Study of the microstructure of asphalt concrete using X-ray computed tomography

A mechanical digital twin (a mechanical finite-element model) of an asphalt concrete sample has been developed in the framework of a project for recycling polymer composite materials with fibrous reinforcement (fiberglass) as an alternative for crushed stone in the asphalt concrete production. A methodology of using X-ray computed tomography (XCT) for analysis of the asphalt concrete microstructure and calculation of the mechanical properties is developed. The data processing chain for developing a digital twin of the asphalt concrete microstructure, based on X-ray micro-computed tomography (XCT) image includes the following steps: 1) image enhancement; 2) image segmentation; 3) analysis of the morphology of pores and solid particles; 4) transformation of the segmented image into a voxels-based finite element (FE) model. It is demonstrated that the XCT resolution of 40 μm is sufficient for a reliable identification of microstructural parameters, i.e., volume fractions of the components, distributions of voids (pores) in size, shape and spatial position, as well as distributions of the crushed brittle additives (fiberglass chips) in size. The FE model constitutes a digital twin of the material, and, after specifying the characteristics of the material components, can be used for simulation of the thermomechanical and functional properties of the material. The developed procedure is exemplified in the calculation of statistics of the compression and shear moduli of the asphalt concrete with addition of crushed fiberglass particles. The dependence of the calculated elastic properties on the size of the digital twin is studied. It is shown that a model size of 10 mm and more is sufficient for the microstructural representativity and calculation of the homogenization characteristics. The results can be used for analysis of the microstructure and structure-dependent thermomechanical properties of asphalt concrete. The developed finite element model can be used for modelling of the visco-elastic response of asphalt concrete and its behavior under cyclic loading.