Impacts of recycled binder availability on volumetric mixture design and performance

ABSTRACT

The use of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt mixtures is a routine process. Recycled binder availability reflects the proportion of the total recycled binder in a given recycled asphalt material (RAM) that is available to blend with the virgin binder. Studies show that agglomerations of adhered RAM particles preclude complete availability. However, the Superpave volumetric mixture design methods adopted by the majority of state agencies assume complete availability. This study makes use of a sieve analysis method and tracer-based microscopy analysis to quantify recycled binder availability. Revisions to asphalt mix design procedures to account for partial availability are proposed, including consideration of the unavailable binder as part of the bulk aggregate volume and the use of the RAM gradation (i.e. black curve) rather than the recovered aggregate gradation (i.e. white curve) to design the mixture’s aggregate structure. Three high RAM content ‘control’ mixtures that were originally designed under the assumption of complete recycled binder availability are redesigned according to the proposed approach. The redesigned mixtures had notably higher virgin binder content than the control mixtures. The redesigned mixtures also had significantly better cracking resistance than the control mixtures while still meeting permanent deformation requirements.

KEYWORDS:

• Recycled asphalt materials
• recycled binder availability
• mix design
• performance

Acknowledgements

This work was supported by North Carolina Department of Transportation under the Research Project 2019–2021. The methodology, discussion, and conclusions presented in this paper reflect the views of the authors only, and not necessarily the views of the North Carolina Department of Transportation. Materials were graciously donated by Barnhill Contracting Co., Fred Smith Co., and Highland Paving Co. The authors would also like to acknowledge Sonja Pape and the staff at Trimat Materials Testing, for their assistance in conducting supplemental analysis of the materials.

Disclosure statement

No potential conflict of interest was reported by the author(s).