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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Density (Specific Gravity) and Absorption of Coarse Aggregate and ASTM C128-22 ： Standard Test Method for Relative Density (Specific Gravity) and Absorption of Fine Aggregate . The maximum size of coarse aggregates is 25 mm, the specific gravity of coarse aggregates is 2.66, the specific gravity of fine aggregates is 2.65, and the specific gravity of type I cement is 3.15. Fig. 1 (a) shows the photo of the cement and aggregates and Fig. 1 (b) is the photo of fresh concrete. Additionally, a chloride ion-selective electrode (ISE) sensor (CL-1B) was employed and calibrated with high (1000 mg/L) and low (10 mg/L) standard solutions. The chloride ISE has resolution about 0.7% of reading (1.8 ± 0.013 or 35500 ± 250 mg/L) and was used to measure chloride-ion concentrations in various aqueous samples of fresh concrete supernatant (W/C = 0.35 and W/C = 0.65) with sodium chloride solutions in different concentration ranges from 0.015% to 12.5% (0.015%, 0.125%, 0.25%, 0.5%, 1.25%, 2.5%, 5.0%, 7.5%, 10%, and 12.5%). Fig. 2 (a) displays the photo of different sodium chloride solution and Fig. 2 (b) shows the photo of chloride ion-selective electrode (ISE) sensor.

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Fig. 1. (a) Photo of cement and aggregates; (b) Photo of fresh concrete.

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Fig. 2. (a) Photo of different sodium chloride solution; (b) Photo of chloride ion-selective electrode (ISE) sensor.

2.2. Optical fiber sensing for monitoring chloride ion concentration in fresh concrete supernatant using Mach-Zehnder interferometer The optical fiber Mach-Zehnder interferometers were fabricated by using a piece of single mode fiber (SMF, Corning SMF-28) by lateral offset fusion splicing method with two SMF fibers, head on head and one on each side using a fusion splicer (FITEL S178A). The MZI (or Mach-Zehnder-like interferometer) was constructed using lateral offset method with a fusion splicer for fabricating the 8-cm MZI sensors [Villatoro et al. (2007) and Villatoro et al. (2009)]. The spectral responses of the MZI for the two aqueous samples of fresh concrete supernatant (W/C = 0.35 and W/C = 0.65) with salt water solutions in different concentration range from 0.015% to 12.5% (150~125000 ppm). were measured; thus, we conducted optical fiber MZI sensing twice for monitoring fresh concrete supernatant (W/C = 0.35 and W/C = 0.65) with sodium chloride solutions (weight concentration: 0.015%, 0.125%, 0.25%, 0.5%, 1.25%, 2.5%, 5.0%, 7.5%, 10%, and 12.5%). Fig. 3 (a) shows the schematic of experimental setup for sensing for monitoring chloride ion concentration in concrete measurement with an optical fiber MZI sensor, which is composed of an 8-cm MZI fiber, a broadband amplified spontaneous emission (ASE) fiber source ( λ = 1520 ― 1620 nm), an optical spectrum analyzer (HP 71450B), and a personal computer for data acquisition. The advantages of this type of MZI sensor are high sensitivity to the external refractive index (RI) and chloride ion concentration measurement [Wang (2011), and Wang et al. (2012)]. Thus, we focused on the use of MZI sensor as chloride ion concentration sensor and the light intensity of the MZI sensor in the output power was used to quantify for sensing in air and