Laboratory investigation on blending process of reclaimed asphalt mixture

With the extensive application of hot recycling technology in maintenance of asphalt pavement, there is a concern on the blending between reclaimed asphalt pavement (RAP) binder and virgin binder. Two main stages, viz. the mobilization stage of RAP binder and the diffusion stage of virgin binder, in the blending process between RAP and virgin binder are investigated in this study. In order to quantify the mobilization rate of RAP binder, a blending chart relating RAP binder content to carboxyl index (CI) of blended binder was established by using Fourier transform infrared spectrometer (FTIR). The effects of RAP particle size, RAP temperature and mixing sequence were taken into account in laboratory experiment. The diffusion of virgin binder was studied by using the tracing method. Cobaltous (Co) naphthenate solution as a tracer was blended with the virgin binder. Based on the distribution of Co element in RAP binder detected by scanning electron microscope equipped with energy dispersive spectrometer (SEM/EDS), an index was proposed to quantify the diffusion degree of virgin binder. The obtained results showed that the proposed indicators could well reflect the variation of mobilization rate and diffusion degree under different test conditions and can be used to comprehensively evaluate the blending efficiency between RAP binder and virgin binder.