## 3 Digital Image Acquisition, Processing and Modelling Reconstruction
### Digital Modelling Reconstruction Technology
The larger the particle size, the larger the effect of temperature on the compaction level of the mixture. Figure 7 shows 3D curved surface plots of the variation in compaction level for the AC16 mixtures with an increasing gyration number for three different temperature conditions. However, the conclusions of their study were affected by the morphological characteristics of the aggregates. Therefore, variations in the parameters of the morphological characteristics of aggregates should be taken into account in subsequent studies to draw more general conclusions. Undoubtedly, high-temperature deformation of asphalt mixtures is a key research direction for asphalt pavement damage. The critical issue in this area concerns the accurate assessment of the effect of aggregate microstructure on the high-temperature deformation of asphalt mixtures. [PERSON] et al. [102] used X-ray CT data to establish the internal microstructure and used DIP techniques to process the 3D model. An adaptive threshold segmentation algorithm based on the annular region was improved and used to extract aggregates and air voids from the gray-scale images. The morphological distribution of pores and aggregates was also determined. The high-temperature damage mechanism of asphalt mixtures was effectively investigated. The air-void areas in the range of 0-20 mm are reduced to a greater extent by the compression of the load. At the same time, the voids expand into macroscopic cracks in the range of 20-50 mm. At high-temperature deformation, the modification of the air voids is considerably affected by the size and content of the aggregates. This confirms that the study of the morphological characteristics of the aggregates is essential, in particular, to analyze the macroscopic properties of the aggregates. In addition, the results of the study indicate that the motion of the aggregates causes the failure of the asphalt mixture. Future work should focus on the effect of the morphological characteristics of aggregates on their motional properties and then investigate the effect of changes in morpho  
Figure 7: Surface plots of the variation in compaction level versus gyration number for the AC16. logical characteristics on the performance of road aggregates when the aggregates move during high-temperature deformation. To investigate the influence of the morphological characteristics of aggregates and the distribution of air voids on the mechanical properties and performance of asphalt concrete and then to investigate the mechanism of microstructural changes in the aggregate. In a subsequent study, [PERSON] et al. [103] used an X-ray CT device to scan the internal microstructure of typical asphalt concrete and used DIP techniques to study the microstructural changes before and after high-temperature damage. An adaptive threshold segmentation algorithm based on image radius was proposed, which was applied to obtain binary images of aggregates, air voids and asphalt mastic. This method effectively distinguishes the target from the background. The distribution of air voids in asphalt mixtures is obviously affected by their gradation and coarse aggregate size. It was concluded that the aggregate shape could affect the RA. Additionally, the maximum value of RA was reached when the SF of the aggregate particles was taken to be between 1.5-3.5. Hence, it can be seen that X-ray CT images, as well as digital model reconstruction techniques, can correlate the gradation design and microstructure of aggregates with macroscopic properties. In general, the introduction of the AIMS system and X-ray CT technology provides great convenience for studying the morphological characteristics of aggregates, and the 3D digital reconstruction technology can better study the microstructural characteristics of asphalt mixtures. At present, most studies mainly use 2D digital image reconstruction and industrial X-ray CT scanning to establish and characterize the 3D morphological model of real aggregates.