Study Of Form And Distribution Characters For Aggregrates In HMA Based On Digital Image Processing

Potential variability is normally in the performance of HMA, it can be seen much difference between two accordant samples even though they have the same gradation and content of asphalt. This result is caused by the complexity of HMA. The particle form and distribution characters of the aggregrates which stay the main content of HMA are different, so we can not get two samples which are absolutely same. The most of recent researches focused on the marco-performance, only little of research involved the micro-structure of HMA. With the help of digital image processing technology, this study focuses on the micro-structure of HMA and tries to find out the internal cause of the variability in marco-performance of HMA.The study firstly takes a brief historical retrospect on the digital image processing and picks out the methods, which can be used to pcocess the sections of HMA samples, including image segmentation, image growth arithmetic and erosin-dilation etc. In order to characterize the geometric distribution of aggregate particle, many indexes are developed, such as perimeter, area and orientation of principal axis etc.Combined with some experiments for macro-performance, the analysis focused on the mirco-structure of the aggregates in HMA has been made, with the help of the methods developed in this study. The main results are:①Image growth arithmetic can distinguish aggregrate particles from HMA section, and it makes calculation the indexes of HMA image easy. Conceptually, the mircostructure of HMA can be fully expressed in terms of come properties: perimeter, area, center gravity etc.②The software, based on the technology of digital image processing, is effectual to research the relationship between micro-structure and marco-performance of HMA. The shape of a coarse aggregrate can be fully expressed in terms of the independent properties: form, angularity and flat index.③In five independent properties, spherality index (SP) and flat index (FI) can describe the three-dimensional characters of coarse aggregates and have stronge relationship with the marco performance. It is easy to control the FI of a pile of aggregate artificially by the means of limiting the content of aggregates which are flat.④It is a fact that there is a trough in the curve of aggregate particles shape index( FI ) vs HMA samples'shear performance. Considering the the relationship between air voids and FI , the reason of the fact can be given: the flat aggregates are easy to interfere each other which result in the increasing of air voids, and the HMA samples become an uneasy to be sheared structure, frame-interspace structure.⑤Standard deviation of area-gradation and eccentricity ratio of particles in HMA section are two effective approachs to express the uniformity of aggregates distribution which is good in horizontal section and bad in vertical section.Using digital image processing technology is a convenient rapid and precise way to research the microstructure of HMA. And it can be used to find out the internal cause which leads to the difference in macro-performance of HMA.