Study on Fracture Behavior of Concrete by means of Fracture Mechanics Approach

研究了确定混凝土断裂能（单位裂缝面积所需能量）和拉伸软化曲线（裂缝区域拉应力与裂缝开度关系）的试验方法。研究了利用这些断裂力学参数和混凝土性能评价方法模拟混凝土断裂行为的数值方法。得到以下结果：(1)采用新提出的筒拉试验方法，在筒拉试验条件下，试件受压缩荷载作用，得到了混凝土的拉伸软化曲线。(2)通过声发射源定位试验检测裂纹扩展过程。有人指出，损害赔偿的分布并不均匀。(3)提出了基于j积分概念确定弯曲试验拉伸软化曲线的新测试方法。用这种新的测试方法得到了钢纤维混凝土的拉伸软化曲线。它们与从最可怕的拉力试验中得到的结果非常相似。通过数值分析，给出了获得稳定结果的试验条件。(4)采用有限元法对碱骨料反应引起的混凝土裂缝进行数值模拟，考虑混凝土的拉伸软化。(6)测量了树脂混凝土、轻量化混凝土、早期混凝土、AAR损伤混凝土等不同类型混凝土的拉伸软化曲线和断裂能。结果表明，这些断裂力学参数适用于混凝土拉伸性能的评价。(7)改进了局部破坏试验之一的断裂试验来测量混凝土的拉伸软化曲线。

We studied the testing methods to determine the fracture energy (energy required for unit crack area) and the tension softening curves (relations between tensile stress and crack opening at cracked region) of concrete. We also investigated the numerical methods to simulate fracture behavior of concrete using these fracture mechanics parameters and the evaluation methods of concrete properties. Following results were obtained.(1) Tension softening curves of concrete were measured from the newly proposed tube tension tests, where specimens with two cylindrical slits were subjected to compression load.(2) The crack propagation process was detected by means of AE (acoustic emission) source location tests. It was observed that the distribution of damages was not uniform.(3) The new testing method based on J-integral concept to determine tension softening curves from bending tests was proposed. The tension softening curves of steel fiber reinforced concrete were obtained by this new testing method. They were quite similar to those obtained from direst tension tests. The testing conditions to obtain stable results were presented by numerical analysis.(4) Concrete cracks due to alkali-aggregate reaction were numerically simulated by FEM, where tension softening of concrete was considered.(6) Tension softening curves and the fracture energy of various kinds of concrete, including resin concrete, light weight concrete, concrete in early ages, damaged concrete due to AAR, etc. were measured. It was observed that these fracture mechanics parameters were suitable for evaluation of concrete tension properties.(7) The beak-off tests, one of local destructive tests, were improved to measure tension softening curves of concrete.