The main objective of this study was to develop 2D and 3D micromechanical finite element (FE) models to predict the shear modulus of two asphalt mixture types. The internal microstructure of the asphalt mixtures were determined by X-ray computed tomography (CT) imaging. X-ray CT images were processed to create 2D and 3D meshed asphalt mixture FE model structures using the software Simpleware. Meshed model structures were exported to the FE modeling software Abaqus®. Elastic and viscoelastic assumptions were used for modeling aggregate and mastic subdomains, respectively. Shear modulus predictions for 2D and 3D models were compared to the measured values to determine the effectiveness of each model type for the simulation of the shear frequency sweep at constant height (FSCH) test. It was concluded that the 3D micromechanical FE model is capable of predicting shear modulus at relatively high test temperatures with high accuracy across a range of loading frequencies.
Simpleware software was used in this study to create masks for each domain based on measured intensity groups. The total volume of the asphalt mixture sample was calculated for the complete intensity range, 0 to 255. The upper limit for the air void intensity range was determined by trial and error to match the measured air void contents.
After the thresholds for each domain were determined, masks with different colors were assigned to clearly visualize the boundaries between each domain.
The mask created for the air void domain was excluded from the material structure because it has no stiffness. Before meshing, both the aggregate and the mastic domains were slightly smoothed while preserving the element quality and volume. This presmoothing stage allows the software to create more realistic meshes. High quality (triangles that are “as equilateral as possible") tetrahedral meshes were created for the aggregate and mastic domains while preserving the empty air void domain. It can be observed that triangle elements in the mastic and aggregate domains are perfectly bonded on the boundaries. The meshed structures were exported to FE analysis software ABAQUS for modeling.