Characterization and Micromechanical Investigation of Recycled Asphalt Shingle Binder Blends

The sustainability movement has established a firm foothold in the Civil Engineering profession. The use of recycled asphalt shingles (RAS) is the latest development in the world of asphalt pavement sustainability. The relative abundance of tear-off shingles and their high asphalt content is driving RAS usage in highway and airfield pavements. However, the ultimate objective of any pavement system is to provide a structural and functional roadway that can allow users to safely travel. Both state highway engineers and the general public need to be assured that the end product will not compromise performance. The performance grade of virgin asphalt binder will likely be altered when RAS is introduced into the asphalt mixture. The resulting Superpave material properties need to be predicted in order to assess that the mixture will perform adequately. In an experimental campaign which sought to investigate this, virgin PG 64-22 and PG 46-34 binders were blended with RAS binder at various percentages. Superpave material properties were measured and the performance grades determined for all binder blends. Prediction of complex shear modulus and flexural creep stiffness were then attempted using Hashin and Shrikman's Arbitrary Phase Model. Use of calibration factors were found to accurately predict high temperature complex shear modulus, however, the model produced unexpected results for low temperature flexural creep stiffness. Micromechanical models that take into account the viscoelastic nature of asphalt would be expected to give an accurate prediction of material properties and should be pursued in further research. Finally, these micromechanical models should be incorporated into a practical system to aid designers in the maximization of recycled materials in asphalt pavements.