Testing of Fine Asphalt Mixtures to Quantify Effectiveness of Asphalt Binder Replacement Using Recycled Shingles

Recycled asphalt shingles (RAS) can be used effectively in asphalt mixtures to replace part of the virgin asphalt binder or virgin aggregates in the mix. The influence of using RAS was studied on fine asphalt mixtures (FAM) prepared with fine aggregates (FM-20) and RAS percentages mixed with either PG 46-34 or PG 64-22 asphalt binder. The study's main objective was to develop alternative testing protocols to evaluate the influence of recycled materials on asphalt mixture performance. FAM specimens were prepared with two types of binder (PG 64-22 and PG 46-34) and at three levels of RAS (0.0%, 2.5%, and 7.1% RAS from two RAS sources). The testing program for the FAM specimens included complex shear modulus, shear strength, and fatigue (stress and strain control modes) using the Superpave dynamic shear rhemeter with modified testing features. Results from FAM specimens were shown to be consistent and sensitive to varying RAS percentages and sources. The complex modulus also changed significantly when another RAS source was used. The FAM results indicated distinct changes in viscoelastic characteristics of materials with RAS similar to those usually observed in mixture level. Strain control fatigue test results showed an increase in fatigue failure potential with higher RAS amounts, whereas stress control fatigue testing showed an opposite trend. With different types of tests and at different scales (mix, FAM, and binder) FAM testing can be used effectively to quantify effects of RAS on asphalt mixtures and can be used effectively to address RAS source variability.