Vol.:(0123456789) 1 3 Journal of Nondestructive Evaluation (2020) 39:64 https://doi.org/10.1007/s10921-020-00710-4 Electrical Impedance‑Based Technique for Estimation of Moisture Saturation Conditions of Hardened Cement Paste at Low Radio Frequencies Gopinandan Dey 1 Received: 15 May 2020 / Accepted: 11 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract The degree of saturation (DoS) of moisture is the main parameter related to the durability of cement-based materials. In this paper, the electrical response of hardened cement paste is investigated at low radio frequency (RF) excitation. Cement paste samples with water to cement ratio (w/c) of 0.40 and 0.45 are used and the samples are conditioned to diferent DoS. A pulse- based electrical input is imposed on the sample and the voltage output is recorded at various locations. Using a simplifed circuit model the values of bulk conductivity for various DoS are estimated, which are found to follow a systematic pattern for various DoS and at diferent excitation frequencies. It enabled the establishment of an empirical quantitative relationship between conductivity and the DoS of cement paste. Further, from this investigation very high values of bulk permittivity at low RF are noticed, which are found to be in good agreement with the values of other porous materials available in the literature in this frequency range. Keywords Hardened cement paste · Degree of saturation · Electrical impedance · Electrical conductivity · Electrical permittivity · Radio frequency 1 Introduction Cement paste is the binding material in all cement-based material (CBM) including mortar and concrete. The major contribution of the porous nature of mortar and concrete is contributed by cement paste. In CBM moisture move- ment through these pores is a common phenomenon. From the durability aspect of CBM, the role of moisture has the utmost importance as most of the degrading chemical reactions caused due to the presence of moisture. Studies have revealed that the degrading chemical reactions such as alkali-aggregate reaction [1], corrosion of reinforcement [2], carbonation [3] and chloride attack [4–6] are afected by the DoS. This degrading phenomenon afects the service life of the concrete structure. Hydraulic difusivity [7, 8] is one of the important parameters that control the water transport phenomenon and is essential for service life prediction of the structure [9], however, hydraulic difusivity itself depends upon DoS of the porous material. Therefore, it is impor- tant to monitor the moisture content or DoS in concrete or its constituents to identify the potentially hazardous condi- tion and make a priori action for the avoidance of damage. Moreover, with regard to the characterization of concrete or mortar, estimation of this property before its actual use can generate an idea about the susceptibility of the material to ingress and difusion of various precarious chemicals during the service life of the structure. Since hydraulic difusivity depends on DoS, the development of techniques for estima- tion of DoS, preferably non-destructive, is essential. Considering the importance of determination of DoS in concrete and other building materials many methods have been developed over the years. Except for the gravimetric method most of the methods are non-destructive in nature and the determination of DoS is done through some indirect technique. The most common methods are nuclear magnetic resonance (NMR) based spectroscopy; methods based on attenuation of electromagnetic radiation (e.g. gamma-ray neutron method and X-ray) and electrical methods [10–12]. Some other popular methods of moisture determination which have also found their recent application in concrete * Gopinandan Dey gopinita@ymail.com 1 National Institute of Technology Agartala, Jirania, Tripura 799046, India