Meso-mechanical characterization on thermal damage and low-temperature cracking of asphalt mixtures

Abstract

As temperature fluctuates, thermal stresses and heterogeneous strains emerge within the asphalt mortar and the interface between asphalt and aggregate in asphalt mixtures, especially under a low temperature domain. This study provides a comprehensive investigation on the characterization of thermal damage in asphalt mixtures and their evolutionary mechanisms from a mesoscale perspective. A 2D numerical model is established based on the bilinear cohesive zone model (CZM), and the cohesive strength (σ_c⁰) and adhesive strength (σ_a⁰) were quantified with pull-off tests and image recognition technology to accurately represent the material’s properties at the mesoscale. On the other hand, the cohesive fracture energy (G_c^C) and adhesive fracture energy (G_a^C) are determined based on the laboratory and simulation results from the semi-circular bending (SCB) tests. Furthermore, the model is verified to be effective to characterize the thermal damage and low-temperature cracking of asphalt mixtures with the thermal stress restrained specimen test (TSRST). The findings reveal that the numerical model established in the study is effective to characterize the low-temperature damage of asphalt mixtures. The transition zones between asphalt and aggregate, as well as the edges of voids or defects, are particularly vulnerable to low-temperature damage under the thermal stress and strain. By decomposing strains and linking them to stress for analysis, a more detailed description of the thermal damage and failure mechanisms of the asphalt-aggregate interface and asphalt mortar within asphalt mixtures has been elucidated. During temperature variation, asphalt mortar experiences a substantially higher total strain than aggregate, contributing to a continuous growth of thermal stress inside of the asphalt mixture. The cohesive damage within the asphalt mortar is dominant compared to adhesive damage on the interface between asphalt and aggregate, whereas thermal damage on the interface can also be perceived in some regions due to stress concentration and accumulation, especially at the stage of cracking initiation.