Research On Influence Of Different Coarse Aggregates On High-temperature Properties Of Asphalt Mixture

Rutting deformation of asphalt mixture has become a major form of corruption for the pavement, development of modern transport demands for better properties of the mixture at high temperature. Of all the factors influencing high-temperature properties of asphalt mixture, the coarse aggregates form the skeleton structure which is the main source of shear strength by embedding with each other. Shape features of coarse aggregates have an important iMPact on the mixture's high-temperature performance. Shape features of coarse aggregates include contour shape, angular features and surface texture. Contour shape represents the overall shape ratio of a particle, angular feature is the prominent degree of the angular on the profile,and texture describes the surface roughness of a particle. In this paper, morphological characteristics of different coarse aggregates will be studied by both laboratory tests and digital image processing techniques, the influence of morphological characteristics on high temperature properties of asphalt mixture will be further analyzed .First of all, the content of flat and elongated particles,the particle index and other indicators of different coarse aggregate were measured. Shear strength of mixtures made of different gradations were measured by single penetration test. By analyzing the influence of different coarse aggregates on high-temperature properties of mixture, the result is found that the shear strength decreases significantly when the content of flat and elongated particles exceeds 12%, and coarse graded mixtures are more sensitive, the particle index also has a strong correlation with the shear behavior of asphalt mixture.In order to quantitatively analyse the influence of morphological characteristics on high temperature properties of asphalt mixture, this article took advantage of digital image processing technology to process two dimensional split images of mixture using Matlab image processing functions and programming, and found the proper way to extract mesostructure of asphalt mixture.When bimodal characteristics of image is not obvious, the gray level transformation could be used to enhance image's features, adaptive threshold segmentation could then used to extract coarse aggregates from the image. In view of the differences of overall morphological characteristics of coarse aggregate in the different gradation types, gradation in the split image was identified. After verification, the result identified by the minor axis of equivalent ellipse has the smallest difference from the real gradation, the identified gradation could get close to the real gradation by amending sieve size to a certain extent and better reflects the internal microscopic structure of the mixture.This article systematically analyzed the current quantitative indicators for morphological characteristics, then selected proper indicators to quantize the particle morphology and analyzed the regularity between the particle morphology and high temperature performance. The result shows that the shape ratio, eccentricity, equivalent elliptical perimeter ratio and texture index have good relevance with high temperature-properties. Quantitative indicators provid a more accurate and objective testing method for the evaluation and selection of coarse aggregate. This article proposed a new method to evaluate the skeleton structure by means of topological properties of image, and studied influence of different coarse aggregates on the skeleton stability. The method which makes use of topological properties of the image could quantitatively evaluate the skeleton's stability.