Evaluation of Fly Ash Stabilization of Recycled Asphalt Shingles for Use in Structural Fills: Fid-Bau Portal

Evaluation of Fly Ash Stabilization of Recycled Asphalt Shingles for Use in Structural Fills

Soleimanbeigi, Ali / Edil, Tuncer / Benson, Craig

The majority of tear-off roofing shingles and manufacturing shingle scraps are currently disposed of as solid waste in landfills. Landfills are also the end place for the majority of coal combustion byproducts like fly ash. In this study, geotechnical properties of recycled asphalt shingles (RAS) stabilized with a self-cementing fly ash (FA) for use as structural fill material were systematically evaluated. Compaction, hydraulic conductivity, compressibility, shear strength, and coefficient of lateral earth pressure at rest ( $K_{o}$ ) of stabilized RAS were evaluated. The maximum dry unit weight ( $γ_{d \max}$ ) of RAS:FA mixtures varies between $11.3 k N / m^{3}$ and $13.8 kN / m^{3}$ qualifying them as light-weight fill material and the compaction curves are not sensitive to water content. The hydraulic conductivity of RAS:FA varies between $2 \times 10^{- 4} cm / s$ and $3 \times 10^{- 5} cm / s$ for FA content varying between 0% and 20% resulting in a largely drainable material. RAS has a friction angle ( $φ^{'}$ ) of 36° and cohesion ( $c^{'}$ ) of 24 kPa. Addition of 20% FA reduces the $φ^{'}$ to 33° but increases the $c^{'}$ to 100 kPa making it sufficiently strong as a fill material. However, compared to compacted sand, RAS is highly compressible. Stabilizing RAS with more than 10% of FA, keeps the long-term settlement of a typical highway embankment below the typical settlement limit. Stabilized RAS has a $K_{o}$ below 0.1 indicating lower lateral pressures behind retaining walls compared to typical soils. Overall results indicate that RAS stabilized with FA has potential as a lightweight material for use as highway embankment fill or retaining wall backfill.