Volume 41, Issue 2 (March 2013)
Thermal Cracking Potential of High RAP-WMA Evaluated With Bending Beam Rheometer Mixture Beam Test
In recent years, increasing cost of the raw materials for asphalt paving has generated interest in using greater quantities of reclaimed asphalt pavement (RAP). During the same period, development of warm-mix asphalt (WMA) technology has allowed use of lower production temperatures that can reduce the amount of short-term aging of the virgin binder. The reduction in short-term aging can be beneficial in reducing problems associated with increased binder stiffness that are normally encountered when using high percentages of RAP in a mixture. This paper presents the results of an investigation that compared the low-temperature performance of WMA with a high RAP content to the performance of mixtures produced in accordance with current practice, which limits the content of RAP in the mixture to 15 % or less. Comparisons were made through a combination of mixture testing with the bending beam rheometer (BBR) and thermal cracking analysis of the BBR data. Emphasis was placed on mixture performance when the mixture is used on the surface of highway pavements. Test results from over 1000 beam specimens tested in the BBR are presented, and the results indicate that low-temperature performance of WMA containing 25 % RAP is likely to be comparable to performance of surface mixtures produced in accordance with current practice. The test results also indicate WMA containing 50 % RAP may be more susceptible to thermal cracking than surface course mixtures produced by the current practice.