Determination of concrete water content by coupling electromagnetic methods: Coaxial/cylindrical transition line with capacitive probes

Abstract

This paper deals with the development and the validation of an innovative, easy-to-use and on site technique for determination of concrete water content. The on-site technique is the capacitive probe, able to characterize in situ dielectric media in the 30-35 MHz frequency band (around 33 MHz). For the evaluation of water content in various civil engineering structures, a calibration methodology has to be developed and is presented herein. It is based on the complex permittivity estimation of various dispersive concretes, which is carried out by a cylindrical coaxial electromagnetic (EM) transition line allowing the characterization in laboratory of material samples in a large GPR frequency bandwidth [50-600 MHz]. This methodology consists then on a coupling between the results of both the capacitive probes and the coaxial EM cell extrapolated at low frequency (33 MHz). The extrapolation procedure used to link physically the results of the two techniques is provided by the 4p-variant of Jonscher's model which is parameterized to obtain dispersion curves of the complex permittivity for very wide frequency bands. The methodology is checked by a parametric study that associates the 4p variant of Jonscher's model with the physical and hydric characteristics of the six concrete mix designs representing high performance and ordinary concretes at various hydric states. The surface testing results measured by capacitive probes on slabs are successfully compared to the extrapolated results obtained on cores.

Effect of transient drying on mechanical properties of concrete specimens

“…With regard to the water content in the samples, the obtained values ranged from 6.5 % to 7.4 % with an average of 6.9%. The values seemed consistent for this type of material, see for example [32,33]. Finally, despite the small number of samples, there was a good consistency between the samples of the batches of the first campaign and those of the second one.…”

Development of a calibration methodology to improve the on-site non-destructive evaluation of concrete durability indicators

“…Furthermore, a fitting and extrapolation process dedicated to the dispersion curves obtained by this EM cell is performed by Jonscher's model [39]. The extrapolation steps yield the permittivity at a lower frequency and thus ensure the accuracy of permittivity at both low and high frequencies, corresponding to the devices used for on-site evaluations [39].…”

“…Furthermore, a fitting and extrapolation process dedicated to the dispersion curves obtained by this EM cell is performed by Jonscher's model [39]. The extrapolation steps yield the permittivity at a lower frequency and thus ensure the accuracy of permittivity at both low and high frequencies, corresponding to the devices used for on-site evaluations [39]. The first extracted observable therefore is the real part of the relative permittivity Eps= r_900MHz (denoted here as permittivity) at 900 MHz, nearly corresponding to the observable obtained on-site with the 1.5 GHz GPR antennas [16] (see Section 3.2).…”

Electrical tomography for characterizing transport properties in cement-based materials: A review

“…These works (among numerous others) led to subsequent research significantly increasing the field's ability to characterize and understand transport properties in cement-based materials using electrical methods. Some representative example include quantifying the influence of salt in cement-stabilized geotechnical applications [120,121], capacitive characterization [122][123][124], and a suite of "on-site" electrical-based non-destructive methods for evaluating durability [125].…”