Abstract To study the influence of creep recovery on the fracture properties of concrete, the pre-notched specimens were firstly subjected to three-point bending (TPB) loading at 60% peak load (Pmax) over 30 days. Afterwards, the load was removed and the creep recovery tests were performed for 1, 2, 3 and 15 days, respectively. Thereafter, the quasi-static TPB tests were conducted on the creep recovery specimens. The deformation versus time curves, initial cracking load (Pini), peak load and fracture energy in the quasi-static TPB tests after creep recovery were obtained. Also, the numerical analyses were conducted by combining with the Norton-Bailey model to investigate the stress variations at the crack tip and the time-dependent behaviour of concrete. By comparing the fracture parameters for the specimens with and without undergoing creep recovery, the effects of creep recovery on the fracture characteristics of concrete were assessed. The results showed that during the creep stage, the stress relaxation generated at the crack tip due to viscoelastic characteristics of concrete enlarged the deformation. In contrast, the reversed stress would occur at the crack tip during the recovery stage, and its relaxation over the time contributed to the time-dependent deformation during the creep recovery stage. By comparing with the specimens under the quasi-static TPB loading, Pini and Pmax for the creep recovery specimens would increase, and the increments slowed down over the recovery time. However, the increases in Pini and Pmax for the creep recovery specimens could not enhance the initial and critical fracture toughnesses and these toughnesses were approximately equal to those under the quasi-static tests.

中文翻译：

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徐变恢复对混凝土断裂性能的影响

摘要 为了研究徐变恢复对混凝土断裂性能的影响，首先在 60% 峰值载荷 (Pmax) 下对预制缺口试件进行三点弯曲 (TPB) 加载，持续 30 天。之后，移除负载并分别进行 1、2、3 和 15 天的蠕变恢复测试。此后，对蠕变恢复试样进行了准静态 TPB 试验。获得蠕变恢复后准静态 TPB 试验中的变形与时间曲线、初始开裂载荷 (Pini)、峰值载荷和断裂能。此外，通过结合诺顿-贝利模型进行数值分析，以研究裂缝尖端的应力变化和混凝土的时间相关行为。通过比较经过和未经过蠕变恢复的试样的断裂参数，评估了蠕变恢复对混凝土断裂特性的影响。结果表明，在徐变阶段，由于混凝土的粘弹性特性，裂纹尖端产生的应力松弛扩大了变形。相比之下，在恢复阶段，裂纹尖端会出现反向应力，随着时间的推移，其松弛有助于蠕变恢复阶段的时间相关变形。通过与准静态 TPB 加载下的试样相比，蠕变恢复试样的 Pini 和 Pmax 会增加，并且随着恢复时间的增加而减慢。然而，