Investigation of reclaimed asphalt pavement blending efficiency based on micro-mechanical properties of layered asphalt binders

The challenge in mix design and application of reclaimed hot mix asphalt (HMA) lies in the unknown blending efficiency between reclaimed asphalt pavement (RAP) binder and virgin binder. By using a combination of staged extraction method and Atomic Force Microscopy (AFM) imaging technique, this paper focused on the investigation of interaction and extent of blending between RAP-virgin binders under different mixing temperature and residence time, based on the micro-mechanical properties of layered binders in real reclaimed HMA. In addition, the impact of chemical solvent used in staged extraction, i.e. Trichloroethylene (TCE), on the AFM images of extracted asphalt binder was also explored. It was found that the topographic features of asphalt binder in terms of “bees” structure were obviously altered by TCE, which were not suitable for analysis on RAP blending. A possible blending scenario, indicating non-homogenous blending between RAP-virgin binders in the layered binder system, was put forward for the mixing stage of reclaimed HMA, in which increased DMT modulus and decreased adhesion force and energy dissipation were observed from the outermost towards to the innermost layers. Both mixing temperature and residence time have significant effects on the blending efficiency between RAP-virgin binders. With the decrease of mixing temperature, diffusion of the virgin binder into RAP binder is impaired, thus leading to less blending efficiency between the two binders. Besides the mixing process, the blending between RAP-virgin binders continues with the passing residence time, until a complete and homogeneous blending being reached after sufficiently long time.