Infrared Thermography for Moisture Detection: A Laboratory Study and In-situ Test

Abstract

Infrared thermography (IRT) was used to map moisture distribution and to identify areas with anomalous water content in modern and ancient building structures. This paper describes two different approaches that used IRT to map evaporative flux on wall surfaces, and to assess the potentials and limits of the technique. The first part of the paper describes a set of laboratory measure- ments to evaluate water diffusion inside the wall, as well as evaporation rate versus moisture content. Measurements of evaporative flux on laboratory samples provided an empirical relation- ship between evaporative flux and cooling under specific conditions inside mesopores and microp- ores allowing the typical trend of the evaporation rate to serve as a key for reading thermographic surveys to identify areas at greatest risk of surface degradation. Capillary rise (water rising from soil due to capillary of porous materials) was also evaluated under laboratory-controlled conditions. In addition, active and passive tests were applied in-situ to map different areas on the building surface according to water evaporation. The output was not the absolute moisture content, but rather a value ranked according to a scale on which the saturated condition represented the minimum negative value and zero represented the physical moisture content (dry). This map was coupled with the surface temperature as given by the natural evaporation when equilibrium conditions with the environment were reached, as in the passive approach. This was obtained by processing the experimental data using a robust algorithm that synthesized the surface temperature history during the test with enhanced evaporation. Finally, outputs of the processing algorithms were over- lapped with the visible image and put in the same file.