Minnesota Department of Transportation

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Road Research

NRRA Flexible Team

Validation of Loose Mix Aging Procedures for Cracking Resistance Evaluation in Balanced Mix Design

MnDOT Contract Number:
Status: Active
Project Start Date: April 1, 2022
Project End Date: September 30, 2023


State highway agencies and the asphalt pavement industry have recognized the importance of asphalt aging for evaluating the cracking resistance of asphalt mixtures in balanced mix designs (BMD) as well as performance-based and performance-related specifications. However, research has indicated that the long-term aging procedure specified in AASHTO R30: aging compacted specimens for 5 days at 85°C, is inadequate. Over the last few years, numerous studies have explored loose mix aging as an alternative yet accelerated method of aging laboratory prepared mixtures to simulate the field aging of asphalt pavements. Some of these studies are briefly described as follows:

  • North Carolina State University recommended the use of loose mix aging at 95°C as the long-term aging of asphalt mixtures for performance testing and prediction in NCHRP 9-54. The duration of aging required to simulate in-situ aging of asphalt pavements ranges from days to weeks.
  • NCAT developed the “critical” aging procedure for aging of surface mixtures to simulate the changes in mix and binder properties to the point in time when top-down cracking begins to appear, which requires loose mix aging for 8 hours at 135°C prior to compaction. The procedure was initially developed based on analysis of aging of surface mixes from projects in WA, MI, and AL.
  • TTI established a “mid-term” loose mix aging procedure for conditioning asphalt overlay mixes which often have performed poorly due to reflective cracking. The mid-term conditioning method calls for 20 hours at 100°C prior to compacting cracking test specimens. Note that the loose mix conditioning time and temperature that are same as those of asphalt binder PAV aging used by DOTs and asphalt industry in the last 30 years.
  • UNH has applied the loose mix aging at 95°C and 135°C protocols for a range of NH mixtures and run a range of performance tests. An aging model was developed based on mixture properties and has been correlated with field cores taken after 4 years of service. Two ongoing NRRA projects (Recycling Agents field sections and Compatibility Innovation project) are further evaluating these protocols for application in these projects.

Although these aging procedures showed promising results, they were developed based on a limited number of field projects and component materials. Therefore, further work is needed to validate these procedures with a wider range of field projects with various mixture components, pavement ages, and climatic conditions.


Task 1: Synthesize the Existing Binder and Mixture Test Results

The objectives of Task 1 are to: (1) critically review current and past research on loose mix aging procedures, (2) synthesize existing aging-focused binder and mixture data available at NCAT, UNH, and TTI, as well as those identified from the literature review and from NRRA member states, and (3) conduct critical data review and analysis. Upon completion of this task, the Research Team will prepare a project update report and deliver a presentation to document the Task 1 findings.

Task 2: Annual Interim Update 1st Year

The Research Team will prepare a project update report and make a presentation to the Technical Advisory Panel (TAP) and NRRA members with the interim findings and project schedule from Year 1.

Task 3: Model Development and Experimental Planning for Phase II

The objectives of this task are to identify research gaps based on literature review findings and critical review of existing aging data in Task 1 and develop a comprehensive experimental plan for Phase II study to address the research gaps. The Phase II experimental plan will specifically focus on developing correlations between loose mix aging and field aging, determining the applicability (and limitations if any) of loose mix aging for specialty asphalt mixtures containing various additives, and selecting appropriate parameters to assess the impact of aging on asphalt binder performance. The anticipated data analyses include, but are not limited to, ANOVA and Tukey-Kramer grouping for comparison of various loose mix aging procedures, General Linear Model (GLM) and machine learning analysis (if applicable) to develop field aging evolution models, and statistical correlation analysis for lab-versus-field aging comparisons.

  • Deliverable: Model Development and Experimental Planning for Phase II
  • Due date: March 31, 2023

Task 4: Annual Interim Update 2nd Year

The Research Team will prepare a project update report and make a presentation to the Technical Advisory Panel (TAP) and NRRA members with the interim findings and project schedule from Year 2.

Task 5: Draft Final Report

The Research Team will prepare a final report and deliver a project close-out presentation to: (1) summarize the literature review findings, existing binder and mixture test results from relevant aging studies, and data analysis results and findings from Task 1; and (2) provide the proposed Phase II experimental plan and the anticipated data analysis approach from Task 3.

  • Deliverable: A draft final report for TAP review, and a revised report that is technically complete and approved by the TL for publication.
  • Due date: July 31, 2023

Task 9: Editorial review and publication of final report

The Research Team will revise the final report based on TAP’s review comments to the report and closeout presentation as well as MnDOT’s editorial review feedback to the report.

  • Deliverable: Final Publishable Report
  • Due date: September 30, 2023

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
  • Josh Heck, Montana DOT
  • Daniel Kopacz, P.E., Wisconsin 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

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