Maria Koui

An application of thermography for detection of delaminations in airport pavements

Since delaminations in airport pavements can lead to failure, cost effective ways must be suggested to inspect the quality of pavements. One of these cost effective ways is the infrared thermography technique. This research paper covers the determination of delaminations in asphalt pavements situated at one of the busiest airports in Greece, the International Airport of Athens, by means of infrared thermography. The infrared thermographic technique is used efficiently in the detection of cracks, flaws and other imperfections appearing on airport pavements. The outcome of this investigation leads to the proposition of a forecasting non-destructive technique intended for assessment of efficient airport pavements.

Infrared thermographic assessment of materials and techniques for the protection of cultural heritage

In this work, infrared thermography was applied and investigated as a non-destructive tool in the assessment of materials and techniques for the protection of cultural heritage. Diagnostic studies on monuments and historic buildings, situated in Greece, were performed. Long wave infrared thermography was used on restoration and traditional - historic materials concerning architectural surfaces and historic structures for research purposes such as: the assessment of moisture impact to porous stone masonries and the evaluation of conservation interventions (materials and techniques) regarding, consolidation interventions on porous stone masonries, restoration of masonries by repair mortars, and cleaning of facades. The results of this work indicate that thermography can be considered as a powerful diagnostic nondestructive tool for the preservation and protection of cultural heritage.

Thermographic, ultrasonic and optical methods: A new dimension in veneered wood diagnostics

Modern production techniques in the wood-based industry reached a high quality standard at high output rates. While the speed of the production machines increases, it is necessary to introduce modern and faster working online inspection methods to supervise constantly the material for defects. For example, thermographic cameras are able to detect not only invisible defects within wood-based materials like laminated particle and fiberboards, but can be used also to detect defects in lumber and veneered wood [1–4]. In the latter case, there is the need to inspect more accurately the final pieces, given the exponential growth in worldwide sales. Therefore, in order to minimize adhesion problems [5], detecting surface and sub-surface cracks, define the geometry of the sub-surface detachment, in the veneered wood products, an integrated non-destructive test method is needed both during the production process that after to it [6]. Our system can provide a continuous control of the process and the product. In fact, this study compares the performance of transient thermography, three optical methods and ultrasonic testing applied together on a veneered wood sample with real and fabricated defects. The use of phase-shifting holography correlated to Double-Exposure HI and the wavelet transform applied as fusion of images between Thermographic Signal Reconstruction and Double-Exposure HI, are explored in this work.

Infrared thermography and ground penetrating radar for airport pavements assessment

Non-destructive techniques, such as infrared thermography and ground penetrating radar, have the potential to produce rapid and accurate assessment of airport pavements. In this work, an examination of asphalt pavements situated at the International Airport of Athens in Greece, is performed. Infrared thermography and ground penetrating radar are introduced with the purpose of providing prompt and accurate condition assessment of airport pavements. These techniques are used efficiently in the detection of cracks, voids and other imperfections appearing either from the ageing of the materials or due to poor workmanship. Finally, this paper describes the problem of deteriorating airport pavements, the procedure and the equipment used for the in situ tests, while the results obtained lead to the suggestion of a predictive monitoring non-destructive technique for the inspection and appropriateness of efficient engineering structures.

Pulsed thermographic inspection of CFRP structures: experimental results and image analysis tools

In this study, three different CFRP specimens with internal artificial delaminations of various sizes and located at different depths were investigated by means of Pulsed Thermography (PT) under laboratory conditions. The three CFRP panels, having the same thickness and defects characteristics but with a different shape (planar, trapezoid and curved), were assessed after applying various signal processing tools on the acquired thermal data (i.e. Thermographic Signal Reconstruction, Pulsed Phase Thermography and Principal Component Thermography). The effectiveness of the above processing tools was initially evaluated in a qualitative manner, comparing the imaging outputs and the information retrieval in terms of defect detectability enhancement and noise reduction. Simultaneously, the produced defect detectability was evaluated through Signal-to-Noise Ratio (SNR) computations, quantifying the image quality and the intensity contrast produced between the defected area and the adjacent background area of the test panel. From the results of this study, it can be concluded that the implementation of PT along with the application of advanced signal processing algorithms can be a useful technique for NDT assessment, providing enhanced qualitative information. Nevertheless, SNR analysis showed that despite the enhanced visibility resulting from these algorithms, these can be properly applied in order to retrieve the best possible information according to the user’s demands.

