| The double-block ballast-less track is one of the most widely used structure on high-speed railway around the world, it was already used in the project of Wuguang and Zhengxi passenger lines. The slab is an important part of double-block ballast-less track. It was constructed by continuous pumping concrete. By the site investigation, it was found that the slab concrete cracked in some sections of the track, the width and spacing exceed the current technical requirements. These situations affected the quality of the project and reducing its service life, and caused a certain amount of security risk. Many factors affect the concrete cracks, and the formation mechanism is different in various stages. The slab cracked and formed fracture is belongs to the type I breakage in fracture mechanics. The concrete micro cracks continues to expanded, interchange and cut through under the stress field which formed in a variety of factors, finally the micro cracks become the macroscopic fracture. Some cracks will continue to expand, possibly become transvers through fracture, it makes the slab breakage. This paper researched and analyzed the computing method and material properties of fracture parameters of the slab concrete based on the revised linear elastic fracture mechanics and combined the fracture test. Therefore, the main research contents and results of this paper is as follows:1. Based on the previous research of Hillemeier and Hilsdorf and our laboratory conditions, we designed tensile fracture test using wedge-splitting method by our self. This test can achieve a stable breakage process more easily. Data was synchronous acquired precisely by multi-channel and the amount is very rich.2. We observed the whole process of the pre-cracks in concrete extended until the specimen breakage. From the load-crack mouth opening displacement (P-CMOD) curve, it can be seen that the concrete breakage showing a clear nonlinear facture. The peak load and limit crack mouth opening displacement can be determined from the curve. In the meantime, the strain gauge which arranged on both sides of the crack mouth tip can monitor the initial cracking load of concrete specimen. This method is simple and feasible.3. Initial fracture toughness and unstable fracture toughness can be calculated by the experimental analysis and double K fracture theory. The initial fracture analytical solution which is can be obtained from the constitutive relations of concrete is little larger than the calculation results.4. The tail of P-CMOD curve is fitted by power function, the fitting degree is up to 99%. The area under overall P-CMOD curve can be calculated by the method of integration by parts. So the area size is the fracture energy of concrete.5. On the basis of reference concrete mix, we designed 4 different mix (C1～C4) by changing the composition of cementations materials and the amount of coarse and fine aggregates. Analyzed and compared the variation characteristics of four different concrete's value of Pini, Pmax, CMODini, CMODC. We calculated the value of double-K fracture parameters of different concrete ratio. It analyzed the fracture parameters variation with age and intensity, and then fitted some data.6. Based on single parameter, it presented the fracture energy prediction model using three parameters such as cube compressive strength fcu, maximum aggregate size dmax and the water cement ratio w/c. We can get the relationship of this model by multi-parameter nonlinear regression analysis.7. Through comprehensive analysis and calculation, the paper thinks that the fracture parameters of concrete which meet the construction and structural requirements are mainly distributed in the following ranges:the initial fracture toughnessh is 0.01～0.1MPam1/2, the unstable fracture toughness is 0.49～0.84MPam1/2, the fracture energy is 230N/m～280 N/m, and the greater value of fracture parameters of concrete show that its ability to resist crack propagation is stronger and crack resistance ability is more better... |
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