MnROAD | NRRA | Structure & Teams | Flexible Team
Validation of Loose Mix Aging Procedures for Cracking Resistance Evaluation in Balanced Mix Design (Phase IIA)
MnDOT Contract Number: 1036333
Status: Active
Project Start Date: May 22, 2024
Project End Date: September 30, 2026
Phase IIA Project Highlights
Background
The overall project seeks to validate loose mix aging for cracking resistance evaluation of asphalt mixtures in balanced mix design (BMD). Phase I efforts included conducting a literature review, research gap analysis, and developing a Phase II work plan to address two major gaps associated with implementing loose mix aging in BMD. Phase II-A aims to establish the conversion of different loose mix aging procedures based on the kinetics model developed in NCHRP project 9-54. To that end, asphalt mixtures covering a wide range of mixture components will be tested with the Indirect Tensile Asphalt Cracking Test (IDEAL-CT) and Disc-shaped Compact Tension (DCT) Test to characterize their intermediate-temperature and low-temperature cracking resistance over various loose mix aging conditions. The results will be used to determine the equivalence of loose mix aging at 95°C versus 100-125°C and 135°C, which allows state highway agencies (SHAs) to use an accelerated, yet robust aging procedure to evaluate the cracking resistance of asphalt mixtures in BMD in cases where the 95°C aging procedure is considered impracticable because of the long aging duration required.
Objective
The research will enhance the current practice of SHAs, including the Minnesota Department of Transportation, for evaluating the cracking resistance of asphalt mixtures in BMD by considering the impact of aging. A successful implementation of BMD will improve the performance and longevity of asphalt pavements while allowing the use of locally available, recycled, and innovative materials for environmental and economic benefits.
Scope
Plant-produced asphalt mixtures covering a wide range of mixture components will first be tested with the IDEAL-CT and DCT at different loose mix aging conditions. The results will be analyzed for each individual mixture to determine the equivalent aging temperature (T20hr) of the 20-hour, 100-125°C aging procedure and the equivalent aging time (t135°C) of the 135°C aging procedure that corresponds to a reference aging condition at 95°C. The aggregated T20hr and t135°C results among all the mixtures will then be used to determine the conversion of loose mix aging procedures at 95°C versus 100-125°C and 135°C based on the aging kinetics model developed in NCHRP 9-54. Finally, the aging conversion relationships will be tested against selected asphalt mixtures prepared in the laboratory to verify their suitability to lab-mixed, lab-compacted (LMLC) specimens for mix design approval versus plant-mixed, lab-compacted (PMLC) specimens for production acceptance.
Tasks
Task 1: Experimental plan development
The research team will develop an experimental plan to determine the conversion of different loose mix aging procedures based on the kinetics model developed in NCHRP 9-54. A wide range of plant-produced asphalt mixtures will be selected, including those containing non-traditional additives, such as recycling agents, recycled plastics, synthetic fibers, and recycled tire rubber. When selecting the mixtures, priority will be given to those with loose mix aging data available from previous studies. The experimental plan will focus on the IDEAL-CT and DCT testing using three loose mix aging procedures: 95°C, 100-125°C, and 135°C. The IDEAL-CT and DCT are selected for several reasons: (1) they are the most common tests used or considered by SHAs to evaluate the intermediate-temperature and low-temperature cracking resistance of asphalt mixtures in BMD (Harman, 2023; NAPA, 2024); (2) they have a strong correlation to field cracking performance in the NCAT/MnROAD cracking group experiments (West et al., 2021; Vrtis et al., 2023); and (3) they are sensitive to loose mix aging as documented in Phase I final report (Yin et al., 2023). Extracted binder testing is not considered because of the challenges associated with solvent extraction and recovery of asphalt mixtures containing dry additives. Furthermore, it is not feasible to use extracted binder data for cracking resistance evaluation in BMD. It is anticipated that approximately 60 and 45 mixture-aging condition combinations will be tested with the IDEAL-CT and DCT, respectively.
