Testing And Analysis Of Surface Free Energy Of Asphalt Based On Image Processing

The adhesion of interface between asphalt and aggregate is one of the main factors that affect water damage of asphalt pavement. Surface free energy of asphalt is the internal cause that affect the adhesion. Therefore, there is important theoretical basis and practical significance to test and analyze the surface free energy of asphalt. The research will be carried out on the testing of surface free energy of asphalt based on the digital image processing method, in order to achieve a goal for fast and accurate determination of surface free energy of asphalt.(1) It was tested the performance of five kinds of asphalt and one kind of SBS modified asphalt through the tests of penetration, low temperature ductility, softening point, short-term aging and so on. Through the analysis of testing principle for surface free energy of asphalt, the dispersion and polar parts in surface free energy of asphalt were determined respectively by measuring contact angles between different probe liquids of known surface tension and asphalt.(2) According to the basic theories of digital image processing, the process analysis of digital image processing was put forward on measuring contact angles between probe liquids and asphalt. It includes some specific steps, for example, image acquisition and image cropping, format conversion, image enhancement, image segmentation and binarization, boundary ellipse fitting and calculation contact angle. The results indicate that the primary images of probe liquids and asphalt are transformed into the binary images with the image cropping and preprocessing, the gray equalization, the median filter enhancement and the edge segmentation of Canny operators, then the images will be clear in boundaries. The boundary of probe liquids are fit with a improved ellipse fitting algorithm which is really robust, efficient, and the mothod for determination of contact angle of probe liquids and asphalt is fast.(3) The contact angle of probe liquids and asphalt is measured by digital image processing method, and the dispersion and polar parts in surface free energy of asphalt were determined respectively. Then the total surface free energy of asphalt can be obtained. The correlation analysis is carried out between the surface free energy of asphalt and the conventional technical performance of asphalt, brookfield viscosity. The results indicate that surface free energy of all asphalt is between 16.68mJ/m2 and 24.62mJ/m2. The dispersion part is dominant in the total surface free energy, which is in accordance with asphalt composition primarily of nonpolar organic hydrocarbons. Meanwhile, there is a good linear functional correlation between the surface free energy of asphalt and the brookfield viscosity, and the correlation coefficient R2 is 0.9315.(4) Through the tests of short-term aging at the time of 45min, 85min and 125min, the analysis was performed on the effect of short-term aging to contact angle of asphalt and distilled water, surface free energy of asphalt and cohesion energy. The results indicate that the adhesion of interface between asphalt and aggregate depend on the surface free energy of asphalt, the polar component and the contact angle of asphalt and distilled water. It provides the basis for the choice of asphalt materials and predition water damage of asphalt pavement.In short, the established method in the thesis for rapid test and analysis of surface free energy of asphalt based on the digital image processing technology can provide a reference for the similar studies.