Infrared Spectroscopy Analysis of the Blending of Virgin and RAP Binders in Hot Recycled Asphalt Mixture with CTBN as Tracer

This study conducted an infrared analysis of a recycled asphalt mixture that contains a high percentage of reclaimed asphalt pavement (RAP) and uses carboxyl-terminated butadiene acrylonitrile (CTBN), which has an absorption peak at 2,238 cm−1, as a tracer in the virgin asphalt. The infrared spectroscopy results of the asphalt test specimens containing 1–15 wt. % of CTBN indicated that 5 wt. % virgin asphalt is most appropriate. Infrared spectroscopy was performed on specimens of recycled asphalt mixture that contained 45 % RAP, and a statistical analysis was performed on the results. The results indicated that the virgin and RAP asphalt binders were not completely mixed, as is typically assumed. The blending degree of the virgin binder and RAP binder in the outer layer of the RAP aggregate particles was higher than that in the inner layer. The blending degree is inhomogeneous and has a three-dimensional hierarchy that depends on the depth and location of the asphalt mastic membrane over the aggregate.