Effects of cement content, polypropylene fiber length and dosage on fluidity and mechanical properties of fiber–toughened cemented aeolian sand backfill (FCASB)

Using aeolian sand (AS) for goaf backfilling allows coordination of green mining and AS control. Cemented AS backfill (CASB) exhibits brittle fracture. Polypropylene (PP) fibers are good toughening materials. When the toughening effect of fibers is analyzed, their influence on the slurry conveying performance should also be considered. Additionally, cement affects the interactions among the hydration products, fibers, and aggregates. In this study, the effects of cement content (8wt%, 9wt% and 10wt%), PP fiber length (6, 9 and 12 mm) and dosage (0.05wt%, 0.1wt%, 0.15wt%, 0.2wt% and 0.25wt%) on fluidity and mechanical propertity of the fiber–toughened CASB (FCASB) were analyzed. The results indicated that with increases in the three aforementioned factors, the slump flow decreased, while the rheological parameters increased. Uniaxial compressive strength (UCS) increased with the increase of cement content and fiber length, and with an increase in fiber dosage, it first increased and then decreased. The strain increased with the increase of fiber dosage and length. The effect of PP fibers became more pronounced with the increase of cement content. Digital image correlation (DIC) test results showed that the addition of fibers can restrain the peeling of blocks and the expansion of fissure, and reduce the stress concentration of the FCASB. Scanning electron microscopy (SEM) test indicated that the functional mechanisms of fibers mainly involved the interactions of fibers with the hydration products and matrix, and the spatial distribution of fibers. On the basis of single–factor analysis, the response surface method (RSM) was used to analyze the effects of the three aforementioned factors and their interaction terms on the UCS. The influence surface of the two-factor interaction terms and the three-dimensional scatter plot of the three–factor coupling were established. In conclusion, the response law of the FCASB properties under the effects of cement and PP fibers were obtained, which provides theoretical and engineering guidance for FCASB filling.