Monitoring Pitting Corrosion Penetration in Steel Rebar Using Optical Fiber

Abstract In this study, an optical fiber corrosion sensor is developed to monitor the penetration of corrosion pits in steel bars. The sensor was simply made by encasing one end of an optical fiber into a steel straw. As the corrosion penetrates through the steel straw wall, the corrosive solution and corrosion products fill inside and contaminate the fiber end surface, resulting in a change in the reflectivity. The change of the optical fiber reflectivity indicates the corrosion pits depth equaling to the wall thickness of the steel straw. Steel straw was fabricated from rebar steel with an inner diameter of 450 μm, and a total of four wall thicknesses were fabricated including 500 μm, 750 μm, 1000 μm, and 1250 μm. The test solution was saturated Ca(OH)2 solution with sodium chloride. The steel straws were immersed in the solution for a year. The change of reflectivity of optical fiber was recorded using an optical spectrum analyzer (OSA), and the pitting corrosion rate of the steel straw was measured with linear polarization resistance (LPR). After corrosion tests, all the steel straws were taken out of the solution and the corrosion pits were observed using an optical microscopy. Finally, a relationship between the corrosion pit penetration depth and the time was established.