PSI - Issue 64

Jian-Neng Wang et al. / Procedia Structural Integrity 64 (2024) 1605–1612 / Structural Integrity Procedia 00 (2019) 000–000

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aqueous samples of fresh concrete supernatant (W/C = 0.35 or 0.65) with sodium chloride solutions in different concentration ranges from 0.015% to 12.5%. 2.3. Optical fiber pH sensing system in standard solutions using UV-NIR spectrometer The pH of concrete structures decreases to a value close to 9.5 that externally exhibits carbonation and durability problems [Liu et al. (2017)]. An optical fiber pH sensing system is proposed to implement structural health monitoring of concrete especially in pH measurement. The optical fiber pH sensing system is composed of a fiber optical sensing system with a Visible-NIR bifurcated fibers (fiber type: VIS-NIR and fiber core diameter: 400 μ m), a CUV-UV cuvette holder, a broadband light source (200-1100 nm), an UV-NIR spectrometer (Ocean-optics HR 4000 UV-NIR), and a personal computer for data acquisition. We measured different pHs of the standard solutions with different pHs of 1, 4.08, 4.95, 5.99, 7.09, 8.07, 9.75. The HR4000 High-Resolution Miniature Fiber Optic Spectrometer provides optical resolution as good as 0.025 nm (FWHM). The different pHs of the standard solutions were used to represent different pH values or conditions for concrete structures and we conducted two samples for each standard solution and average these two testing values. Fig. 3 (b) is the proposed schematic of an optical fiber pH sensing system using an UV-NIR spectrometer in structural health monitoring of concrete structures either aqueous samples from fresh concrete supernatant or harden concrete powder. The pH sensor with HR 4000 UV-NIR spectrometer is designed to measure the signal strength (intensity, counts) with different pH values and a CUV-UV cuvette holder was used to contain different pHs of the standard solutions.

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Fig. 3. (a) Experimental setup for an optical fiber sensing for monitoring chloride ion concentration in concrete using the Mach–Zehnder interferometer sensor; (b) Schematic of an optical fiber pH sensing system using an UV-NIR spectrometer in structural health monitoring of concrete structures either aqueous samples from fresh concrete supernatant or harden concrete powder. 3. Results and discussion 3.1. Optical fiber sensing for monitoring chloride ion concentration in fresh concrete supernatant Fig. 4 (a) shows the transmission spectra of the Mach–Zehnder interferometer for sensing in air and aqueous samples of fresh concrete supernatant (W/C = 0.35) with sodium chloride solutions in different concentration ranges from 0.015% to 12.5%; Fig. 4 (b) is the transmission spectra of the Mach–Zehnder interferometer for sensing in air and aqueous samples of fresh concrete supernatant (W/C = 0.65) with sodium chloride solutions in different concentration ranges from 0.015% to 12.5%. The transmission intensity of the MZI sensor incited by the broadband light source was discovered to possess linear relationship with the increase of the sodium chloride solution concentration. By the transmission intensity of the MZI sensor, we found a linear decrease in the transmission power as the sodium chloride solution concentration increased from 0.015% to 12.5% (150~125000 ppm). Light intensity in output power or transmission loss was calculated where the wavelength is 1557 nm (see Fig. 4) for aqueous samples of fresh concrete supernatant (W/C = 0.35 or W/C = 0.65) with sodium chloride solutions in different concentration ranges from 0.015% to 12.5%. Fig. 5 (a) displays the plot of the transmission loss versus aqueous samples of fresh concrete supernatant (W/C = 0.35) with sodium chloride solutions in different concentration ranges from 0.015% to 12.5% (150~125000 ppm); Fig. 5 (b) show the plot of the transmission loss versus aqueous samples of fresh concrete supernatant (W/C = 0.65) with sodium chloride solutions in different concentration ranges from