Hanz, Andrew

Asphalt rejuvenators, or recycling agents (RA), are used to incorporate higher amounts of Reclaimed Asphalt Pavement (RAP) in Hot Mix Asphalt (HMA) without detrimentally impacting the long-term performance of the pavement. The National Road Research Alliance (NRRA) Flexible Team constructed field test sections as part of a mill and overlay project in northern Minnesota in August of 2019. These field sections included wearing courses with 40% RAP that incorporate seven different RA products, with the dosage determined by the supplier to meet a target extracted and recovered performance grade (PG) of XX-34. In addition to the RA test sections, there were control sections with 40% RAP and 30% RAP (the maximum level allowed on the remainder of this project). The objective of this research project was to evaluate the effectiveness of the seven RA products over time and evaluate their performance as compared to the control mixtures. This was accomplished through a combination of binder (chemical and rheological) and mixture characterization and performance testing using different laboratory aging levels, field core testing, and performance monitoring of the field sections over time. This report documents the results after four years in service with cores taken annually. The study showed that all RAs exhibit improved rheological properties in 1-year field cores. However, the benefits of RA diminish with field aging, and after four years, some RAs show comparable properties with controls. In terms of mixture properties, the inclusion of RA enhances both rheological properties and fracture and fatigue crack resistance initially.

This study evaluated the impact of polymer modification, without changing the base binder, on the intermediate-temperature cracking resistance of asphalt mixtures characterized using the Indirect Tensile Asphalt Cracking Test (IDEAL-CT) and the Illinois Flexibility Index Test (I-FIT). Twelve asphalt mixtures prepared with two mix designs and six virgin binders (including two unmodified and four polymer-modified asphalt binders per mix design) were evaluated. Each mixture was tested at three binder contents and two temperatures: 25°C and an equal stiffness temperature (T=G*). In almost all cases, the polymer-modified asphalt (PMA) and unmodified mixtures with the same base binder had statistically equivalent IDEAL-CT and I-FIT results, indicating a lack of sensitivity to polymer modification. Increasing the binder content or adjusting the test temperature to T=G* did not discriminate the PMA and unmodified mixtures in the two tests. Interaction diagram analysis of the IDEAL-CT and I-FIT results showed that polymer modification generally affected the toughness and post-peak behavior of the mixture, but these effects tended to offset each other on the final cracking index parameters. Unlike the IDEAL-CT and I-FIT, the two cyclic loading tests evaluated in the study demonstrated the benefits of polymer modification. This discrepancy highlighted the potential limitation of the monotonic loading tests in assessing the fatigue cracking resistance of PMA binders and mixtures. Finally, asphalt binders extracted from the PMA versus unmodified mixtures with the same base binder showed distinctly different rheological properties, but these differences were not captured in the IDEAL-CT or I-FIT when the test variability was considered.