Experiment on hydration exothermic characteristics and hydration mechanism of sand-based cemented paste backfill materials

Cemented paste backfill technology can effectively control overburden movement, protect surface buildings and ecological environment. In this study, the early hydration exothermal characteristics, compressive strength evolution and hydration mechanism of sand-based cemented paste backfill materials (SCPB) were studied by hydration heat tests, uniaxial compressive strength tests, x-ray diffraction, scanning electron microscope and energy dispersive spectrometer tests; the hydration model of SCPB and fly ash were also constructed. The results show that: (1) the early hydration exothermic process of the SCPB can be divided into five stages: Dissolution stage, Induction stage, Acceleration stage, Deceleration stage and Slow deceleration stage. The heat release rates in the five stages are 5.64, 2.09, 3.63, 3.16 and 1.07 J·(g·h)-1, respectively; (2) the mechanical strength and elastic modulus of the SCPB increase with the increase of curing age; when the curing age of 7 d, the elastic modulus of the SCPB reaches 67.92% of the final value; (3) the primary hydration products of the SCPB are calcium silicate hydrate, ettringite, calcium hydroxide, Calcium carbonate and Calcium aluminate hydrate; (4) the hydration process of the SCPB can be divided into Dissolution stage, Hydration stage and Hardening stage, and the hydration process of fly ash experienced Adsorption stage and Hydration stage.