Study on strength characteristics and hydration mechanism of composite cementitious material backfill based on titanium-extracted tailings

In order to study the physical and mechanical properties of backfill materials based on titanium-extracted tailings composite cementitious materials, mine backfill slurries were prepared using titanium-extracted tailings composite cementitious materials (TCM) and gold mine full tailings (GMT). The uniaxial compressive strength, fluidity, bleeding rate and pore distribution of the backfill body were studied, and the strength change law and hydration mechanism of the backfill body were analyzed by Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy (SEM) and other microscopic analysis methods. The results indicate that: (1)the compressive strength growth rate of TCM backfill specimens gradually increases with the extension of the curing period. Under the same curing time, the compressive strength of TCM backfill specimens exhibits an overall positive correlation with the cement-sand ratio; (2)the porosity of TCM backfill specimens ranges between 14% and 25%, with decreasing cement-sand ratio, both the quantity and size of internal pores in backfill specimens progressively increased; (3) the 70% concentration TCM slurry demonstrated excellent fluidity with a maximum of 610 mm, and its bleeding performance is better than that of cement group; (4)in the TCM full tailings backfill system, hydration reaction produces hydration products mainly composed of calcium silicate hydrate (C-S-H) gel and ettringite (AFt). In the later stages of the hydration reaction, the quantity of hydration products increases rapidly, resulting in a more compact structure of the backfill material. The research results provide a theoretical basis for the backfill application of composite cementitious material based on titanium-extracted tailings.