One of the principal causes of deterioration in reinforced concrete structures is steel corrosion caused by the penetration of aggressive agents into the protective cover concrete layer (particularly water containing chlorides). Electromagnetic non- destructive evaluation (EM NDE) techniques are sensitive to these aggressive agents and can be used to assess concrete durability in terms of corrosion risk. The electromagnetic (EM) properties that are the focus of the study presented here are electrical resistivity and dielectric permittivity-inherent material properties that are both sensitive to degree of saturation and the salinity of the pore solution. Three EM NDE techniques suitable for the in situ investigation of concrete are used to obtain these EM properties: electrical resistivity tomography, capacimetry and ground penetrating radar. Experimental work is conducted on in a controlled laboratory environment with the aim of comparing the ability of the three EM NDE techniques to monitor the ingress of saline solutions into concrete slabs and discern between their chloride content. All three methods are found to be capable of detecting variation in water and chloride content and therefore show promise for the in situ monitoring of water and chloride ingress. However, more research is needed on the quantification of the EM properties over depth as well as on the combination of these methods in order to separate the influence of these two parameters on the EM responses

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In civil engineering, ground penetrating radar is widely used for road pavement surveys. In contrast to the existing literature, the influence of interface roughness (surface and interlayer roughness of stratified media) is accounted for within the scope of the data processing of radar signals. The rigorous electromagnetic method PILE (propagation inside layer expansion) provides the simulated data. The observed frequency variations of the radar magnitude introduce some shape distortion on the radar wavelet. An adaptation of the root-MUSIC algorithm is proposed on the basis of the work in [4]. As a result, it is allowed to jointly estimate the time delay and the interface roughness.

This paper deals with the use of three electromagnetic non‐destructive in situ techniques to assess concrete conditions: electrical resistivity, capacimetry, and ground‐penetrating radar. It shows the potential of these methods to monitor the ingress of water and chlorides into concrete. The electromagnetic properties that are studied here are dielectric permittivity and electrical resistivity, both sensitive to volumetric water content and chloride content. Results are presented from an experimental study conducted on concrete slabs (and corresponding core cylinders) in a controlled laboratory environment. Then, the discussion is focused on the ability of three electromagnetic techniques to assess the depth of the ingress front of different salt solutions and to discern between the 3 NaCl concentrations (0, 15 and 30 g/L).

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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.

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