Performance and mechanism of bio-oil "chain-pyrolytic" crumb rubber and SBS composite modified asphalt

To enhance the high-temperature performance of bio-oil degraded crumb rubber (CR) modified asphalt, a "chainpyrolysis" treatment of CR was conducted using waste frying oil. This involved adding the CR in batches to the high-temperature waste oil to increase the CR-to-oil ratio, and control the degree of CR degradation. The effects of pyrolysis batch on the physicochemical properties of CR were evaluated through solubility, particle size analysis, thermal analysis, and scanning electron microscope. The performance and mechanism of "chain-pyrolytic" crumb rubber/Styrene-Butadiene-Styrene composite modified asphalt (PCR/SBSCMA) were investigated using conventional performance tests, rheological tests, Fourier transform infrared spectroscopy, fluorescence microscopy, and atomic force microscope. Results show that during the "chain-pyrolysis" process of CR, the sol content decreases, reaching a plateau after 3 batches and decreasing after 7 batches, indicating a decline in degradation degree. The particle size increases, whereas the rubber hydrocarbon content marginally rises, and the surface texture complexity diminishes with each batch. With an escalation in pyrolysis batch of CR, the penetration of the PCR/SBSCMA hits a minimum, the ductility gradually diminishes and the softening point slowly increases after 3 batches. The phase angle and non-recoverable creep compliance decrease, while the complex shear modulus and recovery rate enhance, significantly boosting the elasticity of the modified asphalt. The preparation of PCR and modification of PCR/SBSCMA contain the cleavage of sulfur bonds, the formation of oxygen functional groups, and the CR swelling. The uniform dispersion of polymer phases, presence of fine carbon black, and establishment of a stable colloidal system contribute the high-temperature mechanical properties and stability of the PCR/SBSCMA. The reduction of light components in the PCR/SBSCMA caused by swollen CR results in diminished surface roughness, disappeared "bee-like" structure, and improved homogeneity, which is conducive to low-temperature ductility. Overall, the PCR/SBS composite modification method promotes the high-quality and sustainable development of the utilization of waste tires and biomass in asphalt pavement.