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Effect of internal crack defects on fracture properties of concrete
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摘要: 为研究混凝土梁内部贯穿裂缝缺陷对其断裂性能的影响，设计了含不同裂缝缺陷混凝土梁的三点弯曲断裂试验，研究不同长度、位置及数量的水平裂缝缺陷对混凝土断裂性能的影响。通过试验测得的P-Dm曲线以及相关试验数据计算得到含不同裂缝缺陷的混凝土断裂参数与断裂能。对比结果可知：混凝土三点弯曲梁的起裂荷载和起裂韧度受水平裂缝缺陷参数变化的影响较小，而失稳荷载和失稳韧度受水平裂缝缺陷的影响较大；水平裂缝越长，试验测得其失稳荷载越小，计算得到的失稳韧度和断裂能也越小。水平裂缝距离试件的底部越近，试验测得其失稳荷载越小，计算得到的失稳韧度和断裂能也越小。水平裂缝数量越多，试验测得其失稳荷载越小，计算得到的失稳韧度越小，断裂能也越小。该现象表明混凝土试件中含线性缺陷导致材料的缺失量越大，其完全断裂所消耗的能量越小，且测得的断裂参数值也越小。Abstract: 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-Dm 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.
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图 11 断裂参数随水平裂缝数量变化曲线
Figure 11. Fracture parameters versus number of horizontal cracks
表 1 试件设计参数
Table 1. Design parameters of specimens
试件编号 w/mm n h1/mm h2/mm TPB-W1-x 60 1 40 - TPB-W2-x 80 1 40 - TPB-W3-x 100 1 40 - TPB-W4-x 120 1 40 - TPB-H1-x 60 1 20 - TPB-H2-x 60 1 40 - TPB-H3-x 60 1 60 - TPB-H4-x 60 1 80 - TPB-N1-x 60 0 - - TPB-N2-x 60 1 40 - TPB-N3-x 60 2 40 20 TPB-N4-x 60 3 20 20 注：试件编号中，TPB代表三点弯曲梁试验；W，H，N分别代表含不同长度w、间距h1和h2以及数量n的水平裂缝缺陷的试件；x = 1，2，3，代表相同参数的试件各有3个。 
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