Electrical Conductivity and Permittivity of Partially Saturated Concrete Under Drying and Wetting Cycles

Abstract

Concrete is a versatile construction material, which is often chemically attacked by various environmental agents. Concrete, being porous, allows movement of chemicals within its interior. The transport property of various chemicals depends on hydraulic diffusivity, which in turn depends on the degree of moisture saturation (DoS). Therefore, DoS is an important parameter and its estimation is highly significant with regards to material characterization. In this paper, cement concrete samples of size 75 mm × 75 mm × 300 mm are fabricated with water to cement ratio (w/c) of 0.45, 0.55 and 0.65. These samples are conditioned to various DoS in two methods described as drying and wetting cycles. A set-up for electrical measurements along the length of the sample is proposed, in which a pulse-based electrical input is imposed, which enables simultaneous acquisition of the material response at multiple frequencies, ranging between 100 and 500 kHz. Using a simple circuit model, the real and imaginary parts of impedivity are calculated along the length of the samples and the bulk conductivities and bulk relative permittivities at various DoS are estimated. The conductivity values are found to follow a regular pattern for various DoS and at different excitation frequencies, which facilitates the establishment of an empirical quantitative relationship between conductivity and the DoS of concrete. Further, on evaluation of permittivity it is found that the value of this parameter is much higher than that of its constituents which was seen in the literature.