Research on High-RAP Mixtures with Rejuvenators - Field Implementation

Background The use of reclaimed asphalt pavement (RAP) materials has been increasing quite rapidly over the past few decades, and many Departments of Transportation (DOTs) have been consistently interested in increasing the amount of RAP in their asphalt concrete (AC) mixtures. Currently, Nebraska DOT allows RAP materials in some plant mixtures for asphalt pavements up to about 50%. The major motivation for the utilizing of high-RAP content mixes for the pavement is due to the advantage of lowering the use of expensive virgin aggregates and binders, recycling of construction materials and environmental preservation. The use of high-RAP mixture is typically incorporated with softening agents (usually referred to as rejuvenators) to improve AC mixture properties. This inherently induces various complexities such as: (1) the interaction of the aged RAP materials with the virgin materials and their influence on the overall performance of the AC mixture, and (2) the interaction of the softening or rejuvenating agent with the aged RAP and virgin binder. Another important factor that affects the performance of the high-RAP pavements in the field is the methods and technologies adopted by the plants or manufacturers producing mixtures. Although many studies have investigated the influence of rejuvenators on the laboratory performance of high-RAP AC mixtures, the laboratory-level investigation is not sufficient to address how production parameters affect blending of rejuvenators, RAP and virgin materials and eventually their influence on the field performance of the rejuvenator treated high-RAP AC mixtures. When using high-RAP in our AC mixtures the key factors to be considered include but are not limited to: (i) the use of right rejuvenators based on their chemical-mechanical properties, (ii) the use of an optimal dosage and blending method of the selected rejuvenator to satisfy desired mixture and pavement performance. Performance indicators such as rutting, cracking and moisture susceptibility are some of the important distresses that need to be evaluated in the laboratory. For the last four years, the Pl has conducted NDOT-sponsored research projects on high-RAP mixtures treated with rejuvenators. The research was conducted in two phases and in both, 65% RAP was applied to a typical Nebraska AC mixture. Three different rejuvenators: petroleum-tech based, green-tech based, and agriculture-tech based materials were used, this ensured variability in the chemical properties of the rejuvenators. The research project evaluated various mechanical and chemical properties of AC mixtures, fine aggregate matrix (FAM) mixtures, and binders modified by the rejuvenators. Test results in different length scales (i.e., AC, FAM, and binder) demonstrated that the rejuvenators made high-RAP mixtures are more compliant (ductile), which decreased stiffness and improved the fatigue resistance of high-RAP materials. Also, the recommended practices of different rejuvenators were sought by further investigating properties and performance of mixtures/materials at different treatments (i.e., blending dosages and curing methods) of rejuvenators. After determining the optimal dosages, a series of laboratory testing on mixtures treated with the rejuvenators were undertaken to evaluate two primary mixture-level characteristics such as cracking and rutting. The mixture testing results confirmed the observations from the binder-level in that, rejuvenators softened AC and improved its cracking resistance. Several rejuvenator blending methods were also evaluated, and it was concluded that they did not significantly affect the testing outcomes. This implied that after mixing RAP with rejuvenator, curing was not necessary. Furthermore, it was also found that blending rejuvenator into a virgin binder before mixing with virgin aggregates and RAP minimally affected the testing results as well. From the AC mixture testing, it was concluded that homogenous mixing of rejuvenator into RAP was the most important factor in achieving consistent performance from AC mixtures with high-RAP content. Research findings from the Phase I and II imply potential implementation of the high-RAP projects in our state with proper use of rejuvenating agents. Toward that, we propose this field implementation research to monitor and identify critical factors responsible to achieve realistic field-level implementation into future projects. Several measurable indicators such as variability, producibility, properties, and performance of AC mixtures to evaluate the significance of new mixtures into field-level implementation will be used with ample data so that statistically significant findings and outcomes can be reached. This will provide core information to reduce costs in mixture production and improve mixture quality when high amounts of RAP are involved. Objective The objective of this research is to implement the findings from Phase-I and II into field­ level and investigate the performance of the high-RAP mixture treated with optimal dosage of selected rejuvenators. Plant production parameters that influence blending of rejuvenators, RAP, and virgin materials will also be investigated. More specifically, we will collect and evaluate plant-produced and field-implemented mixtures where high-RAP (e.g., 50% RAP) was modified by optimal treatment of rejuvenators to evaluate variability, producibility, properties, and performance of AC mixtures placed in pavements.

    Language

    • English

    Project

    • Status: Active
    • Funding: $ $99,950.00
    • Sponsor Organizations:

      Nebraska Department of Transportation

      1500 Nebraska 2
      Lincoln, Nebraska  United States  68502
    • Project Managers:

      Halsey, Lieska

    • Performing Organizations:

      University of Nebraska, Lincoln

      1400 R Street
      Lincoln, NE  United States  68588
    • Principal Investigators:

      Kim, Yong-Rak

    • Start Date: 20190701
    • Expected Completion Date: 20201231
    • Actual Completion Date: 0
    • USDOT Program: Transportation, Planning, Research, and Development

    Subject/Index Terms

    Filing Info

    • Accession Number: 01705871
    • Record Type: Research project
    • Source Agency: Nebraska Department of Transportation
    • Files: RiP, STATEDOT
    • Created Date: May 24 2019 3:37PM