Nondestructive testing (NDT), in general, is defined as “an examination, test, or evaluation performed on any type of test object without changing or altering that object in any way, in order to determine the absence or presence of conditions or discontinuities that may have an effect on the usefulness or serviceability of that object.” NDT methods have been increasingly used for quality control, quality assurance and quality assessment of both new and old structures.

Unchecked damages and the potential failure of civil structures could not only have a significant economic impact, but also threatens public safety. As such, they should be inspected between short intervals to prevent the exacerbation of potential damages and failure. These damages, after detection, should be repaired or appropriately rehabilitated to pre-vent future catastrophic failures. It goes without saying that detecting the damages is the first step in this process.

Most of these damages in their advanced stage can be detected easily with a visual inspection. However, the detection of internal and subsurface defects requires inspection and testing techniques with capabilities above and beyond visual inspection. To address this, various NDT methods have been practiced over recent decades. The type of NDT method required for the inspection should incorporate the most practical and cost-effective technique to successfully assess the condition of the structural components and to determine the need for maintenance and repair action. In addition to a familiarity with, and skill in, the use of these various available methods, the inspector needs to be aware of the environment in which the inspection takes place, as well as the bridge section that is under survey, to determine the proper procedure.