The Influence of Coal Gangue Particle Gradation on the Performance of Inorganic Foamed Paste Backfill Materials

The issue of top contact in paste backfill materials is a common technical challenge in coal mine filling processes, and overcoming this problem has become a significant research direction in current studies and engineering practices. This paper utilizes coal gangue as aggregate and hydrogen peroxide as a foaming agent to prepare foamed paste backfill materials. Three close-packing theories were employed to investigate the effects of different coal gangue particle gradations on the mechanical properties, expansion ratio, water absorption, and dry density of foamed paste backfill materials under the same foaming agent content. The hydration mechanism and pore structure evolution were analyzed using XRD, SEM, and OSM techniques. The results indicate that when the hydrogen peroxide addition is 5%, the foamed paste backfill material regulated by MAA gradation theory exhibits the best comprehensive performance, achieving a 28-day compressive strength of 0.89 MPa, an expansion ratio of 155.5%, and a dry density of 1.24 g/cm3. The regulation of coal gangue aggregate particle gradation not only improves the foaming efficiency but also allows the formation of CH to fill the material pores, enhancing the overall structural support capacity and forming a closer microstructure. This research provides new insights into controlling the properties of foamed paste backfill materials.