Multiscale Evaluation of the Composite Asphalt Binder in High-Reclaimed Asphalt Pavement Mixtures

In this paper, various nanomechanical and macromechanical techniques were used to study the effect of a reclaimed asphalt pavement (RAP) binder on the microstructure and properties of a virgin asphalt binder and to evaluate the degree of blending that occurs between those binders. To this end, different atomic force microscopy (AFM) experiments (i.e., AFM tapping mode imaging, AFM nanoindentation, AFM force spectroscopy experiments) were conducted on a virgin asphalt binder, a recovered RAP binder, and their composite. In addition, dynamic shear rheometer (DSR) tests were conducted on the evaluated binders, and the dynamic modulus tests were performed on mixtures prepared using those binders to evaluate the degree of RAP blending and compare it with those obtained using the AFM test results. The results of the AFM images indicated that blending between the RAP and virgin binders occurs at the nano/microscale level in the composite binder at a fairly uniform manner. Furthermore, the nanoindentation test results indicated that the composite asphalt binder had a significantly lower modulus than the RAP binder and closer to the virgin binder; however, the virgin binder modulus was still significantly lower than that of the composite. The force spectroscopy results indicated that the RAP had adverse effects on the adhesion properties of the composite binder. The results of the DSR tests showed similar trends to that observed using the AFM nanoindentation results; however, the DSR was found to underestimate the effect of the RAP binder on the mechanical properties of the composite. Finally, the AFM test results suggested that about 85% of RAP was effective in the composite. (C) 2014 American Society of Civil Engineers.