Active IR-applications in civil engineering

• Published in: Infrared physics & technology 2002-06, Vol.43 (3), p.233-238
• Main Author: Wiggenhauser, H
• Format: Article
• Language: English
• Subjects: Active thermography; Applied sciences; Building insulation; Buildings; Buildings. Public works; Civil engineering; Exact sciences and technology; External envelopes; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Moisture measurement; Non-destructive testing; Physics; Quantitative analysis; Thermal instruments, apparatus and techniques; Thermal insulation
• ISSN: 1350-4495; 1879-0275
• DOI: 10.1016/S1350-4495(02)00145-7

Applications of IR-thermography in civil engineering are not limited to the identification of heat losses in building envelopes. As it is well known from other areas of non-destructive testing, active IR-thermographic methods such as cooling down or lock-in thermography improves the results in many investigations. In civil engineering these techniques have not been used widely. Mostly thermography is used in a quasi-static manner. The interpretation of moisture measurements with thermography on surfaces can be very difficult due to several overlapping effects: emissivity changes due to composition, heat transfer through wet sections of the specimen, cooling through air flow or reflected spurious radiation sources. These effects can be reduced by selectively measuring the reflection in two wavelength windows, one on an absorption band of water and another in a reference band and then combining the results in a moisture index image. Cooling down thermography can be used to identify subsurface structural deficiencies. For building materials like concrete these measurements are performed on a much longer time scale than in flash lamp experiments. A quantitative analysis of the full cooling down process over several minutes can reliably identify defects at different depths. Experiments at BAM have shown, that active thermography is capabale of identifying structural deficiencies or moist areas in building materials much more reliable than quasi-static thermography.