Mechanism of Sodium Percarbonate and HPMC on the Properties of Expansive Cemented Tailings Backfill: Microstructure and Hydration

Underground mines frequently encounter inadequate contact between the cemented tailings backfill (CTB) and the stope’s roof due to consolidation shrinkage in the CTB, which significantly affects mining safety. The purpose of this study is to solve the problem of insufficient contact between CTB and the roof by preparing an expansive cemented tailings backfill (ECTB). The expansion behavior, mechanical strength, hydration mechanisms, and microstructural characteristics of ECTBs with different contents of expansive agents and foam stabilizers were systematically studied through methods such as single free surface expansion rate test, fluidity test, uniaxial compression test, CT scanning, scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric-differential thermal analysis (TG-DTG). The research results demonstrate that (1) When the dosage of stabilizing expansion agent is 0, as the dosage of expansion agent increases from 0.5 wt% to 1 wt%, the expansion rate of the ECTB’s single free surface increases from 1.00% to 30.01%. At the same time, the uniaxial compressive strength (UCS) decreases from 2.38 MPa to 1.03 MPa. The flowability of the filling slurry decreases from 18.75 cm to 17.75 cm. (2) With the dosage of expansion agent kept constant, as the dosage of stabilizing expansion agent increases from 0 wt% to 0.3 wt%, the expansion rate of the filling body’s single free surface initially increases and then decreases. The UCS shows a trend of first decreasing and then increasing. The slurry spreadability gradually decreases as the dosage of the stabilizing expansion agent increases. (3) The expansion agent leads to an increase in the total porosity and average pore diameter of the CTB, while reducing pore uniformity and sphericity and enhancing pore connectivity. Additionally, the OH⁻ and CO₃²⁻ ions produced from the decomposition of the expansion agent consume Ca²⁺, which inhibits the formation of CH and Aft, promotes the precipitation of secondary CaCO₃, and subsequently delays the hydration process. (4) Foam stabilizers can improve the stability of bubbles, thereby increasing the expansion rate, while optimizing the pore size distribution, inhibiting bubble coalescence, and reducing the number of connected pores, thus promoting the formation of relatively independent pore structures.