Minnesota Department of Transportation

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NRRA Flexible Team

An Innovative Practical Approach to Assessing Bitumen Compatibility as a Means of Material Specification

Contract: TPF-5(341); MnDOT Contract Number: 1036816
Status: Active
Project End Date: April 30, 2022


This project will extensively leverage existing and recently completed MnROAD, NRRA, and national studies; for example, it will utilize materials in on-going MnROAD trials. The project will include an application specific optimization tool for binder formulation; at present, such tool is considered severely impractical. There is need for this high-risk high-reward innovative research that can fill the current knowledge gap and provide a practical tool that can be readily implemented. The application of this work would not be limited to hot-mix asphalt pavements. A similar knowledge gap exists for preservation treatments, specifically for spray applied rejuvenators, whereby chemical compatibility between the existing pavement and the rejuvenator is usually unknown. Similarly, for cold recycling applications, the compatibility between the emulsion or foamed asphalt and RAP is not evaluated due to lack of a characterization method. Another potential application would be in specification of tack coat materials (especially for bonded pavement construction), whereby the asphalt emulsion properties are only controlled in terms of emulsion’s physical properties and emulsifier ionic characteristics.

While the project will focus on utilizing all available tools in the analytical and mechanical characterization processes, the emphasis of this project will be to develop a simple and easy to implement tool kit. The simplicity of the test protocol will be a primary factor in the development process. The University will also develop educational materials as part of this project (such as, implementation manuals and recorded webinars) to aid in implementation of the research outcomes. This project will bring an academic and industry member of NRRA together with complementary strengths in areas of analytical chemistry characterizations and performance testing and modelling.

The research activities for this contract will be undertaken in four main thrusts:

  1. Material Selection: This thrust will focus on additional review of published literature on the topic as well as on
    developing a detailed testing plan that will be executed in subsequent stages. During review of literature, compatibility evaluation systems outside of the asphalt materials domain will also be explored, specifically in fields of organic chemistry and polymer science. In this stage, the materials for field and laboratory evaluation will also be identified. Specific focus will be on identification of known incompatible and known compatible materials, these will serve as control cases in evaluation of different analytical and performance based assessment methods. Note that subsequent thrusts will be conducted in parallel in order to maximize the time and effort, as well as to cross-inform new findings from various tasks and make necessary adjustments.
  2. Analytical Compatibility Assessment: This research thrust will utilize analytical instrumentation for evaluation of the known incompatible, known compatible and intermediate material systems. All testing will be conducted on asphalt binders (virgin and recycled) as well as asphalt binders and rejuvenators.
  3. Binder Performance Assessment: Asphalt binder performance assessment using traditional (such as, standard binder grading tests) as well as recently developed techniques (such as, linear amplitude sweep and rheological indices) will be conducted. This is critical in assessing factors such as impacts of aging on binder blends (virgin and recycled as well as virgin, recycled and rejuvenator) which cannot be done using data coming only from field sections (due to each section only representing one age and substantial costs of installing new sections for each material combination). While field core samples will be sliced to obtain samples representing different levels of aging (due to presence of aging gradient), there will still be question of limited control over the extent of aging. As primary concern with use of recycled asphalt as well as primary application of rejuvenation is typically geared towards cracking performance, major emphasis will be on cracking related performance parameters.
  4. Mixture Performance Assessment: Similar to the binder performance assessment, this research thrust will conduct asphalt mixture performance assessment at various aging levels to expand the data set that will be evaluated using analytical techniques as well as through binder performance assessment beyond the materials represented through pavement test sections. Even with use of slicing techniques to obtain materials with different levels of aging from field cores, most of mix performance tests are unable to utilize sliced specimens with small thicknesses (typically 0.25 inch), thus necessitating lab age conditioning. As with binder performance assessment, the main emphasis will be on cracking performance parameters, however, rutting indices from complex modulus will be evaluated to ensure that final project recommendations do not lead to rutting prone outcomes.


Task 1: Initial memorandum on expected research benefits and potential implementation steps

During the proposal phase and the development of the work plan, key benefits were selected to clearly define the benefits the state will receive from the results and conclusions of this research. Provide an initial assessment of research benefits, a proposed methodology, and potential implementation steps.

