Abstract
In this paper, a novel kind of method to monitor corrosion expansion of steel rebars in steel reinforced concrete structures named fiber optic coil winding method is proposed, discussed and tested. It is based on the fiber optical Brillouin sensing technique. Firstly, a strain calibration experiment is designed and conducted to obtain the strain coefficient of single mode fiber optics. Results have shown that there is a good linear relationship between Brillouin frequency and applied strain. Then, three kinds of novel fiber optical Brillouin corrosion expansion sensors with different fiber optic coil winding packaging schemes are designed. Sensors were embedded into concrete specimens to monitor expansion strain caused by steel rebar corrosion, and their performance was studied in a designed electrochemical corrosion acceleration experiment. Experimental results have shown that expansion strain along the fiber optic coil winding area can be detected and measured by the three kinds of sensors with different measurement range during development the corrosion. With the assumption of uniform corrosion, diameters of corrosion steel rebars were obtained using calculated average strains. A maximum expansion strain of 6,738 με was monitored. Furthermore, the uniform corrosion analysis model was established and the evaluation formula to evaluate mass loss rate of steel rebar under a given corrosion rust expansion rate was derived. The research has shown that three kinds of Brillouin sensors can be used to monitor the steel rebar corrosion expansion of reinforced concrete structures with good sensitivity, accuracy and monitoring range, and can be applied to monitor different levels of corrosion. By means of this kind of monitoring technique, quantitative corrosion expansion monitoring can be carried out, with the virtues of long durability, real-time monitoring and quasi-distribution monitoring.
Highlights
Steel corrosion has become a major problem worldwide, especially for structures exposed to aggressive environments
Based on fiber optical Brillouin technique, we propose a novel kind of fiber optic coil winding method to monitor the steel rebar corrosion expansion in reinforced concrete structures
The design scheme of the BCES-II [sensor name: S.3 (II) unit illustrated in Figure 6 makes the following changes based on BCES-I: (1) a porous soft material was added on the surface of the steel rebar and waterproof lubricating film and fiber optic were wound; (2) the sensing optical fiber was coated with epoxy glue so that the optical fiber can deform in a coordinated fashion as a whole
Summary
Steel corrosion has become a major problem worldwide, especially for structures exposed to aggressive environments. This problem has reached alarming proportions in the past three decades, leading to very high repair costs, sometimes even above the initial construction cost, or in extreme situations, to the final collapse of the structures [1,2,3,4]. Concrete normally provides a high degree of protection to the reinforcing steel against corrosion, by virtue of the high alkalinity (pH > 13.5) of the pore solution. When sufficient chloride ions (from de-icing salts or from seawater) have penetrated to the steel rebar in concrete or as the pH value of the pore solution drops to low values due to the carbonation process, the protective film on the steel rebar surface is destroyed and the reinforcing steel is depassivated
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