Preservation and rehabilitation of valuable historic heritage buildings require effective and efficient monitoring systems to ensure proper maintenance of durability and functionality of the building structures and materials. Moisture transport and retention in building infrastructure are some of the most common problems, often inducing structural damage and resulting in harmful microbial growth affecting human health. This work presents an evaluation of measurement techniques for moisture content (MC) in three types of building stone specimens. Moisture measurements, using weight, relative humidity (RH), electrical resistance, capacitance and inductance–capacitance (LC) resonant sensors, were carried out to evaluate moisture measurements in stone. The measurement techniques were evaluated through moisture saturation and drying cycles by partially submerging the stones in water and drying them in air. The results of the MC measurements demonstrate that: (1) RH moisture sensor is not fully capable of measuring the MC in the specimens due to sensor saturation; (2) electrical resistance is nonlinear traversing a large dynamic range from GΩ to kΩ and encounters ion accumulation and polarization problems; and (3) the capacitance and the LC resonant moisture-sensing techniques have a much better signal response to the variation of the moisture content, since both are directly related to the changing dielectric constant in relation to the moisture content. In addition, the LC resonant-sensing technique has an advantage in wireless sensing over other moisture measurement methods. Also, weight measurement results reveal that the moisture behavior in the stone specimens is dominated with capillary transport providing a better understanding of the MC behavior in these three types of building stones. These results lead to the conclusion that the MHz frequency dielectric properties of stone (capacitance) provide better estimates of moisture content than the RH of closed cavities within the stone or DC resistance of the stone.
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