Abstract
Concrete is the most widely used for construction materials in the world. Water content of concrete is an important parameter in terms durability of concrete structures. Terahertz (THz) waves, for which concrete is a porous and absorbable material, have been studied in order to establish a new non-contact inspection technology for maintenance of concrete structures. In this study, THz transmittance and reflectance of concrete in drying process were measured with a 60 GHz GUNN diode and absorption coefficient is analyzed for concrete with various water contents. It is shown that quantitative detection below 10% is possible for the water content at surface area of concrete.
Highlights
Terahertz Waves and ApplicationsTerahertz (THz) waves are electromagnetic waves in the frequency range between approximately 0.1 and 10 THz, which is just the middle of the radio wave and the light wave
We report the non-contact inspection of water content inside the concrete by sub-THz waves which are relatively low frequency in the THz band
It shows that the absorption of THz waves increases as the amount of water increases, but as shown in Figure 5, the absorption coefficient rapidly increases around 10% water content
Summary
Terahertz (THz) waves are electromagnetic waves in the frequency range between approximately 0.1 and 10 THz, which is just the middle of the radio wave and the light wave. THz wave has both of characteristics as represented by transparency of radio wave to non-polarized substance and good reflectivity to metal of light wave. The energy of a THz wave corresponds to molecular interactions such as hydrogen bonding, van der Waals interactions and lattice interactions. THz spectroscopy can be used for non-destructive diagnosis of mechanical deformation in polymers [4]. We report the non-contact inspection of water content inside the concrete by sub-THz waves which are relatively low frequency in the THz band. Water has a large absorption in the THz frequency region. THz wave has a high sensitivity in detecting water in concrete. Based on quantitative relation between THz absorption coefficient and water content, which is measured in this study, non-destructive THz inspection is available for water content in concrete of infrastructure buildings itself. THz wave generator and detector are recently developed with small size
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