Application of infrared thermography in anomalies detection of Covão de Ferro dam waterproofing membrane

Abstract

Infrared thermography (IRT) is a non-destructive testing method, which allows the examination or inspection of part of material or system without impairing the future usefulness, and it is applied to “see the unseen”. IRT uses the distribution of surface temperatures (thermograms) to assess the structure or behaviour of what is under the surface of an element without any contact. IRT has a large information potential and a wide field of application, because it is a testing technique that can assess large area and can be operated as an indicating method, giving either qualitative or quantitative data. Nowadays, thermographic method has proved to be an effective and economic method, very valuable in several branches of engineering, namely in structural engineering. It can detect internal voids, delaminations, and cracks in concrete and masonry structures such as bridge decks, dams, and building envelopes. The Covão do Ferro dam, a masonry gravity dam, located at high elevation in Serra da Estrela, Portugal, with a maximum height of 32.5 m and a total length of about 400 m, was rehabilitated between 2004 and 2006 in order to restore the structural stability. The main works included the injection of cement grout into the dam body and the rock mass foundation, the installation of a PVC geomembrane on the upstream face, and the strengthening of the drainage system through the opening of new drains. Eleven years after this rehabilitation, IRT was used to analyse the dam state of conservation and mainly the eventual detection of anomalies in the waterproofing membrane. For this, several themograms were obtained during two days, in a period of low level of water. This paper shows the potential of IRT on the assessment of dam’ state of conservation providing a global vision of the infrastructure accompanied by detailed inspections, but also some limitations.