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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1. Introduction Since 2018, the durability verifications pertaining to steel corrosion have begun incorporating considerations for water ingress as per the Standard Specifications for Concrete Structures ‘ Design. ’ In line with this, a test method for the water penetration rate coefficient of concrete (JSCE-G 582) was proposed with use cases of the water penetration rate coefficient in predicting the progression of steel corrosion in the said specification ‘ Maintenance ’ enacted in 2022. Although this coefficient is anticipated to use for maintenance management in the future, its current application is considered difficult as it is due nine circular samples ( φ 100 x 200 mm) are required. In this study, we utilized the RIKEN Accelerator-driven compact Neutron Systems (hereinafter referred to as RANS) to non-destructively observe water movement in concrete using neutron imaging. As a result, neutron imaging demonstrated that the water penetration rate coefficient could be obtained with a single circular sample. Furthermore, when the sample was cylindrical, we clarified the influence of the sample shape on the transmitted images obtained through neutron imaging. 2. Experimental method 2.1. Neutron imaging Neutron imaging is a technique used to obtain transmitted images of materials by irradiating them with neutron beams, which are strongly scattered by light elements such as hydrogen and lithium. Unlike X-ray radiography, which is widely used and exhibits a nearly monotonic decrease in transmission with increasing atomic number, neutron transmission does not follow such regularity. Figure 1 illustrated the transmitted images obtained with X rays and neutron beams for both dry and saturated 1 cm-thick concrete. As shown in the figure, inverted grayscale transmitted images are obtained. Furthermore, neutron beam transmitted images show that the cement-pasted areas bound with water are less transparent. The shadows become even darker when water permeates into those areas. Figure 2 shows the experimental setup. Neutron beams generated from RANS are directed onto the sample, and thermal neutrons reaching the detector behind are captured as digital images. A commercially available neutron image intensifier (hereinafter referred to as neutron I.I.) is utilized as the detector. The detector surface measures 9 inches, with a field of view size of 180 x 120 mm. The image sensor used is a cooled CCD camera. RANS, the neutron source, is a compact neutron source aimed at industrial applications, capable of operation throughout the year. It has been in stable operation since 2013, catering to various measurement techniques beyond neutron imaging and yielding numerous research results.

Saturated condition (weight=151 g)

Dry condition (weight=144 g)

RANS

(a) Neutron

Neutrons

Transmittance High

Detector (Neutron I.I.)

Neutrons

Low

(b) X-ray

Fig. 1. Comparison of neutron and X-ray transmission images

Fig. 2. Experiment setup