Application of infrared thermography and geophysical methods for defect detection in architectural structures: Fid-Bau Portal

Application of infrared thermography and geophysical methods for defect detection in architectural structures

Meola, Carosena / Maio, Rosa di / Roberti, Nicola / Carlomagno, Giovanni Maria

The scope of the present study was a multi-methodological approach to non-destructive evaluation of architectural structures. Three different techniques such as infrared thermography, ultrasonics and electric-type geophysical methods were analysed to acquire information for a synergic use of the different methods, which may be useful for the estimation of the buildings degradation sources. The investigation was carried out in laboratory by considering specimens, which were made of a plaster layer over a support of marble, brick, or tuff to simulate masonry structures. Air bubbles were intentionally created inside specimens to simulate detachments. Examples of in situ applications are also reported. In particular, infrared thermography was used for the inspection of the status of the tiles covering the walls of a building. Infrared thermography is the easiest and quickest technique for detection of defects in cement-based materials. In particular, LT is capable of supplying detailed information about size, position and nature of defects and of discriminating between layered structures and local variations of concrete consistency. Unfortunately, LT is limited to thin concrete layers. The PT technique allows for a more in-depth analysis since it was capable of detecting, with good contrast, defects which were very thin (1 mm), quite deep (55 mm) and of thermal characteristics close to the hosting material. The thermal images brought also evidence of the influence of the type of support on the defects visibility. However, it is very difficult to identify with PT the interface between stratified materials. In fact, the same signal degradation may be induced by the support (specific thermal characteristics), or by the defect (thermal characteristics too close to the sound hosting material, or too small, or too deep). The ultrasonic technique, unlike infrared thermography, cannot supply in a fast way detailed information about size and location of small defects in thin layers of concrete. Instead it can provide, through the attenuation of the P-wave, information useful for the evaluation of structural disomogeneities also in presence of very thick materials. The electric-type geophysical methods seem not properly adequate for detection of small and near-surface defects. Conversely, through 3D representations of the natural electric charge accumulations (SP) and of the electrical resistivity (DCG), it can be established the porosity level and the distribution of voids and micro-cracks in the whole masonry structure (plaster + support). In particular, the highest porosity level was found on side B of the specimen with tuff support; this finding justified the worst defect visibility observed over such side in the thermal image. From the resistivity values distribution inside the investigated volumes, it was possible to identify the three different kinds of support.