Revising NCDOT Asphalt Binder Specifications

The North Carolina Department of Transportation (NCDOT) currently specifies asphalt binders in accordance with AASHTO M 320. However, the AASHTO M 320 performance-graded (PG) specification was developed over 30 years ago. Since then, there have been significant changes in the formulation, manufacturing, and modification of asphalt binders. These changes have rendered the AASHTO M 320 specification ineffective at capturing the performance of today’s asphalt binders. The introduction of AASHTO M 332 and the associated Multiple Stress Creep and Recovery (MSCR) test addressed the shortcoming of current binder specifications with respect to rutting resistance. However, the NCDOT has yet to adopt AASHTO M 332, and AASHTO M 332 retains the AASHTO M 320 measures of asphalt binder durability. Before the adoption of AASHTO M 332, it is important to conduct transitional testing of existing asphalt binders in North Carolina using both specifications and identify AASHTO M 332 grades attainable regionally. This will ensure that future binder characteristics are at least as good as, if not better than, those of the past. Furthermore, it would be beneficial to simultaneously assess alternative binder durability parameters that can be derived from standard AASHTO M 320 and M 332 test results (e.g., ΔTc, Glover-Rowe). These alternative parameters may provide a better reflection of mixture cracking performance and can be readily implemented. Evaluating the sensitivity of asphalt mixture rutting and cracking performance test results to AASHTO M 320, M 332, and alternative durability parameters is crucial to identify the parameters that best reflect mixture performance for specification. Given that reclaimed asphalt pavement (RAP) is present in nearly all asphalt mixtures, it is essential to assess this sensitivity with knowledge of both virgin and RAP binder properties within the mixtures. While standard extraction and recovery is too cumbersome for routine practice, efficient alternatives to measure RAP binder properties merit evaluation. Correspondingly, the objectives of the proposed research are to: (1) Provide informed guidance for the NCDOT to revise their binder specifications to align with AASHTO M 332, (2) Evaluate the ability of alternative asphalt binder parameters to better address durability, and (3) Identify a practical method to characterize RAP binders. The objectives will be accomplished by executing the following six tasks: (1) Conduct a state of the art review of suppliers to identify familiarity with AASHTO M 332 and available grades, M 332 grades specified by other Southeastern states and their implementation processes, binder properties indicating mixture durability, and efficient methods for characterizing RAP binder. (2) Acquire a diverse selection of 16 virgin binders from NCDOT-approved suppliers and the component materials corresponding to 3 job-mix formulas (JMFs). The acquired binders will encompass the current NCDOT-specified AASHTO M 320 grades of PG 64-22, PG 58-28, and PG 76-22. (3) Perform comparative AASHTO M 320 and M 332 testing on the acquire binders to identify grade equivalencies between the two specifications. Additionally, leverage these binder test results to investigate if standard and alternative durability measures, obtainable from PG tests, offer unique or redundant insights into asphalt binder performance. Based on measured binder properties, select five virgin binders to use in combination with each JMF, resulting in 15 asphalt mixtures, and subject the mixtures to rutting and cracking performance testing. Characterize the RAP binders using both conventional extraction and recovery methods and practical alternatives to assess their viability. (4) Explore the relationships between measured binder properties and mixture performance to determine the binder parameters that best relate to mixture performance. (5) Recommend changes to asphalt binder specifications based on the results from the previous tasks and propose an implementation plan. (6) Prepare a final report summarizing the findings from the preceding tasks. The research results are anticipated to yield improved asphalt binder specifications that better ensure satisfactory mixture performance and capture the benefits of modification. Screening of asphalt binders is a necessary step to prevent premature pavement failure.

Language

• English

Project

• Status: Active
• Funding: $336333
• Contract Numbers:

  RP2025-17

• Sponsor Organizations:

  North Carolina Department of Transportation

  Research and Development
  1549 Mail Service Center
  Raleigh, NC  United States  27699-1549
• Managing Organizations:

  North Carolina Department of Transportation

  Research and Development
  1549 Mail Service Center
  Raleigh, NC  United States  27699-1549
• Project Managers:

  Kadibhai, Mustansir

• Performing Organizations:

  North Carolina State University

  Department of Civil, Construction and Environmental Engineering
  Raleigh, NC  United States  27695
• Principal Investigators:

  Castorena, Cassie

• Start Date: 20240801
• Expected Completion Date: 20260731
• Actual Completion Date: 0
• USDOT Program: Pavements and Materials

Subject/Index Terms

• TRT Terms: Asphalt mixtures; Binders; Durability; Reclaimed asphalt pavements; Specifications
• Identifier Terms: North Carolina Department of Transportation
• Subject Areas: Highways; Materials;

Filing Info

• Accession Number: 01926672
• Record Type: Research project
• Source Agency: North Carolina Department of Transportation
• Contract Numbers: RP2025-17
• Files: RIP, STATEDOT
• Created Date: Aug 8 2024 10:58AM