Corrosion Monitoring By Fiber Sensing Techniques And Corrosion Expansion Evaluation In Reinforced Concrete Members

Fiber optic sensing is a cutting-edge technique in the field of structure health monitoring. Because of its good durability, resistance to electromagnetic interference, high sensitivity, corrosion resistance, etc., it has become a hot field of scientific research at home and abroad. In recent years, its widespread use in engineering practice makes important contributions to the safe operation of structures, the routine maintenance and reinforcement during the service life of structures, and the social economic development.This thesis mainly carries out the following research work based on the fiber optic sensing techniques:(1) A kind of BOTDA steel corrosion sensor is developed with high sensitivity and large measuring range, which could be used for both early detection and the whole life-circle monitoring of steel corrosion in RC structures. The sensor’s performances are studied in the electrochemical accelerating corrosion test system.(2) A kind of FBG steel corrosion sensor is developed with relatively high sensitivity and large measuring range, which could be used for the whole life-circle monitoring of steel corrosion in RC structures. The sensor’s performances are studied in the electrochemical accelerating corrosion test system. But the performances of the FBG steel corrosion sensor are not as good as the BOTDA steel corrosion sensor in the aspect of accuracy and stability.(3) To solve the problem of large errors of the BOTDA technique in the field of small-scale monitoring, the concepts of valid sampling points and the selecting method of the valid sampling points are proposed here, which has considered the spatial resolution, sampling interval and the length of sensing fiber comprehensively, and this method makes the most use of the valid sampling points on the sensing fiber. The appearance of this method solves the problem that valid sampling points are too few and too difficult to select on the small-scale measurements.(4) For the corrosion damage problem of RC structure members, the concept of expansion damage factor is proposed here to evaluate the damage degree. This damage factor could quantitatively evaluate the concrete damage from the beginning of corrosion expansion stress to initial cracking of inner concrete, and it could also evaluate the whole process of concrete cracking even if the concrete cracks have developed to the surface of the RC structure members. This damage factor could also be used to evaluate the width of cracks on the surface of RC structure members if the definition of the damage factor is extended a little outward.(5) The mapping relation between the concrete strain at a certain section and the concrete stress or the crack depth in the RC structure members is established through the finite element analysis of the structure members. So the mapping relation between the monitoring data of fiber sensors and the damage factor is also established, which makes damage factor able to evaluate the damage of structure members.(6) Based on the LabVIEW programming language platform, the corrosion monitoring and evaluation system for RC structure members is developed in this paper. The system includes nearly all the contents illustrated above, such as corrosion monitoring with sensors, data acquisition, data processing and storage, and damage evaluation. The system could also send out different warnings according to the different levels of structure damage. And the system could be directly used in the practical engineering for the monitoring and evaluation of corrosion damage of RC structure members.The study shows that:BOTDA sensing technique and FBG sensing technique could effectively monitor the steel corrosion of reinforced concrete structures and accurately quantitatively assess the corrosion degree through the corrosion damage factor.