Mechanical properties and fractional-order creep constitutive model of steel fiber-reinforced coal gangue-based CLSM
To promote the high-value utilization of coal gangue, this study developed a steel fiber-reinforced coal gangue-based controlled low-strength material (CLSM) as a green backfill material. The effects of fiber content (0%–2.0%) on its mechanical properties were investigated, and a fractional-order creep constitutive model was established based on short-term creep tests. The results show that with increasing fiber content, the compressive strength, peak strain, and elastic modulus all exhibit a trend of first increasing and then decreasing. When comprehensively considering stiffness, strength, and deformation performance, the optimal fiber content range is 1.0%–1.5%. The creep behavior exhibits significant stress dependence: deceleration creep under low stress, ‘deceleration + steady-state’ creep under medium stress, and full three-stage ‘deceleration + steady-state + acceleration’ creep under high stress. Fiber content nonlinearly regulates the creep behavior, with peak stress and peak strain reaching maximum at Vf = 1.5%, while performance deteriorates at Vf = 2.0% due to fiber agglomeration. Scanning electron microscopy analysis reveals that an appropriate fiber content (Vf = 1.5%) reduces porosity and enhances material compactness through physical filling and interface optimization. To overcome the limitations of integer-order models, fractional derivative theory was introduced to construct a nonlinear constitutive model capable of describing the entire creep process under short-term loading conditions, and its validity was verified against the experimental data. The research findings provide a reference for the resource utilization of solid waste and the application of novel backfill materials in backfill engineering.