Modification of grouting materials and mechanical properties of coal slurry couplings

Abstract

Overrunning grouting is used to reinforce the weak zone of the large mining face to prevent accidents, such as flake gangs and roofing, caused by surrounding broken rock and soft coal body. In this study, hydroxypropyl methyl cellulose (HPMC) was used to improve the bonding performance of cement. The influence mechanism of HPMC on cement hydration was analyzed from the perspective of the chemical composition at the microscopic level by testing the properties of the modified material to comprehensively investigate the performance of the material. The results revealed that (1) a novel type of grouting material obtained by adding a certain proportion of HPMC to ultrafine cement effectively improved slurry performance and enhanced the grouting effect; (2) the modification effect was the best when 0.5 wt% HPMC was added. Furthermore, the stability of cement slurry increased by 16.5 %, and the initial setting time was delayed to 2945 min, which provided sufficient time for the slurry to penetrate fractured coal rock; (3) HPMC changed the polymerization morphology of cement particles in the slurry and induced the reaction of large particles with ultrafine cement particles to form an elastic network structure in the solution, which was adsorbed on the surface of the coal body to enhance bonding performance; (4) HPMC changed the pore structure of the specimen, provided space for the formation of alumina, and polymerized with cement particles to form super flaky and bundled aluminite. It improved the mechanical properties of the added solids; and (5) HPMC-modified cement slurry and the added solids form the mutual bite, calcium alum interspersion, and network elastic suction cups, which improved the bonding performance of the coal slurry coupling by 172.8 times and boosted the tensile strength of coal slurry coupling.