Non Destructive Tests

Non Destructive Tests typically use equipment able to generate pulses passing through the material. The measure of the intensity or modification of the signal propagation provides information about the characteristics of the different areas under analysis. The radar surveys, for example, are carried out using high frequency electromagnetic waves that allow the tracking of the separation of surfaces between materials with different dielectric property. The sonic or ultrasonic tests, in their simplest form, provide the measurement of the velocity propagation of such pulses in the material: their velocity can be correlated with the elastic properties of the material. The thermographic surveys detect the thermal conductivity of different materials by measuring their emissions in the infrared range. For example, these surveys identify the presence of gaps and cavities within the masonry; however, they provide information that is generally limited to the superficial part of the wall. The magnetometric surveys measure the changes of a magnetic field caused by the presence of metal objects and are used for the localization of tie rods or, dealing with concrete, for the location and sizing of the reinforcement bars.

Other types of non-destructive surveys are based on the measurement of mechanical events, such as the measurement of the vibration frequency of metal tie-rods struck by a hammer which can be used to determine the tie-rods state of stress as a function of their boundary conditions.