Asphalt mixture is a skeleton filling system consisting of aggregate, asphalt, and mineral powder. High performance asphalt mixture design is directly affected by internal stress transmission of skeleton filling system. In this paper, the discrete element method based on digital image was employed to study the stress transmission. By analyzing the effect of skeleton structure on the contact force between aggregate and mortar, it is concluded that the skeleton aggregate in the asphalt mixture is the main stress transmission medium. The lower the degree of disruption, the higher the contact force of skeleton aggregate. At the same time, the variation coefficient of contact force of asphalt mortar with low filling coefficient is larger and the localization phenomenon is more serious. By analyzing the effect of mortar properties on the contact force between aggregate and mortar, it is concluded that the lower the modulus of asphalt mortar, the higher the degree of localization of contact force and the more likely to have local damage.

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The service performances of asphalt pavement, especially rutting, will be inevitably affected by climate change. However, existing studies have generally focused on the rutting depth and rutting life, and thus became insufficient for comprehensively evaluating the influence of climate change on rutting over the service life. A resilience assessment method for asphalt pavement rutting is developed to solve the above problem. First, the original resilience method is extended to fit the system whose performance level continues to decline. Then, the calculation formulas of rutting resilience are derived by combining the rutting prediction model and the level assessment model. Subsequently, the influence degrees of climate change in representative cities on rutting resilience are studied. The results suggest that neglecting climate change in rutting design of asphalt pavement will lead to insufficient resilience, especially in northern China. Furthermore, the predicted temperature under RCP8.5 should be employed for asphalt pavement design.

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Asphalt mixture is a kind of granular material, which consists of aggregates with different particle sizes. Extracting the particle distribution around the failure location of asphalt mixture is important for revealing the failure mechanism. In this paper, the digital image correlation (DIC) method is used to obtain the full-field strain of asphalt mixture, and then the high strain zone of asphalt mortar is extracted by digital image processing technology. For getting the aggregate distribution around the failure position, aggregate extraction method is proposed based on the image dilation algorithm. For AC-16, SMA-16 and OGFC-16 asphalt mixtures, under different temperature and loading speed conditions, according to the analysis of the aggregates distribution around the high strain area, it can be seen that the proportion of the main skeleton aggregates and the disruption aggregates around the high strain area is constantly changing with the loading process. It shows that the proportion of the main skeleton aggregates around the high strain area is decreasing, while the proportion of the disruption aggregates is increasing. This phenomenon shows that the damage evolution of asphalt mixture is expanding from the surrounding area of main skeleton aggregates to that of disruption aggregates.

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Aggregate skeleton is the main load carrying part, which is important for the performance of asphalt mixture. Fine aggregate break the skeleton of coarse aggregate is defined as disruption. Based on the X-ray computed tomography and digital image process method, this paper aim to evaluate and verify the disruption in asphalt mixture, and then discuss the effect of disruption on the mesostructure and aggregate contact. Firstly, the aggregate classification and contact property calculation method are proposed. Based on the methods, the relation between disruption factor and contact property is analyzed. The results indicate that there is a strong linear trend between the distance of the main skeleton aggregate and disruption factor, and the disruption factor can well represent the expanding effect of disruption aggregate on the main skeleton aggregate. Additionally, higher disruption factor will leads to the decrease of the number of contact between the main skeleton aggregate and the increase of the contact number of the disruption aggregate. Further, if asphalt mixture has lower disruption factor, the internal contact between the main skeleton aggregates is closer.@en

Gradation measurement is important for quality control of pavement construction. Computed tomography (CT) can capture the microstructure images of asphalt mixture. However, an accuracy digital image processing method should be developed. In this study, fuzzy network, multilevel threshold and morphological methods are utilized to reduce the noise, enhance the contrast and segment images. The 2D aggregate gradation obtained from the digital image segmentation procedure is transferred into 3D gradation by stereological method. The results show that fuzzy network can balance the noise reduction and contrast enhancement. The multilevel Otsu's threshold method can obtain the two thresholds automatically. The morphological processing and watershed transformation can fill the holes in the image and break the aggregate connections. By comparing the calculated gradation and the designed gradation, the image processing procedure proposed in this paper can be utilized to obtain the gradation information of AC, SMA and OGFC accurately and effectively.@en

Failure behavior of asphalt mixture is the process of local deformation accumulation, therefore, local deformation investigation is the base work of failure behavior. Digital image correlation (DIC) method is an optical method which can calculate the local deformation in the failure process. This paper aims to evaluate the precision, select the optimal test parameters for DIC deformation measurement based on natural speckle image, and investigate the local deformation characteristic in the failure process for different mixtures. The results show the image quality of AC with smaller normal maximum aggregate size (NMAS) is better for DIC deformation calculation, the relative deviation of virtual translation and shear test can satisfy the precision requirement, the optimal subset size is 31. Based on the strain distribution, the optimal local deformation measure length for indirect tensile test is set as 50 mm, the critical steady strain is proposed based on R² obtained by the least squares fitting method, according to local deformation characteristic, the results show SMA can bear more deformation before unstable deformation stage and failure.

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