Micro- and Meso-scale homogeneity of asphalt mixtures with RAP in thermal-non-equilibrium condition

Reclaimed asphalt pavement (RAP) is a promising material that can be partially substituted into the newly constructed pavement. An appropriate production procedure is of great significance to produce high-quality recycled asphalt mixtures. This study performed an investigation on the micro and mesoscale homogeneity of asphalt mixtures produced by different mixing conditions. To this end, 36 mixing combinations, including three preheated RAP temperatures, three mixing times, and two aggregate types, were considered in this study. The diffusion sample composed of new and aged bitumen was obtained non-destructively using the aggregate tracking method (ATM). In what follows, the Fourier Transform Infrared Spectroscopy (FTIR) and Dynamic Shear Rheometer (DSR) tests were conducted to quantify the diffusion sample from the mechanical and chemical aspects, respectively. Accordingly, the homogeneity of asphalt mixtures containing RAP was analysed at the micro and mesoscales. The results indicated that mixing temperature dominantly controlled the migration behavior of binders, further determining the diffusion behavior between new bitumen and aged bitumen. Notably, the estimation of homogeneity of asphalt mixtures was found to be indicator-dependent. Using different indicators could induce distinct evaluation results or even opposite results. In general, the increase of mixing time would improve the complex modulus of the diffusion sample. The worst homogeneity was observed when the mixing temperature was around 110℃. Due to the variation in adhering to the bitumen binder, the aggregate type also influenced the micro and mesoscale homogeneity of asphalt mixtures.