Effect of RTPF on Fracture Properties of Cement-Stabilized Soil

Recycled tire polymeric fiber (RTPF) is a type of nylon fiber recovered from end-of-life tires. Depending on the processing stages, RTPF exists in two forms, fibrils (FS) and fiber bundles (FB). Although fiber reinforcement has been widely investigated for cement-stabilized soils, the fracture behavior and reinforcing mechanisms of RTPF remain insufficiently understood. Three-point bending tests using DIC, CT, and SEM analyses were conducted. The results indicate that RTPF delays crack initiation, increasing both the time interval from initiation to fracture and the ultimate crack width. Flexural strength increases with RTPF content and exhibits a power-law relationship. Both FS and FB significantly improve unstable fracture toughness, increasing it from 0.19 MPa·m1/2 in the control specimen to 0.37 MPa·m1/2 and 0.78 MPa·m1/2, respectively. Fracture energy increases by 49% and 228%, respectively. The peak reinforcing efficiency was achieved at the RTPF content of 0.2–0.4% for FS and 1–2% for FB. The higher distribution coefficients and lower orientation reflect an isotropic fiber distribution, which is beneficial for inhibiting multi-directional crack propagation. A calculation method was developed to estimate fracture toughness from the fiber reinforcing parameter, with the findings showing good agreement with experimental results. These findings demonstrate the feasibility of utilizing RTPF as a sustainable reinforcement material for improving the fracture resistance of cement-stabilized soils in geotechnical engineering applications.