Evaluation of Alternative Approaches to Restore the Rheology of Recycled Asphalt Binders

Abstract

This study evaluates the ability of softer virgin binders, recycling agents (RAs), and extenders to restore the rheology of reclaimed asphalt pavement (RAP) binders to that of control binders. Control binders are those binders that would be specified for use with virgin mixtures. Two procedures for RA dosage selection are examined: 1) dose to restore the intended high-temperature grade; and 2) dose to restore the intended low-temperature grade. A broad range of point parameters and rheological parameters that measure the balance of relaxation and stiffness characteristics are examined at two long-term age levels. The results of recycled binder blends are compared with the control virgin binders statistically. Using softer virgin binders generally resulted in blended binder performance-graded properties that were similar to or better than the control. However, these softer binder systems often exhibited other rheological properties that were inferior to the control. The rheological characteristics of the RA blends varied with the RA type and dosage. Blends with dosages that restored the intended high-temperature grade generally yielded the most favorable comparisons to the control binders. RAs derived from triglycerides and fatty acids and from tall oils generally yield more favorable rheological characteristics than those derived from aromatic extracts. In addition, a vacuum gas oil extender achieved similar blend rheological characteristics to RAs but extenders containing re-refined engine oil bottoms generally yielded a poor balance of stiffness and relaxation characteristics. Rheological balance parameters are generally weakly correlated, suggesting they provide unique insight into the rheological behavior of binders.