Different Coarse Aggregate And The Strength Grade Of Concrete Fracture Properties Of The Experimental Method

By using 5000kN pressure-bent testing machine, the specimens of boulder concrete and crushed stone concrete were tested through three-point-bending method and wedge-split tensile method, the scale division of the index dial of pressure-bent testing machine is larger, whereas the predicted test-load is lesser, so the velocity of exerted load is controlled through observing the reading of the multimeter which is connected with the collecting systerm in order to continuously exert test-load. The experiment determined the fracture process and the parameter of the fracture properties of two different aggregate concrete and recorded the stable whole fracture curves of boulder concrete and crushed stone concrete separately, which are determined through three-point-bending method and wedge-split tensile method.According to the recorded full process fracture curve, the paper calculated andcompared the fracture toughness(KIC), the fracture energy(GF) and crack tip openingdisplacement(CTOD) of the different strength grade boulder concrete and crushed stone concrete, it is found that the maximal load( Fmax) and the fracture toughness (KIC) of boulder concrete and crushed stone concrete increase when the strength ofthem increases, so does the fracture energy of boulder concrete, but the fracture energy of crushed stone concrete doesn't obviously increase when it's strength increases. The crack tip opening displacement(CTOD) of all specimens chang less when the strength of concrete increases, so it is concluded that the location of the axle in the ligament of the specimens is relatively stable.By comparing the fracture toughness(KIC), the fracture energy(Gf) and the crack tip opening displacement(CTOD) of the same strength grade concrete, it is found that the values of the fracture toughness( KIC ), the fracture energy( GF) and the crack tip opening displacement(CTOD), tested by three-point-bending method and wedge-split tensile method approach, so it is proved that the fracture toughness( KIC ), the fractureenergy( GF) and the crack tip opening displacement(CTOD) are related to its ownproperties such as material, specimen size, and crack size, but unrelated to the test-method. Since the specimens used in the wedge-split tensile method are smaller, cheaper and the testing is more convenient, it is proposed that using the wedge-split tensile method tests the fracture toughness and the fracture energy of concrete.