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Steel Corrosion Monitoring in Concrete Slab Using a Long Period Fiber Grating Assembly

Picture for Steel Corrosion Monitoring in Concrete Slab Using a Long Period Fiber Grating Assembly
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Steel corrosion in concrete structures. Accelerated corrosion tests were performed periodically and the corrosion rates at different time intervals were measured with linear polarization resistance (LPR). The change in the resonant wavelength over time was recorded using an optical spectrum analyzer (OSA).

Product Number: 51317--9272-SG
ISBN: 9272 2017 CP
Author: Fujian Tang
Publication Date: 2017
Industries: Corrosion Monitoring and Control , Science of Corrosion
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$20.00

Steel corrosion in concrete structures is a slow process that usually takes several years to a degree that induces concrete cover cracking and the corrosion amount or the penetration depth is hard to detect due to the presence of concrete cover. Long period fiber grating (LPFG) couples incident light from propagating core mode to co-propagating cladding mode producing a series of attenuation bands of transmission spectrum. The resonant wavelength of the spectral attenuation bands is closely related to the effective refractive index of the medium surrounding the fiber gratings. As the chemicals in the surrounding medium change the resonant wavelength is shifted. Therefore it is widely used for physical chemical and biochemical sensing. In this study a corrosion sensing assembly to monitor steel bar corrosion in concrete slab based on the LPFG sensing principle is proposed and its performance is experimentally investigated. The assembly was made by encasing the grating part of a LPFG in a steel straw which was made of rebar steel. The steel straw has a inner diameter of 450 um and five wall thicknesses were considered including 400 um 800 um 1000 um 1200 um and 1500 um. The corrosion sensing assemblies were cast in concrete slab and then subjected to periodical wetting and drying cycles. The wetting and drying cylce consisted of one week immersed in 3.5 wt.% NaCl solution and another week exposed to air. The change of resonant wavelength over time was recorded using an optical spectrum analyzer (OSA) and the corrosion evolution of the steel straw was monitored with open circuit potential and linear polarization resistance. After 12 months all the steel straws were taken out of the concrete slab and visual observation was performed. Results show that the corrosion sensing assembly can be effectively used to monitor the steel corrosion penetration in concrete structures.

Key words: Corrosion, LPFG sensor, Resonance wavelength, Concrete, LPR  

Steel corrosion in concrete structures is a slow process that usually takes several years to a degree that induces concrete cover cracking and the corrosion amount or the penetration depth is hard to detect due to the presence of concrete cover. Long period fiber grating (LPFG) couples incident light from propagating core mode to co-propagating cladding mode producing a series of attenuation bands of transmission spectrum. The resonant wavelength of the spectral attenuation bands is closely related to the effective refractive index of the medium surrounding the fiber gratings. As the chemicals in the surrounding medium change the resonant wavelength is shifted. Therefore it is widely used for physical chemical and biochemical sensing. In this study a corrosion sensing assembly to monitor steel bar corrosion in concrete slab based on the LPFG sensing principle is proposed and its performance is experimentally investigated. The assembly was made by encasing the grating part of a LPFG in a steel straw which was made of rebar steel. The steel straw has a inner diameter of 450 um and five wall thicknesses were considered including 400 um 800 um 1000 um 1200 um and 1500 um. The corrosion sensing assemblies were cast in concrete slab and then subjected to periodical wetting and drying cycles. The wetting and drying cylce consisted of one week immersed in 3.5 wt.% NaCl solution and another week exposed to air. The change of resonant wavelength over time was recorded using an optical spectrum analyzer (OSA) and the corrosion evolution of the steel straw was monitored with open circuit potential and linear polarization resistance. After 12 months all the steel straws were taken out of the concrete slab and visual observation was performed. Results show that the corrosion sensing assembly can be effectively used to monitor the steel corrosion penetration in concrete structures.

Key words: Corrosion, LPFG sensor, Resonance wavelength, Concrete, LPR  

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