A novel silica alumina-based backfill material composed of coal refuse and fly ash

► Coal refuse shows improvements in pozzolanic property from 20 °C to 950 °C. ► Fly ash has agglomeration phenomenon when thermal activated from 550 °C to 950 °C. ► For coal refuse, muscovite 2M1 gradually dehydroxylated to muscovite HT at 750 °C. ► 5% 750 coal refuse + 15% 20 °C fly ash presents an optimal design of backfill material.