Deterioration of bond performance between rebar and concrete with initial cracks under alternating salt-freezing and fatigue cycles

To investigate the degradation of bond performance between rebar and concrete in cracked RC structures under the combined effects of salt freezing and fatigue loads, 11 sets of pullout specimens with cracks were subjected to alternating actions. Pullout tests were then performed to assess the bond strength deterioration. The deterioration mechanism was analyzed, and a bond-slip constitutive model considering effect of crack width under alternating salt-freezing and fatigue conditions was established. The results showed that salt-freezing damage in concrete progressed under alternating actions, leading to a continuous decline in bond fatigue performance. Larger initial crack widths resulted in more significant reductions in peak bond strength. After three cycles of alternating actions, the ultimate bond strength decreased by 41.39% for specimens without initial cracks and 48.07% for specimens with an initial crack width of 0.05 mm. Specimens with a 0.10 mm initial crack failed during the fatigue loading phase of the third cycle. All specimens exhibited a combined pullout-splitting failure mode. The salt-freezing cycles and fatigue loads jointly accelerated the degradation process. Initial cracks provided pathways for saline solution to penetrate the interface and cause stress concentration in cover concrete, thereby further weakening the interface's fatigue performance. Consequently, the degradation of bond performance under alternating actions was accelerated by initial cracks. The adverse effects were more distinct as the crack width increased.