Hybrid Stabilization of Kaolin Clay Using Biopolymer, Polypropylene Fiber, and Trivoltherm Waste: Mechanical Performance and Freeze–Thaw Durability

This study investigates the mechanical behavior and durability performance of kaolin clay stabilized using a hybrid system composed of Xanthan Gum biopolymer, polypropylene fibers, and Trivoltherm waste fibers. Experimental studies were designed according to the Taguchi L16 orthogonal array to evaluate the effects of different additive combinations. Unconfined compressive strength tests were performed after curing periods of 7, 28, and 90 days, while durability behavior was assessed through 5 and 10 freeze–thaw cycles. In addition, scanning electron microscopy analyses were conducted to investigate the microstructural characteristics of the stabilized soils. The results indicated that strength increased significantly with curing time, reaching a maximum value of 1186 kPa after 90 days. Statistical analyses showed that Xanthan Gum was the dominant parameter affecting strength development, contributing approximately 57–63% to the unconfined compressive strength behavior. Fiber additives also improved ductility, crack resistance, and freeze–thaw durability through reinforcement and crack-bridging mechanisms. The best-performing mixtures exhibited markedly lower strength losses under freeze–thaw conditions compared with untreated soil specimens. Analysis of variance results confirmed that the investigated parameters were statistically significant (p < 0.05), and the developed models showed high prediction accuracy (R2 > 85%). Overall, the findings demonstrate that the synergistic interaction between the biopolymer matrix and fiber reinforcement system provides an effective and sustainable hybrid stabilization approach for improving the engineering performance of clay soils.