Interfacial strength characteristics between modified iron tailings and profiled fibers under dry-wet and freeze-thaw environments

The interfacial properties of fibers and matrix materials have an important effect on the mechanical properties of fiber-reinforced materials. To study the role of fiber morphology and the environmental effects on the interfacial properties of fibers and matrix materials, the interfacial strength characteristics of undulation polypropylene fiber (UPF) and serrated polypropylene fiber (SPF) with cement-modified iron tailings (CIT) were analyzed through single-fiber pullout tests. The effects of curing age, freeze-thaw cycles, and dry-wet cycles on interfacial strength were analyzed. The energy dissipation during fiber pullout under different environmental conditions was verified, and the microscopic mechanism of interfacial strength change was determined. The results show the following: (1) The interfacial strength of UPF and SPF is positively correlated with curing age, while freeze-thaw and dry-wet cycles can impair their interfacial properties; also, the interfacial strength decreases substantially and tends to flatten out after 3 cycles. (2) The dissipation energy of UPF and SPF increases with curing age, but decreases as the number of dry-wet cycles and freeze-thaw cycles increases. The critical reinforcement length of UPF is better than that of SPF by 363% and 50% under freeze-thaw and dry-wet cycles, respectively. Also, its performance and reinforcement effect in reducing crack development under freeze-thaw and dry-wet environments are better compared to SPF. (3) The interfacial strength of the profiled fibers consists of adhesion and friction. Freeze-thaw cycles cause a significant damage to adhesion and friction, while dry-wet cycles mainly affect adhesion. Interfacial strength is related to the curvature of the fiber and the unconfined compressive strength of CIT, which follows a linear function.