AAPT symposium: Investigating the aging mitigation capabilities of rejuvenators in high RAP mixtures using black space diagrams, binder rheology and mixture tests

This study was undertaken to better understand the effects of rejuvenators on high Reclaimed Asphalt Pavement (RAP) mixtures and to examine these effects after both short and long-term aging to determine if rejuvenators can assist in mitigating the mixture aging due to the RAP. A two tier evaluation was undertaken: (1) examine the rheology of extracted and recovered binders and (2) mixture performance tests. Tests performed on extracted and recovered binders included rheological plots of shear modulus (G^∗) versus phase angle (δ) (commonly known as a Black Space Diagram), rheological parameters derived from master curves using the Christensen-Anderson model (ω₀ - R-value Space diagrams), Superpave Performance Grading (PG) results, critical cracking temperatures, and Multiple Stress Creep Recovery (MSRC) results. The results from these tests were compared to mixture test results for rutting and moisture damage susceptibility, fatigue cracking and low temperature cracking to determine if they correlate. Testing was conducted on a Superpave 9.5mm mixture incorporating 50% RAP by weight of aggregates and a base binder of PG 58-28. A control mixture using all virgin materials was also developed and tested for comparison purposes. A total of four different rejuvenators were evaluated including an aromatic oil, a paraffinic oil, an organic blend developed using green chemistry, and an organic blend based on organic oils. Overall, the data indicated that Black Space diagram and the ω_o - R-value Space diagram were able to capture the aging mitigation effects of each asphalt rejuvenator. These effects were varied based on rejuvenator type. The magnitude of the aging was less severe for certain rejuvenators, which indicated that the type of rejuvenator can play a role in the degree of mitigation of aged binder. Generally the mixture experienced less aging with the use of a rejuvenator regardless of aging period and moved toward the behavior of the control mixture and away from the 50% RAP mixture without rejuvenator. The Black Space diagram and the ω_o - R-value Space diagram agreed with the mixture tests for rutting and moisture damage, fatigue cracking and low temperature cracking. The binder grading results exhibited subtle variances based on the rejuvenator used and aging period. These variances were not always consistent. This indicated that PG tests may not have been as sensitive to aging; however Black Space analysis did show sensitivity to aging. Thus, because the Black Space diagram and the ω_o - R-value Space diagram are simple to develop, these diagrams have the potential to be used as a tool to evaluate the effect of rejuvenators on the mitigation of aging of high RAP mixtures.