Study On K_R Resistance And Fracture Toughness Of Flattened Brazilian Disk Specimen Of Concrete

Concrete is a very important material for buildings, bridges, roads, ports and other aspects today. However, there are different degrees of damage for various factors in the construction and using process. As a quasi-brittle material, it is also in a state which works with cracks for concrete because its tensile strength is much smaller than the compressive strength and due to the heterogeneous and multiphase features of concrete, there are many micro-cracks and gaps in concrete.Therefore, for concrete structures, cracks contribute much to the destruction of the concrete structures..The nonlinear behavior of concrete can be taken into account in an approximate manner in linear elastic fracture mechanics (LEFM) for the theory’s proposition of linear asymptotic superposition assumption. In this paper, we conducted experiment study on the fracture toughness, T-stress and the crack extension resistance of concrete based on the platform Brazilian disc specimens and three-point bending beam specimens.Central-notched split-tension platform discs which have different ages and different initial crack/depth ratio have been used to carry out fracture tests under static loading. In contrast with previous experimental study of three-point bending concrete beams, central-notched split-tension cubes and wedge splitting specimens, we confirmed the rationality of the fracture toughness of concrete in the platform Brazilian disc specimens. The fracture toughness of concrete increases with the increase in age, and it first increases and then decreases by increasing the ratio of the initial crack/depth.Stress intensity factor (SIF) is so significant in the study on the fracture characteristics concrete that people believed it is the single controlling parameter for the fracture process Nevertheless, further explorations have shown higher order terms of the crack tip asymptotic field are also of great importance, especially the second nonsingular term, the so-called T-stress. In order to explore the influence of T-stress on fracture toughness of concrete three-point bending beams are used for testing fracture parameters in ordinary laboratories in this paper.In the process of concrete crack cohesive stress have a direct impact on the fracture toughness calculation. In this paper, a test is carried on for the effect on the crack extension resistance curve of concrete by considering the variation of the fracture process zone (FPZ) length during the whole fracture process. In this paper, the FPZ length is determined by using the linear asymptotic superposition assumption. Dividing the whole fracture process into three different stages of the cohesive stress distribution within the FPZ, the crack extension resistance curve is formulated by superposition of the intrinsic fracture toughness of concrete and the fracture toughness caused by the cohesive stress within the FPZ. The effect of the variation of the FPZ length on the crack extension resistance curve is evaluated on the basis of the numerical results. The crack extension resistance first increases with an increase in ratio of the effective crack length to the beam depth and then reach a plateau value when the FPZ is fully developed.