Enhancing the Mechanical and Rheological Properties of Coal-Based Geopolymer Grouting Materials with Nano-SiO2 and Polypropylene Fibers

In order to address the ineffective utilization of industrial solid wastes-particularly fly ash-under the "coal-power integration" model, and to improve the performance of coal-based solid waste geopolymer grouting materials (CBGWG) under dynamic water conditions, this study selected fly ash and coal gangue as the main raw materials to jointly prepare dynamic water grouting slurry. The effects of nano-SiO₂ and polypropylene fibers (PPF) on gelation time, initial setting time, bleeding rate, apparent viscosity, compressive strength, and flexural strength were systematically investigated. The experimental results indicate that when the nano-SiO₂ content was increased to 1%, the water separation rate decreased by 85.8%, viscosity increased by 17.5%, and both gelation time and initial setting time were reduced by 51.5% and 18.6%, respectively. At a nano-SiO₂ content of 0.75% and a PPF dosage of 1.5%, the compressive strength and flexural strength increased by 43.3% and 53%, respectively. However, when the PPF dosage was further increased to 2%, fiber agglomeration occurred during mixing, impairing uniform dispersion. Nano-SiO₂ predominantly enhanced the early stiffness of the consolidated body, while PPF significantly improved ductility, residual load-bearing capacity, and energy dissipation, albeit at the expense of some stiffness. These two modifiers exhibited complementary effects in improving the mechanical properties of the grouting material. The optimal dosages of nano-SiO₂ and PPF were determined to be 0.75% and 1.5%, respectively, achieving the best balance between mechanical properties and workability.