Biochar has been utilized as a renewable biomass resource to develop sustainable and eco-friendly pavements. This study focuses on the influence of biochar as an asphalt modifier on the improvement of high-temperature performance of asphalt. A series of tests were performed to comprehensively evaluate the high-temperature performance of the biochar modified binder. The interaction mechanism between the biochar and the binder was explored using scanning electron microscopy and Fourier-transform infrared spectroscopy (FTIR). The results indicated that the complex modulus and penetration of the biochar-modified asphalt binder could be increased by up to 35% and 36.5%, respectively, compared with those in case of the matrix asphalt, thereby improving the deformation resistance. In addition, the observed increase in the complex modulus, rutting factor, and viscosity-temperature index contributed to the improvement of temperature sensitivity and anti-rutting properties. These relationships are attributed to the fact that biochar has a fibrous porous structure and forms a skeleton and stiffening zone in the binder. Although biochar has a negative effect on the low-temperature properties of the binder, this can be alleviated by controlling the biochar content. Moreover, the FTIR results showed that no new chemical functional groups appeared after the incorporation of biochar into the binder. The internal chemical environment of the biochar-modified asphalt binder was different from that of the matrix asphalt. In conclusion, biochar is feasible as a modifier for binders owing to its high-temperature properties.

In order to solve the problems caused by asphalt diseases and prolong the life cycle of asphalt pavement, many studies on the properties of modified asphalt have been conducted, especially polyurethane (PU) modified asphalt. This study is to replace part of the styrene-butadiene-styrene (SBS) modifier with waste polyurethane (WP), for preparing WP/SBS composite modified asphalt, as well as exploring its properties and microstructure. On this basis, this paper studied the basic performance of WP/SBS composite modified asphalt with a conventional performance test, to analyze the high- and low-temperature rheological properties, permanent deformation resistance and storage stability of WP/SBS composite modified asphalt by dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests. The microstructure of WP/SBS composite modified asphalt was also observed by fluorescence microscope (FM) and Fourier transform infrared spectroscopy (FTIR), as well as the reaction between WP and asphalt. According to the results of this study, WP can replace SBS as a modifier to prepare WP/SBS composite modified asphalt with good low-temperature resistance, whose high-temperature performance will be lower than that of SBS modified asphalt. After comprehensive consideration, 4% SBS content and 15% WPU content (4 S/15 W) are determined as the suitable types of WPU/SBS composite modified asphalt.