PSI - Issue 64

M. Mizuta et al. / Procedia Structural Integrity 64 (2024) 214–219 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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transmission thickness of 50 mm and 10 mm) concrete samples by Yoshimura et al. (2018, 2019). The temporal changes in brightness difference (averaged over a width of 18 mm as in Fig. 4) are shown in Figure 5, and images representing brightness difference in shading are in Figure 6. These images reflect the difference in water content before and after water absorption, with darker shading indicating the presence of hydrogen-rich areas in neutron imaging. Additionally, the brightness difference on the vertical axis of Fig. 5 would be 1.0 if there is no change in normalized brightness before and after water absorption, decreasing below 1.0 as hydrogen content increases. As the water absorption time elapsed, the water absorption increased, and the range where the brightness difference became less than 1.0 expanded, indicating the penetration of water into the interior. Thus, it reveals that it is possible to distinguish the extent of water penetration even in circular samples by taking the difference between normalized images before and after water absorption, suggesting the potential of neutron imaging as a nondestructive test method for water penetration depth. Here, considering the change point in Fig. 5 (indicated by arrows in the figure) as the penetration depth, the water penetration rate coefficients were calculated as 10.0 mm/ √ hr near the axis and 13.4 mm/ √ hr near the circumference. However, since the range where the brightness difference becomes less than 1.0 differs between the axis and circumference, further investigation is required to interpret the images of circular samples obtained through neutron imaging accurately.

1.05

1.05

(b) near the circumference

(a) near the axis

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1

Water absorption time

0.95

0.95

吸水 4h 吸水 22h 4 hr 22 hr

吸水 4h 吸水 22h 4 hr 22 hr

Brightness difference

Brightness difference

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Distance (pixel)

Distance (pixel)

Fig. 5. Changes in brightness difference due to water absorption

Top view

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Near the axis Near the circumference Front view

Permeation direction

Permeation direction

(a) Water absorption 4 hr

(b) Water absorption 22 hr

Fig. 6. Transmission image of water

4. Conclusion

・ The potential of applying neutron imaging in water permeation tests of circular concrete samples is demonstrated. ・ Obtaining the nondestructive water penetration rate coefficient for each sample would be greatly beneficial for maintenance management of existing structures. ・ It is necessary to further investigate the effects of sample shape, edge effects, and methods to remove or mitigate the influence of scattered neutrons, with the aim of establishing nondestructive water penetration rate coefficient test using neutron imaging.