- Deliverable: A progress report summarizing the experimental plan, including mixture selection, material sampling, laboratory testing plan, and data analysis
- Due date: September 30, 2024
Task 2: Experimental plan execution
The research team will execute the experimental plan developed in Task 1. Each plant-produced mixture will be aged with various loose mix aging procedures and tested in a single lab to avoid additional variability associated with specimen preparation in different labs. The IDEAL-CT and DCT results will be analyzed to develop conversion relationships for loose mix aging at 95°C versus 100-125°C and 135°C. Figure 1 presents a conceptual illustration of the anticipated mixture-specific aging data analysis for each cracking index parameter [i.e., cracking tolerance index (CTIndex) for the IDEAL-CT, and fracture energy (Gf) for the DCT], where the 135°C aging results are plotted against the 95°C aging results to determine the equivalent aging time (t135°C). The same analysis will be conducted for the 20-hour, 100-125°C aging results to determine the equivalent aging temperature (T20hr). The aggregated t135°C and T20hr results across all the mixtures will then be used to develop the aging conversion relationships while considering the NCHRP 9-54 aging kinetics model. This approach has been proven successful in Zhou et al. (2022). As illustrated in Figure 2, the aging conversion relationships provide alternative aging procedures at 100-125°C and 135°C that are equivalent to a given reference aging condition at 95°C in terms of their impacts on the IDEAL-CT and DCT results, but are more practical for use in BMD because of the shorter aging durations (for example, loose mix aging for 6 hours at 135°C versus 3 days at 95°C).
- Deliverable: A progress report documenting the laboratory test results and aging conversion relationships for the IDEAL-CT and DCT.
- Due date: October 31, 2025
Task 3: Validation of aging conversion relationships
The research team will validate the aging conversion relationships developed in Task 2 with three additional mixtures using both LMLC and PMLC specimens. This validation effort aims to determine if the aging conversion relationships would apply to LMLC specimens for mix design approval versus PMLC specimens for production acceptance in BMD. Each mixture will be tested with the IDEAL-CT and DCT at three loose mix aging conditions, including a pre-determined reference aging condition at 95°C and two equivalent aging conditions for the 20-hour, 100-125°C and 135°C procedures, respectively. The aging conversion relationships will be considered validated if the mixtures have equivalent IDEAL-CT and DCT results at the three aging conditions for both LMLC and PMLC specimens.
- Deliverable: A progress report documenting the development of loose mix aging conversion relationships and the validation results.
- Due date: April 30, 2026
Task 4: Final report and National Road Research Alliance (NRRA) Webinar
The research team will submit a final report and conduct an NRRA Research Pays Off webinar to document the test results and findings of the project and provide recommendations on implementing loose mix aging for evaluating the cracking resistance of asphalt mixtures in BMD.
- Deliverables: 1) A final report and 2) an NRRA Research Pays Off webinar.
- Due date: September 30, 2026
Project team
Email the Project Team
Principal Investigator: Fan Yin, f-yin@auburn.edu, National Center for Asphalt Technology
Co-Principal Investigators: Raquel Moraes, moraes@auburn.edu; and Chen Chen, czc0105@auburn.edu, National Center for Asphalt Technology; Jo E. Sias, Jo.Sias@unh.edu; Eshan Dave, Eshan.Dave@unh.edu, University of New Hampshire; and Fujie Zhou, f-zhou@tti.tamu.edu, Texas A&M Transportation Institute
Technical Liaison: Joseph Podolsky, MnDOT, Joseph.Podolsky@state.mn.us
Technical Advisory Panel (TAP): Contact us to join this TAP
- Brandon Brever, MAPA
- Ashley Buss, Iowa DOT
- Curt Dunn, North Dakota DOT
- Daniel Kopacz, P.E., Wisconsin DOT
- Oak Metcalfe, Montana DOT
- Dan Oesch, Missouri DOT
- Joseph Podolsky, Minnesota DOT (TL)
- Punyaslok Rath, University of Missouri
- Dylan Specht, Illinois DOT
- Joseph Voels, Minnesota DOT
- Hao Yin, Horizon Engineering Consulting
Related materials
- Workplan (PDF), 5/31/2024