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Abstract for presentation (Poster or Podium) with a Paper in the Conference Proceedings

Highway Pavements

Impact of Laboratory Air Voids Using AASHTO T 166 Versus AASHTO T 275 for Asphalt Concrete Specimens

Monday, June 17, 2024
10:15 AM - 11:30 AM ET
Room: Galleria

    Primary Author(s)

  • Biplab B. Bhattacharya, P.E.

    Senior Transportation Engineer
    California Department of Transportation
    Sacramento, CA, United States

    • Presenter(s)

  • Biplab B. Bhattacharya, P.E.

    Senior Transportation Engineer
    California Department of Transportation
    Sacramento, CA, United States

    • Co-Author(s)

  • SJ

    Shweta Jayant, B.S.

    Transportation Engineer
    California Department of Transportation
    Sacramento, California, United States

    • Presenter(s)

  • SJ

    Shweta Jayant, B.S.

    Transportation Engineer
    California Department of Transportation
    Sacramento, California, United States

    • Co-Author(s)

  • TC

    Thomas Carter, Senior Technical Expert

    Senior Technical Expert
    Atlas Technical Consultants Inc.
    Sacramento, CA, United States

    • Presenter(s)

  • TC

    Thomas Carter, Senior Technical Expert

    Senior Technical Expert
    Atlas Technical Consultants Inc.
    Sacramento, CA, United States

    • Co-Author(s)

  • PC

    Paul Curren, P.E.

    Technical Materials Expert
    Alta Vista Solutions Inc.
    Sacramento, California, United States

    • Presenter(s)

  • PC

    Paul Curren, P.E.

    Technical Materials Expert
    Alta Vista Solutions Inc.
    Sacramento, California, United States

    • Co-Author(s)

  • AH

    Aemero Hailemichael, M.S.

    Transportation Engineer
    California Department of Transportation
    Sacramento, California, United States

    • Presenter(s)

  • AH

    Aemero Hailemichael, M.S.

    Transportation Engineer
    California Department of Transportation
    Sacramento, California, United States

    • Co-Author(s)

  • PS

    Peter Sebaaly, Ph.D.

    Senior Technical Expert
    Atlas Technical Consultants Inc.
    Sacramento, California, United States

    • Presenter(s)

  • PS

    Peter Sebaaly, Ph.D.

    Senior Technical Expert
    Atlas Technical Consultants Inc.
    Sacramento, California, United States

    • Co-Author(s)

  • Baron Colbert, PhD

    Senior Engineer
    Atlas Technical Consultants Inc.
    Sacramento, CA, United States

    • Presenter(s)

  • Baron Colbert, PhD

    Senior Engineer
    Atlas Technical Consultants Inc.
    Sacramento, CA, United States

    • Submitter(s)

  • Biplab B. Bhattacharya, P.E.

    Senior Transportation Engineer
    California Department of Transportation
    Sacramento, CA, United States

Abstract: Hot mix asphalt (HMA) materials engineering is the process of identifying mix characteristics that accurately reflect expected field performance. HMA mixes are developed in the laboratory for mix design and produced at the hot plant for construction. The mixes are thoroughly tested to ensure they meet the requirements of the applicable specification and meets expected performance as designed over their intended service life. Mix air voids are a fundamental mix property used for the acceptance of HMA mixes. Two test methods, AASHTO T 166 (saturated surface-dry) and AASHTO T 275 (paraffin-coated), are currently used by Caltrans to determine the bulk specific gravity of the compacted HMA mix to determine percent air voids in accordance with AASHTO T 269. The AASHTO T 166 procedure is required to determine bulk specific gravity and the determination of mix air voids for California Test 389 and AASHTO T 283; both test procedures are required by the 2022 Caltrans Standard Specifications. AASHTO T 275 is specified in the 2022 Caltrans Standard Specifications for the determination of laboratory mix air voids and density of cores taken in the field to verify compaction. Thus, based on a previous interlaboratory study conducted by Caltrans Independent Assurance and Reference Sample Program, the current study aims to evaluate the practicality of using AASHTO T 166 in lieu of AASHTO T 275 for the determination of laboratory air voids for dense-graded HMA mixes as part of AASHTO T 269. The study was done using a ¾″ Type A HMA (dense-graded) with 15% reclaimed asphalt pavement (RAP) meeting Caltrans specifications. Seventy-six Caltrans-accredited laboratories participated in this study. Results showed that the average bulk specific gravity (Gmb) using AASHTO T 166 and AASHTO T 275 were 2.475 and 2.484, respectively. The resulting air voids calculated based on theoretical maximum specific gravity (Gmm) using AASHTO T 209 were slightly higher when using AASHTO T 166 (5.2%) as compared to AASHTO T 275 (4.9%). The practical implication of this change would be that, in order to achieve a target 4% air voids when using AASHTO T 166 in place of AASHTO T 275, a marginal increase in binder content of 0.1% would be required for this dense-graded HMA mix.

Learning Objectives:

Attendees can expect to learn the following from this session:
  • Upon completion, participant will be able to describe the advantages of using AASHTO T 166 compared to AASHTO T 275 for determining laboratory air voids.
  • Upon completion, participant will be able to learn the background information on why is Caltrans still using AASHTO T 275 and how to move forward and adopt AASHTO T 166.
  • Upon completion, participant will be able to conduct testing on their local HMA mixes using AASHTO T 166 for further validation.