A microwave system for measuring moisture of hollow concrete blocks

In this paper, the authors aim to present a microwave system for measuring moisture of hollow concrete blocks. The idea is to use this system as a new technique for Structural Health Monitoring (SHM). The hollow concrete block is an element widely used in civil construction. For that, five samples of blocks were selected and analyzed. Next, antennas and a frequency selective surface (FSS) that is used as a sensor element were designed to measure the frequency responses for various moisture levels of concrete blocks combined with the FSS. The results show a high level of correlation between the frequency variation and the relative humidity level (r = -0.98). The numerical treatment and the statistical analysis of the results were fundamental to determine a first-order function that met the dynamics of the resonance frequency and the relative humidity. Linear regression is performed that results in R-2 = 0.96, being statistically proven that the defined function meets the proposed study within the range of 10 to 90% relative humidity, as well as a specific methodology for this type of study, is established. (C) 2021 Elsevier B.V. All rights reserved.