Emissivity of Building Materials for Infrared Measurements

Abstract

Infrared thermography (IRT) is a technique increasingly used in building inspection. If in many applications it is sufficient to analyze the thermal patterns, others exist in which the exact determination of the surface temperature is a fundamental aspect. In these circumstances, the emissivity of the surfaces assumes special relevance, being probably the most important property in the definition of the boundary conditions. However, information on the uncertainty involved in its measurement, as well as the conditions that influence it, is scarce. This article presents an innovative contribution both to the characterization of the emissivity of various construction materials, and to the discussion of emissivity measurement procedures and the attendant uncertainty. In this sense, three experimental campaigns were carried out: T.I, preliminary tests to assess the initial conditions required for an accurate IRT measurement of the emissivity (reference tape and position of the camera); T.II, assessment of the emissivity of nine different building materials, in dry conditions, using the emissometer and the IRT and black tape methods; and T.III, assessment of the emissivity of three materials during the drying process. The results confirmed that emissivity is a crucial parameter for the accurate measurement of surface temperature. Emissivity measurements carried out with IRT (black tape method) and with the emissometer returned meaningful differences when compared with the values available in the literature. This disagreement led to surface temperature differences of up to 7 °C (emissometer versus reference values). This research also highlighted that the moisture content of the materials influences the emissivity values, with fluctuations that can be greater than 10%, and that the effect of moisture is visible even for low values of moisture content.

Rock Emissivity Measurement for Infrared Thermography Engineering Geological Applications

“…In this case, a piece of electrical tape, with known high emissivity (ε = 0.97), was placed on the specimen face, adjacent to the area where the emissivity was to be measured (Figure 3). This method is based on the rock emissivity estimation by comparing its optic features with the ones of a nearby blackbody at the same temperature, simulated by the black tape [43]. The rock was then oven-heated to reach, at least, 20 K above room temperature, according to the specifications, and the temperature difference between the specimen and the ambient was stable during the quick test, thus minimizing potential measurement errors.…”

Latest Advances in Common Signal Processing of Pulsed Thermography for Enhanced Detectability: A Review

“…Sfarra et al [110,111] performed research on damage behavior, deformation measurement, and thermal stress measurement of building structures and composites using hybrid infrared thermography technology. Barreira et al [112] performed an emissivity evaluation study of black tape to measure the exact emissivity using infrared thermography and radiometer. Through this, the degree of influence on the emissivity according to the moisture content of the building material was confirmed.…”

Close-Range Sensing and Data Fusion for Built Heritage Inspection and Monitoring—A Review

“…Nevertheless, thermal infrared images can be difficult to interpret. To obtain high quality and useful thermographic data, it is usually necessary to take into account the prevailing conditions (ambient temperature, relative humidity, recording distance, materials emissivity factor) to adjust the camera, eliminating the noise errors they cause in measuring the temperature changes of a target's surface [123,124]. For this reason, IRT should be used in controlled environments.…”