Study on Rheological Properties of SBS/Crumb Rubber Modified Direct Coal Liquefaction Residue Asphalt Prepared Through an Extraction–Blending Process

To address the insufficient low-temperature performance of asphalt modified with direct coal liquefaction residue (DCLR), this study proposed a composite modification strategy based on an extraction–blending process using styrene–butadiene–styrene (SBS) and crumb rubber (CR). The high- and low-temperature rheological properties, phase morphology, and functional-group characteristics of DCLR-blended asphalt with different formulations were systematically evaluated using a dynamic shear rheometer (DSR), a bending beam rheometer (BBR), fluorescence microscopy (FM), and Fourier transform infrared spectroscopy (FTIR). The results demonstrate that the combined addition of SBS and crumb rubber significantly enhances the high-temperature stability and elastic response of the asphalt. Specifically, formulation 5# (8 wt.% SBS and 10 wt.% CR) maintained a rutting factor of 1.007 kPa at 82 °C, indicating superior high-temperature rutting resistance. Meanwhile, this formulation satisfied the Superpave low-temperature requirements at −18 °C, achieving a balanced improvement in both high- and low-temperature performance. Microstructural analysis suggests that an appropriate SBS/CR ratio contributes to the formation of a relatively continuous and uniformly distributed polymer-rich phase, whereas excessive modifier contents may lead to rubber agglomeration and phase-structure imbalance. FTIR results showed that the characteristic absorption peaks of the modified binders were generally consistent with those of the base asphalt, and no obvious new absorption bands were observed. This indicates that the extraction–blending process mainly involved physical blending, swelling, and phase interaction rather than the formation of new covalent functional groups. This study provides a technical reference for the high-value utilization of DCLR and the development of high-performance modified asphalt.