Quantitative Analysis of the Blending Degree of Virgin and RAP Binders in Recycled Asphalt Mixtures with a High RAP Content

Recycled asphalt mixtures (RAM), which are prepared by blending reclaimed asphalt pavement (RAP), virgin bitumen and mineral additives, provide a variety of advantages, including resource recycling, reductions in costs, and reduced negative environmental impacts. However, multiple agencies have expressed concerns about the utilization ratio of RAP; thus, a comprehensive understanding of the blending degree of virgin and RAP binders in RAM would be significantly helpful for promoting the application of RAP. This study aims to quantitatively analyze the blending degree of virgin and RAP binders in RAM with high RAP contents. Carboxyl-terminated butadiene acrylonitrile (CTBN) was utilized as a tracer to mark the virgin bitumen; in addition, Fourier transform infrared (FTIR) spectroscopy was used to develop the structural index of CTBN (ICTBN). By establishing the standard curve between ICTBN and the CTBN content, the blending degree of virgin and RAP binders at different locations within RAM can be determined quantitatively. The study results indicate that the RAP binder was completely blended with the virgin bitumen in the outer RAP layer. However, the blending degree decreased with an increase in the RAP depth, and the blending degree in the inner RAP layer was only approximately half that which was found in the case of complete blending