Continuous Measurement of Moisture Content in Consolidated Building Materials with the Time-Domain Reflectometry Technique

Abstract

Measuring moisture content in construction materials is extremely important both for professional practice as well as for research. However, despite the wide variety of techniques available for moisture content determination, performing in-depth, in-situ and long-term minor destructive measurements is still a great challenge. The Time-Domain Reflectometry (TDR) technique is commonly used for soil moisture measurements, but its application in construction materials is considered a relatively new method, especially for low-porosity building materials. The major challenges to its current use in hard construction materials are: (1) the difficulty of ensuring good contact between the TDR probe and the material; (2) the lack of appropriate calibration functions between the measured relative permittivity and the moisture content for building materials; (3) the absence of standardized procedures to obtain appropriate calibration curves for construction materials; and (4) the need to develop automatic tools capable of processing the data and providing the evolution of moisture content over time. This paper presents a methodology to overcome these obstacles in order to obtain successful moisture content measurements with the TDR technique. The proposed procedure was applied and tested on limestone and solid brick samples. The results obtained show that TDR is a suitable solution for monitoring moisture content on low-porosity building materials, encouraging further developments that may lead to a more widespread use of the technique.