Reinforcing effects of polypropylene on energy absorption and fracturing of cement-based tailings backfill under impact loading

Polypropylene (PP) fiber-reinforced cement-based tailings backfill (FRCTB) is a green compound material with superior crack resistance and has good prospects for application in underground mining. However, FRCTB exhibits susceptibility to dynamic events, such as impact ground pressure and blast vibrations. This paper investigates the energy and crack distribution behavior of FRCTB under dynamic impact, considering the height/diameter (H/D) effect. Split Hopkinson pressure bar, industrial computed tomography scan, and scanning electron microscopy (SEM) experiments were carried out on six types of FRCTB. Laboratory outcomes confirmed fiber aggregation at the bottom of specimens. When H/D was less than 0.8, the proportion of PP fibers distributed along the θ angle direction of 80°–90° increased. For the total energy, all samples presented similar energy absorption, reflectance, and transmittance. However, a rise in H/D may cause a rise in the energy absorption rate of FRCTB during the peak phase. A positive correlation existed between the average strain rate and absorbed energy per unit volume. The increase in H/D resulted in a decreased crack volume fraction of FRCTB. When the H/D was greater than or equal to 0.7, the maximum crack volume fraction of FRCTB was observed close to the incidence plane. Radial cracks were present only in the FRCTB with an H/D ratio of 0.5. Samples with H/D ratios of 0.5 and 0.6 showed similar distributions of weakly and heavily damaged areas. PP fibers can limit the emergence and expansion of cracks by influencing their path. SEM observations revealed considerable differences in the bonding strengths between fibers and the FRCTB. Fibers that adhered particularly well to the substrate were attracted together with the hydration products adhering to surfaces. These results show that FRCTB is promising as a sustainable and green backfill for determining the design properties of mining with backfill.