Study Of Double-K Fracture Parameter Of Roller Compacted Concreteinduced

As one heterogeneous composite, the fracture mechanism of concrete is very complicated and difficult to study because of the physical characteristics, combination aspects and state of stress of the component of concrete. But concrete is in the massive use with architectural project, which needs the researchers must to strengthen the research of the concrete. What the author does in this text is to study the influence of specimens size and initial ratio of the notch depth to the beam depth on double-K fracture parameter via physics test, which the fracture parameter including initial cracking toughness KIcini and unstable fracture toughness KIcun are studied as well as the size effect.The author carries out physical tests of with different sizes and ratio of the notch depth to depth. The data are analyzed carefully. Through the analysis of many group’s test data, the author gets some conclusions of the following, some of them are different from the past to some extent:1. The influence of concrete specimen size on double-k fracture parameter is also investigated by using specimens with the different sizes. The result shows that specimen initial cracking toughness KIcini and unstable fracture toughness KKIcun increase with the increase of concrete size, which the size effect exists.2. The initial cracking toughness KIcini and unstable fracture toughness KKIcun of specimen are almost the constant with the different ratio of the depth to the specimen depth a0/h, which do not change with ao/h on the whole. The result shows that the unstable fracture toughness IKKIcun. initial fracture toughness KIcini are independent of a0/h when a0/h of the specimen is≥0.4. While the KIcini calculated from different cohesive stress equation will not be constant.3. The wholly integrated process of pre-cast cracks initial and final failure on all wedge splitting specimens, whose largest size is500x500x150mm3, are systematically analyzed. The result shows that specimen initial cracking toughness KIcini and unstable fracture toughness Ic increase with the increase of concrete size, which the size effect exists. The results show that the confinement of back boundary of specimen to the development of fracture process zone is responsible for the observable size effect on fracture toughness of concrete material. For small specimens with the depth of less than400mm4. Through a limited number of measured data of crack effect propagation length, it can be found that crack effect propagation length increases with the increasing of the height of specimen.