Development of a Direct Addition Asphalt Modifier from Coal Liquefaction Residue Based on Rheological Properties

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.