A comparative study on the workability, mechanical properties and microstructure of cemented fine tailings backfill with different binder

Abstract

With the increasingly prominent problems of cement cemented fine tailings backfill (CFTB), the demand for higher performance, economical, and low-carbon new binder is constantly increasing. This paper comparatively studies the workability and mechanical properties of ordinary Portland cement (PC) and two types of new binders (SC and SGL) CFTB. Additionally, the microstructural and gel products of CFTB are analyzed by hydration heat, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), thermos-gravimetry (TG), and mercury intrusion porosimetry (MIP). The results reveal that compared to CFTB-PC, CFTB-SC and CFTB-SGL exhibit reduced fluidity and bleeding rates, alongside increased yield stress and plastic viscosity. CFTB-PC sets and hardens rapidly, but its uniaxial compressive strength (UCS) increases slowly. CFTB-SC and CFTB-SLG set and harden more slowly than CFTB-PC, but their UCS increases more rapidly. The 3 d UCS of CFTB-SC and CFTB-SGL surpasses that of CFTB-PC, and the 7 d-360 d UCS reaches 1.66–2.66 times that of CFTB-PC. The 3 d-14 d UCS of CFTB-SC is lower than that of CFTB-SGL, but the 28 d-360 d UCS is 13.78 % higher than that of CFTB-SGL on average. The hydration rate and total hydration heat release follow the order PC > SC > SGL. The hydration products of CFTB-PC mainly consist of fibrous C-S-H gel with unidirectional distribution, while those of CFTB-SC and CFTB-SGL are characterized by foil-like C-S-H gel with three-dimensional non-directional distribution and needle bar-like ettringite with skeleton support function, facilitating closely embedded with fine tailings. The pores in CFTB-PC are predominantly large pores (d ≥ 1000 nm), whereas those in CFTB-SC and CFTB-SGL are mainly transition pores (10 nm ≤ d < 100 nm) and capillary pores (100 nm ≤ d < 1000 nm). The research results provide theoretical guidance for the development of new filling binder.