Probing the microstructure of cement mortars through dielectric parameters’ variation

• Published in: The Journal of physics and chemistry of solids Vol. 70; no. 3; pp. 576 - 583
• Main Authors: Tsonos, C., Stavrakas, I., Anastasiadis, C., Kyriazopoulos, A., Kanapitsas, A., Triantis, D.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-03-2009; Elsevier
• Subjects: A. Microporous materials; Applied sciences; Buildings. Public works; Cement concrete constituents; Cements; D. Dielectric properties; D. Electrical conductivity; D. Electrical properties; D. Microstructure; Exact sciences and technology; Manufacture; Materials; Miscellaneous; D. Microstructure; A. Microporous materials; D. Dielectric properties; D. Electrical conductivity; D. Electrical properties; Electrical conductivity; Tantalum nitride; Porous material; Dielectric relaxation; Complex impedance; Electrical measurement; Cement mortar; Humidity; Curing; Microstructure; Complex permittivity
• ISSN: 0022-3697; 1879-2553
• DOI: 10.1016/j.jpcs.2008.12.015

The present work deals with the electrical properties of typical cement mortars during the hardening process, cured at low relative humidity. Measurements were made by using dielectric spectroscopy (DS) over a broad frequency range of 10
Hz–1
MHz and isothermal depolarization current (IDC) techniques, for several weeks after sample preparation. This work presents a coherent study of the various formalisms employed in dielectric spectroscopy. Each of these formalisms contributes to the development of the complete relaxation mechanisms that are responsible for the frequency spectrum. After the first week of hardening, when the DC conductivity effects were absent, two distinct dielectric relaxation mechanisms were observed in the frequency spectrum of the complex permittivity
ε* and tan
δ functions. The mechanism positioned at low-frequency region (few kHz) is observed for the first time, as we know from the literature, on cement mortars. The relaxation times of both mechanisms were found to increase gradually, while the strength of the relaxation mechanisms varied also as a function of the hardening time. Fitting analysis in complex impedance
Z* and electric modulus
M* formalisms revealed also the existence of two short-range relaxation mechanisms of conductivity. We suggest that the low-frequency relaxation is related to the closed capillary pores and the high-frequency relaxation to the C-S-H gel pores. An increase of the mean dimension, of both types of pores, estimated from our data analysis with hardening time.