The permittivity and conductivity of concretes at ground-penetrating radar frequencies

A full understanding of the behaviour of ground-penetrating radar pulses as they propagate through concrete structures requires knowledge of the variation of the permittivity and conductivity of the concrete across the frequency spectrum of the radar pulse. Variations in concrete composition and the fractional water content can effect these electrical properties. This paper describes a large-diameter transmission line that can accommodate removable concrete specimens and the various methods that have been used to analyse frequency domain reflection and transmission measurements on the transmission line up to a maximum frequency of 1 GHz. The effects of fractional water content, ordinary Portland cement strength, cement replacement and lightweight aggregates are considered. The effects of high water contents on radar pulse shapes are illustrated to demonstrate the effects of frequency-dependent electrical properties.