51315-5862-Corrosion Monitoring of Steel Bars Embedded in Motar Using Fe-C Coated Long Period Fiber Gratings

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Product Number: 51315-5862-SG

ISBN: 5862 2015 CP

Author: Fujian Tang

Publication Date: 2015

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The corrosion evolution of steel bars embedded in mortar cylinder and immersed in 3.5 wt.% NaCl solution is monitored by long period fiber gratings (LPFG) sensors in this study. The LPFG was firstly deposited with a thin layer of silver and then electroplated with a thick layer of Fe-C film. Two silver layer thicknesses (600 nm and 1000 nm) and two Fe-C film thicknesses (6 um and 10 um) were considered. The coated LPFGs with various thicknesses of silver and Fe-C film were attached to the surface of a steel bar that is then embedded in mortar cylinders. Twelve mortar cylinders were cast cured for 28 days and tested in 3.5 wt.% NaCl solution for a period of 100 days. The corrosion evolution of steel bars in mortar cylinder was monitored weekly with electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LPR). The wavelength change of the LPFG was measured weekly with an optical spectrum analyzer (OSA). Both LPR and EIS results showed that the steel bars experienced two states of corrosion: passive and active. In passive state the steel bars were protected by a layer of passive film. In active state the passive film broke down and corrosion initiated due to penetration of chloride. It was observed that the wavelength of a LPFG sensor changed in three stages: I). steady wavelength corresponding to the passive state of steel bars II). Continuously reduced wavelength corresponding to initial corrosion and corrosion propagation due to the arrival of chloride and III) slightly increased wavelength due to build-up of corrosion products. Therefore the Fe-C coated LPFG sensor can be applied to successfully monitor the corrosion of steel bars in mortar.