Synthesis and Characterization of a High-Performance Asphalt Modified with Lignin–Waste Cooking Oil Composite

As one of the most important aromatic renewable natural resources, lignin has the potential to improve the high-temperature rheological properties and antiaging properties of asphalt. However, it will adversely harden the asphalt and reduce its low-temperature cracking resistance and self-healing ability. To promote the utilization rate of lignin (L) waste, this study aimed to synthesize a high-performance lignin-modified asphalt by incorporating waste cooking oil (WCO). First, a series of asphalts modified with lignin and WCO (in different mass ratios) were synthesized. Their performance properties were then systematically evaluated using the physical-rheological property tests. Finally, the underlying modification mechanism of lignin–WCO was revealed by the molecular dynamics (MD) simulation and Fourier transform infrared (FTIR) test. The results showed that the incorporation of lignin could increase the cohesive energy density (CED) of asphalt and thus improve its high-temperature performance. However, this would have reduced the mobility of the asphalt molecules and compromised its resistance to low-temperature cracking and self-healing potential. The addition of WCO could effectively promote the movement of asphalt molecules by providing some lightweight components, thus offsetting the loss of low-temperature performance and healing potential of lignin-modified asphalt. However, the dosage should be less than 1.0% to maintain the high-temperature performance of the asphalt. The modification mechanism of lignin–WCO involved only physical modification without chemical reaction, and L7.5%+WCO0.5% was identified as the best combination for asphalt modification that achieved satisfactory overall physical-rheological performance.