Concerns with the durability and performance of asphalt concrete that contains recycled materials have recently become the focal point of the asphalt industry. The goal of this research was to improve the performance of asphalt concrete pavements that contain recycled materials in Washington state.
The Washington State Department of Transportation (WSDOT) has successfully used recycled asphalt pavement (RAP) since the mid-1970s. Recycled materials used in hot mix asphalt (HMA) in Washington may include reclaimed asphalt pavement, reclaimed asphalt shingles, and recycled engine oil bottoms. This project sought to help enhance WSDOT’s asphalt concrete materials selection, mix design, and standard specifications to allow it to responsibly optimize the use of recycled materials, given readily implementable technologies, in collaboration with industry stakeholders.
The scope of the project included a literature review; an assessment of the supply of reclaimed asphalt material (RAM) in the state; a statewide comparison of performance data from low and high RAM usage to determine whether differences were observed; evaluation of raw materials and field mixtures; evaluation of laboratory mixed-laboratory compacted, field mixed-laboratory compacted, and field cored samples; and statistical analysis of results.
The laboratory analyses included short-term and long-term aging of binders and mixtures and then performing rheological and cracking tests on them.
The primary recommendations of this study include the following:
- Integrate volumetric parameters along with further performance testing in a balanced mix design approach to increase effective binder content.
- Implement all of the volumetric criteria in the AASHTO M323 specification during mix design, testing, and acceptance.
- Use the ΔTc parameter as an aging parameter in asphalt binder specifications.
- Include RAM in all mix designs, regardless of proportions.
- Maintain an Indirect Tensile (IDT) strength specification and transition to the Cracking Tolerance (CT) Index.
- Add long-term aging for IDT/CT-Index test specimens, maintaining the current Hamburg Wheel Track rutting test and criteria.
- Revise short- and long-term standard specifications.
- Re-evaluate the performance of RAM pavements over time.
These recommendations should help WSDOT modify its overall recycled materials strategy so that it can be informed by current national best practices, take into account observable local issues and test results, and lead to more durable HMA pavements.
Report: WA-RD 912.1
Authors:
Adam J.T. Hand
Peter E. Sebaaly
Murugaiyah Piratheepan
Elie Y. Hajj
Kiran Bhandari Chhetri
Nicole Elias
University of Nevada, Reno
Stephen T. Muench
Ryan Howell
UW Department of Civil and Environmental Engineering
Joe DeVol
Steve Davis
Washington State Department of Transportation
Sponsor: WSDOT
WSDOT Technical Contact: Joe DeVol
WSDOT Project Manager: Jon Peterson