Investigation of the internal structure change of two-layer asphalt mixtures during the wheel tracking test based on 2D image analysis

A modified wheel tracking test was developed to investigate the internal structure change of asphalt mixture under wheel loading. The sectional images of two-layer specimens after different loading times were acquired and analyzed by 2D image analysis. Microstructure indices from different positions in the sectional images with reference to the loading point, such as average contact length (L-ave), total contact length (L-sum), orientation of contact lines and aggregates (average angle theta and vector magnitude Delta), were obtained. The multi-factor analysis of variance method was used to evaluate the sensitivity of varying microstructure indices to mixture types, locations and loading times and a linear regression model was developed to investigate the relationship between microstructure indices and the average rutting depth. The results show that the internal structure indices L-ave, L-sum and theta of contact lines were significantly affected by the loading times. The linear regression shows that multiple of L-ave, L-sum and sin value of contact lines' theta could successfully capture the internal structure change of asphalt mixtures during the wheel loading. (C) 2019 Elsevier Ltd. All rights reserved.