Effect of internal crack defects on fracture properties of concrete

Concrete beams with different types of horizontal crack defect were designed and tested through the three-point bending test to investigate the influence of internal crack defect on the fracture behavior of concrete. The effects of different lengths, locations, and numbers of horizontal crack defects on the fracture performance of concrete were analyzed. The fracture parameters and fracture energy of the concrete within different crack defects were calculated and compared on the basis of P-D_m and related test data. Results show that the initial cracking load and initiation fracture toughness of the concrete beams were slightly affected by the internal horizontal crack defects, whereas unstable load and fracture toughness were seriously affected by the additional horizontal crack defects. A large horizontal crack length and a small distance between the horizontal crack and the bottom of the beam corresponded to a small carrying capacity of the beam and a small unstable fracture toughness and fracture energy. The more the horizontal cracks in the concrete beams were, the smaller the unstable load and the unstable fracture toughness were and the smaller the fracture energy was. This phenomenon shows that the larger the material loss caused by crack defects in the concrete beams, the smaller the energy consumed by complete fracture and the smaller the fracture parameters measured.