Development of cement-based self-stress composite grouting material for reinforcing rock mass and engineering application

Grouting is an important method to reinforce fractured rock mass in underground engineering. To improve the grouting reinforcement effect of fractured rock mass, the theory of self-stress grouting reinforcement was put forward for the first time, and the self-stress grouting material was developed. The swelling stress of self-stress grouting material was tested by self-developed testing device to analyze the relationship between swelling stress and expansive agent content. Then, with cement, bentonite, silica fume, FZ expansive agent, accelerator, water reducer and water as raw materials, the effects of bentonite-cement ratio, silica fume content, accelerator content and water reducer content on the fluidity, initial setting time, uniaxial compressive strength at 3 days and 28 days of grouts were investigated by orthogonal test. Finally, the optimum proportion of the cement-based self-stress composite grouting material was applied to reinforce crushed coal blocks and the surrounding rocks of mine roadway, respectively. The results shown the optimum expansive agent content of the grout was 10%, corresponding swelling stress of 0.82 MPa. The proportion of the cement-based self-stress composite grouting material was bentonite-cement ratio of 1, FZ expansive agent content of 10%, silica fume content of 6%, accelerator content of 2.9%, and retarder content of 2.5%. The uniaxial compressive strength of the crushed coal blocks after reinforcement was 12.1 MPa, which was greater than the strength of the original coal. The cement-based self-stress composite grouting material had significant effect on the reinforcement of the surrounding rocks of mine roadway.