PSI - Issue 72

Andrey Yu. Fedorov et al. / Procedia Structural Integrity 72 (2025) 453–457

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approaches utilize various sensors that record controlled values, typically on the surface of structures (Stepinski et al. (2013)). In the last two or three decades, research on the use of fiber-optic sensors (FOS) in concrete structures has emerged. The paper of Leung (2001) demonstrates the advantages of FOS over other sensor types. Research on FOS applications in concrete structures can be divided into two groups. The first group includes studies related to technological features of FOS application, such as ensuring protection for sensors embedded in concrete (Biswas et al. (2010)). The second group focuses on solving specific problems using FOS, including registration of corrosion cracking in reinforced concrete (Mao et al. (2016)) and detection of cracking in concrete floors (Slowik et al. (2004)). The geometrical dimensions and physical characteristics of FOS allow them to be integrated into materials during their production, provided that the temperature of technological processes does not lead to a malfunction of the sensors. This paper demonstrates the unique possibilities of implementing a non-destructive method based on measuring strains by FOS embedded in materials through long-term measurements of technological strains in a concrete sam ple. Optical fiber provides the capability for distributed strain measurement when using sensors based on Rayleigh scattering, or alternatively, the placement of numerous point strain sensors based on Bragg gratings on a single fiber. Consequently, FOS enables the collection of extensive information about strains in various zones of the observed ob ject. This capability opens new possibilities for defect registration. One method for detecting defects is demonstrated in this paper using a cement mixture sample. 2. Measurement of strain by fiber-optic sensors embedded in the material volume Demonstration of the ability to measure strain by FOS embedded in concrete was carried out on a cylindrical sample with a diameter of 150 mm and a height of 400 mm. The formation and hardening of the sample was carried out in a polypropylene vessel. After placing the optical fiber with five FBGs along the axis of the cylindrical container, the vessel was filled with concrete mixture in layers with vibration. The optical fiber with sensors located at a distance of 10 mm from each other remained submerged in the concrete mixture. Fig. 1 shows a scheme of the sample with embedded FOS. In this paper, unlike most studies, the optical fiber does not contain protective shells, except for the standard polyimide coating. This eliminates problems associated with strain transfer from the material to the sensor and, as a result, the need for correction factors. Sensor readings were taken continuously (24/7).

Fig. 1. The scheme of FOS locatio ◘ ns in a concrete sample.