Assessment of Damage due to Reinforcement Corrosion using Optical Fiber Sensor-Based Data

Reinforcement corrosion is one of the major causes of the deterioration of reinforced concrete structures worldwide. Damage caused by reinforcement corrosion reduces the service life of structures and results in huge costs (billions of dollars annually) in repair and maintenance. Although the reinforcing bars embedded in concrete initially possess passivity due to high alkalinity of concrete, however, the passivity is lost due to penetration of chloride ions or due to destruction of alkalinity by carbonation initiating the corrosion of steel bars. Reinforcement corrosion results in the loss of cross-section of bars, loss of bond between steel bars and concrete, and formation of rust layer on the surface of steel bars. While the formation of rust layers on steel bars causes cracking of cover concrete due to swelling pressure (tensile stress) inside concrete, the loss of bond and cross-section results into the loss of load-bearing capacity of the corroding structural members. Time of corrosion initiation, time of cracking of cover concrete and rate of reinforcement corrosion are needed to be determined in order to assess the corrosion damage and to predict the remaining service life of a reinforced concrete member subjected to reinforcement corrosion. Conventionally, electrochemical and gravimetric tests are conducted to estimate corrosion rate that is essentially required for the assessment of corrosion damage. However, the measured values of corrosion rate using such techniques lack accuracy due to many factors, which lead to inaccurate assessment of the corrosion damage and inaccurate prediction of remaining service life. Therefore, there is a need for a reliable inspection technique that can be employed to collect the data required for estimating the reinforcement corrosion rate accurately. In the proposed work, Fiber Bragg grating (FBG) sensors-based technique will be used (i) to monitor the hoop strain due to increase in diameter of corroding steel bars embedded in concrete and (ii) to record the time of cracking of cover concrete due to corrosion. The FBG sensors will be installed at close locations along the length of the corroding embedded steel bars to record hoop strain due to the increase in the diameter of the bar owing to corrosion. In order to record the time of cracking, sensors will also be installed on the surface of concrete. The recorded hoop strain will be used to determine the increase in diameter with time due to rust formation. This information will be used to estimate the reinforcement corrosion rate, which will be compared with the reinforcement corrosion rate obtained for similar specimens tested using electrochemical and gravimetric methods. Finally, a methodology for assessment of corrosion damage and prediction of remaining service life will be developed based on the recorded values of corrosion cracking time and increase in the diameter due to rust formation using FBG sensors-based technique.