Using Binder and Mixture Space Diagrams to Evaluate the Effect of REOB on Binders and Mixtures after Aging

This study was conducted to address some of the New England state transportation agencies’ concerns associated with the use of Re-refined Engine Oil Bottoms (REOB) in asphalt binders and mixtures. The effects of REOB on the physical and rheological properties of an asphalt binder were investigated. This evaluation was completed after AASHTOspecified short-term and long-term aging and after extended long-term aging. Also, the effect of REOB modified binders on the performance of asphalt mixtures after short- and long-term aging was evaluated in terms of moisture damage, rutting, and cracking. Two straight run binders (PG 58-28 and PG 64-22), a typical PG 64-28, two sources of REOB, an aromatic oil, and PolyPhosphoric Acid (PPA) were utilized. The PG 64-22 was modified with each source of REOB separately to attain a PG 58-28. These modified PG 58-28 binders were compared to the straight run PG 58-28. The modified and the straight run PG 58-28 binders were further modified with PPA to attain a PG 64-28 which is commonly specified in the Northeast. This modified PG 64-28 was compared to a typical PG 64-28 that has been used in the past without REOB. This same binder modification to attain a PG 58-28 and PG 64-28 was repeated with the aromatic oil for comparison purposes. Rheological results plotted on the Black Space and wo—R-value Space diagrams showed that the addition of REOB to attain the PG 58-28 caused the binders to age more relative to the straight run binder. The results also indicated that the use of higher dosages of REOB can cause increased binder aging. Mixture moisture damage tests showed that REOB could result in mixture premature failure. The rutting tests indicated that generally the REOB did not cause the mixtures to fail. Cracking tests conducted at intermediate temperature on REOB-modified mixtures generally indicated a reduction in fracture energy, as compared to the straight run or typical binder counterpart. A flexibility index (FI) calculated from the same cracking test showed that the aromatic oil modified mixtures generally had a higher value than the REOB modified mixtures suggesting less susceptibility to cracking. Interaction plots developed using the FI and Hamburg test results revealed significant differences among mixes with various binder formulations and the effects of long-term aging on the interaction plots were evident. Low temperature cracking evaluations detected minor effects on low-temperature fracture properties associated with various combinations of REOB tested. Performance space diagrams indicated that the REOB modified mixtures remained within the passing zone in a Hamburg Wheel Tracking-Disc Shaped Compact Tension DC(T) tests diagram for low to medium traffic level. Overall, the particular mixture tests used in this study did not provide evidence that using REOB decreases performance. The performance data collected by using the two REOB sources varied by the particular test, and sometimes by the type of REOB or by the PG of the binder. The use of aromatic oil did not show this variability and the results generally indicated good performance. The variability of the data when REOB was used underscores the importance of thoroughly testing REOB modified binder and mixture for performance. Finally, other important issues like dosage and consistency of REOB are still currently being investigated.