A Study On The Meso-Structure Of Cold Recycled Mixture With Emulsified Asphalt

The laboratory test results and engineering application indicate that the mechanical properties of cold recycled mixture with emulsified asphalt(CR mixture) is different from hot-mix asphalt mixture(HMA mixture) a lot. Because the meso-structure of asphalt mixture has a large influence on its mechanical properties, thus, it is necessary to analyze the meso-structure of CR mixture comprehensively before studying its mechanical properties. This paper focuses on the research of the meso-structure of CR mixture using digital image processing and X-ray CT technology.First, the CT images of CR specimens are obtained using industrial CT. After the CT images are processed, the OTSU algorithm is improved to compute the grayscale threshold, which solves the uneven brightness problem of CT images. Finally, the images of air voids, cement emulsified asphalt mortar and coarse aggregate particles are extracted from the CT images of CR mixture successfully.Second, the characterization of space distribution of air voids in CR mixture is analyzed, and the "gradation of air voids" is proposed to study the statistical property of air voids. The results show that, as the aggregate gradation becomes coarser, the air voids in CR mixture tend to have larger size and less number. The gradation of air voids, which can be fitted with the Weibull model, reflects the statistical property of air voids in CR mixture well. Compared with HMA mixture, CR mixture has more air voids, and the gradation of air voids is finer.Third, the sampling method of the thickness of asphalt mortar is designed, and the "thickness spectrum" is proposed to study the distribution of cement emulsified asphalt mortar in CR mixture. The results show that the thickness spectrum, which can be fitted with the logarithmic normal distribution model, reflect the thickness status of asphalt mortar well. Compared with HMA mixture, the thickness spectrum of asphalt mortar in CR mixture has smaller expectation, modal and maximum weight value.At last, the research focuses on the coarse aggregate particles in CR mixture. The results show that the uniformity of CR mixture decreases as the aggregate gradation becomes coarser. Compared with marshall compaction and static loading, the SGC compaction can make the CR mixture more uniform, and decrease the spindle direction angle of the coarse aggregate particles. Compared with new aggregate particles, the recycled aggregate particles have smaller FER and STI, and larger AI.