Study on the blending behavior of asphalt binder in mixing process of hot recycling

The blending behavior of aged and virgin asphalt binder is one of the most critical problems in the mixing process of hot recycling. To accurately measure the participation degree of aged asphalt and optimize the mixing process of hot recycling, a series of laboratory tests were designed by using magnetite aggregate and thin-layer chromatography with flame ionization detection (TLC-FID) for the first time. In this study, 24 different lab-mixing conditions were deliberately adopted to investigate the impact on the DoB of aged and virgin asphalt binders, including mixing amount of RAP, mixing amount of rejuvenating agent, mixing time, mixing temperature, mixing orders and the thickness of asphalt film. The results indicated that the aged and virgin asphalt cannot be completely blended in the mixing process and DoB is only about 40–60 % in general. The DoB decreases with the increase of asphalt film thickness and it decreases by 30 % when asphalt film thickness is 9 µm. DOB increased with the content of RAP and rejuvenating agent up to 70 % which same as mixing sequence. Although the mixing time and temperature can promote DOB, the mixing time and temperature should be controlled within 240 s and 170 °C, otherwise the accuracy of DOB will be affected.