Evaluation of Stone-Matrix Asphalt Mixtures Containing Recycled Asphalt Shingles (RAS)

About the report:

In recent years, there has been increased interest in the use of reclaimed material in asphalt mixtures. The use of recycled asphalt shingles (RAS) has been of interest because of the high asphalt content, although this asphalt is considerably stiffer than that typically used in paving mixtures. The Virginia Department of Transportation has specifications allowing the use of post-manufacturing waste and post-consumer RAS, although use has been limited. In addition, the specifications do not provide for the use of RAS in stone-matrix asphalt (SMA). In response to producer requests for RAS use in SMA, this study investigated the use of RAS in SMA mixtures in VDOT’s Salem and Staunton districts.

Mixtures were sampled during production, characterized, and evaluated using a suite of laboratory tests including dynamic modulus, flow number, rut depth, and bending beam fatigue. Test results indicated that, as expected, the inclusion of RAS appears to improve high temperature / low frequency modulus values and rutting resistance. The inclusion of RAS had mixed effects on the mixture performance in laboratory fatigue testing. Binder testing on one set of mixtures indicated that the virgin binder grade may significantly affect the degree of blending of the RAS binder. In addition, extracted binder Delta Tc values indicated that the inclusion of either RAP or RAS may have adverse impacts on cracking susceptibility. These findings should be validated with field performance and additional mixtures.

The study recommends that the Virginia Department of Transportation not change specifications to allow RAS in SMA at this time. In specific situations, the use of RAS in SMA should be approached judiciously, as when effectively located and properly designed, produced, and placed. RAS mixtures have the potential for improved rutting performance, although impacts on cracking performance must be carefully assessed.

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