Laboratory Performance of Re-Refined Engine Oil Bottoms (REOB) Modified Asphalt

Re-refined engine oil bottoms (REOB) are one of several products obtained in the refining of recovered engine oil and have been used in the asphalt industry since the 1980’s. Generally, REOB is used to help soften the base asphalt binder and is commonly used from 3 to 10% by weight in order to achieve desired low temperature asphalt binder properties. Recently, poor cracking performance in a number of Canadian and northern United States pavement sections have been blamed on the use of REOB to modify the asphalt binder. This has prompted state agencies in the northeast United States to ban its use, without necessarily understanding how REOB affects asphalt binder and mixture performance. A research effort was conducted to evaluate the laboratory performance of asphalt binders and mixtures modified with REOB. Two different sources of REOB were blended with different base asphalt grades at varying dosage rates in the study to achieve “softer” asphalt binders—similar to the current practice of REOB modification in the asphalt industry. Performance grading, master stiffness curves, double edged notch tension test, and Black Space analysis were conducted on the asphalt binders at different levels of laboratory aging. Additionally, the asphalt binders were used to produce asphalt mixtures for stiffness, permanent deformation, fatigue cracking and low temperature cracking performance. The research study showed that while being able to achieve softer asphalt binder grades in accordance with AASHTO R 29, the addition of REOB accelerates the age hardening effects in the asphalt binder, with higher levels of age hardening occurring at higher REOB dosage rates. The study also indicated that while the stiffness properties at low temperatures are not impacted by the REOB, the relaxation properties, as measured using m-slope of the Bending Beam Rheometer (BBR), are highly affected. Both the Black Space analysis, using the Glover-Rowe approach, and the DENT test show promise at identifying the age hardening effects and correlated well to mixture fatigue cracking in the Overlay Tester. Differences were found between the various asphalt mixture fatigue cracking tests in their respective ranking of fatigue cracking performance. Asphalt mixture permanent deformation and dynamic modulus of REOB modified asphalt mixtures showed similar performance to the neat asphalt binders when compared to the REOB modified asphalt binders of the same PG grade.