Freeze–Thaw Resistance and Microstructure of Reused Waterborne Unsaturated Polyester Concrete from PET Recycled Material for Pothole Repair of Asphalt Pavement

Recycling and application of polyethylene terephthalate (PET) bottles in road engineering is a promising utilization strategy for sustainable development. However, few studies have investigated the internal microstructure and the attenuation law of freeze–thaw (FT) resistance of waterborne unsaturated polyester concrete (WUPC) made from PET recycled material for pothole repairing mixture in asphalt pavement. In this study, waterborne unsaturated polyester resin (UPR-WEP) was prepared via alcoholysis and copolymerization synthesis of PET, as well as inversed-phase emulsification. The early-age hydration and kinetics characteristics were analyzed based on the Krstulović–Dabić model. Qualitative and quantitative analyses of the hydration products were conducted using microcosmic detection. The morphological characteristics of micropores were investigated utilizing fractal dimension algorithms. Quantitative analysis of the FT-resistance attenuation and the microcrack evolution were conducted by combining periodic monitoring and digital image processing (DIP). The experimental results demonstrated that a wraparound effect of UPR-WEP could retard the hydration process, manifesting as delays of the induction and acceleratory periods, and the reduction of cumulative hydration heat and exothermic rate. A rational dosage of UPR-WEP had a replenishing and refining effect on the interior pores and decreased the variability and complexity of the pore structure of WUPC, coupled with the formation of a cross-linked interpenetrating UPR-WEP reticular structure inside matrix, which increased FT resistance. After 350 FT cycles, 3%–6% UPR-WEP could delay the progress of microstructure deterioration, manifesting as a 27.58%–30.32% and 16.41%–18.56% decrease in area density and maximum length crack, respectively, and an increase in the crack complexity and inhomogeneity at the microscopic scale; from the macroscopic perspective, UPR-WEP could retard the emergence of the accelerated destruction stage, characterized as an 17.05%–32.52% increase in the denuded amount, and a 14.38%–26.59% decrease in the dynamic elasticity modulus.