The use of recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS) is growing due to their economic and environmental benefits. However, the recycled asphalt effective binder availability 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 RAP or RAS.
NCHRP Web-Only Document 450: Recycled Asphalt Materials: Binder Availability and Its Impact on Mix Performance, produced by TRB's National Cooperative Highway Research Program, explores the Glass Beads method for determining the amount of recycled binder from RAP or RAS that activates and contributes to the total effective binder content in an asphalt mixture containing recycled asphalt material. The Glass Beads method was adapted from existing literature and refined based on proof-of-concept evaluations of mixtures prepared with laboratory-prepared RAP samples under different aging conditions. The report includes background on the project, the research approach used to develop the Glass Beads method, findings, applications, and suggestions on area where additional research is needed.
National Academies of Sciences, Engineering, and Medicine. 2026. Recycled Asphalt Materials: Binder Availability and Its Impact on Mix Performance. Washington, DC: The National Academies Press.
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