Evolution Law And Stability Evaluation Of Meso Skeleton Structure Of Asphalt Mixture During Compaction

Asphalt mixture is a kind of multiphase composite material composed of aggregate,asphalt,mineral powder,and void.Many structures are interwoven in the process of compaction.The traditional research methods are mostly based on the macro scale domain,which makes it difficult to obtain the distribution of asphalt mixture internal structure in the different compaction process.With the development of digital image processing technology,industrial CT scanning technology,and computer-aided technology,the research on the mesoscale area of asphalt mixture has become a hot topic.The research on the distribution law of fine structure and the influence of fine structure on the macro performance of asphalt mixture have become a new way to solve the performance characterization of asphalt mixture.In this paper,the rotary compactor is used to form specimens in different compaction processes,and the compaction times are selected as the control index.According to the rotary compaction curve,the compaction times of 10,16,25,40,and 70 are selected to represent the compaction process.The digital images of Asphalt Mixture Specimens at different compaction stages were obtained by using industrial CT scanning technology.Based on the digital image processing technology,the two-dimensional digital image of asphalt mixture is enhanced,denoised and segmented.Several commonly used segmentation algorithms are compared and selected.The improved Otsu segmentation algorithm is used to segment the coarse aggregate,mortar,and void of asphalt mixture.The 3D reconstruction of asphalt mixture is realized by using avizo software,and the location characteristics and geometric information of coarse aggregate are obtained by combining with the minimum bounding box(OBB)algorithm.Based on digital image processing technology,the micro response characteristics of asphalt mixture skeleton structure in different compaction processes are studied.The results show that the transverse distribution of voids in different compaction processes has similar rules,and the void ratio presents a "V" curve from the center to the outside of the edge of the specimen;the longitudinal distribution of voids presents the distribution characteristics of "high at both ends,low in the middle";and the void coordination number and void ratio are closely related The larger the aggregate size is,the smaller the possibility of producing "invalid particles";with the increase of compaction times,the "effective average coordination number" of each grade of aggregate will increase;with the increase of compaction times,the center of mass of coarse aggregate on the upper layer of the specimen shows a downward trend;the inclination angle of the main axis of coarse aggregate of different compaction times specimens is between 0° and 180°The frequency distribution curve shows Gaussian distribution,with the increase of compaction times,the standard deviation of Gaussian distribution decreases,and the inclination angle of aggregate principal axis tends to the range of 80° to 100°more and more,which indicates that there are less and less "standing" coarse aggregate and more and more "lying"coarse aggregate;with the increase of compaction times,the anisotropy amplitude of XY plane increases,which indicates that the direction of aggregate principal axis is more and more obvious With the increase of compaction times,the characteristic s value of the direction of the skeleton force chain decreases gradually,and its value is closer to-1,which indicates that the inclination angle of each main axis tends to be more and more 90°and the direction of the skeleton force chain is closer to the vertical.A simple performance tester was used to test the macro performance of asphalt mixture at different compaction stages,and the correlation between the micro skeleton structure characteristics and macro stability of asphalt mixture was analyzed.The results show that the correlation between the direction characteristics of the skeleton force chain and the flow times is small.The main axis inclination angle,XY plane anisotropy amplitude,and flow times have a good correlation,which shows that these two mesoscopic characteristics can well characterize the stability of asphalt mixture in the compaction process.