Research on Properties and Microstructure of Waste Polyurethane/Crumb Rubber Composite Modified Asphalt

The disposal of waste polyurethane (WPU) poses a significant environmental challenge. This study investigates the use of WPU and crumb rubber (CR) as composite modifiers for asphalt, aiming to enhance binder high-temperature rheological behavior while offering an alternative recycling route for solid polymer waste. Formulated via high-shear blending across various modifier dosages, the WPU/CR composite asphalts underwent a comprehensive evaluation protocol. The binder's performance was systematically evaluated using conventional physical tests, rotational viscosity, temperature sweep, and multiple stress creep recovery (MSCR) tests. Microstructural and chemical mechanisms were analyzed via fluorescence microscopy (FM) and Fourier-transform infrared spectroscopy (FTIR). The results demonstrate that integrating WPU into crumb rubber-modified asphalt (CRMA) yields remarkable improvements in both high-temperature rheological stability and resistance to permanent deformation. This structural upgrade is driven by a two-fold synergistic effect: the physical swelling of the CR and WPU modifiers via the absorption of light asphalt fractions, coupled with the physical intertwining, particle reinforcement, and polymer network formation within the binder matrix. However, the microstructural analysis revealed a critical trade-off: excessive WPU content led to particle agglomeration and phase separation. WPU/CR composite-modified asphalt is a promising material, but the modifier ratio is critical for balanced performance. To achieve balanced overall performance, the study recommends a composite formulation combining the selected 15% CR reference matrix with 15% WPU. Ultimately, this work delivers a viable technical framework for the premium recycling of WPU within highway engineering.