Investigation of Binder Aging and Mixture Performance in Service: Reclaimed Asphalt Pavement Mixtures

About the report:

In 2007, the Virginia Department of Transportation piloted a specification allowing up to 30% reclaimed asphalt pavement (RAP) in certain dense-graded asphalt surface mixtures while changing virgin binder grade requirements. The change affected only mixtures requiring an end binder grade of either PG 64-22 or PG 70-22. For mixtures specifying PG 64-22 binder, the virgin binder grade at RAP contents of 30% or less was no longer required to change. For mixtures specifying PG 70-22 binder, the virgin binder grade at RAP contents of 21% to 30% was no longer required to change from PG 64-22 to PG 64-28. Prior to this, both types of surface mixtures were allowed to contain only up to 20% RAP before binder grade adjustments were required. An initial laboratory study of mixtures produced under the pilot specification indicated that there were no significant differences for fatigue, rutting, and susceptibility to moisture between the higher content (21% to 30%) RAP mixtures and comparison mixtures (20% RAP or less).

The current study evaluated the in-service performance of these mixtures after approximately 7 years and encompassed field visits and a laboratory investigation of a sample of 23 in-service pavements used in the initial laboratory evaluation. Cores were collected from each site and used to evaluate the binder and mixture properties. These data were compared to data from the original construction, when available, to assess the changes in the mixtures over time. Historical performance and maintenance data were also collected and evaluated to investigate the long-term performance characteristics of the sites.

Laboratory testing, including dynamic modulus determination, repeated load permanent deformation analysis, and extracted binder grading and analysis, consistently showed no trends in the results with regard to RAP content. Overlay test results were influenced by more than just RAP (air-void content, etc.), and therefore no trend directly related to RAP content was shown. No trends in field performance could be determined because of the underlying structural conditions. Individual locations were found to show better or worse pavement performance, but this was attributed primarily to structural differences in the pavements and preexisting conditions. Surface deterioration observed in numerous test sections included fatigue cracking, longitudinal cracking, transverse cracking, raveling, and potholes. Binder analysis indicated that depth within a layer (in this case, top half versus bottom half) significantly affects binder properties, with stiffness decreasing with depth. However, increasing RAP contents appeared to mitigate the differences between the top half and bottom half of layers, possibly because of the preexisting aged composition of the RAP and its influence on the virgin binder properties.

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