Field performance evaluation of asphalt mixtures containing high percentage of RAP using LTPP data

Abstract Recycled asphalt pavement (RAP) has been used in production of new mixtures for many decades and has become a common practice in highway agencies. However, concerns about field performance of RAP mixtures have been lingering on since the beginning of RAP usage. In this study, the field performance of RAP was verified through the Long-Term Pavement Performance (LTPP) program. Particularly, pavement overlays constructed with virgin asphalt and those constructed with a significant RAP percentage were examined and compared regarding their field performance. To achieve this goal, data from the Specific Pavement Study experiment 5 (SPS-5) of LTPP were retrieved and statistically analyzed for comparison. A total of eighteen projects comprised of 162 sections were collected. Various performance measures were incorporated, including alligator cracking, longitudinal cracking (wheel path and non-wheel path), transverse cracking, patching, potholes, rutting, roughness, and pavement surface deflections. In addition to the key variables used in the SPS-5 experiment (thickness, materials and pre-overlay treatment), the impacts of other important factors, including climatic conditions, initial surface condition and subgrade soil classification, were also investigated. Exploratory data analyses and logistic regression were used to compare the performance of RAP and virgin asphalt overlays. Results from the analysis results show that RAP had little effects on longitudinal cracking, transverse cracking, and roughness, but slightly increased the risk of fatigue cracking and weakened pavement structure. As expected, use of RAP was beneficial in reducing the rutting potential of thick overlays. For both RAP and virgin asphalt overlays, thicker overlays performed better than thinner ones in all performance measures except for rutting. Pre-overlay treatment methods and subgrade soil types were found to be critical factors affecting fatigue cracking and roughness. The initial surface condition also showed significant effects on pavement structural capacity and fatigue cracking over the long run.