Fatigue behavior of naturally corroded plain reinforcing bars

Segments of corroded plain reinforcing bars were firstly extracted from an aged reinforced concrete (RC) pole after its breaking. The testing specimens were then taken from these segments. The cause for corrosion of the specimens was analyzed, and the corrosion degree of the specimens was measured before testing. Tensile loading tests were performed with 3 non-corroded specimens to obtain the mechanical properties of the plain reinforcing bars prior to any corrosion. Axial tensile fatigue tests were conducted with 34 corroded specimens to investigate the fatigue behavior of the naturally corroded plain reinforcing bars. Corrosion of the specimens was initiated by the carbonation of concrete. Two corrosion levels and five stress ranges were considered. Fatigue test results showed that the median fatigue life of lightly and medium corroded plain reinforcing bars was reduced by 48 and 75% respectively under the same stress range of 240 MPa by compared with that of non-corroded plain reinforcing bars. Based on the test results, the fatigue Src-N curves of the lightly and medium corroded specimens were presented by using least square method. Then, the predicted fatigue lives and fatigue strengths of naturally corroded plain reinforcing bars were suggested and compared with those of other related literature. The fatigue strength with 50% guarantee rate of lightly and medium corroded plain reinforcing bars is reduced by 18 and 28% respectively under a fatigue loading with cycles of 2 million by compared with that of non-corroded plain reinforcing bars. The fatigue fracture mechanism of the corroded specimens was interpreted by using Scanning Electron Microscope (SEM) images. Further, the pit depth was measured, and the relationship between the relative maximum pit depth and fatigue life of the corroded specimens was explored. It was found that one or more crucially localized pits of a specimen leading to the reduction of fatigue strength had an important influence on its fatigue life. A linear relationship between the relative maximum pit depth and the relative fatigue life of the corroded specimens was observed under three given stress ranges. This study provides a necessary basis for the determination of the remaining fatigue life of aged existing RC bridges.