Updates to Mechanistic-Empirical Design Inputs for Illinois Flexible Pavements

Hajj, Ramez; Thompson, Marshall; Santos Maia, Renan; Lu, Yujia; Vyas, Abhilash; Asadi, Babak; Regmi, Bibek

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https://hdl.handle.net/2142/122988 Copy

Description

Title

Updates to Mechanistic-Empirical Design Inputs for Illinois Flexible Pavements

Author(s)

• Hajj, Ramez
• Thompson, Marshall
• Santos Maia, Renan
• Lu, Yujia
• Vyas, Abhilash
• Asadi, Babak
• Regmi, Bibek

Issue Date

2024-05

Keyword(s)

• Asphalt
• Fatigue Endurance Limit
• Dynamic Modulus
• Traffic Speed Deflectometer

Abstract

This study reviews the Illinois Department of Transportation’s full-depth asphalt, limiting strain criterion, and asphalt over rubblized concrete design procedures, considering technological advancements in hot-mix asphalt—namely, the increased use of recycled materials and modified asphalt binders. The researchers evaluated the current |E*| algorithm by conducting laboratory tests with four mix designs and seven asphalt binders of different Superpave performance grades. They compared predictive models, including the current Illinois modulus algorithm as well as the Witczak, Hirsch, and newly developed Illinois Center for Transportation (ICT) Bayesian neural network (BNN) models. The ultrasonic pulse velocity (UPV) nondestructive test for modulus and field modulus measurements was evaluated as well. Subsequent tasks involved reviewing current fatigue endurance limit (FEL) criteria from an adapted protocol for the four-point bending beam fatigue test. This study found that typical hot-mix asphalt modulus values in Illinois are underestimated compared to modern mixes, suggesting potential savings by allowing an increased modulus value to be used, reducing layer thickness design. Low-temperature performance grades significantly influenced modulus, and the developed ICT BNN predictive model outperformed traditional ones. While UPV was promising for modulus screening, challenges related to material properties assumptions were identified. The current stage of research on assessing modern mixes’ FEL reveals the complexity of observing FEL using simplified methods. To advance this objective, a concept of acceptable stiffness ratio (SR) is introduced. In these cases, exceptionally long fatigue life would be obtained for mixes that demonstrate an acceptable drop in SR within 10,000 cycles, with no apparent evolution of the damage state. The most conservative estimation of strain level that would result in acceptable SR aligned with IDOT’s current 70 microstrain FEL criteria. On the less conservative side, allowing a 10% drop in SR within 10,000 loading cycles could increase the acceptable SR < 1 strain level as high as approximately 180 microstrain, with caution needed regarding evolving mobility trends and environmental stressors including the changing climate.

Publisher

Illinois Center for Transportation/Illinois Department of Transportation

Has Part

• https://doi.org/10.36501/0197-9191/24-010
• ISSN: 0197-9191

Series/Report Name or Number

FHWA-ICT-24-008

Type of Resource

text

Language

eng

Sponsor(s)/Grant Number(s)

IDOT-R27-233

Copyright and License Information

No restrictions. This document is available through the National Technical Information Service, Springfield, VA 22161

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