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

研究了混凝土断裂能（单位裂缝面积所需能量）和拉伸软化曲线（裂缝区拉应力与裂缝张开度的关系）的测定方法。研究了利用这些断裂力学参数模拟混凝土断裂行为的数值方法和混凝土性能的评价方法。获得了以下结果。(1)混凝土的拉伸软化曲线测定从新提出的管拉伸试验，其中试件与两个圆柱形狭缝进行压缩载荷。(2)通过声发射源定位试验检测了裂纹扩展过程。据观察，损害的分布并不均匀。(3)提出了一种基于J积分概念的弯曲试验确定拉伸软化曲线的新方法。利用该方法得到了钢纤维混凝土的拉伸软化曲线。它们与直接拉伸试验所得结果十分相似。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了数值模拟，其中考虑了混凝土受拉软化的影响。(6)测定了树脂混凝土、轻骨料混凝土、早龄期混凝土、碱骨料反应损伤混凝土等混凝土的拉伸软化曲线和断裂能。据观察，这些断裂力学参数是合适的混凝土拉伸性能的评价。(7)对局部破坏性试验之一的折断试验进行了改进，使之能用于测定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.