BACKGROUND

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.

OBJECTIVE

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;

• Binders;

• Aggregate;

• Optional additives; and

• Production conditions.

STATUS

Research in progress.