Early Corrosion Monitoring of Reinforcing Steel Bars by Using Long-Gauge Carbon Fiber Sensors

Corrosion of main steel reinforcements is one of the foremost causes of early deterioration and shortening of service life of reinforced concrete structures. Early detection of corrosion can aid in reducing the maintenance cost and extending the service life of structures. This research proposes an approach for early corrosion monitoring of steel reinforcements in concrete structures using strain measurements of long-gauge packaged carbon fiber line (PCFL) sensors. An accelerated corrosion method utilizing a salt solution and constant current was used to achieve the required corrosion levels. The effects of the salt solution, electrical current, and change in temperature during the corrosion process on the signals of the proposed packaged sensors were studied. A PCFL with temperature compensation and a protective cover was installed on a steel bar and tested under accelerated corrosion and a constant tensile load. Monitored measurements of the PCFL sensors during the corrosion progress were compared with a laboratory-scale model and measurements of packaged fiber Bragg grating (PFBG) sensors. The results confirmed that the proposed packaging could effectively protect the carbon fiber sensors from electric effects, long-term salt attack, and temperature variation during the corrosion process. The experimental results of both the PCFL and the PFBG sensors were in good agreement with the corrosion values calculated theoretically from Faraday’s law with a relative weight loss ratio error of less than 0.8. Therefore, the use of long-gauge PCFL sensors can be considered as a promising approach for monitoring the corrosion progress of steel reinforcements of large-scale structures.