  • Deliverable: A memorandum providing initial estimates of expected research benefits, documentation of the methodology, and potential implementation steps.
  • Due date: September 30, 2020

Task 2: State of the art review, material selection, and testing plan

Conduct a thorough literature review regarding the available tools and techniques to assess compatibility of asphalt binders with respect to virgin and recycled asphalt sources as well as rejuvenators. Focus on literature both in asphalt materials domain as well as those available in fields of organic chemistry and polymer science. Focus on identification of materials for field and laboratory evaluations. Select a set of clear reference binders to represent a “compatible”, “incompatible”, and “in-between” bitumen, as conventionally understood. Make selection from material utilized in field sections to enable future field verification. Work closely with project Technical Advisory Panel (TAP) to obtain panel feedback and prioritization on the material selection. Based on literature review as well as through identification of the materials for evaluation, develop finalized sampling plans. Include information regarding types of materials sampled, their quantities and, timing and location of sampling. Finalize the testing and analysis plans for Tasks 4, 5 and 6 and submit for review.

  • Deliverable: Annotated literature review and summary document, sampling plans and testing plans will be submitted.
  • Due date: September 30, 2020

Task 3: Material sampling and specimen preparation

Execute the material sampling plan that is developed in Task 2. Utilize several materials already accessible in this project, resulting in only a limited number of new materials to be sampled. Revaluate a total of eight material sources (one source represents at a minimum one virgin binder type and one recycled binder type). Evaluate binder samples extracted and recovered from plant produced asphalt mixtures. Simultaneous to sampling efforts, obtain materials that are currently stored at subcontractor location. Undertake various material processing activities, including binder extraction and recovery from mixtures, mixture long-term lab aging, and preparation of mixture test specimen for use in Task 6. For mixture long term lab aging, perform conditioning at two aging levels. Adapt the long term aging procedures developed through the National Cooperative Highway Research Program (NCHRP) 09-54 study (multi-day aging at 95 degrees C in loose mix). In consultation with TAP, determine the exact number of days for conditioning based on location of material sampling.

  • Deliverable: A task memo will be submitted that summarizes the activities of this task.
  • Due date: December 31, 2020

Task 4: Analytical assessment

Undertake direct analytical assessment of bitumen compatibilities (between various chemical fractions within the binder, between virgin and recycled binders and, between virgin and recycled binders and rejuvenating agents). A list of analytical assessment methods is presented in the Task 4 tab of this spreadsheet (xls).

Finalize the above list at conclusion of Task 1. Conduct a full suite of testing for the material sources representing clearly distinguished as “compatible”, “incompatible” and “in-between.” Based on findings from these three sets of materials, utilize the most discriminating test methods for the verification samples.

  • Deliverable: A task report documenting the results of analytical assessment will be submitted. The report will include processed data and summary of findings from analytical assessment
  • Due date: June 30, 2021

Task 5: Binder performance assessment

Undertake various laboratory physical and mechanical tests and data analyses to determine the mechanical performance properties of asphalt binders. A list of binder lab evaluation methods is listed in Task 5 tab of this spreadsheet (xls).

The current asphalt binder specification limits as well as recently developed and validated binder rheological performance properties will provide an initial baseline comparison with analytical measurements as well as provide initial thresholds to assess binder and aging index parameters binder/rejuvenator compatibilities.

Determine fatigue performance of asphalt binder blends at various aging levels. LAS testing protocol determines continuum damage-based fatigue performance indicators by conducting cyclic tests are increasing strain magnitudes on binder samples. It is significant to expand the limited performance dataset obtained from pavement sections.

To ensure that the compatibility methodology does not result in binder blends that are susceptible to rutting, it is important that rutting performance is assessed. The MSCR properties go above and beyond those derived from linear viscoelastic characterization. Refine above list of testing methods in consultation with the TAP. Perform binder performance assessment on the same materials as those assessed in the analytical stage. Compare properties obtained from binder performance assessment against established threshold values from previous and on-going studies.

