Study on the performance and microscopic mechanism of activated crumb rubber synergistic polyurethane composite modified asphalt

The purpose of this study was to reveal the macroscopic performance and microscopic mechanism of the synergistic effect of activated crumb rubber (ACR) and polyurethane (TPU) on asphalt binders, and to promote the resourceful utilization of polymer materials in pavement engineering. In the laboratory, the crumb rubber was subjected to microwave activation treatment, and its activation effect and microstructure characteristics were investigated. Secondly, the performance of composite modified asphalt with different ACR and TPU contents was analyzed through traditional physical property tests. The optimal dosage was determined based on the optimized design of the response surface method, and the dispersion state was characterized using digital fluorescence images. Finally, the rheological properties and microscopic mechanisms of the modified asphalt were analyzed using temperature sweep tests, linear amplitude sweep (LAS) tests, low-temperature bending beam rheological (BBR) tests, and Fourier transform infrared spectroscopy (FTIR) tests. The results showed that the surface of the crumb rubber became fluffy and the internal cross-linking bonds were broken after activation, with the optimal microwave treatment time being 4 min. Based on the response surface method, the optimal dosages of ACR and TPU were determined as 20 % and 5 %, respectively, at which the dispersion state of the modified asphalt in the digital fluorescence images was best. The synergistic effect of ACR and TPU significantly improved the rheological properties and fatigue life of the asphalt binder during its service life. In addition, the addition reaction between the isocyanate in TPU and the carboxylic acid in the aromatic compounds of the asphalt occurred, and the swelling and development process of the activated crumb rubber played a connection role between the TPU and asphalt matrix, thus enhancing the stability of the spatial structure. The research results can provide scientific guidance for the application and promotion of ACR/TPU composite modified asphalt technology.