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Study on Wireless Sensors for Monitoring the Corrosion of Reinforcement in Concrete Structures

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Tutor: WuZuo
School: Nanjing University of Aeronautics and Astronautics
Course: Structural Engineering
Keywords: reinforcement corrosion,wireless sensor,monitoring,LC circuit,resonant frequency
CLC: TU375
Type: Master's thesis
Year:  2007
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Abstract:
Reinforcement corrosion has a large impact on durability and safety of the concrete structures. Compared with the traditional monitoring techniques, the wireless monitoring techniques have more advantages. But domestic research of wireless sensors for the monitoring of reinforcement corrosion has not yet started. In this paper, the wireless sensor based on radio frequency technology is improved. Then the circuit simulation of the sensor and the experiment on the sensor is carried out. The main works and conclusions are as follows:1. The radio frequency technology and the monitoring mechanics are studied. And the circuit simulation of the sensor is carried out using the circuit simulation program Electronics Workbench (version 5.12), which identifies the relationship between the range of the resonant frequency and the resistance of the steel wire during the corrosion process. Based on the research, whether the steel wires of the basic sensor, the sensor with reference circuit and the sensor with two switch circuits are fractured or not can be assessed by monitoring the resonant frequency. For the sensor with two switch circuits, only when the difference of the diameter of the steel wires is large enough, can the resonant frequency be measured.2. Based on the circuit simulation, the sensor is improved in the effect of measurement, reference circuit, sensor circuit and the encapsulation, and the circuit is modified according to the accelerated corrosion experiment. Then the sensor is composed with appropriate circuit component and the encapsulation is studied. Finally, the experiment on the sensor is carried out, which shows the improvement is feasible.3. According to the experiment, it is found that whether the steel wire of the basic sensor is fractured or not can be assessed by monitoring the resonant frequency, but the“transition zone”exists. The sensor with spring switch in this paper can solve the problem of the transition zone. There is only initial frequency and finial frequency, and no“transition zone”is found. The experiment also shows that the improvement of the sensor with two switch circuits is feasible. They can indicate two corrosion status of the reinforcement. Based on the analysis of the sensors’response, we find a way to monitor the whole corrosion process of the steel wire by monitoring the value of Q’before“transition zone”and the amplitude of the voltage corresponding to the final resonant frequency in“transition zone”.4. Based on the experiment, it is found that the loss of weight increases with the increase of the diameter of the steel wire, and the relationship between them is linear when the diameter is between 0.25mm and 0.8 mm. The linear relationship between the loss of weight and the diameter of the steel wire is obtained in this paper.
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