The 8 th International Conference of the Slovenian Society for Non-Destructive Testing »Application of Contemporary Non-Destructive Testing in Engineering« September 1-3, 2005, Portorož, Slovenia, pp. 401-407 NON DESTRUCTIVE DAMAGE ESTIMATION ON ROCKS WITH LABORATORY MEASUREMENTS OF DIELECTRIC LOSS ( tan ) δ C. Anastasiadis, I. Stavrakas, A. Kyriazopoulos, D. Ninos, D. Triantis Department of Electronics, Technological Educational Institution of Athens Ag Spiridonos, 12210, Athens, Greece, E-mail: cimon@ee.teiath.gr ABSTRACT Non–destructive testing methods constitute a fast growing field of study that concerns various materials. In addition to the up today bibliography a novel technique is presented here. It deals with the use of Dielectric Spectroscopy (DS) or Impedance Spectroscopy (IS) techniques for the verification of mechanical damages introduced in geomaterial structures. The main merit is that these techniques do not influence the materials structure or properties, thus it can be tested with several other methods. In this work damages are introduced in a geomaterial by uniaxial stress application while temperature is constant. Specifically, the damage caused to marble samples and its influence on the dielectric loss angle were measured and examined with respect to the externally applied uniaxial stress. Results indicate that when the applied stress is capable of leading to microcrack generation then tanδ values increase while for high values of stress, a loss peak is evident in the studied frequency range. Keywords: Dielectric losses, Geomaterials, Uniaxial stress, Damages 1. Introduction Marble is a rock, which from a geological point of view belongs to the metamorphic rocks used for constructions of buildings and monuments. Imperfections in its structure are usually due to either internal or external factors such as mechanical strain, chemical or physical processing and play an important role in the electrical behaviour of the material. Mechanical stresses upon rocks create microscopic or macroscopic discontinuities resulting in changes in the mechanical behaviour of the material[1-3]. Microscopic and macroscopic defects can be studied indirectly through the understanding of the electrical properties of the samples. It is common for this purpose to measure the dielectric characteristics of the studied samples. Dielectric properties relate to the ability of a material to polarise under the influence of an electric field. The polarisability of a material depends on the structure and molecular properties and therefore dielectric measurements can provide information in this respect. The technique for measuring dielectric properties is known as Dielectric Spectroscopy, DS [4-7]. DS can be used to measure the complex relative permittivity of materials over a wide frequency range. For homogeneous and isotropic materials complex relative permittivity (hereafter, * ε 401