Investigation of dielectric properties of brick materials as a function of moisture and salt content using a microwave impulse technique at very high frequencies

A pulsed microwave method using a frequency range of about 7 GHz has been developed based on the principle of the pulsed radar method. This method is employed for the non-destructive quantitative determination of the moisture content and distribution in brickwork. The measurements are more precise than previous measurements that have used frequencies below 1 GHz. Owing to the shorter wavelength and the higher absorption coefficient of water in this frequency region, both real and imaginary parts of the complex dielectric properties are measured with a higher accuracy. The expected non-linear relationship between the dielectric properties of several building materials and their moisture content and salt concentration (NaCl) requires calibration measurements. Therefore, systematic measurements on brick material, like sand-lime brick, solid brick, hollow brick and porous concrete, have been carried out. The results are demonstrated and compared with actual theoretical models. (C) 1998 Elsevier Science Ltd. All rights reserved.