Research and application of micro-nano inorganic grouting materials

As the depth of coal mining has increased gradually, the large-deformation issue of the strata of roadways at 1 000 m deep or more needs to be solved urgently. The strata control and intelligent mining technology in coal mines at 1 000 m deep, a national key research and invention program, proposes a "three-in-one" cooperative control technology, which is for bolting-grouting-destressing of coal mine roadways. The key point for the modification of grouting is that the specific modified material should possess high permeability and early strength. In this study, a kind of micro-nano inorganic grouting material has been developed using raw materials including sulphoaluminate cement clinker, gypsum and lime, in combination with the optimization of the mixing ratio and ultra-fine grinding methods. The particle size, specific surface area, compressive strength, bleeding rate and setting time of this material have been tested. The self-made grouting simulation system was used to test the effect of micro-nano inorganic grouting materials strengthening the coal body. Finally, this modified material was put into field application in Kouzidong Mine, China. The experimental results of material performance show that the optimal mass ratio of sulphoaluminate cement clinker to gypsum to lime is 10: 8: 2.After ultra-fine processing, the particle size of the material reaches 6.7 μm, and the specific surface area is 1 200 m2/kg, meeting the micro-nano level. When the water-cement ratio is 1.0, the compressive strength at 6 hours is 6.8 MPa, the bleeding rate is as low as 2.8%, and the initial setting time is 10 minutes. The results of coal grouting reinforcement simulation show that the strength of coal samples subjected to grouting has been increased by 24.4%. The results of field engineering application manifest that the pullout force of anchor bolts after being subjected to grouting has been increased by 2 times. These may be due to that the slurry fills coal cracks, enhancing the integrity of coal. In addition, it was observed by SEM that the slurry can pass through the 10 μm cracks, suggesting good permeability. Compared with traditional cement-based grouting materials, the micro-nano inorganic grouting materials have higher permeability and early strength. Compared with organic chemical grouting materials, the micro-nano inorganic grouting materials are non-combustible with much lower cost and better safety, due to their inorganic mineral components. © 2020, Editorial Office of Journal of China Coal Society. All right reserved.