general use Portland limestone cement (Type GUL) at a fixed binder rate (Bw) of 7%. The findings provide valuable insights into the application of admixtures to counteract the adverse effects of muscovite (phyllosilicate) on: 1) the water demand by decrease it to zero-water demand for low to medium muscovite-rich CPBs and up to 55.4% for high muscovite-rich CPB, 2) compressive strength by helping to gain up to 136% of UCS and, 3) the yield stress by decreasing it up to 58.5% .This article presents the potential of admixture to optimise complex and phyllosilicate-rich CPB mix formulations.