Corrosion Monitoring And Performance Evaluation Of Reinforced Concrete Structures By Using A Low Coherent Fiber-Optic Sensor

The steel corrosion of reinforced concrete structure is a major problem in structural health monitoring, because it is lack of an effective method to monitor the corrosion procedure. The methods based on optical fiber sensing technology mainly employed Brillouin Optical Time Domain Analyzer (BOTDA), Fiber Bragg Grating (FBG) and other specific optical methods. However, there is no effective method available until now to evaluate the BOTDA distributed sensors. Thus, the performance of the BOTDA sensing data cannot be well analyzed. This paper proposed a low coherent fiber strain sensor (LCFS) method to monitor the deformation of the structure to verify the BOTDA in the meantime.The LCFS is designed as a quasi-distributed sensing system configuration and measured the deformation of the structure at the accuracy of5micrometers over arbitrary sensing length. The BOTDA based measurement is the stain distributed along with the sensing fiber. These two sensors can be related by an integral function, which stems from the deformation of the sensor equals to the integral of the distributed strain.The goal of this thesis was to design a LCFS system and employed to implement the fine evaluation purpose. The LCFS system was based on the Michelson interferometer configuration. The system includes superluminescent light-emitting diode(SLED) light source, fiber optic sensor module, central control module based DSP2812, stepping motor driver design, photoelectric detection module and industrial personal computer (IPC), etc. The major achievements of this work were:(1) Firstly, the stepping motor driving system was designed based on a DSP2812and carried out the experiment on the corrosion monitoring for the test purpose. The system has high stability with5-micrometer precision by writing drive program, designing control algorithm and positioning algorithm combined with optical grating ruler that makes a closed-loop control on the stepping motor.(2) Secondly, the signal processing was carried out to extract the information from the measured signal. We employed Labview software to acquire data and designed an algorithm to filter the noise.(3)Thirdly, the sensing fiber was designed. The embedded sensor was designed for corrosion monitoring and the system was employed as a compact design.(4) Both in lab and practical applications were tested for the corrosion monitoring. The LCFS was employed to monitor the expansion induced by the steel corrosion in the reinforced concrete specimens under an electrochemical accelerating corrosion experiment in the simulated oceanic environment. The results demonstrated that BOTDA-based sensors had an advantage in multipoint measurements, but as the corrosion developed, the signal will be more reduced. The measured upper-limited strain was about1000micro-strain, which was a limitation for the long-life structure monitoring. On the other hand, the LCFS had a high sensitivity in the whole life of the structure, from the beginning of the corrosion to the destruction of the structure. This provided a potential method for study the steel corrosion process in the reinforced concrete structure.