AUT Journal of Civil Engineering

AUT Journal of Civil Engineering

Experimental Evaluation of Asphalt Concrete Interlayer Shear Strength: Role of Thermal, Bonding, and Structural Factors

Document Type : Research Article

Authors
Ali Dehqani 1
Mahdi Shojaei 2
Fereidoon Moghadas Nejad 2
1 Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, Iran.
2 Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, Iran
10.22060/ajce.2026.24563.5938
Abstract
Bonding characteristics between asphalt concrete layers have been a major concern for decades, as poor adhesion can lead to premature pavement distress, including cracking and fatigue. Hence, this study investigates the individual and interactive effects of temperature, tack coat application rate, confinement load, aggregate interlock, surface preheating, and geocomposite reinforcement on interlayer shear strength. The results showed that temperature is the most detrimental factor, reducing the strength overall by more than 2.5 times as it increased from 10°C to 40°C. Meanwhile, confinement load and aggregate interlock are the most important contributors to strength. Applying a 100 kPa confinement pressure boosted average strength by 60%, and aggregate interlock increased strength by 28% at high temperatures. Furthermore, statistical analysis revealed that surface preheating has no significant impact on the final strength. Importantly, critical interactions between confinement load and tack coat rate, as well as a negative interaction between aggregate interlock and the geocomposite, were recognised. Specifically, while aggregate interlock significantly increased strength by 28% at 40°C, the addition of geocomposites introduced a negative interaction, reducing the shear strength by approximately 17%. This finding quantifies the trade-off, demonstrating that geocomposites can partially negate the mechanical benefits of interlock. These results provide a robust framework for optimising pavement design by prioritising synergistic factor combinations.
Keywords
Asphalt overlay
tack coat
interlayer shear strength
shear bonding
double-shear test
Subjects
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AUT Journal of Civil Engineering
Volume 10, Issue 3
Summer 2026
Pages 261-274