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

Status: Contract Development


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.

Project goal

The NCAT-TTI-UNH research team proposes a two-phase study to accomplish the research objective. Phase I study seeks to extensively leverage the ongoing research efforts in different regions of the U.S. on the development, evaluation, and preliminary validation of candidate loose mix aging protocols. The research team will synthesize the existing binder and mixture test results, conduct critical data review and analysis, identify research gaps, and develop an experimental plan for Phase II.

It is anticipated that the Phase II experimental plan will include the following tasks:

  1. Selection of several existing and new field projects in different climate zones in the U.S. that allow the sampling of field cores at various in-service times, plant mixes, and raw component materials for research evaluation.
  2. Laboratory characterization of field cores, plant mixes, and laboratory produced mixes at various aging conditions based on comprehensive mixture performance testing as well as rheological and chemical testing of extracted asphalt binders.
  3. Data analysis to determine the correlation between field aging and the candidate loose mix aging procedures.
  4. Identification of appropriate parameters to assess aging effects on asphalt binders’ performance, considering the complexity introduced by various additives such as recycling agents, recycled plastics, crumb rubber, etc.

From the experimental plan that will be used in Phase II existing and new test sections on MnROAD and the NCAT Test Track as well as roads in NRRA states can be used where the research team will obtain raw materials, loose plant mix, and field cores (annually sampled for up to five years); thus, it will significantly leverage existing research projects without needing dedicated test sections. It is anticipated that the Phase II study based on the developed experimental plan in Phase I will lead to recommendations and guidance for implementation of loose mix aging processes that simulate field aging through balanced mix design performance testing for NRRA members.

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) - email the 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
  • 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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