Infrared Thermography in Civil Engineering: From Non Destructive Testing in Laboratory to Outdoor Thermal Monitoring
Résumé
Being able to perform full field easily noninvasive diagnostics for surveillance and monitoring of transport infrastructures and structures is a major preoccupation of many technical offices. Among all the existing electromagnetic methods, active infrared thermography [1] up to long-term thermal monitoring using uncooled infrared cameras is a promising technique [2]. Anyway, except for vision applications [3], there is few results available in literature (mainly on buildings) for outdoor measurements by infrared thermography. So, to complete, a review of specificities and constraints for in situ measurements on large scale structures is proposed. Key points identified are analyzed versus infrared system technological potential solutions available on the shelf or at laboratory level. To introduce transfer from laboratory conditions to real field, we will lean on some laboratory works on active thermography applied to quality control of reinforcement operations by gluing composite (CFRP) plates or tissues on concrete structure [4] or voids in pavement [5]. First, we will introduce and discuss the benefit of using numerical heat transfer modeling to optimize the control process [6,7] or generate virtual thermal image sequences to test post-processing methods [8_,9]. It will be followed by presentation and discussion on experiments carried out using laboratory specimen. Then, some post-processing analysis approaches will be discussed. Finally, considerations on requirements to move from laboratory conditions to real site field measurements will be proposed. Following the laboratory level presentation, a review of various experiments carried out, with an adapted infrared system, on different transport infrastructures or large scale element of Civil Engineering structures in outdoor conditions is given [10,11]. Raw results analysis is proposed. Processed data, obtained from few thermal images [12] to few days of experiments [10-11,13] up to several month of experiments, are presented and discussed. Lessons learned from in situ outdoor experiments are then addressed. In particular, field expertise acquired was used to initiate the development of a new infrared system architecture " Cloud2IR " dedicated to long term monitoring [14]. An overview of this new architecture is proposed and discussed. In particular, benefit of using standards for measured data, but not only, is addressed. Finally, a summary of results obtained and current limitations of studied solutions [15] is given. Perspectives in term of in-situ inspection solutions by active infrared thermography (i.e. under natural solicitations) or by coupling techniques [16] are proposed .
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