Study on high-performance spraying self-healing material for gas sealing in coal mines

To overcome the problems of poor toughness and ease of cracking failure of inorganic spraying materials for gas sealing, this study proposes to modify traditional cement-based materials through the addition of slag, CaSO4 whiskers and MgO. The optimal composition of the high-performance sealing material (HPSM) was determined to be a mass ratio of slag to cement of 0.5, and CaSO4 whisker and MgO content of 7.5 wt% and 2.5 wt%, respectively. The results showed that: (1) slag participates in the hydration reaction; (2) CaSO4 whiskers promotes slag to form needle-like ettringite crystals, which increases the ability of HPSM to withstand bending and resist matrix shrinkage; (3) MgO is slowly hydrated in the connected pores of the system to form MgCO3 which fills the pores and increases the matrix strength; (4) when HPSM cracks, unreacted CaO in the crack produces a large amount of CaCO3 humid environments, which promote the self-healing of cracks. The results of small-scale gas sealing tests showed that HPSM can completely plug the gas at pressures of ≤0.075 MPa after 1 day and with a coating thickness of 5–10 mm.