Mechanical and microstructural characterization of fiber-reinforced polyurethane-treated clays under freeze-thaw cycles

Expansive clays with high plasticity are vulnerable to deterioration under repeated freeze–thaw (F–T) cycles, posing challenges for infrastructure durability in cold climates. To enhance their resilience, this study explores a sustainable stabilization-reinforcement approach using polyurethane (PU) foam as a chemical binder and waste tire textile fibers (WTTFs) as mechanical reinforcement. Laboratory investigations encompassing unconfined compressive strength (UCS) and scanning electron microscopy (SEM) were performed to examine how different WTTF contents interact with PU stabilization in improving soil resistance to F–T cycles. The results revealed that while repeated F–T cycling led to notable strength degradation in all specimens, the presence of WTTFs significantly mitigated these losses. In particular, PU-treated soils reinforced with an optimal dosage of WTTFs exhibited superior durability, retaining 15% to 40% more strength post–F–T exposure compared to unreinforced or solely PU-stabilized samples. Microstructural observations confirmed these findings, highlighting enhanced interparticle bonding, reduced microcracking, and minimized mass loss and volumetric instability in the composite specimens. These outcomes demonstrate the synergistic potential of PU and WTTFs in enhancing the long-term mechanical performance of expansive clays under harsh environmental conditions. Incorporating recycled fibrous waste into polymer-stabilized soils offers a practical, eco-friendly strategy for improving the service life of earth structures in freeze-prone regions.