Fiber Bragg grating based sensing system: Early corrosion detection for structural health monitoring

Fiber optic sensors have been widely used in chemical and biomedical applications and are now being extended to structural health monitoring (SHM) in the civil engineering field. Due to the destructive nature of tests for corrosion monitoring, a non-destructive system was developed to monitor rebar corrosion via fiber Bragg grating (FBG). In this study, two different methods are proposed and tested; FBG with Polydimethylsiloxane (PDMS) coating and bare FBG. FBG sensors were embedded on the specimen to monitor the expansion strain caused by rebar corrosion, and their performances were monitored by observing the Bragg wavelength shift. A significant wavelength shift for the FBG without coating was observed on day 17, whereas for the PDMS coating, the significant wavelength shift occurred on day 10. This proves that PDMS coated FBGs have a higher sensitivity for corrosion detection as compared to non-coated ones. The overall results of both methods after etching have shown a good linear response. Strain induced by the corrosion shows good linear response as corrosion rate increased. Corrosion rate were calculated from the conventional weight loss measurement method. These sensors can be installed for real-time and non-destructive SHM monitoring in civil engineering.