Study of migration and diffusion during the mixing process of asphalt mixtures with RAP

The mixing degree of virgin and aged asphalt binders is one of the main factors that can significantly affect the performance of reclaimed asphalt pavement (RAP). On the other hand, an important factor that contributes to the mixing is diffusion, which dominantly determines the general performance of asphalt mixtures with RAP. In this study, twelve different lab-mixing conditions were deliberately adopted to investigate the impact on the diffusion between virgin and aged bitumen binders, including three mixing temperatures (110°C, 130°C, 150°C) and four mixing times (30 s, 60 s, 120 s, 240 s). Specially fabricated cubic aggregates were designed and deposited for collecting pure binders, so that virgin or aged binders can be tracked and the effect of chemical reagents be avoided. Based on the Dynamic Shear Rheometer (DSR) and Fourier Transform Infrared Spectroscopy (FTIR) tests, the performance and blending rate of binders under various conditions were clearly shown. The results show that blending temperature can play a more crucial role in diffusion than mixing duration, which means the higher temperature is capable of accelerating the inter-diffusion rate between virgin and aged bitumen binders, thus increasing the efficiency of recycling ulteriorly. The blending degree investigated in this study could not achieve the complete mixed state with the highest value being around 50%. Furthermore, the Asymmetric Gaussian Model is proposed to mathematically describe the change of blending rate with the mixing time.