Prediction of the Rejuvenator Diffusion Coefficient in Aged Asphalt Based on Free Volume Theory

A method for predicting the diffusion behavior of rejuvenators in aged asphalt was developed based on free volume theory to avoid the influence of experimental conditions or speculative simulation models on results. Three types of rejuvenators (straight saturate, cyclic saturate, and naphthene aromatic) with different molecular structures and AAA-1 aged asphalt were selected to verify the model. According to the prediction of diffusion coefficients of typical types of rejuvenators, the influencing factors of the diffusion behavior of rejuvenators were comprehensively analyzed. The results show that the prediction method can predict the diffusion coefficients of rejuvenators in aged asphalt and avoid experimental error through standardized methods. The diffusion coefficient of the rejuvenators is affected by the interaction of temperature, rejuvenator dosage, and rejuvenator type. At normal temperature, it is easier for the naphthene aromatic to diffuse in aged asphalt than the cyclic saturate and straight saturate. The increase of temperature makes the saturate-based rejuvenators more active, and the cyclic saturate shows the highest diffusion coefficient at high temperature. A similar trend occurred when the rejuvenator dosage was increased. According to the molecular chemical characteristics, rejuvenators with small or light molecules have the advantage of diffusion at high temperature, while at normal temperature, it is recommended to select the rejuvenator with a benzene ring structure.