Performance of clay soil reinforced with PET plastic waste subjected to freeze-thaw cycles for pavement subgrade application

The freeze-thaw (F-T) cycle is a common weathering process that often occurs in cold climates, and it can deteriorate the mechanical performance of the subgrade soil, leading to pavement failure and economic loss. Plastic wastes have been adopted as a soil reinforcement element to improve the geotechnical properties and stability of expansive clay soils used as subgrade material. Previous research has mainly focused on the application of polyethylene terephthalate (PET) plastic waste to soil reinforcement under ambient temperature, but few studies have investigated the geotechnical performance of expansive clay soils reinforced with PET plastic waste under freeze-thaw conditions for pavement subgrade application. Moreover, there is a lack of knowledge on the dynamic properties of expansive clays modified with PET plastics exposed to the F-T process. This study conducted a series of mechanical experiments, including repeated load triaxial tests and unconfined compressive strength tests, for the first time to investigate the mechanical performance of expansive clay soil reinforced with different percentages of PET strips (i.e., 0, 1, 1.5, and 2% by the weight of dry soil) after being exposed to 0, 2, 5, and 8 F-T cycles. The experimental results showed that the F-T process significantly reduced the compressive strength and resilient modulus. However, the compressive strength and resilient modulus of the PET strips-reinforced samples were higher than those of the unreinforced samples after F-T cycles. The optimum content of PET strips was found to be 1% by weight of dry soil, as it exhibited the highest strength and stiffness under various F-T cycles.