  • Deliverable: At conclusion of this task a report will be submitted to the TAP that will provide a summary of lab testing results on various asphalt binders and blends. The report will be organized to present results from each set of materials discussed above. Basic statistical analysis of test results from replicate specimens will be included in the report along with preliminary comparisons between binder mechanical properties and analytical assessment test results.
  • Due date: August 31, 2021

Task 6: Mixture performance assessment

Undertake mechanical tests on asphalt mixture specimen. Mixture performance assessment is critical in this study due to the presence of RAP in the mixtures, which makes it challenging to conduct only binder performance assessment where new and recycled binder as well as rejuvenators fully blend during the recovery process.Focus testing on plant-produced mixtures. Prepare all test specimens at 7 +/-0.5% air void levels. Conduct the main three study materials mixture tests at 2 or 3 long term aging levels (pending findings from Task 1). For the verification materials (materials 4 thru 8), conduct testing at one long term aged condition. Employ an initial list of mixture performance tests, as shown in table below. On the basis of the literature review and in consultation with the TAP, update tab Task 6 on this spreadsheet (xls) as needed. In addition to full LVE and fatigue cracking performance testing, include various cracking lab performance tests that are currently being adopted by several NRRA partners. Often times these have simpler testing procedures and these can serve as quicker proofing tests for validating the findings from binder analytical and performance assessment tasks. Using the results of the laboratory performance tests, conduct pavement analyses to predict fatigue and thermal cracking performances. Conduct FlexPAVE and IlliTC analyses. The main purpose of these analyses is to supplement the field performance data and to also conduct parametric evaluation for the expected cracking performances of pavements with varying degree of compatibilities between virgin and recycled asphalt binders. Evaluate the property measurements from Tasks 4, 5 and 6 through statistical analyses. Utilize Pearson’s matrix to determine presence of correlations between analytical measurements and mechanical properties. Conduct t-tests to determine whether compatibility assessed through different methods are statistically different or not. Compare the results from all assessment using Tukey-Pairwise comparisons to determine if the tests pair mixtures with “compatible” and “incompatible” materials are discriminated or not.

  • Deliverable: A task report with details of mixture performance test and prediction results along with the results of the statistical analyses will be submitted. The task report will provide summary results as well as discussions of the key findings which will be used in developing final project deliverables.
  • Due date: August 31, 2021

Task 7: Final memorandum on research benefits and implementation steps

Produce a final memorandum that clarifies and documents the methodology used to calculate benefits, including any assumptions and steps required. In addition to quantitative calculations (when feasible), include a qualitative discussion of the estimated benefits. Include key steps that agencies can take to implement the research.

  • Deliverable: A final technical memorandum at the end of the project that provides details of the methodology, steps and approach for evaluating benefits, benefits quantification results, and discussion of next steps for implementation.
  • Due date: February 28, 2022

Task 8: Draft final report

Prepare a draft final report, following State publication guidelines, to document project activities, findings, and recommendations. This report will be reviewed by the TAP, updated by the University to incorporate technical comments, and then approved by the Technical Liaison (TL) before this task is considered complete. Schedule a TAP meeting to facilitate the discussion of the draft report.

  • 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: February 28, 2022

Task 9: Editorial review and publication of final report

Work directly with State contract editors to address editorial comments and finalize the document in a timely manner. The contract editors will publish the report and ensure it meets publication standards.

  • Deliverable: Final Publishable Report that meets State Editorial Guidelines and standards.
  • Due date: April 30, 2022

Project team

Principal Investigator(s): Eshan V. Dave, Ph.D., Department of Civil and Environmental Engineering, University of New Hampshire, eshan.dave@unh.edu; Jo E. Sias, Ph.D., P.E., Department of Civil and Environmental Engineering, University of New Hampshire, jo.sias@unh.edu
Co-Investigator: Hassan Tabatabaee, Ph.D., Cargill Bioindustrial, hassan_tabatabaee@cargill.com
Project Technical Advisory Panel (TAP) - email the TAP
Contact us to join this TAP

  • Andrew Cascione, Flint Hills Resources
  • Mohamed Elkashef, University of California-Davis
  • Brian Hill, IL DOT
  • Brett Lambden, Husky Energy
  • Erik Lyngdal, WisDOT
  • Tirupan Mandal, WisDOT
  • Kiran Mohanraj, The Transtec Group
  • Dan Oesch, MoDOT
  • Michael Vrtis, MnDOT
  • Richard Willis, National Asphalt Pavement Association (NAPA)

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