What Is The Optimal Mixture Design For A Hot Mix Asphalt (HMA) Pavement Layer With A 50 Mm Nominal Aggregate Size, Incorporating Reclaimed Asphalt Pavement (RAP) At 30% Replacement Rate, To Achieve A Minimum Of 30 Years Design Life Under Heavy Traffic Loading Conditions, While Also Meeting The Stringent Low-temperature Cracking Criteria Outlined In The AASHTO PP 67 Protocol, For A Pavement Section Located In A Region With A Mean Annual Air Temperature Of 12°C And An Average Annual Precipitation Of 800 Mm?

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To design an optimal hot mix asphalt (HMA) pavement layer with a 50 mm nominal aggregate size incorporating 30% reclaimed asphalt pavement (RAP) for a 30-year design life under heavy traffic and meeting AASHTO PP 67 low-temperature cracking criteria, follow these steps:

Mixture Design Steps:

  1. Traffic Loading and Design Life:

    • Calculate design ESALs for a 30-year life under heavy traffic to determine the required mixture's stability and durability.

  2. Aggregate Selection:

    • Use a dense-graded aggregate with high quality, preferably crushed, for good interlock and stability.
    • Ensure compatibility with RAP gradation to avoid excessive fines or large particles.

  3. Binder Selection:

    • Choose a polymer-modified binder (e.g., PG 64-28PM) to enhance flexibility and thermal cracking resistance, balancing the stiffness from RAP.

  4. Mixture Design Process:

    • Combine RAP and virgin aggregate to meet gradation requirements, adjusting for RAP's higher fines.
    • Determine binder content considering RAP's contribution, using blending charts or the Bailey method.
    • Optimize asphalt content (OAC) for 4% air voids, 2.0-3.0% VMA, and 1.0-2.0% VFA.

  5. Testing and Performance:

    • Conduct Superpave Gyratory Compaction for density and voids.
    • Perform IDT or TSRST for low-temperature cracking resistance per AASHTO PP 67.
    • Test rutting resistance using APA and moisture susceptibility via AASHTO T 283.

  6. Durability and Adjustments:

    • Ensure resistance to stripping with anti-stripping agents if necessary.
    • Adjust mixture components based on test results to meet all criteria.

  7. Verification:

    • Use MEPDG to verify the 30-year design life, ensuring the mixture meets all performance requirements.

Key Considerations:

  • Climate: The temperate maritime climate with moderate temperatures and high rainfall necessitates a focus on moisture susceptibility and durability.
  • RAP Management: Balance RAP's benefits with potential impacts on mixture stiffness and cracking resistance.
  • Material Compatibility: Ensure aggregate and binder compatibility for optimal performance.

This approach balances sustainability with performance, ensuring a durable, long-lasting pavement under heavy traffic and varying climatic conditions.