This study elucidates the diffusion mechanism between rejuvenators and aged asphalt molecules, aiming to provide theoretical guidance for the development and design of rejuvenators. The diffusion behavior of a rejuvenator in aged asphalt was investigated from a multi-scale perspective, and the underlying diffusion mechanism was revealed. The results indicate that in light aged asphalt, the DOB (degree of blending) value of the specimens approached 100%, reflecting a state of complete blending. In contrast, in heavy aged asphalt, the DOB value only reached about 60%-70%. Moreover, the DOB value at the interface between the rejuvenator and light aged asphalt was 1.3 to 1.8 times that at the interface with heavy aged asphalt, demonstrating that asphalt aging significantly hinders the diffusion and blending process. The DS ( diffusion speed) values of the rejuvenator R a -, R b -, and R c -aged asphalt specimens were significantly higher than that of the R d -aged asphalt specimen, confirming the excellent diffusion and blending performance of the bio-rejuvenator in aged asphalt. Among the components studied in aged asphalt, fatty acid glyceride, aromatic hydrocarbon C₁₂H₁₆, and alkane C₈H₁₈ showed similar and optimal diffusion effects, followed by oleic acid and linoleic acid. Glycerol exhibited the poorest diffusion, primarily due to its high polarity, strong intermolecular electrical interactions, and excessively high total electrical potential energy, which collectively obstruct its diffusion in aged asphalt. Therefore, the development of rejuvenators should prioritize compounds with low molecular weight, low molecular polarity, minimal content of polar functional groups, and either a linear chain molecular structure or a small-molecule terminal benzene ring structure to maximize diffusion in aged asphalt and ensure effective rejuvenation of waste asphalt materials.
Fang et al. (Sun,) studied this question.