Damage Mechanism of Ultra-thin Asphalt Overlay (UTAO) based on Discrete Element Method

Aiming to analyze the damage mechanism of UTAO from the perspective of meso-mechanical mechanism using discrete element method (DEM), we conducted study of diseases problems of UTAO in several provinces in China, and found that aggregate spalling was one of the main disease types of UTAO. A discrete element model of UTAO pavement structure was constructed to explore the meso-mechanical mechanism of UTAO damage under the influence of layer thickness, gradation, and bonding modulus. The experimental results show that, as the thickness of UTAO decreasing, the maximum value and the mean value of the contact force between all aggregate particles gradually increase, which leads to aggregates more prone to spalling. Compared with OGFC-5 UTAO, AC-5 UTAO presents smaller maximum and average values of all contact forces, and the loading pressure in AC-5 UTAO is fully diffused in the lateral direction. In addition, the increment of pavement modulus strengthens the overall force of aggregate particles inside UTAO, resulting in aggregate particles peeling off more easily. The increase of bonding modulus changes the position where the maximum value of the tangential force appears, whereas has no effect on the normal force.