Research On Evaluation Method Of Coarse Aggregate Angularity Based On Skeleton And Convex Hull

Aggregate is the main material which bears the mechanical properties of asphalt concrete pavement.The skid resistance and rutting resistance properties of pavement significantly affect the road quality and driving security,and the angularity of aggregate morphology is the key factor influencing the skid resistance and rutting resistance performance of concrete pavement.Traditionally,the coarse aggregate angularity detection is mainly based on the mechanical sieving test to determine the quality of the aggregate by subjective judgment.At present,there is no uniform standard in our country while most of the existing methods mainly focus on qualitative analysis rather than quantitative analysis.Considering this,imaging technology provides a cost-effective way towards quantifying aggregate morphological characteristics,conveniently.This paper,therefore,works on the quantification and evaluation methods of the angularity of aggregates morphology.Firstly,three grades of limestone aggregates of 4.75~9.5mm,9.5~13.2mm and 13.2~16mm were obtained by screening tests.To obtain coarse aggregates with different morphological characteristics,Los Angeles abrasion tester is employed to wear 0,400,800,1200 times respectively.Then the hardware and software of the aggregate image acquisition system was designed according to camera,Lens,backlight,supplemental light source and others selected.Captured high-level aggregate images would be processed by a series of image processing such as graying,denoising,enhancement,segmentation,target extraction and pit filling to get interested aggregate target area.A series of particle characteristic parameters such as perimeter,area,convex hull perimeter,and convex hull area could be accumulated by the calculation of self-designed aggregate angularity detection system.Based on this,two methods for detecting angularity of aggregates are proposed in this paper.They are skeleton angularity point method and convex hull area deviation method and the indicators of them are quantified and the feasibility of two methods are verified.The key point of the skeleton angularity point method is to extract the complete skeleton image and angularity points to represent the entire edge information of the aggregate before and after abrasion.The key to the convex hull area deviation method is to obtain the aggregate image before and after convex hull and area deviation to represent the change of the aggregate morphology characteristics before and after abrasion.Limestone coarse aggregates with different morphological characteristics obtained by abrasion were used to form AC-13 C gradation type mixture specimens,and the angular road performance of skid resistance and rutting resistance tests were conducted.A large number of aggregate data were mined and analyzed by IBM SPSS Statistic software.AIMS gradient angular method,uncompacted void ratio method,skeleton angularity point method and convex hull area deviation method were compared horizontally and related to the aggregate angular.Road performance is used for longitudinal correlation analysis.In addition,the geometric characteristic parameters of aggregate were quantified,including indices of angularity,dimension,texture,and roundness.Then the maximum factor affecting the angularity of aggregates and the statistical distribution of aggregate angularity were analyzed.Finally,the evaluation system of aggregate angularity was proposed and optimized,which improved the accuracy of the evaluation of the angularity of each aggregate.