This study combines the digital image processing (DIP) technique and extended finite-element method (XFEM) to analyze the crack initiation and propagation mechanism of an asphalt mixture in the indirect tensile test (IDT) at a mesoscopic level. Digital camera images (DCIs) of an asphalt mixture were used to generate mesoscale geometric information of the mixture structure, which was then processed by the free mesh generation technique to build a mesh model of the mixture mesostructure. By introducing a bilinear cohesive zone model (CZM) and the XFEM, the mesh model was used to simulate the complete failure process of the asphalt mixture in the IDT. After validation with laboratory test results and theoretical solutions, the model was used to investigate the crack initiation and propagation process and the stress distribution in the asphalt mixture. It was found that the developed finite-element model cannot only produce simulation results that are consistent with laboratory test results and theoretical solutions, but also provide detailed information, such as the stress distribution in between the aggregate and mastic. In the IDT, crack initiates in weak areas around the interface between asphalt mortar and aggregates. Multiple cracks would occur in the stress concentration areas, and then propagate along both ends at various rates. During crack propagation, crack width plays a leading role. Results of this study showed that the adopted mesostructure analysis method can overcome some shortcomings of conventional finite-element methods and, hence, may provide an effective way for improving the design of flexible pavements.
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