An Evaluation of Reclaimed Asphalt Shingles for Beneficial Reuse in Roadway Construction

A large-scale recycling and reuse application of scrap shingles would utilize an otherwise wasted resource while clearing landfill space and creating new business opportunities. One potential reuse application is the use of reclaimed asphalt shingles (RAS) as an additive or substitute for the earth materials typically used in the aggregate base (AB) and subbase (ASB) layers of roadway pavements. The purpose of this study was to determine the technical specifications of RAS, the effect of fly ash stabilization on RAS strength, and the practicality of the widespread implementation of RAS in the AB and ASB layers of roadway pavements. RAS, fly ash stabilized RAS (S-RAS), RAS-aggregate mixtures, and RAS-silt mixtures were evaluated for particle size characteristics, compaction characteristics, CA Bearing Ratio (CBR), unconfined compressive strength, and resilient modulus. According to the results of the testing protocol, unstabilized RAS is unsuitable as base material although RAS could potentially be used as subbase or general fill material. RAS-aggregate mixtures are suitable for use as subbase and are potentially suitable as base course in an unstabilized state; however, RAS-aggregate mixtures exhibited decreasing resilient modulus with increasing RAS content. Fly ash stabilized RAS (S-RAS) was less susceptible to penetrative deformation than unstabilized RAS, however, S-RAS was still highly susceptible to penetrative deformation when unpaved. Fly ash stabilization of RAS generally provided less improvement in resilient modulus compared to fly ash stabilized low-plasticity clays. This may be due to the high asphalt content of RAS particles and resulting diminishment in pozzolanic activity and/or the diminished particle interconnectedness for cementation. Other forms of stabilization, such as cold asphalt emulsion, may be more effective in strengthening RAS. Further evaluation of alternative stabilization methods and additional studies to evaluate the practicality of RAS in other geotechnical applications such as embankment fill, filter, and/or drainage material are recommended.