EM characterization of concretes focused on water and chloride contents in the frame of multi-linear experimental designs

This study is devoted to the electromagnetic (EM) characterization of concrete mixes within the ground penetrating radar frequency band. Defining two specific experimental designs, water and chloride contents are studied in order to establish their relative sensitivity compared to the other parameters describing the mixes. The evaluation of the complex dielectric properties is carried out in laboratory on 24 and 36 different concrete samples (for the moisture and chloride studies respectively), for which composition parameters are the aggregate nature, the cement nature, the cement content, and the water to cement ratio, and conditions are the water saturation degree or the chloride content. In the case of the chloride experimental design, the mixes are tested dry and saturated. EM characterization is performed using a coaxial-cylindrical cell working in the frequency band [50 MHz-~1000 MHz]. The models of relative permittivity associated with the experimental designs are multi-linear polynomials of the 4 or 5 chosen engineering parameters, depending on the study. The exploitation of the data sets consists of a calculation of the coefficients of the models independently for the real and imaginary parts of the relative permittivity, for different frequencies. This reveals the significant relationship between the dielectric properties and the composition parameters, and their evolution as a function of the frequency. Raw results in terms of the real and imaginary parts of the dielectric permittivity along frequencies are presented for the different concretes, in dry and saturated conditions for the chloride experimental design, and the sensitivity of the parameters are discussed.