DIELECTRIC-PROPERTIES OF PORTLAND-CEMENT CONCRETE AT LOW RADIO FREQUENCIES

This paper presents a nondestructive evaluation method to characterize portland cement concrete (PCC) based on its dielectric properties. The work reported is part of an ongoing study to develop a nondestructive evaluation method for PCC structures using electromagnetic waves. A custom-designed parallel plate setup with an HP 4195A Network/Spectrum Analyzer was used to form the measurement system. A model was established for the measurement system and a set of calibration standards was developed for the system calibration. Six different PCC batches were cast and their complex permittivity was measured over 28 days of moist curing, with an average of four specimens per batch. The selected batches covered a representative variation of water to cement ratio and two aggregate types using Type I portland cement. The complex permittivity of PCC was evaluated over a frequency range of 0.1-40 MHz. Preliminary measurements showed significant changes in the real part of the dielectric constant versus the curing time. However, the change in the loss tangent was less pronounced. Significant differences were also observed in the dielectric properties of PCC specimens due to mix-design parameters' variations and the curing state.