Dielectric permittivity of concrete between 50 Mhz and 1 Ghz and GPR measurements for building materials evaluation

A new dielectric measurement device has been designed and constructed for permittivity measurement of concrete consisting of aggregates of up to 30 mm in diameter. The permittivity is measured in the frequency range 50 Mhz-l GHz. The samples can be removed from the measurement cell and stored in controlled conditions. The dielectric constant of 0-30 aggregate concrete is measured as a function of hydration level and chloride content. Different mixing laws were compared with the measurements. This comparison shows that volumetric laws such as the complex refraction index model cannot fit the frequency variation and that the Cole-Cole model is the only acceptable one. The influence of chloride content on the permittivity of the concrete is measured and can be used to develop special GPR data processing for the location of salt ingress in civil engineering structures. (C) 1998 Elsevier Science B.V. All rights reserved.