Investigation of concrete structures with pulse phase thermography: Fid-Bau Portal

Investigation of concrete structures with pulse phase thermography

Weritz, F. / Wedler, G. / Brink, A. / Röllig, M.

The applicability of Pulse Phase Thermography (PPT) for the investigation of building structures is studied in the frame of a DFG (German Research Foundation) funded project. We have applied PPT for the investigation of concrete specimens with voids in near surface regions. The voids are implemented in different depths and with different sizes, representing voids, honeycombing, delaminations of plaster at concrete and masonry and delaminations and voids behind tiles on concrete embedded in mortar. The method is contactless, fast and allows the inspection of broad surface areas. The heating process with an external radiation source as well as the recording of the surface temperature is the same as for Impulse Thermography (IT). In PPT the transient behaviour is analysed by Fourier Transformation, separating the information according to different frequencies of thermal waves and delivering amplitude and phase images. Especially the phase images provide a deeper probing with maximum available depths in the order of magnitude of 10 - 15 cm. Images in the frequency domain facilitate the visibility and detectablity of defects. Phase images show only slight influence by surface inhomogeneities and non uniform heating. The geometrical configuration of the defects can be determined from phase images. Semi-quantitative estimation of defect depths by analogy with the thermal diffusion length results in the right order of magnitude, but further theoretical work has to be done for quantitative determination of defect depth. The presence of moisture inside a specimen has a clear influence on the phase image.