The use of recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS) is growing due to their economic and environmental benefits. However, the availability of recycled asphalt binder is not known despite having a substantial impact on mixture performance. Currently there is no accepted method to quantify or account for the effective binder content available from these materials. AASHTO guidance on the design of asphalt mixtures with RAP and/or RAS assumes that 100% of the recycled binder is available to blend with virgin binder and any additives such as recycling agents or warm mix asphalt products. However, research has shown that the amount of recycled binder availability varies, with lower availability expected for heavily aged RAP or RAS binder and for mixtures produced at lower temperatures. Thus, the AASHTO guidance of 100% availability may lead to inadequate mixture durability and cracking performance in service.
Asphalt mixture performance is impacted by the interactions within each unique combination of its component materials. These interactions are not captured by current mix design practices. Without a method to quantify or account for recycled binder availability, all recycled materials are considered equal during mix design despite the many factors that affect their contribution to asphalt mixture performance. A better understanding of recycled binder availability and its impact on performance will support the greater use of recycled asphalt materials and minimize the risk of premature failure.
The objective of this research is to identify or develop methods to (a) quantify binder availability from recycled asphalt materials and (b) based on availability, measure the impact of recycled asphalt materials incorporated in asphalt mixes prepared with a range of virgin, rubberized, and modified asphalts on mix performance. These methods shall be used to improve mix design procedures and specifications by accounting for binder availability and its impact on performance.
The research shall address the important factors affecting the binder available in recycled asphalt materials and their impact on mix performance; these factors may include, but are not limited to:
- Recycled asphalt materials;
Proposers are asked to provide a detailed research plan for accomplishing the project objective and producing the deliverables required by each phase of the project. Proposers are expected to describe research plans that can realistically be accomplished within the constraints of available funds and contract time. Proposals must present the proposers' current thinking in sufficient detail to demonstrate their understanding of the issues and the soundness of their approach to meeting the research objective. The work proposed for each phase must be divided into tasks and proposers must describe the work proposed in each task in detail.
Deliverables shall include, at a minimum:
1. A review of the literature and the current practices of U.S. and international organizations to estimate and incorporate recycled binder availability into mix design.
2. A work plan for Phase II to identify or develop methods to (a) quantify binder availability from recycled asphalt materials and (b) based on the availability of recycled asphalt binders, measure the impact on mix performance of recycled asphalt materials incorporated in asphalt mixes prepared with a range of virgin, rubberized, and modified asphalts.
3. An interim report that presents (a) the review of the literature and current practices and (b) the proposed Phase II work plan.
Note: The contractor shall meet with NCHRP within 2 months of submitting the Phase I interim report to obtain approval to conduct the Phase II work plan.
1. A report presenting the results of the conduct of the work plan approved in Phase I, their analyses, and proposed AASHTO standard methods to (a) quantify binder availability from recycled asphalt materials and (b) based on the availability of recycled asphalt binders, measure the impact on mix performance of recycled asphalt materials incorporated in asphalt mixes prepared with a range of virgin, rubberized, and modified asphalts.
2. A proposed AASHTO standard practice to incorporate binder availability of recycled asphalt materials into mix design procedures and measure the impact of the recycled asphalt materials on mix performance, with supporting commentary.
3. Proposed revisions to existing AASHTO standard specifications and mix design procedures for recycled asphalt materials to incorporate recycled binder availability and its impact on performance, with supporting commentary.
4. Guidelines for incorporating proposed AASHTO methods and practice into routine use.
5. A final report that documents results, summarizes findings, draws conclusions, and presents (a) the proposed AASHTO standard methods and practice with supporting commentary and (b) the proposed guidelines. An appendix to the report shall include electronic files of all data obtained in the project and the results of the analyses conducted with the data.
STATUS: Proposals have been received in response to the RFP. The panel will meet to select a contractor to perform the work.