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The traditional room-and-pillar mining method benefits from the use of unclassified tailings-based concrete (UTC) to reinforce X-shaped broken pillars, offering advantages such as tailings utilization, reduced demand for sand aggregates, increased pillar strength, and improved stability of mined-out areas. This study investigates the influence of polypropylene (PP) fiber dosage (0 %, 0.3 %, 0.6 %, and 0.9 %) on the macro-strength and microstructure of fiber-reinforced UTC for reinforcing broken rock (F-UTCRR), and analyzes the toughening and crack resistance mechanisms of the fibers. Uniaxial compressive strength (UCS) test and SEM were employed to examine compressive and microstructural features of F-UTCRR. The results indicate that fiber dosage significantly affects the stress-strain behavior of F-UTCRR. As fiber content increases, both peak stress and strain first increase, then decrease, with the F-UTCRR-0.6 mixture exhibiting the highest compressive and deformation resistance, showing a 6.6 MPa rise in uniaxial strength and a 0.9 % rise in peak strain rate. At the macroscopic level, fiber concentration influences crack types, with the dominant crack pattern evolving from 'tension-tension-shear mixing-shear' as fiber content increases. The fibers primarily function through the bridging effect, inhibiting crack propagation. At the microscopic levels, fibers mainly compact the matrix and enhance the strength by bonding and interfacial friction behavior. Among the indexes in this paper, the performance advantage of F-UTCRR with 0.6 % fiber content is significant. Consequently, the findings of the research provide a theoretical foundation to explore strength and failure behavior of F-UTCRR, with significant practical implications for improving pillar damage resistance, extending pillar service life, maintaining roof plate stability in mining areas, and certifying employee/equipment's security.
Jiang et al. (Thu,) studied this question.