Design and validation of a multi-electrode embedded capacitive sensor to monitor the electromagnetic properties in concrete structures

Abstract

This paper discusses the development of a capacitive sensor embedded within concrete blocks in order to continuously monitor water content, which is a crucial parameter in the assessment of concrete degradation. The embedded capacitive sensor undergoes continuous interrogation by an automatic monitoring system, in order to track permittivity changes over time through a frequency measurement system. The methodology involves a two-step calibration process: first, obtaining permittivity from frequency, then converting permittivity profiles into water content profiles. This paper focuses on the sensor design and first calibration in the aim of assessing permittivity profiles. Numerical methods enable optimizing both electrode geometry and design of the embedded capacitive sensor. Experimental validation of the sensor in liquid and concrete environments, along with a metrological validation, reveals the sensor’s ability to monitor permittivity profiles as well as its uncertainty at 8 different depths inside the concrete structure. Permittivity measurements were also conducted using reference methods. The results demonstrate very good agreement with less than 10% difference between the embedded sensor and the reference results. This step provides insights into its applicability and potential perspectives for future research.