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MTE Services was contacted by MN DOT to investigate the low temperature fracture - properties and fatigue properties of three research bituminous mixes which had been constructed at the MNROAD test facility near Rogers, MN in 1999. In addition the SHRP PG test properties of the three binders used on each respective test section were to be determined. The bituminous mixes to be investigated utilized the same aggregate structure and differed only in the binder grade used for each test section. The grades were PG 58-28 (unmodified), PG 58-34 (polymer modified) and PG 58-40 (polymer modified)

The requested work called for the determination of fatigue properties of these mixes using torsional fatigue procedures. This test procedure has been described in detail in a previous report to MN DOT and the interested reader Is referred to that reports. The initial work request was to determine the fatigue properties of the mix as near the surface as impossible. During testing we were asked to also determine and compare the fatigue properties of the binder lift of each core as well. Although that work was not part of the original contract, MTE felt the information was of sufficient value in understanding the rate of fatigue development that we agreed to perform these tests at no charge to the department.

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.