Abstract
This paper presents the feasibility of utilizing fiber Bragg grating (FBG) and long-period fiber grating (LPFG) sensors for nondestructive evaluation (NDE) of infrastructures using Portland cement concretes and asphalt mixtures for temperature, strain, and liquid-level monitoring. The use of hybrid FBG and LPFG sensors is aimed at utilizing the advantages of two kinds of fiber grating to implement NDE for monitoring strains or displacements, temperatures, and water-levels of infrastructures such as bridges, pavements, or reservoirs for under different environmental conditions. Temperature fluctuation and stability tests were examined using FBG and LPFG sensors bonded on the surface of asphalt and concrete specimens. Random walk coefficient (RWC) and bias stability (BS) were used for the first time to indicate the stability performance of fiber grating sensors. The random walk coefficients of temperature variations between FBG (or LPFG) sensor and a thermocouple were found in the range of −0.7499 °C/ to −1.3548 °C/ . In addition, the bias stability for temperature variations, during the fluctuation and stability tests with FBG (or LPFG) sensors were within the range of 0.01 °C/h with a 15–18 h time cluster to 0.09 °C/h with a 3–4 h time cluster. This shows that the performance of FBG or LPFG sensors is comparable with that of conventional high-resolution thermocouple sensors under rugged conditions. The strain measurement for infrastructure materials was conducted using a packaged FBG sensor bonded on the surface of an asphalt specimen under indirect tensile loading conditions. A finite element modeling (FEM) was applied to compare experimental results of indirect tensile FBG strain measurements. For a comparative analysis between experiment and simulation, the FEM numerical results agreed with those from FBG strain measurements. The results of the liquid-level sensing tests show the LPFG-based sensor could discriminate five stationary liquid-levels and exhibits at least 1,050-mm liquid-level measurement capacity. Thus, the hybrid FBG and LPFG sensors reported here could benefit the NDE development and applications for infrastructure health monitoring such as strain, temperature and liquid-level measurements.
Highlights
Technologies for real-time non-destructive evaluation (NDE) of engineering structures are very important to access the performance of in-service infrastructures
The random walk coefficients of temperature variations between fiber Bragg grating (FBG) sensor and thermocouple were found as −0.9134 °C/ h and −1.1293 °C/ h for asphalt and concrete specimens, respectively
This paper illustrates the great potential of fundamental structural health monitoring using optical fiber grating sensors (FBG and long-period fiber grating (LPFG) sensors) for nondestructive evaluation (NDE) of infrastructure materials, such as Portland cement concretes and asphalt mixtures
Summary
Technologies for real-time non-destructive evaluation (NDE) of engineering structures are very important to access the performance of in-service infrastructures. The most attractive feature of fiber optic sensors is their inherent ability to serve as both the sensing element and the signal transmission medium, allowing the electronic instrumentation to be located remotely from the measurement site This is especially useful for remote monitoring of the condition of infrastructures. The use of hybrid FBG and LPFG sensors are shown to combine the advantages of both kinds of fiber grating to work on nondestructive evaluation of infrastructures such as bridges, pavements, and reservoirs for strains or displacements, temperatures, and water-levels under different environmental conditions. Researchers or engineers could potentially use FBG and LPFG sensors with the same measurement apparatus, such as the ASE light source and optical spectrum analyzer (OSA), to monitor changes of strain, temperature, and liquid-level over time
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