| Current design method on asphalt mixture has been traditionary experiment-abservation method, which is one kind of phenomenon based research method, although traditional research methodology that contributed to the achievement of road engineering before couldn’t satisfy the engineering requirement any more. The conventional research method didn’t pay so much attention on the relationship between HMA’s internal mesostructure and macroscopic behavior, that sometimes, the mechanical performance of specimens vary a great deal even with the same macroscopic properties (gradation, air void, bind content).Along with interdisciplin infiltrate continuously into pavement engineering and the enrichment of research techniques, more and more scholars begin to working on the mesoscopic distribution regularity of asphalt mixture(Granular form, and void space distribution), microscopic interaction ability between asphalt and aggregate, and also its effect on the macro properties of mixture. Lots of valuable research results are obtained.In this paper, the correlation between mesoscopic structure of asphalt mixture and its mechanical properties were mainly studied. The research on mesoscopic composition and structure distribution were carried out based on X-ray CT and digital image processing technique. The qualitative and quantitative analysis methods on the composition and structure for asphalt mixture were established. The skeleton structure of asphalt structure were also described. The main research contents and results are summarized in the following: Firstly, seek for optimal scanning parameters of asphalt mixture specimenunder different conditions based on the Phoenix v|tome|x s microfocus X-ray CT scanning system of German.The accuracy of CT reconstruction for3-D volume was verified by method of equivalent volume, that the ‘standard material’ was utilized for scanning. The different materials were separated under the best scanning parameters, which lay the foundation for subsequent analysis. Secondly, The nondestructive X-ray CT was utilized to scan asphalt mixture,including different gradings(AC-16,SMA-16,OGFC-16),different molding modes (Marshall, SGC) and also different degrees of compaction. Then the software VGStudio MAX2.2was utilized to analyze the transverse and longitudinal distribution rules of voids in asphalt mixture, which reveals the uneven distribution of voids in asphalt mixture. Thirdly, aggregate morphology and distribution characteristics oftwo-dimensional images were analyzed by means of digital image processing technology based on Matlab platform, statistical model were used for fitting of the results as well. In addition, geometry information that obtained from continuous cross-sections of asphalt mixture was studied combining with the fractal theory in mathematics, in which the asphalt mixture were molded under different gradings, different molding modes (Marshall, SGC) and also different degrees of compaction.Fourth, skeleton features of asphalt mixture were compared through the macroscopic and mesoscopic, respectively. Contact numbers of aggregates along the height direction were analysis through designing contact algorithm, the whole process were completed based on MATLAB image processing toolboxes, as well as combine with medium mechanics theory.At last, the relation between internal mesoscopic structure and macroscopic mechanical properties of asphalt mixture was established. Splitting test method was introduced to evaluate mechanical properties, at the same time, DIC technology was utilized to analyze failure mode and the uniformity of strain field under different mesoscopic structure. In addition, the software PFC-2D was utilized to simulate the stress pattern of different structure types of asphalt mixture, which clarified the importance of skeleton contact.Grey rational analysis was also used to analyze influence degree of mesoscopic indicators on its mechanical performance. |
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