Advantages of infrared thermology in civil engineering

In Civil Engineering, the application of infrared thermography is not limited to the passive investigations of the thermal insulation quality of the envelopes of buildings. The basic principles of the two main techniques of active infrared thermography, which are pulse thermography (PT) and thermography Lock-in (LT), are briefly recalled. This paper presents the use of the technique of passive infrared thermography for the detection of defects in reinforced concrete structures and the possible use of active thermography with post - treatment techniques applicable to the characterisation of defects.

Infrared thermography is one of the non-destructive thermal methods that is becoming increasingly popular in non-destructive testing of materials and structures since it is completely con-tactless and may be faster than many other techniques being used. Thermal methods generally consist of the thermal stimulation of the object (under study) and the control of its variation of surface temperature during the transient phase of heating or cooling. The analysis of the heating and cooling processes during and after heating with an internal or external heat source is a well-established technique for the characterisation of composite and metallic materials. In Civil Engineering, the application of infrared thermography is not limited to the passive investigations of the thermal insulation quality of the envelopes of buildings. Defects such as voids in concrete or masonry, delamination at interfaces of compounds having different density, heat capacity and / or thermal conductivity compared to the bulk material can be localized and characterised. Infrared thermography, due to its non-contact character allowing rapid 2D surface mapping, represents a powerful non-destructive evaluation tool (NDE) for materials and structures. Despite this, infrared thermography is still not fully exploited. In contrast to conventional use where natural temperature gradients are used, NDT applications take an active approach. A heat pulse is applied and the surface temperature is monitored and analysed. Typically, the temperature distribution on the surface at the time of maximum contrast is used for the detection of any defect. The most important condition for infrared thermography to provide useful results is that there is a temperature difference or thermal contrast ΔT between the characteristic of interest, People in a scene or an internal fault in a sample; And its surroundings. A second condition is to have the appropriate thermal imaging equipment for producing thermal images or thermograms. It is necessary to have an experienced thermographer to interpret the thermographic results.