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.

To improve the low-temperature performance of direct coal liquefaction residue (DCLR)-modified asphalt, a direct-addition composite modifier (DCLAM) containing DCLR, SBS, crumb rubber, activated nano-CaCO₃, and aromatic oil was developed. A four-factor, three-level orthogonal design was used to optimize the formulation based on dynamic shear rheometer (DSR) and bending beam rheometer (BBR) tests. The optimal formulation contained 5% DCLR, 1% SBS, 15% crumb rubber, 3.5% nano-CaCO₃, and 2% aromatic oil. At 64 °C, the optimized mastic exhibited a complex shear modulus of 18,506.7 Pa and a rutting factor of 19.4 kPa, while its phase angle decreased to 72.4°. At −12 °C, the creep stiffness was 167.3 MPa and the m-value was 0.383. Mixture-level performance was further evaluated through wheel-tracking, low-temperature beam bending, freeze–thaw splitting, and dynamic modulus tests. The DCLAM-designed mixture exhibited a dynamic stability of 7176.0 cycles/mm, a maximum flexural tensile strain of 3087 με, and a freeze–thaw tensile strength ratio of 78.3%. It also showed higher complex modulus and lower phase angle values than the base mixture over the investigated temperature–frequency range. These results demonstrate the potential of the optimized DCLAM formulation for balancing high-temperature deformation resistance and low-temperature cracking resistance in asphalt pavement materials.

To enhance the overall performance of direct coal liquefaction residue (DCLR)-modified asphalt, particularly its low-temperature cracking resistance, SBS and aromatic oil were employed for composite modification. Nine composite-modified asphalt formulations were prepared based on an orthogonal experimental design. High-and low-temperature rheological properties and microstructure of all modified asphalts were systematically evaluated using a dynamic shear rheometer (DSR), a bending beam rheometer (BBR), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results indicate that composite modification significantly enhanced the high-temperature performance of the asphalt. Modified asphalt labeled as Sample No. 9 (9% DCLR, 4% SBS, and 6% aromatic oil) demonstrated the minimal non-recoverable creep compliance ($J_{nr}$) value of 0.58 kPa⁻¹ at 64 °C, indicating a 78.6% decrease relative to the matrix asphalt. In terms of low-temperature performance, Sample No. 3 satisfied the Superpave cracking resistance criterion, exhibiting a creep rate ($m$-value) of 0.312 at −12 °C. It was revealed by FTIR analysis that the interaction between the composite modifier and the base asphalt was mainly physical blending, and no new functional groups were generated either before or after aging. The improvement in performance was attributed to the physical compatibility and structural reorganization among the components. Microstructural analysis revealed that the uniform dispersion of modifiers in matrix asphalt and the subsequent formation of a dense micelle structure after aging contributed to the enhanced macroscopic performance. This study provides theoretical and technical support for the high-value application of DCLR in asphalt pavements.

To address the issue of insufficient low-temperature performance in asphalt modified with Direct Coal Liquefaction Residue (DCLR), this study developed a direct addition DCLR composite modifier (DCLAM). The DCLAM-modified asphalt was prepared by blending DCLR with SBS, crumb rubber, activated nano-CaCO3, and aromatic oil to systematically optimize its high- and low-temperature performance and rheological characteristics. A four-factor, three-level orthogonal experimental design was adopted. Key parameters of the modified asphalt mastic, including the complex shear modulus (G*), phase angle (δ), rutting factor (G*/sin δ), creep stiffness (S), and creep rate (m), were analyzed using a Dynamic Shear Rheometer (DSR) and a Bending Beam Rheometer (BBR). The results indicate that DCLAM markedly improves the high-temperature stability and low-temperature cracking resistance of asphalt. At 64℃, the optimal formulation (5% DCLR, 1% SBS, 15% crumb rubber, 3.5% nano-CaCO3, 2% aromatic oil) achieved a G* of 17,749 Pa, which represents an increase of approximately 65% compared to the base asphalt. The rutting factor reached 75.2 kPa, showing an improvement of about 48%, while the phase angle decreased to 34.9°, indicating a stronger elastic response. At -12℃, the creep stiffness was reduced to 167.3 MPa, and the creep rate increased to 0.383, meeting the low-temperature specifications of the Superpave system. This composite modifier demonstrates promising engineering applicability, offering a novel approach for the efficient utilization of coal-based asphalt.