Non-destructive testing or non-destructive testing (NDT) represents the set of examinations, checks and surveys conducted by engaging methods that do not alter the material and do not require the destruction or removal of samples from the structure under examination. The benefit offered by nondestructive testing is the use of instruments that directly or indirectly measure certain characteristic quantities of interest to designers to make appropriate assessments, without damaging the structure.
CNDs help identify defects, cracks, porosity or other imperfections that could compromise the structural integrity and safety of the material or component. They fall under nondestructive testing in the construction industry:
- Sclerometric tests: use the sclerometer to measure the rebound of a metal mass against the concrete surface and determine, through the use of appropriate correlation tables, the mechanical strength of the structural member
- Ultrasonic tests: estimate the propagation velocity of the ultrasonic pulse within a medium and, with the support of appropriate experimental correlation tables, estimate the compressive strength of the material
- Pacometric tests: employ the pacometer to detect the position of reinforcing bars placed within the concrete and estimate their diameters and depths
- The measurement of lengths: assesses the size and location of defects or discontinuities in materials by making a direct comparison between a standard measurement – metre, rib-gauge, gauge – and the size under consideration
- Georadar tests: use electromagnetic waves to explore structural and nonstructural elements and return radar images or radargrams of objects that may be present in the medium under investigation
- Thermographic tests: employ infrared radiation to detect temperature changes and identify possible problems, such as heat loss or hidden defects
Nondestructive testing can be considered a subset of site investigations.