Geometric Characteristics Study Of Aggregates For Asphalt Mixture

Geometric features of Aggregates include shape and texture in asphalt mixture. Aggregate shape and surface texture significantly affect the road performance of asphalt mixture and are directly related to the durability, the workability, shear strength, flexural strength and fatigue performance of asphalt mixture. In order to design an asphalt concrete pavement with long life, aggregates must have reasonable shape and texture features. At present, morphological study of aggregates are considered from macroscopic view while the results are subjective due to the lack of specific test methods and quantitative indicators. In order to determinate the geometric characteristics of aggregates fast, objectively and accurately, a variety of aggregates in different material source were taken as carriers in this dissertation, the shape and texture were studied by the self-developed system of aggregate digital image evaluation system and the dense point cloud three-dimensional optical scanning system to reveal the change laws.In this dissertation, the shape index, shape factor and sphericity of aggregate are used to analyze the shape characteristics of coarse and fine aggregates, and it is found that the shape of basalt-2 index is better than basalt-1. The average shape indexes of 11 coarse aggregates were 1.092-1.207, the extreme value is 0.11-0.34 and the space of different shape indexes of coarse aggregates is 0.23; The average shape factor of different fine aggregates is 0.937-1.043 and the extreme value is 0.60-1.49; The average sphericity of fine aggregates is 0.67-0.97 and the overall value fluctuates above and below 0.806. The aggregate standard deviation is 0.039-0.067. The sphericity of a number of aggregate particles changes around the average value and is consistent with the overall change in shape. Meanwhile, based on fractional Brownian random field model in the dissertation, the fractal parameters, the surface profile arithmetic average slope factor and the average deviation are proposd to estimate the surface texture of coarse and fine aggregates. It is found that basalt-1 and basalt-2 have the same change laws in texture. Fractal index, average surface slope factor and arithmetic mean deviation increase, and the texture of basalt-1 is greater than that of basalt-2. The fractal index of coarse aggregates has little difference for the same size of basalt-1 and basalt-2, but the difference of the average surface slope factor and the arithmetic average deviation is greater, namely, rough degree of surface texture of coarse aggregates has nothing to do with the particle diamter.In addition, the dissertation classifies the aggregate topography and morphology and proposes the geometric characteristics of aggregates and laws to improve the road performance index based on the quantitative parameters and evaluation index of the aggregate shape and texture. Based on the laws, optimal design is carried out for the geometric characteristics of aggregates, the strategy in selecting aggregates is proposed based on the shape and surface texture, and the relevance between mechanical sieving and theoretical screening is analyzed.