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Study on the Granular Characteristics and Segregation Mechanism of Aggregates

Author: HuZuo
Tutor: ShaAiMin
School: Chang'an University
Course: Road and Railway Engineering
Keywords: segregation granular matter segregation index aggregates heap silo vibration particle size ratio
CLC: U414
Type: Master's thesis
Year: 2010
Downloads: 92
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Abstract


Segregation is an important factor that causes the early damage of asphalt concrete pavement. Studies on segregation at home and abroad focus on its evaluation criteria or some other aspects, lacking of research on its mechanism. In order to control segregation more effectively, it is necessary to start research on the mechanism of it. The system like aggregates that consists of particles and voids is defined as granular matter, which has many special characteristics. In this paper, the movement characteristics and segregation mechanism of aggregates will be studied from the perspective of its granular characteristics, which is aimed at finding a viable method to study segregation of asphalt mixture. In this tentative research, the objects of the experiments are simple.First of all, the relative research of granular matter is related and the feasibility to study aggregates segregation combined with the granular matter theory is demonstrated. Then, aggregates segregation is studied in the following three processes:heap forming, discharge from silo and undergoing vibration caused by transport. All the studies are carried with the following steps:experiment designing, data analysis and mechanism summary. The conclusions are as follows. In the heap forming process, as the angle of aggregates heap increases, both of the overall and layering segregation indexes grow. When the heap’s angle equals to the angle of repose, the overall segregation index still increases while the layering segregation index tends to be a constant. The author believes that the angle of repose segregation is the main mechanism in the heap forming process. When aggregates discharge from silo, both of the external conditions and aggregate properties affect the segregation in this process. The external conditions include the loading height of aggregates, the angle of hopper and the discharge height. The most important factor among them is the loading height. The aggregate properties also have significant impact on segregation in this process, such as the particle size ratio, the fines content and the average particle size. The larger of particle size ratio, the more prone to severe segregation. The probability of segregation reduces with the increase of fines content. The influence of average particle size on segregation is related to the outlet size of hopper, as the ratio of outlet size of hopper and the average particle size increases, the segregation degree reduces. The author concludes that it is the infiltration segregation mechanism that works when aggregates discharge from silo. The study on segregation of aggregates under vibration is carried on a modified vibration compactor. The result shows that after a certain vibration time，the deviation of coarse aggregate content in each layer keeps on a constant value, and infiltration segregation mechanism still plays an important role in this process.

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CLC: > Transportation > Road transport > Road works > Road construction materials
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