Preliminary Scope

Reclaimed asphalt pavement (RAP) has been used in pavement rehabilitation and construction for decades. Due to the potential engineering, economic, and environmental benefits, FHWA has highlighted the importance of using RAP in the highway construction industry. In recent years, several state DOTs have introduced special provisions and specifications to allow the use of high RAP contents in asphalt mixtures. NCHRP Project 09-58 defines high RAP mixtures as those characterized by high recycled binder ratios (RBRs), typically greater than 0.3. Nevertheless, the definition of “high RAP mixtures” remains state specific. Some state DOTs have had challenges specifying, designing, and controlling the quality of asphalt mixtures containing RAP, especially those with high contents. The primary concern with such mixtures is that using high RAP contents may stiffen asphalt mixtures, making them brittle and prone to premature cracking. In addition, improper design of high RAP mixtures can lead to numerous construction challenges and performance issues such as poor compactability and workability and increased risk for cracking (e.g., thermal cracking, reflection cracking) and raveling.

Not all state DOTs have experience with mixtures containing higher RAP contents than allowable according to their current specifications. The main roadblocks to greater use of RAP in asphalt mixtures have included limitations related to specifications; lack of performance engineered based design methods; limited access to quality RAP material; lack of expertise in RAP processing; and the absence of a comprehensive resource detailing current advancements and practices to educate agencies about the benefits, challenges, and responsible implementation of high RAP mixtures.

This objective of this synthesis is to document current DOT practices regarding the design, production, and construction of high RAP content mixtures.

 Information to be gathered includes (but is not limited to):

• DOT policies, specifications, definitions (e.g., RAP usage by mix type), and guidelines related to designing, producing, and placing high RAP mixtures (existing and/or under development);
• DOT policies, specifications, and guidelines related to RAP stockpile management and testing;
• Mix design strategies adopted by DOTs to design high RAP mixtures, including balanced mix design (BMD);
• Challenges faced during design and/or production;
• State DOT field experience with high RAP mixtures;
• Documented case examples of long-term field performance;
• DOT incentives to contractors for using high RAP mixtures; and
• Factors limiting the use of high RAP contents in asphalt mixtures.

 Information will be gathered through a comprehensive literature review, a survey of state DOTs, and follow-up interviews with selected DOTs with relevant experience to develop case examples. Information gaps and suggestions for research to address those gaps will be identified and presented.

 Information Sources (Partial)

• Diefenderfer, S. D., Habbouche, J., and Boz, I. (2023). “Balanced Mix Design for Surface Asphalt Mixtures: 2020 Field Trials.” VTRC 23-R13. Virginia Transportation Research Council, Charlottesville, VA.
• Sias, J. E., Dave, E. V., and Zhang, R. (2022). NCHRP Synthesis 586: Use of Recycling Agents in Asphalt Concrete Mixtures. Transportation Research Board, Washington, DC.
• Hand, A. J. T., and Aschenbrener, T. B. (2021). “Successful Use of Reclaimed Asphalt Pavement in Asphalt Mixtures.” WRSC-TR-21-10. University of Nevada, Reno.
• FHWA (2021). “Resource Responsible Use of Reclaimed Asphalt Pavement in Asphalt Mixtures.” FHWA-HIF-22-003. Washington, DC.
• Diefenderfer, S. D., Boz, I., and Habbouche, J. (2021). “Balanced Mix Design for Surface Asphalt Mixtures: 2019 Field Trials.” VTRC 21-R21. Virginia Transportation Research Council, Charlottesville, VA.
• Habbouche, J., Boz, I., Underwood, B. S., Castorena, C., Gulzar, S., Fried, A., and Preciado, J. (2021). “Review From Multiple Perspectives for the State of the Practice on the Use of Recycled Asphalt Materials and Recycling Agents in Asphalt Concrete Surface Mixtures.” Transportation Research Record 2676, pp. 407-420. Transportation Research Board, Washington, DC.
• Epps-Martin, A., Kaseer, F., Arámbula-Mercado, E., Bajaj, A., Cucalon, L.G., Yin, F., Chowdhury, A., Epps, J., Glover, C., Hajj, E.Y., Morian, N., Daniel, J.S., Oshone, M., Rahbar-Rastegar, R., Ogbo, C., and King G. (2020). NCHRP Research Report 927: Evaluating the Effects of Recycling Agents on Asphalt Mixtures With High RAS and RAP Binder Ratios. Transportation Research Board, Washington, DC
• Federal Highway Administration (2018). State of the Knowledge for the Use of Asphalt Mixtures with Reclaimed Binder Content. FHWA-HIF-18-059. Washington, DC.
• Stroup-Gardiner, M. (2016). NCHRP Synthesis 495: Use of Reclaimed Asphalt Pavement and Recycled Asphalt Shingles in Asphalt Mixtures. Transportation Research Board, Washington, DC.

TRB Staff
Dr. Zhiye Li
Email: zli@nas.edu

Meeting Dates
First Panel Meeting Date: TBD, 2024 (Virtual via Microsoft Teams)
Teleconference with Consultant: TBD
Second Panel Meeting Date: TBD (Virtual via Microsoft Teams)