Research On Meso-damage Of Asphalt Mixture Under Freeze-Thaw Cycle Based On CT Digital Image Processing Technology

With the improvement of highway network,highway plays an increasingly important role in road construction in China.Expressways are usually laid in the wild and are greatly affected by natural factors.In northern China,a large area is the seasonal freezing area.The road performance of expressway decreases rapidly under the combined action of vehicle load and freeze-thaw cycle,so it is urgent to improve road frost resistance and durability.With the continuous deepening of research on road materials,the study of asphalt mixture has gradually shifted from the macro level to the meso level.The traditional research methods can not reflect the changes of the real internal structure of the mixture.To analyze the meso-damage mechanism and structural changes under the freeze-thaw cycles,the non-destructive testing methods such as CT scan must be used.In this paper,combined with the transportation science and technology project of Jilin Province “the damage characteristics and mechanism of basalt fiber asphalt concrete under the coupling of water-temperature” to study the freeze-thaw resistance of SMA-13 basalt fiber asphalt mixture and SMA-13 lignin fiber asphalt mixture.First of all,the variation rule of void mechanical index of two asphalt mixtures with freeze-thaw cycle was studied from macroscopic level.Then,the CT machine was used to acquire the scanning images of two asphalt mixtures in different freeze-thaw damage cycles,and the scanned images were processed using digital image processing technology to analyze the variation of the internal structure of the test pieces with the freeze-thaw cycles.The research work in this paper is as follows:1.Based on previous research results of the research group,basalt fiber was used instead of lignin fiber in SMA-13,and the mix ratio of the two asphalt mixtures was designed;2.The experimental conditions for freeze-thaw cycle damage were drawn up,and the freeze-thaw time,freeze-thaw temperature and number of freeze-thaw cycles were mainly analyzed and determined.The void ratio test,stability test,split test,and indirect tensile test were performed on the two types of asphalt mixture under freeze-thaw cycles.The evolution rule of volume index and mechanical index of asphalt mixture with the number of freeze-thaw cycles was studied,and the damage resistance of two asphalt mixtures against freezing and thawing was evaluated.3.Use CT scan to obtain the scanning images of two asphalt mixtures in different freeze-thaw cycles.Analyze and determine the scanning parameters,such as scanning layer thickness,tube voltage,milliseconds and so on.The digital image processing technology was used to process the acquired images,making the images more suitable for statistical analysis.The statistics of the voidage and number of voids in each section of the specimen were taken to study the spatial distribution of voids in the specimen.4.There are various reasons for the decrease of mechanical properties of asphalt mixture under freeze-thaw cycles.And the analysis of porosity alone is not an accurate description of the meso-structure damage mechanism of asphalt mixture.This paper studies the variation of void characteristics in asphalt mixtures with freeze-thaw cycles by taking the index of the number of void Spaces in scanning voidage,the fractal dimension of roundness,the axial ratio of length to length and the angular property.