Freeze–Thaw Durability of a High-Plasticity Clay Treated with Polymeric Binder and Waste Fibrous Materials

High-plasticity soils are highly susceptible to degradation given freeze-thaw (F-T) cycles, particularly in cold climates. Stabilizing these soils with sustainable polymeric binders and reinforcing them with fibrous materials offers a promising strategy to improve their durability and mechanical performance. This paper investigates the effects of consecutive F-T cycles on the mechanical behavior of an expansive clay stabilized with polyurethane (PU) foam and reinforced with varying percentages of waste tire textile fibers (WTTFs). A comprehensive series of experimental tests, including unconfined compressive strength (UCS), indirect tensile strength (ITS), ultrasonic pulse velocity (UPV), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR), were performed. Results showed that increasing the number of F-T cycles generally reduced the UCS, ITS, and UPV of tested samples. However, these reductions were significantly more pronounced in untreated and PU-treated soils compared to those reinforced with WTTFs. When added in optimal proportions, WTTFs markedly enhanced the durability of PU-treated clay, with improvements in strength retention ranging from 15% to 40% after F-T exposure. These enhancements were supported by microstructural evidence, including improved bonding, reduced crack propagation, and lower mass loss and volume change. Overall, the PU-WTTF composite demonstrated high potential in preserving mechanical performance given repeated F-T action. These findings suggest that incorporating WTTFs into PU-stabilized clays offers a practical and sustainable approach to improving the long-term behavior of earth-based construction materials, especially in cold regions exposed to harsh climatic conditions.