Investigation of Strength Characteristics and Microstructure of Cemented Tailings Backfill

The strength of cemented tailings backfill (CTB) is influenced by multiple factors, with the type of cementitious material playing a crucial role in determining the strength of the backfill. To investigate the influence of two different cementitious materials on the strength of CTB, based on the fundamental physicochemical properties of tailings, flow characteristic tests and uniaxial compressive strength (UCS) tests of the backfill were conducted using a cementitious backfill slurry prepared from tailings. Representative proportioned backfill specimens were selected for X-ray diffraction (XRD) and scanning electron microscope (SEM) microstructural analysis to study the evolution patterns of backfill strength influenced by cementitious material type, cement-to-tailing (c/t) ratio, and slurry concentration. The results indicate that the tailings exhibit favorable gradation but unstable continuity. Furthermore, a high content of clay minerals such as kaolinite, along with the presence of fluorine (F) and phosphorus (P), adversely affects the strength of fillers. In terms of slurry flowability, the fluidity of cementation powder filling slurry is generally superior to that of cemented filling slurry. In identical conditions, the strength of cementation powder fillers at all ages is significantly higher than that of cement. As the c/t ratio decreases, the strength advantage of cementation powder fillers becomes even more prominent. Compared to cemented fillers, the hydrated product calcium silicate hydrate gel (C-S-H gel) in cementation powder fillers is more abundant, while the hydrated product calcium aluminate hydrate (CAH) is coarser. This microscopic structural difference explains the strength characteristics of the fillers.