Terahertz (THz) Wave Imaging in Civil Engineering to Assess Self-Healing of Fiber-Reinforced Cementitious Composites (FRCC)

Abstract

Although numerous studies have proven the effectiveness of self-healing technologies in concrete, its practical application is limited to only few trials. One of the reasons lies in the lack of self-healing in-situ non-destructive evaluation methods as opposed to invasive and extensive laboratory testing. In this study, a novel Terahertz (THz) wave imaging technique is proposed as a simple, non-destructive, and non-contact measurement methodology to quantitatively evaluate the selfhealing effectiveness of cementitious materials. Experiments were conducted in fiber-reinforced cementitious composites (FRCC), which confirmed self-healing performance based on a combination of stimulated autogenous and autonomous healing by using supplementary cementitious materials (FRCC), and PVA fibers; the self-healing index was also calculated by using novel THz wave measurement and compared with existing evaluation methods. Simultaneously, sorptivity test and microstructural characterization on damaged and healed specimens were conducted as the conventional methods. As a result, the proposed THz imaging successfully quantified the self-healing performance on cementitious samples. Also, a correlation between the recovery rate (cracked/healed) measured by sorptivity test and THz wave imaging was defined.

Fundamental Properties of Sub-THz Reflected Waves for Water Content Estimation of Reinforced Concrete Structures

“…The results suggest that it may be possible to identify the location of the water injection and the location of the dry state in the transmission method [20]. The same results are expected to be obtained in the present study; however, they do not necessarily coincide with those obtained for a specimen simulating a real structure.…”

“…The frequencies employed in our study, 8.5 to 12.5 GHz, fall slightly below the conventional sub-THz range of 0.1 to 1 THz. However, our research group has been investigating the application potential across a broad frequency spectrum from approximately 0.01 to 10 THz, encompassing frequencies higher than those discussed in this paper [20][21][22][23][24][25]. Based on this foundation, we have classified this spectrum as the "sub-THz" range.…”

“…Figure 1 shows schematic diagrams of the (a) transmission and (b) reflection methods in the sub-THz wave optical system. There are two measurement methods for sub-THz wave optics: the transmission method [20] and the reflection method [21]. The transmission method requires the oscillator and detector to be placed in a straight line, which is difficult to align in measurements on real structures.…”

Fundamental research on non-destructive testing of reinforced concrete structures using sub-terahertz reflected waves

“…Transmitter Specimen Camera Lens easily absorbed by water has been used to detect minute cracks in concrete using water as a sensitizer, and to estimate the concentration of chloride ions [8,11]. Other studies have been conducted to evaluate the self-healing effect inside the self-healing concrete, which cannot be visually confirmed [12].…”

Design and computation on high transmission metasurface for subwavelength focusing of terahertz waves

“…Terahertz (THz) radiation has manifested some promising for THz wave imaging [1,2] , THz communications [3,4] and spectroscopy [5] , etc because of its unique properties including wide frequency band, low THz photon energy, high spectral resolution [6] and so on. Especially, THz wave imaging offers attractive properties for non-destructive testing applications, correspondingly, the crucial factors for the THz imaging is how to focus THz wave at different wavelength or different plane [7] .…”