The principle of thermography is based on the fact that any object at a certain temperature emits an energy flow.
Imagine that a composite structure, like a masonry, exposed to the same thermal conditions (eg solar radiation), the individual elements
(stone, mortar, brick, steel, etc.) will lead to a different temperature depending on their thermal properties, and in particular their specific heat and thermal conductivity.
Each element will emit a flow of energy depending on the temperature reached and its emissivity. Thermography
consists of recording, by means of an infrared detector, the temperatures reached by the various elements present in a structure.
By means of an optical system (consisting of several lenses) and electrical (capable of transmitting the intensity of the radiation in an electrical signal
received), temperature differences, are recorded, through a thermogram,
consisting in the graphic recording of monochrome or colored tones (variants,
for example, from white to black) proportional
at different temperatures.
A particular application of thermography,
consists in detecting the surface distribution of moisture: by artificially heating
and homogeneously the outer surface of a masonry, the temperature reached in each surface element depends strongly from the local moisture content; the temperature rise
in humid areas it will be smaller than in the dry ones, and therefore a thermographic recording allows you to extract
a comparative moisture mapping
surface. It will then be possible, with a few targeted drawings based on the indications
thermograms, determine absolutely
and precisely the moisture content by the drying tests of the withdrawals
in the laboratory.
This is a typical example to demonstrate the complementarity of a non-destructive test
(such as thermography) with a destructive test (such as moisture determination in the drying laboratory)
of the withdrawals).
The advantages of this method are due to the fact that it is absolutely non destructive, fast execution, with the ability to record