Laboratory determination of the dielectric permittivity of building stones in the 0.2 - 6 GHZ band.

Dielectric permittivity can be a useful parameter to describe the behaviour of building stones subjected to the effects of weathering. An open ended-coaxial line has been used as a sensor to measure the permittivity of rock specimens placed in contact with the line. The measurements were carried out on 20 selected rock samples of building stones that are used in man-made structures or that were employed in historica Ibuildings. The equipment was an HP85070B dielectric probe kit connected to a HP network analyser, under the remote control of a personal computer. The measurements furnished the electromagnetic properties of rock samples in a frequency range of200 MHz to 6 GHz. The final goal was to determine the electromagnetic properties of the rock specimens in natural conditions and after artificial ageing; this furnishes the near surf ace alteration process of the materiais. These results could be relevant as an aid for the interpretation of high frequency ground probing radar, either for detecting near surface anomalies in historical buildings, such as reinforcement bars, or for an analysis of the weathered layer. This paper describes the measurement procedure and the results of the first steps of laboratory tests on specimens, before the ageing procedure.