Mechanical properties and damage evolution mechanisms of cemented backfill with tailored particle size range of coal gangue aggregates

The aggregate size distribution and curing age are the key factors affecting the mechanical properties of cemented backfill, which can significantly affect the mechanical properties of cemented backfill. To study the mechanical properties and damage evolution characteristics of backfill with different aggregate size range under different curing ages, uniaxial compression and electron microscope scanning tests were carried out on the backfill. The mechanical properties, microstructure and the damage evolution characteristics of the backfill with different aggregate size range are studied. The results show that the stress-strain curve morphology is generally consistent across different particle size ranges. The compressive strength and elastic modulus of backfill with different particle size range increase gradually with the extension of curing age, and the extension of curing age is more conducive to improving the compressive strength of backfill with particle size range of 5-10 mm. The elastic modulus and compressive strength of the backfill with particle size range of 5-10 mm are the highest among all specimens, and they increase by 335 % and 411 %, respectively, with the increase of curing age. The backfill with a particle size range of 0-5 mm under uniaxial compression maintains high integrity, while the extension of curing age can suppress the propagation and penetration of failure cracks. The density of the backfill microstructure is the best when the aggregate size distribution is 0-5 mm, and the extension of curing age can reduce the size and range of the void structure in the backfill. The damage evolution of backfill with different particle size distributions shows the characteristics of "flat-slow growth-accelerated growth-linear growth". The damage value of the backfill with aggregate size of 0-5 mm increases most slowly, and the extension of curing age can inhibit the damage value growth rate.