Effect of Hot Mixing Duration on Blending, Performance, and Environmental Impact of Central Plant Recycled Asphalt Mixture

When using a high concentration of reclaimed asphalt pavement (RAP) in a recycled hot-mix asphalt mixture (RHMA), the degree of blending of the reclaimed asphalt binder significantly affects the performance of the RHMA. Hence, it is essential to know the degree of blending of the RAP and its effect on the performance and the environmental impact of RHMA in order to determine the optimal mixing duration. To this end, the dispersion of reclaimed asphalt was observed using artificial RAP and the image analysis method, and the blending of reclaimed asphalt in RHMA with different mixing durations was also evaluated using physical properties tests, a rheometer test, a Fourier-transform infrared spectroscopy (FTIR) test, a gel permeation chromatography (GPC) test, and an atomic force microscope (AFM) test. The performance of RHMA with the different mixing durations in the plant and in the laboratory was tested using a Marshall stability test, rutting resistance test, freeze–thaw splitting test, and low-temperature bending beam test. In addition, the environmental impact of RHMA at different mixing durations was evaluated, and the optimal mixing duration was determined. The results showed that the mixing duration had a significant influence on the dispersion and blending of reclaimed asphalt in RHMA. The longer the mixing duration was, the higher the dispersion and the degree of blending of the reclaimed asphalt in the RHMA were. With the increase in the mixing duration, the properties, chemical composition, and micromorphology of the blended asphalt binder tended to become similar to those of reclaimed asphalt. The performance of RHMA was improved with the increase in mixing duration; however, the energy consumption and CO2 emissions for the RHMA increase significantly with the increase in mixing time. The recommended optimal mixing durations in the mixing plant and in the laboratory were found to be 60 s and 90 s, respectively, considering the environmental impact, the RHMA production efficiency, and the performance of the RHMA.