Thermal, hydraulic and mechanical performances of cemented coal gangue-fly ash backfill

Cemented coal gangue-fly ash backfill (CGFB, a mixture of binder, coal gangue, fly ash and water) is introduced and applied to fill underground voids in coal mines. Once placed, the CGFB mixtures should have favorable stability and environmental performance, and these are closely related to the thermal, hydraulic and mechanical properties of the CGFBs. In this study, column and block experiments are conducted to investigate the coupled evolutions of the main performance characteristics (thermal, hydraulic and mechanical) of CGFB structures. A test apparatus is designed and equipped to investigate the thermal (temperature development), hydraulic (water drainage) and mechanical (lateral expansion) performances of CGFB columns under pressure in drained and laterally constrained conditions. The CGFBs are cured at room temperature and monitored for 30 days. Additionally, water drainage and uniaxial compressive strength (UCS) of CGFB blocks at different curing temperatures (20 and 50 °C) are also tested. The results indicate that the hydraulic and mechanical behaviors of the CGFBs are significantly affected by thermal factors (heat generated by binder hydration and heat transfer between the CGFB and its surroundings). This study will contribute to a better understanding of the thermo-hydro-mechanical behavior of underground CGFB structures, and thus a better design of stable and environment-friendly CGFBs.