Localization and monitoring of initiation and propagation of corrosion-induced mortar cracking based on OFDR distributed optical fiber sensor

Optical frequency domain reflectometry (OFDR) optical fiber is characterized to monitor corrosion-induced mortar cracking, including localization and determination of crack initiation time, crack size, and crack length. Mortar cylinders containing a steel bar were prepared and subjected to accelerated corrosion test. The change of mortar surface condition due to steel bar corrosion was recorded with an OFDR optical fiber which was attached by using epoxy resin before corrosion test. Three fiber wrap spacing were considered including 20 mm, 50 mm, and 100 mm. Visual inspection was performed after corrosion test. Calibration test was also conducted to determine the transfer coefficient of cracking. Results show non-uniform corrosion occurred on steel bar and resulted in mortar surface cracking, which was reflected by the strain peaks appeared in the OFDR fiber strain curve. OFDR optical fiber can be used to identify the time of crack initiation, localize the position of cracks, and determine the width and length of cracks. Both the sensitivity and spatial resolution of OFDR optical fiber sensor increase with a decrease of the fiber wrap spacing.