Optimizing Truck Platoon Spacing to Minimize Asphalt Concrete Permanent Deformation
Advisor: Professor Imad L. Al-Qadi
Abstract:
Despite truck platoons’ benefits, their reduced lateral wander and shorter headway characteristics are expected to accelerate flexible pavement damage, particularly rutting. Existing pavement design methods often rely on layered elastic theory and empirical transfer functions, which limit their ability to capture complexity associated with the pavement system and vehicular loading, especially platoon traffic.
To address this challenge, firstly, a conventional Burger model, containing a nonlinear power-law dashpot, was introduced, which allows predicting asphalt concrete (AC) deformation behavior. The model parameters were obtained from the AC flow number and dynamic modulus tests. The verified and validated model was able to predict AC deformation accurately across various stress levels. The nonlinear Burger model was incorporated into a validated 3D robust finite element (FE) pavement model. The pavement model accurately accounts for tire loading complexities, material characteristics, temperature variation, and layer interface interactions, ensuring realistic pavement behavior simulation. The predicted rut accumulation results showed trends that are logical and closely aligned with real-world observations.
The proposed robust mechanistic pavement model for AC rutting can serve as a reliable tool for pavement design applications. An enhanced response prediction framework was developed to evaluate rut progression in flexible pavements under truck platoon loading. The framework was modified to account for the nonlinear rut accumulation of AC using a per-cycle normalization approach. The influence of axle configuration and load sequence was incorporated through equivalence analysis to capture their impact on rut accumulation. Results indicated that higher wander and increased platoon penetration distributed loading more evenly, reducing localized rutting. A rest period of 0.57 sec (i.e., 60-ft truck spacing) minimized rutting, representing a balance between AC hardening–relaxation and strain recovery phenomena.
Finally, as an extension of the developed pavement model, structure-induced rolling resistance force (𝐹𝑅𝑅𝑠𝑡𝑟) was calculated using a deflection-based approach. As steady-state deflection evolved over loading cycles, 𝐹𝑅𝑅𝑠𝑡𝑟 was calculated for each cycle, revealing three distinct trends: constant, increasing, or decreasing. Comparisons with a linear viscoelastic model showed that the permanent deformation model consistently produced higher 𝐹𝑅𝑅𝑠𝑡𝑟, approximately 125% and 50% at 104 and 130°F, respectively.
Temperature had the most significant impact on 𝐹𝑅𝑅𝑠𝑡𝑟, followed by material properties, while rest period and speed had minimal effects. The study demonstrated the importance of mechanistic approaches (e.g., accurate prediction of AC rut behavior) to mitigate potential rutting through optimization.