著者

Daisuke Kambayashi Hiroshi Sasano Shohei Sawada Kiyoteru Suzuki Ippei Maruyama

出版者

Japan Concrete Institute

雑誌

Journal of Advanced Concrete Technology (ISSN:13473913)

巻号頁・発行日

vol.18, no.10, pp.618-632, 2020-10-27 (Released:2020-10-27)

参考文献数

29

被引用文献数

8

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In nuclear power plants, concretes used for biological shielding walls are exposed to radiation such as neutrons and gamma rays over the long-term operation of the plant. Previous studies have reported that neutron irradiation causes aggregate expansion due to the metamictization of quartz and feldspar leading to reduced density and a loss of the compressive strength and Young' s modulus of the concrete. Therefore, it is crucial to understand the current state of a concrete biological shield (CBS) and predict its future soundness. In this study, a rigid-body spring model, which can easily evaluate fracture behavior by using springs between each element, is used to conduct numerical analyses on a CBS. A three-phase (mortar, aggregate, and interfacial transition zone) model of a 2000 mm thick CBS is used to investigate the varying deformation responses depending on the presence or absence of reinforcing bars (rebar), creep, and an inner steel plate with five types of analyses, i.e. analysis to understand the impacts of temperature distribution, re-inforcement bars, an internal steel plate, and creep of mortar. The results show that cracking and delamination occur inside the CBS, resulting in a lack of cracking on the outside. They also show that the cracks are reduced by rebar and creep, resulting in cracks extending from the innermost edge to a depth of approximately 150 mm.

著者

Hiroshi Sasano Ippei Maruyama Shohei Sawada Takahiro Ohkubo Kenta Murakami Kiyoteru Suzuki

出版者

Japan Concrete Institute

雑誌

Journal of Advanced Concrete Technology (ISSN:13473913)

巻号頁・発行日

vol.18, no.10, pp.648-677, 2020-10-28 (Released:2020-10-28)

参考文献数

80

被引用文献数

19

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To evaluate the radiation-induced degradation of concrete, a rigid-body spring network model is introduced that takes into account the three phases in concrete: mortar, aggregate, and the interfacial transition zone. The proposed model enables evaluation of the change in the physical properties of concrete affected by aggregate expansion under the free restraint condition. Good agreement with previous experimental data is found for the linear expansion of the concrete specimen and the compressive strength, Young’s modulus, and splitting tensile strength. Based on the numerical results, it is concluded that, to reproduce the physical property changes in concrete, the expansion of mortar due to the radiation-induced expansion of fine aggregate and/or creep behavior must be considered. In addition, it is clarified that an isolated expansion of mortar with a lack of expansion in the coarse aggregate also degrades the concrete and, consequently, analysis of the type of aggregate used is critical for predicting the properties of concrete under neutron irradiation. Furthermore, the impact of inhomogeneous expansion of rock-forming minerals in coarse aggregates on physical property changes is studied, showing that such a partial expansion in the aggregates and the resultant cracks in aggregates greatly influences the reduction of the Young’s modulus, with minimal impact on the reduction of compressive strength. The proposed model can be used to evaluate concrete degradation due to radiation-induced volumetric expansion of aggregate caused by the metamictization of rock-forming minerals.