Sub-terahertz waves, electromagnetic waves with a frequency band of approximately 10 to 300 GHz, can penetrate non-polar materials like concrete while being absorbed by polar substances such as water. These waves exhibit high reflectivity against metals, including rebar, yet the corrosion products on the metal surfaces provide absorption or scattering. This study explores a non-destructive, non-contact methodology for assessing the corrosion level of rebar in concrete. Findings indicate that suitable frequencies exist for each cover concrete depth capable of evaluating rebar condition irrespective of moisture or chloride ion presence. Selecting the suitable frequencies enables the visualization of rebars up to a cover depth of approximately 50 mm. Furthermore, the study demonstrates that the magnitude of differential reflection intensity, adjusted for cover concrete depth, can indicate assessing rebar corrosion degree.
