Influence of RAP Dispersion Characteristics on Mixture Performance

Due to the ever-dwindling level of natural aggregate/asphalt resources and shrinking budgets for infrastructure assets management, engineers have been striving to incorporate more and more recycled asphalt pavement (RAP) materials into pavement maintenance and rehabilitation activities. One critical issue with using RAP is characterizing the actual dispersion characteristics of RAP in the mixture. This study addresses this issue through image analysis and a series of mixture performance tests, including the Marshall stability test, volumetric property test, wheel tracking test, three-point bending test, and freeze-thaw splitting test. The results showed that scanned images of asphalt mixture slices were effective in identifying the dispersion characteristics of the RAP in the mixture. An aggregate five pixels and an aggregate centroid distance of 55 pixels were proposed as the threshold for RAP dispersion, and the dispersion ratio was employed to evaluate the RAP dispersion characteristics of a mixture. With the extension of mixing time, the Marshall stability of the mixture increased but the air voids decreased, which then caused a decrease in the optimum asphalt content of the mixture. In addition, the rutting resistance and cracking resistance of the mixture were significantly improved, whereas the moisture susceptibility was slightly enhanced.