Ling Hu, Peiyuan Zhou, Huadong Guan, Daopei Zhu
• Investigated effects of PP fiber length (3–19 mm) and content (0.2 %–0.8 %) on LSCB fluidity, strength, and microstructure. • Identified optimal fiber (0.6 %, 6 mm) boosting 28 d UCS by 31 % and revealing the crack-bridging mechanism. • Established a double-log fluidity model (R 2 = 0.96) describing exponential decay of fluidity with fiber parameters. This study examines the effects of polypropylene (PP) fiber content and length on lithium slag cement backfill (LSCB), which is of great significance for promoting the resource utilization of industrial solid waste and improving the engineering performance of mine backfill bodies. Fluidity tests show that increasing fiber content and length reduces slurry fluidity. Uniaxial compression tests reveal that fiber-reinforced samples exhibit similar stress–strain behaviors, with shorter fibers enhancing initial strength but offering limited large-deformation resistance. Under the same fiber content (0.2 % − 0.8 %), compared with short fibers (3 mm) and long fibers (19 mm), the reinforcing effect of medium-length fibers (6 mm, 12 mm) was more significant. When the PP fiber content was 0.6 % and the length was 6 mm, the 28-day compressive strength of LSCB was 31 % higher than that of the blank group (3.46 MPa) and reached 4.53 MPa. SEM analysis indicates that PP fibers provide a skeletal structure within hydration gels, while adhesion, friction, and cohesion between fibers and the matrix help resist crack propagation. An economic feasibility analysis, it was concluded that adding 0.6 % − 6 mm PP fibers is feasible in engineering applications.