Flexural properties and damage evolution laws of scrap tire steel fiber-reinforced constructional backfill body

The constructional backfill body (CBB) serves as an underground mining structure intended to form a stable void space within the goaf. However, CBB typically exhibits high brittleness and poor flexural performance. In this study, scrap tire steel fiber (SSF) was utilized to enhance the properties of CBB, and the effects of varying SSF dosages (0 %, 0.5 %, 1 %, and 1.5 %) on the three-point flexural properties and the damage evolution of the scrap tire steel fiber-reinforced constructional backfill body (SSF-reinforced CBB) were investigated. The results indicated that incorporating 1 % SSF significantly enhanced the mechanical properties of CBB. Specifically, the initial cracking flexural strength , peak flexural strength, initial cracking deflection, peak deflection, stiffness, initial cracking toughness and peak toughness of the modified CBB increased by 70.99 %, 55.72 %, 19.05 %, 19.61 %, 104.86 %, 60 %, and 100 %, respectively; the toughness at post-peak load (50 % of the peak load) of increased by 655 % compared to the control group. This indicates that 1 % dosage of SSF optimally enhances damage tolerance in the tested materials. Acoustic emission testing results showed that the incorporation of SSF significantly reduced both the ringing count and the fluctuation amplitude of the b- value during the fracture of the CBB, indicating that the addition of SSF can enhance the crack-resisting capabilities of the CBB. However, incorporating excessive SSF may lead to the formation of weak structural planes within the SSF-reinforced CBB, thereby reducing its flexural performance and damage resistance. Therefore, the optimal dosage of SSF in engineering applications is recommended to be 1 %. • A novel approach was proposed to improve the flexural properties of CBB using SSF. • The impact of SSF on the flexural properties of CBB was investigated. • The unique attributes of SSF and its advantages and disadvantages were discussed. • The engineering suggestions for SSF-reinforced CBB were given.