Experimental and Microstructural Assessment of High-Plasticity Clay Stabilized with Recycled PVC Powder and Polyester...

High-plasticity clays present significant challenges in transportation infrastructure because of their low strength, high compressibility, and pronounced moisture sensitivity. This study investigates the effects of recycled polyvinyl chloride (PVC) powder and recycled polyester fibers, used individually and in combination, on the compaction behavior, unconfined compressive strength (UCS), and microstructural characteristics of a high-plasticity clay. PVC powder was incorporated at 5%, 10%, and 15%, while recycled polyester fibers were added at 0.5%, 0.75%, and 1.0% by dry weight of soil. Standard Proctor compaction, UCS, and scanning electron microscopy (SEM) analyses were performed to evaluate the engineering performance of the modified mixtures. The results showed that the incorporation of both PVC powder and recycled polyester fibers reduced the maximum dry unit weight of the clay, with 5% PVC and 0.5% fiber exhibiting the most favorable compaction characteristics. The specimen containing 15% PVC powder achieved the highest UCS (204.08 kPa), corresponding to an increase of approximately 108.6% compared with the untreated clay, whereas the specimen reinforced with 1.0% recycled polyester fiber exhibited an approximately 89.7% increase in compressive strength while maintaining greater deformation capacity. The hybrid mixture containing 5% PVC powder and 0.5% recycled polyester fiber produced a 53.7% improvement in UCS and exhibited a balanced stress-strain response. SEM observations revealed that PVC powder primarily enhanced the soil through physical void filling and particle rearrangement, whereas recycled polyester fibers improved the continuity of the soil skeleton through fiber bridging and mechanical interlocking. Overall, the results demonstrate that recycled PVC powder and recycled polyester fibers represent promising and environmentally sustainable stabilization materials for improving the engineering performance of high-plasticity clays used in transportation infrastructure.