Mechanical behaviors and meso analysis of asphalt mixtures under moisture damage induced by hydrodynamic impacts

Moisture damage significantly affects the performance and integrity of asphalt pavement. The water immersion method commonly used in laboratory is considered as a static water intrusion technique to simulate the moisture damage on asphalt mixtures. However, field conditions mainly involve dynamic water impacting due to moving tires and pressurized pore water. In this study, the in-situ moisture damage induced by repeated traffics was recurred with the Moisture Induced Sensitivity Tester (MIST), and their mechanisms and impacts on the void structure, viscoelastic properties, and fracture performance of the asphalt mixture were assessed. The findings revealed that hydrodynamic impacts with various loading cycle (0, 2000, 4000, 6000 cycles) could lead to an increase in the porosity of the mixture, with isolated voids eventually merged under water intrusion and erosion. The growth rate of the connected voids was more drastic in the initial stage and gradually decreased with the increased loading cycle. Besides, the dynamic water damage could enlarge the overall permeability of the asphalt mixtures and aggrandize the complexity of the water flow paths in a non-linear manner. The dynamic water damage factor (D_m) reflecting the variation of porosity was introduced to characterize the damage severity of the mixture. The results indicated that a severer damage was normally observed for the mixture with a higher initial porosity. Furthermore, significant effects of hydrodynamic damage on the dynamic modulus of the asphalt mixtures, especially in the high temperature (low frequency) domain, were also observed on the MIST-conditioned specimens. The CT-scanning analysis implied that the impaired adhesion between asphalt and aggregates and mechanical damage from pore water pressures were the primary causes of the damage. A degradation in crack resistance is observed from the Semi-Circular Bending (SCB) tests considering the hydrodynamic damage at various MIST-conditioning cycle.