This study aims to monitor the spatial distribution of pitting corrosion occurring in steel rebars in concrete structures using an optical frequency domain reflectometry (OFDR) distributed optical fiber sensor. A concrete slab was fabricated containing eight steel rebars. After curing for 28 days, the top surface of the slab was polished with a sand wheel, and then an optical fiber sensor was attached to the surface using epoxy resin. The direction of the fiber is perpendicular to the direction of steel bars, and a total of four loops were applied so that four intersection points are present between the fiber and steel bars. The slab was subjected to accelerated corrosion testing. During the test, open circuit potential (OCP) was measured, and the change of the surface strain induced by steel bar corrosion was recorded with the optical fiber. Results show that the OCP is affected by the presence of chloride, and the spatial distribution of localized corrosion of steel bars can be monitored with the OFDR fiber. An empirical equation was proposed between the corrosion-induced area loss of steel rebars and the measured OFDR strain, which can be used to monitor distributed steel rebar corrosion.
Steel rebars in concrete structures are usually protected from corrosion by a thin layer of passive film, which is formed due to the high alkalinity of concrete pore solution.1-2 However, this protective passive film could be damaged by penetration of chloride into concrete structures in marine environments or exposure to the use of de-icing salt for the removal of snow and ice in winter times.3 Penetration of chloride would impair the passive film locally and initiate pitting corrosion.4 Over time, the buildup of corrosion products generates internal tensile stress in the concrete cover, and causes concrete cracking, delamination, spalling, and subsequently reduction in the carrying capacity and service life of structures.5-6