This paper presents an experimental investigation into the mechanisms altering the pull-out behaviour of partially pulled hooked-end steel fibres inside an artificial crack exposed to wet–dry cycles of chlorides and carbon dioxide for 6 months. Mechanical and corrosion damage at the surface of the steel fibre was investigated using three-dimensional optical interferometric profiling, and petrographic analyses were used to describe damage and healing processes at the matrix surrounding the fibre. Mechanical damage observed in the cementitious matrix and at the fibre's surface confirmed that the pull-out process was governed by yielding of the fibre, fracture of the adjacent matrix, and friction between the hook and the matrix. Increases in the pull-out force of partially pulled-out fibres after exposure were connected to accumulation of corrosion products from the steel fibre and to alteration of the cement matrix surrounding the fibre. This study concluded that autogenous healing and carbonation of the damaged cement matrix around the fibre are the main mechanisms responsible for the increase in the fibre–matrix bond strength of hooked-end steel fibres bridging cracks in concrete exposed to wet–dry cycles.

中文翻译：

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干湿循环下开裂混凝土中钢纤维的拔出行为——劣化现象

本文对暴露于氯化物和二氧化碳的干湿循环 6 个月的人工裂缝内部分拉出的钩端钢纤维的拉拔行为的机制进行了实验研究。使用三维光学干涉仪分析钢纤维表面的机械和腐蚀损伤，并使用岩相分析来描述纤维周围基体的损伤和愈合过程。在水泥基体和纤维表面观察到的机械损伤证实，拉出过程受纤维屈服、相邻基体断裂以及钩子和基体之间的摩擦控制。暴露后部分拉出的纤维拉出力的增加与钢纤维腐蚀产物的积累和纤维周围水泥基体的改变有关。该研究得出的结论是，纤维周围受损水泥基体的自生愈合和碳化是导致纤维-基体结合强度增加的主要机制，钩端钢纤维桥接暴露于干湿循环的混凝土中的裂缝。