| The double-block ballast-less track is one of the most widly used structure on high-speed railway around the world. Slab, continuous casted with pumping concrete, is an important part of double-block ballast-less track. The cracking phenomenon of slab is serious, and the crack width and spacing requirements exceed the current technical conditions, which affects the performance and service life of ballast-less track structure.Meanwhile, cracks on the concrete slab, is a huge project, there are excessive influencing factors of cracking on continuous casting concrete, and its formation mechanism is also different in varying stage. The article explains the influence factors and mechanism of cracking on slab concrete from the view of material properties and structural characteristics of slab. Therefore, four parts of work are included in the research:1. According to the crake status of concrete slab on the line of Wu-Guang and Zheng-Xi, the paper put forward the state and characteristics, the types and actual causes of crack on continuous casting concrete slab. The research results show that the cracking of concrete slab mainly due to drying shrinkage and temperature shrinkage.2. By monitoring the stress-strain sensors embedded in slab on the line of test section in Changsha, the author analyzes the correlation between ambient temperature, sensor temperature and the strain of measuring points on construction site. Besides, the impact of temperature difference on measured strain in concrete is also analyzed. The ambient tempereture and sleeper have greater influence on surface of slab than that of understructure, the maximum tensile strain is 344μεon upper layer and the maximum compressive strain is 292μεon lower layer.3. The research starts from the material propertities of slab concrete, the development of basic mechanic properties, static elastic modulus, shrinkage and compressive stress-strain relations with age were taken into consideration. The author also presents the prediction model about compressive strength, elastic modulus, drying shrinkage of concrete related to the age development, obtaines the parameters of stress-strain on different strength grade, the complete stress-strain model and law of damaged concrete, the relationship between peak stress and peak strain. The square error of the fitting results on stress and strain curve of concrete is not more than 0.0042 and the correlation coefficient R is more than 0.98442.4. Based on the research of influencing factors about drying shrinkage performance of mortar, the paper analyzes the influencing factors about drying shrinkage of concrete, studies the variation of drying shrinkage under different curing conditions. Based on the experimental study on the influence of water-cement ratio, strength level, content of mineral admixtures and other on crack resistance of concrete, the paper obtaines the crack resistance and regularities of crack distribution of concrete slab under different intensity levels, different mixed ratio of mineral admixtures, and then explored the relationship between the material properties of concrete and the crack on concrete slab.5. The paper analyzes the influence law of different constraints and concrete material properties on stress and strain distribution inside the concrete slab, under drying shrinkage and temperature shrinkage by establishing a finite element model of concrete slab, and also obtaines the cracking characteristics of concrete slab structures, the control index of concrete material properties and the crack distribution by numerical analysis. The areas around the sleeper and the corner near the outboard of slab will generate great stress and strain; these sites are more prone to crack. |
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