Abstract
The asphalt industry continues to be the country’s most consistent recycler of highway pavement materials with more than 99% being used as Reclaimed Asphalt Pavement (RAP) in the construction and rehabilitation of pavements. The average RAP percentage utilized in asphalt mixes has increased from 15.6% in 2009 to 21.1% in 2018. The increase in RAP content in asphalt mixtures may result in stiffer mixtures which are more prone to cracking. The use of softer asphalt binder or increased binder content can improve the cracking performance, but this may compromise the rutting resistance of the asphalt mixtures. This study examined the sensitivity of rutting performance and compactability to mix composition including RAP content and source, binder content and grade, mix design, and aggregate type. In addition, this study evaluated the moisture susceptibility of asphalt mixtures prepared with RAP and the use of anti-stripping agents to improve the resistance of these mixtures to moisture damage. The results of this study demonstrated that mixtures with RAP within a range of ± 0.75% of optimum binder content had good resistance to cracking. Increasing the binder content and using softer binders at various RAP contents resulted in higher rutting but this increase was less than the maximum threshold for various rut tests. This means that using softer binders or increasing binder content to improve the cracking resistance should not significantly affect the rutting performance for the mixtures evaluated in this study. The results also showed that the rutting was less sensitive to RAP content and binder grade. The stiffening effect of RAP materials in asphalt mixtures was not significant on rutting performance.
Furthermore, the results showed that the inclusion of RAP had a negative effect on moisture susceptibility and resulted in a lower tensile strength ratio. In addition, the use anti-stripping agents was found to improve resistance to moisture damage.
This study developed a correlation between rutting and compactability of asphalt mixtures. Mixtures with less resistance to densification during laboratory compaction were found to experience higher rutting than those with higher resistance to densification. Such correlation may be used to evaluate the rutting resistance from the compaction data during the mix design or mix production. It can be also used during project construction to assess significant variations in mix composition.