Experimental Research On The Low-cycle Fatigue Of Corroded R.C. Beams

The corrosion of the reinforcement, a worldwide disaster, has become a major cause which leads to the lack of durability and premature destruction of reinforced concrete structures. Studies have shown that:reinforcement corrosion has more critical effect on the dynamic or fatigue performance than the effect on static performance of the structures. Therefore, studying the fatigue performance of the corroded reinforced concrete members has a particularly important practical significance,which can be used to predict the residual life of the structures resisting cyclic loading in a corrosive environment and to provide the basis for repairing and reinforcing of the damaged members. Now that little studies has been done in the field of the fatigue behavior of the corroded R.C. members until now, this paper has carried out a experiment to investigate the fatigue behavior of the corroded R.C. beams comprising two comparison R.C. beams (not corroded) and twelve corroded (corrosion rate ranging from 0.93 percent to 12.56 percent). The only test variable is the longitudinal reinforcement corrosion rate. The objective of the research is to figure out how the longitudinal reinforcement corrosion rate is affecting the fatigue behavior of the corroded R.C. beams. The content and the conclusions of the paper are as follows:(1)The accelerated corrosion of the R.C. beams has been completed by exerting a direct current, using wet salt sand as the medium and applying the Faraday's law to calculate the corrosion rate. The results showed the process of that this kind of method is in line with the process of the reinforcement corrosion in the natural environment. The corrosion products of the reinforcement are fully oxidized and the effects of the corrosion are similar to the actual situation.(2)The natural potential of the corroded R.C. beam has been measured to complete the non-destructive testing of the reinforcement corrosion in the concrete. The results showed that the half-cell potential method can only be used in the qualitative detection of corrosion. The relationship between the maximum corrosive crack width and the longitudinal reinforcement corrosion rate is given, which can be used to provide the basis of non-destructive testing of corrosion status of reinforcement in concrete.(3)The fatigue life, cracking load, flexural stiffness, concrete strain, the regular pattern of the development of fatigue crack are obtained through the low-cycle fatigue test of the corroded R.C. beams. The results showed that:the fatigue life is extremely sensitive to the longitudinal reinforcement corrosion rate; both the cracking loading and flexural stiffness decline while the longitudinal reinforcement corrosion rate increases; the growth of the concrete strain and the development of fatigue crack show an obvious three-stage law under the cyclic loading; the crack width of corroded R.C. beams increase as the load cycles increase; the crack width of the high corrosion rate beams is greater that the width of low corrosion rate beams at the same life ratio.(4)A fatigue life prediction model for the concrete crushed failure of corroded R.C. beams under cyclic loading is built according to the fatigue failure criteria of concrete strain space. The formula gives the direct relationship between the longitudinal reinforcement corrosion rate and the low-cycle fatigue life. According to the three-stage development law of the residual strain of the concrete and based on the analysis of concrete fatigue damage development law, a fatigue accumulative damage equation using the residual strain as the damage variable is built to predict the remaining fatigue life of different longitudinal reinforcement corrosion rate corroded R.C. beams.