Importance of integrated results of different non-destructive techniques in order to evaluate defects in panel paintings: the contribution of infrared, optical and ultrasonic techniques

The increasing deterioration of panel paintings can be due to physical processes that take place during exhibition or transit, or as a result of temperature and humidity fluctuations within a building, church or museum. In response to environmental alterations, a panel painting can expand or contract and a new equilibrium state is eventually reached. These adjustments though, are usually accompanied by a change in shape in order to accommodate to the new conditions. In this work, a holographic method for detecting detached regions and micro-cracks is described. Some of these defects are confirmed by Thermographic Signal Reconstruction (TSR) technique. In addition, Pulsed Phase Thermography (PPT) and Principal Component Thermography (PCT) allow to identify with greater contrast two artificial defects in Mylar which are crucial to understand the topic of interest: the discrimination between defect materials. Finally, traditional contact ultrasounds applications, are widely applied for the evaluation of the wood quality in several characterization procedures. Inspecting the specimen from the front side, the natural and artificial defects of the specimen are confirmed. Experimental results derived by the application of the integrated methods on an Italian panel painting reproduction, called The Angel specimen, are presented. The main advantages that these techniques can offer to the conservation and restoration of artworks are emphasized.

Macro- and micro- non destructive tests for environmental impact assessment on architectural surfaces

Several non destructive techniques are recently applied to assess and evaluate weathering damages. In the present work several macro- and micro- non destructive tests, have been employed, in the Fortress of the Medieval City of Rhodes, for the examination of the weathering: Digital Image Processing for the mapping of the decay patterns, Fibre Optics Microscopy for the examination of the morphological characteristics of the surface, and Infra Red Thermography for the assessment of the humidity distribution within the masonries and the degradation of the stone texture. The results of the above methods are supported by porosity and humidity measurements regarding the evaluation of the microstructural characteristics of the stone and the water percolation within the masonry. It is proved that these three methods can be combined into a reliable assessment tool concerning environmental impact on architectural surfaces and particularly in the form of a thorough characterization of the materials degradation.

A thermographic survey for evaluating in situ the performance of photovoltaic panels

Infrared thermography could be an important diagnostic tool for assessing the performance of photovoltaic panels. Malfunctions, material and insulation defects can be detected easily and fast without complicated proceedings. It can be applied to large and small scale systems so as to secure the best possible function and thus performance of the panel(s). In this work, a thermographic survey was performed on a photovoltaic plant of 1 MW in Greece. Various deficiencies were detected by using in situ thermography. Although these panels were only a few months into use, there were defected areas spotted by thermography, indicating the poor performance of these panels and thus affecting the total power output of the photovoltaic plant.

Assessment of Cleaning Conservation Interventions on Architectural Surfaces Using an Integrated Methodology

In this work, pilot cleaning interventions applied by a wet micro-blasting method on architectural surfaces of three historic buildings in marble and porous stone were evaluated in situ and in the laboratory. The investigation was performed on characteristic stone surfaces (marbles and porous stone) of the following historic buildings: Athens Academy and National Library of Greece in Athens center polluted urban environment and Bank of Greece in Piraeus marine environment. The materials of the facades were characterized, and the mechanism of decay was diagnosed. In addition, the cleaning method’s efficiency was evaluated based on the acceptability of the alteration of the cleaned architectural surfaces. Criteria were both aesthetic and physico-chemical. In particular, the architectural surfaces were examined in situ by the means of fiber optic microscopy, infrared thermography and colorimetry. In the laboratory, methods of investigation were optical microscopy, X-ray diffraction, scanning electron microscopy with energy dispersion by X-ray analysis, mercury intrusion porosimetry, Fourier transform infrared spectroscopy, conductivity and pH measurements. The majority of measurements and analyses were applied before and after the pilot cleaning interventions. Finally, the results of this study contribute to the development of an integrated methodology for the assessment of cleaning interventions applied on architectural surfaces.

Thermography as an evaluation tool for studying the movement of water through various porous materials: capillary rise and evaporation

In this work, infrared thermography is used for detecting the movement of water - moisture in various porous materials in the laboratory, with the intention of validating the examination of real scale material systems in situ. Different materials have been subjected to capillary rise tests and to cycles of evaporation with water under controlled environmental conditions (Relative Humidity and Temperature). Material samples of a reference porous stone, of three basic categories of repair mortars, of consolidated porous stones and of simulating prototype porous materials were examined in lab. Furthermore, systems like historic masonries, were examined in situ, more specifically the Venetian Fortification in Heraklion, Crete and the Medieval Fortifications in Rhodes, undergoing severe alveolation in the aggressive marine atmosphere of the Aegean. Infrared thermography has been shown to be an effective technique for verifying relations between moisture and environmental conditions. Hence, infrared thermography can be used as an evaluation tool for studying the movement of water through porous materials - water absorption and evaporation.