Three-dimensional microstructure based model for evaluating the coefficient of thermal expansion and contraction of asphalt concrete

The coefficient of thermal expansion (CTE) and contraction (CTC) are critical parameters for pavement design and thermal analysis. This paper develops a 3-D microstructure-based FE model to evaluate the CTE and CTC of asphalt concrete. The 3-D random microstructure of asphalt concrete was generated with an image-aided algorithm. In the presented algorithm, the random 3-D geometry of a single aggregate was generated with a single 2-D image captured by Aggregate Image System 2 (AIMS2). The randomly generated 3-D aggregates were packaged with PFC 3D to construct the 3-D microstructure for asphalt concrete with prescribed gradation. Then the 3-D microstructure of asphalt concrete was imported into FE software ABAQUS to calculate the CTE and CTC. To validate the results from the numerical simulation, a laboratory experiment was conducted to test the CTE/CTC of the asphalt concrete with the same material composition. With the validated FE model, the effect of aggregate type, shape, and spatial orientation on the CTE/CTE was analyzed. Results show that the relative differences between the average values of numerical and experimental data were 1.63%∼4.64% for the CTE, and 3.01%∼7.20% for the CTC. With the increase of temperature, the CTE first decreased and then increased, while the CTC first increased and then decreased. Compared with the 3-D microstructure-based model, both the 2-D plain stress and plain strain models tended to overestimate the CTE of asphalt concrete. When the aggregate orientation tended to be inclined to a certain direction, the CTC and CTE of the asphalt concrete parallel to that direction tended to be smaller. Asphalt concrete prepared with quartz gravels and sand stones tended to have higher CTC and CTE. While the CTC and CTE of asphalt concrete could be reduced by using limestones.