Minnesota Department of Transportation

511 Travel Info

Road Research

NRRA Flexible Team

Orange barrels on a highway

MnROAD | NRRA | Structure & Teams | Flexible Team

Long-term Testing and Analysis on Asphalt Mix Rejuvenator Test Sections (Phase II)

Status: Active
MnDOT Contract #: 1036343-WO1
Project Start Date: August 24, 2020
Project End Date: August 31, 2024

Project objectives

Asphalt rejuvenators 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. Rejuvenating agents (RAs) are relatively new in the HMA industry and there are many different products marketed to transportation agencies. However, most of these products have limited field and laboratory test data available to support their effectiveness over time. Several recent research efforts have shown that some products, while effective immediately after production, show rapid decrease in effectiveness with aging. Therefore, there is a need for a better understanding of how various RAs perform over time through both laboratory and field evaluations to help guide engineers on appropriate usage of these materials.

The National Road Research Alliance (NRRA) Flexible Team constructed field test sections as part of a mill and overlay project on Trunk Highway 6 (TH6) located in Emily, MN in August of 2019. These field sections include 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 are control sections with 40% RAP and 30% RAP (the maximum level allowed on remainder of this project).

The objective of this research project is to evaluate the effectiveness of the seven RA products over time and evaluate their performance as compared to the control mixtures. This will be accomplished through a combination of binder and mixture characterization and performance testing using different laboratory aging levels, field core testing, and performance monitoring of the field sections over time.

Project tasks

Task 1: State of the art review, determination of additional laboratory long-term mixture conditioning method

The research team will review the NRRA Mix Rejuvenator Synthesis and perform a search for subsequent publications (e.g. from TRB 2020 and 2020 AAPT Symposium) that should be included for informing the coring and monitoring plan as well as the testing and analysis to be conducted in this project. Based on existing literature and experience of the research team, changes due to the inclusion of RAs occur quickly (typically within first two years of pavement service).  Therefore, coring of the field sections is recommended to occur once every year for the four years of the project. The next coring cycle would be September/October of 2020. Field monitoring of the sections is recommended twice per year: at the time of coring and at the conclusion of each winter season (since substantial cracking distress is expected to occur over winter months). Refinements to the recommended coring and field monitoring schedule will be done based on information from the literature review and discussion with the TAP. In addition, the monitoring and coring schedule may be adjusted on the basis of initial binder testing results (Task 2) and observed field performance during the course of project.

Task 2: Annual Interim Update 1st Year - Initial Construction Results

The research team will summarize and report as-built details of each rejuvenator field section provided by MnDOT, including pavement structure information, mix design details, the type of rejuvenator that was added in each section, available quality assurance process information, and pre-existing pavement condition, if available. Binder extraction and recovery from the loose mixtures sampled during production will be conducted using ASTM D7906 procedure (toluene extraction and rotovap recovery). Rheological and chemical characterization of the recovered binders as well as the virgin and blended binders sampled during production will be performed. Appropriate aging (RTFO and/or 20 hours PAV) will be conducted for grading the various binders according to the Superpave procedure. The binder performance grade (PG) and various rheological indices (e.g. binder Glover-Rowe parameter, ΔTc and R-value) will be calculated. Chemical characterization will be performed using the SARA analysis to determine the typical four fractions of asphalt binders and the FTIR test to evaluate the functional groups within the binder samples. The measured binder low temperature performance grade (LTPG) will be compared to the target LTPG value (-34°C, after 20 hours PAV aging). The two virgin binder sources will be compared to determine how similar/different they are; this will determine if all sections can be grouped together for analysis or the one section with the different source needs to be analyzed separately. Additional comparisons among the various rejuvenators and between the recovered and virgin/in-line sampled binders will be conducted.

Task 3: Plant Produced Mixture and Field Core Testing

Testing and analysis of the various plant mixtures and field cores using laboratory performance tests will be conducted in this task. In addition to the performance tests and aging conditions on plant produced mixtures that are conducted by NRRA members, the research team will conduct complex modulus and direct tension cyclic fatigue tests on all mixtures in the unaged and the 6 hour aging condition (designated by X in Table 1). These two tests will also be performed on the binder layer mixture that is common to all test sections. The evaluation of an additional long-term aging condition would allow for greater differentiation of how the mixtures will perform over time and the Stress Sweep Rutting (SSR) test would complete the suite of testing in the FHWA Performance Engineered Mixture Design approach. Due to the limited amount of plant produced mixture available, not all the desired testing can be conducted on all mixtures. Therefore, the research team proposes that initial test results from the DCT testing, the DTCF at the one aging condition, and field performance to date be used to determine which mixtures should be tested at an additional aging condition. Similarly, the results from the HWTT will be used to determine which mixtures should be tested with the SSR.

