Federal Highway Administration State Planning and Research Funding
Iowa Department of Transportation
Iowa Highway Research Board
University of Iowa
About the research
Federal, state and local public agencies encourage the use of recycled asphalt pavement (RAP) in constructing pavements to the maximum extent possible with an equal performance. According to the recent NAPA’s report, average percent used in asphalt pavement was 21% based on total reported tons of RAP divided by reported total tons asphalt mixtures produced. 24% of RAP mixtures were estimated to be produced using softer binders whereas 7% of RAP mixtures produced using a rejuvenator.
The main purpose of this research is to develop a scientific method to effectively identify the most appropriate rejuvenators for Iowa’s high RAP mixtures. The specific objectives of this study are to provide the Iowa DOT with: 1) a screening method for approving rejuvenators in asphalt mixtures and 2) a method of field evaluation for HMA containing rejuvenators. The effects of different rejuvenators were evaluated through applying each product to aged asphalt binder and high-RAP mixtures. Fourier Transform Infrared (FTIR) test indicated all rejuvenators were effective in decreasing the aging level of hardened asphalt binder. Cryo-SEM technology was then utilized to measure cracking developed on the surfaces of both aged and rejuvenated asphalt binders when the temperature was lowered to -165ºC. Significantly less cracking was observed from the surface of rejuvenated asphalt compared to that of aged asphalt, which indicates an improved resistance to low-temperature cracking. All rejuvenators lowered both PG high-temperature and low-temperature limits of aged asphalt binder. The optimum dosage rate of each rejuvenator was identified using the Bending Beam Rheometer (BBR) test. G-R parameter was then calculated to determine the level of aging. All rejuvenators lowered the aging level to different extents but could not bring its properties to those of the original virgin binder.
To evaluate the low-temperature cracking potential, Disk-Shaped Compact Tension (DCT) test was performed on the laboratory high-RAP mixtures with 27.6% and 70% of RAP materials (by binder replacement). In addition, cores and lab- compacted specimens from field loose mixtures were also tested using both DCT and Hamburg Wheel Tracking (HWT) devices. Based on the DCT test result, it was concluded that high-RAP mixtures with rejuvenators were more resistant to a low–temperature cracking than the high-RAP mixtures without it. However, based on HWT test results, a rejuvenator did not improve the moisture susceptibility and rutting potential. Overall, it can also be concluded that Rejuvenators “A” and “B” performed better than Rejuvenator “C” at their optimum dosage rates. Test sections using Rejuvenators “B” and “D” were successfully constructed in Crawford and O’Brien Counties in Iowa.