Laboratory Evaluation of Vacuum Tower Asphalt Extenders Impact on HMA Fatigue Resistance and Asphalt Binder Aging

Interest has increased related to the impact of asphalt binders containing Vacuum Tower Asphalt Extender (VTAE), the non-distillable fraction from the re-refining of used engine oils, on Hot Mix Asphalt (HMA) performance. Recently published research has provided conflicting results that the addition of VTAE to asphalt may cause premature aging and cracking in HMA pavements. This laboratory study provides information on binder aging characteristics and HMA fatigue resistance of specimens with and without VTAE. One source of VTAE at 9% was blended with performance grade (PG) 64-22 to achieve binder grade of PG 58-28. A second PG 58-28 of similar binder stiffness was formulated with the same PG 64-22 and PG 52-28 to serve as control binder. HMA mix designs following Illinois Department of Transportation volumetric requirements were completed for each binder. The mixes were then evaluated for fatigue resistance using the four point repeated flexural bending test in short and long term aged conditions. Asphalt binders from both the short and long term aged beam samples were extracted, recovered and tested for binder grade characterization. The results indicate that the HMA mixture with the VTAE blended asphalt had equal or increased fatigue resistance in both the short term and long term aged conditions. Binder grade characterization results showed that no appreciable difference in the aging between PG 58-28 VTAE sample and neat PG 58-28 samples after rolling thin-film oven (RTFO) and pressure aging vessel (PAV) aging. Binders extracted and recovered from HMA subjected to long term aging showed no significant difference in stiffness or low temperature properties.