Research and application of inorganic and organic composite grouting reinforcement materials in deep weak rock

In response to the problems of large deformation, fracture closure and poor permeability of the surrounding rocks in the weak rock roadways of the 1 000 m or deeper coal mines, it is required that the grouting material has good injectability, fast solidification speed, high early strength, and strong bonding performance. A new method of synergistic preparation of inorganic grouting materials was designed using “component optimization + ultra-fine + nano-reinforcement + organic modification”. An inorganic grouting material with an optimum composition ratio of 50∶40∶10 for the ternary cementing system of calcium sulphate aluminate, gypsum and lime was developed. After ultra grinding, the compressive strength of the concretion increased by 163.0% within 4 hours, achieving initial early strength and rapid solidification. A nano-lithium-aluminium hydrotalcite reinforcement material with synergistic effects of nano-nucleation-induced crystallization and lithium ion promotion was developed, resulting in a 183.7% increase in the 2 h strength of the ultra grinding grouting material. The organic modifier with directional coupling effect at the coal-rock interface was synthesized, which formed a bridge through bonding with the grout and coal interface, significantly improving the bonding between the slurry concretion and the coal rock interface. The synergistically prodeuced inorganic-organic composite grouting reinforcement materials has small particle size (D95<10 μm), fast setting (<8 min), high early strength (2 h strength 11.5 MPa), and strong bonding performance (sandstone bonding strength 3.12 MPa). The inorganic-organic composite grouting reinforcement materials with “high early strength, high injectability and high bonding” properties for weak rocks in deep mines have been developed. The field application test adopted high-pressure grouting method, and the grout can be injected into large and micro cracks of the coal sample, connecting isolated cracks to achieve high-pressure splitting, and the loose coal mass was compacted. Microscopic observation showed that the grout under high pressure injection can increase the fissure opening and inject more grout into microfissures. Finally, the development direction of grouting materials in the future is proposed.