Design Of Fiber Grating Sensor For Rebar Corrosion And Study On Durability In Concrete Structure

Attention is being paid globally to the durability of traffic and civil engineering. Due to undesirable durability, the safety of reinforced concrete structures decreases, and even concrete structures fail early.One of the most predominant factors responsible for the structural deterioration in concrete structures is identified as corrosion of reinforcement. Especially in the marine and de-icing salt environment, corrosion may result in damage to the structures in the form of expansion, cracking and eventually spilting of the cover concrete. In addition, the structural damage may result from loss of the bond between reinforcement and concrete, and the loss of reinforcement cross-sectional area, at last, the structural failure becomes inevitable.In this study, an attempt has been made to assess the issue on a quantitative basis. With financial supports of the Natural Science Foundation of Jiangsu Province and the National Natural Science Foundation of China, some efforts have been made in design of fiber Grating sensor for rebar corrosion and study on durability in concrete structures. The research work is following.①From the viewpoint of electrochemical theory, the corrosion process was analyzed to deduce the relation of the expansion rate and the diameter of corrosion reinforcement in marine environment. Chloride penetration models derived from Fick's second law of diffusion was used to analyze the random characters of ions and the ununiformity of corrosion in the reinforcement. Furthermore an index was carried out to define the corrosion initiation. Finally, the quantitative relation of corrosion product, rate and current was derived from the Faraday's Law.②Based on hollow thick cylinder model and elastic-plastic method, corrosion process(such as initial cracking, cracking, cracking to some width) was analyzed, and the relationship between corrosion products, corrosion-induced expansive pressure, and the displacement of concrete was obtained.③Based on volume expansion, two types of optical fiber grating sensors for reinforcement corrosion, as well as encapsulated methods, were designed and tested. At the same time, the relationship between monitoring data and corrosion degree was calibrated by experimental study. Finally, an improved sensor was put up and tested.④In order to make full use of different time space multi-sensors information resources and to obtain the coincidence decision of corrosion assessment from reinforcement corrosion monitoring system, in this paper, the model of multi-sensor data fusion were put forward. The corrosion degree was described by fuzzy intervals instead of the average value.⑤Because of a substantial decrease of load-bearing capacity due to corrosion, the models of load-bearing capacity of flexural members were built up, and the effect of corrosion on residual load-bearing capacity was discussed.⑥A study on reliability-based durability of reinforced concrete structures was conducted in this paper. The model was provided to predict deterioration of residual bearing capacity varying with time. Based on the random characteristic of load and bearing capacity, as well as ununiformity of corrosion in steel bars, a time-dependent structural reliability method is provided, which agrees with the method in current standard of structural design. This method is convenient to be used for reliability analysis and assessment of deteriorating structures.⑦Multiple guidelines about durability assseement of the concrete structures exposed to marine environment were studied, according to these guidelines, the residual survival life and durability would be predicted.⑧The optical fiber grating sensors for reinforcement corrosion have been applied in practical engineering, for which encapsulation, embedding and calibration was emphasized. According to the measuring results, the stabilization of sensors was proved.