Study on Radio Wave Transparency Improvement of Concrete Focusing on Internal Water Content

This study aims to actively control the radio wave propagation environment through the physical properties of concrete itself rather than through communication devices, and investigates the radio wave transparency of various types of concrete and their influencing factors to identify the conditions that improve transparency. First, the theoretical equations for electromagnetic wave propagation in concrete and the forms of water present in concrete are reviewed, and the influence of water on radio wave transparency is discussed. Based on these considerations, radio wave transmission tests were conducted on plate specimens with controlled internal moisture conditions. The results revealed that reducing evaporable water by lowering the water-to-powder ratio alone had little effect on improving radio wave transparency. In contrast, a significant improvement in radio wave transparency was achieved by simultaneously reducing evaporable and non-evaporable water using geopolymer instead of hardened cement paste, in combination with a low water-to-powder ratio. This paper is the English translation from the authors’ previous work [Sakamoto, R., Chijiwa, N., Saito, K., Nakayama, K., & Kang, C. (2025). Study on radio wave transparency improvement of concrete focusing on internal water content. Japanese Journal of JSCE, 81(3), 24-00070. (in Japanese)].