Field cores taken over time will be subject to complex modulus and fatigue testing using the small specimen geometry to track the material property changes occurring in the field and to allow for comparison to laboratory aged conditions. Fatigue and rutting analysis will be conducted using the FlexMATTM and FlexPAVETM software. Pavement evaluation of each test section will be conducted using the as-built section information, actual traffic, local climate information, and measured material properties.

Task 4: Binder Testing

Task 4 will focus on laboratory testing of the binder samples included in this project. Various types of binders will be evaluated. In addition to the same rheological and chemical characterization performed in Task 2 (complex modulus and phase angle master curves, rheological indices, continuous PG temperatures, SARA and FTIR), the LAS test will be conducted to characterize the binder fatigue properties. Testing on the binders with various laboratory aging conditions and field aging durations will: (1) fully capture linear and non-linear performance properties of the binders containing the study rejuvenators over full range of aging conditions (construction to long term); and, (2) correlate the different laboratory aging conditioning methods with field aging durations. Including the characterization of the RAP binder will provide more information on how the different project rejuvenators improved the binder performance properties to lower the impacts of aged binder in the mix. The testing and analysis of results from the binder tests in this task will be used to compare and correlate with mixture performance test results from Task 3.

  • Scheduled Date to Submit Draft Deliverable: August 2023
  • Deliverables: A Task 4 report will be submitted to summarize the results from the binder tests conducted on the virgin and plant produced materials; available field core results will also be included. The comparisons and correlations between the binder measurements with the mixture test results will also be reported. A project update presentation will be given by the research team to Technical Advisory Panel.

Task 5: Annual Interim Update 2nd and 3rd Year

The research team will prepare reports that summarize the results of additional testing and analysis conducted on project materials and field cores and field performance of the test sections 24 and 36 months after the contract start date. A presentation of the results to date will be given to the TAP and/or through the NRRA Research Pays Off webinar series at these times as well.

  • Scheduled Date to Submit Draft Deliverable: August 2023; August 2024
  • Deliverable: 3rd Year report (PDF), 12/5/2023

Task 6: Final Report

The research team will prepare a draft final report, following MnDOT publication guidelines, to document project activities, findings, and conclusions. The report will also include any recommendations for further testing and monitoring of the sections. The draft final report will be submitted six weeks prior to the contract end date for review by the TAP.  A TAP meeting will be scheduled approximately one month prior to the contract end date for presentation of the results and to facilitate the discussion of the draft report.  The report will then be updated to incorporate TAP comments and feedback.

  • Scheduled Date to Submit Draft Deliverable: August 2024
  • Deliverable: Final report following MnDOT publication guidelines

Project team

Email the Project Team
Principal Investigator: Jo Sias, University of New Hampshire, jo.sias@unh.edu
Technical Liaison: Michael Vrtis, MnDOT, michael.vrtis@state.mn.us
Project Technical Advisory Panel (TAP): Contact us to join this TAP

  • Jason Bausano, Ingevity
  • Curt Dunn, NDDOT
  • Mohamed Elkashef, UC Davis
  • John Garrity, MnDOT
  • Andrew Hanz, Mathy
  • Brian Hill, Iowa DOT
  • Bob Kluttz, Kraton
  • Alex McCurdy, Poet
  • Pete Montenegro, Collaborative Aggregates
  • Nathan Moore, NCAT
  • Terry Naidoo, Asphalt and Wax Innovations
  • Paul Nolan, MnDOT
  • Dan Oesch, MoDOT
  • Barry Paye, WisDOT
  • Brad Roderick, Bakelite
  • Raghu Shrestha, Caltrans
  • Hassan Tabatabaee, Cargill
  • Nam Tran, NCAT
  • Michael Vrtis, MnDOT (TL)
  • Randy West, NCAT
  • Chris Williams, Iowa Sate University
  • Tyler Wollmuth, NDDOT

Related materials