Nondestructive Testing and Evaluation
Nondestructive Testing and Evaluation (NDT&E) techniques are often necessary for the assessment of critical components and systems that must be tested without damaging their structural integrity. Visual inspection is the simplest version of nondestructive evaluation; however, complex problems often require the use of advanced solutions (e.g. impact-echo, ground penetrating radar).
Paradigm Consultants, Inc. has experience developing and implementing nondestructive test methods specifically for the evaluation of concrete, building materials, and structural systems. Our NDT&E services provide unique solutions to challenging problems, benefiting contractors, designers, and engineers.
Ground Penetrating Radar
Ground penetrating radar (GPR) is an effective nondestructive technique for determining reinforcement location and spacing in concrete elements up to 18 inches. While many organizations possess cover-meters (i.e., Ferroscan), which only detects objects up to 3½ in. thick, we have made the additional investment into more sophisticated technology. GPR or subsurface radar has become well established for inspecting concrete in a wide range of applications. The GPR antenna transmits and receives electromagnetic waves through the concrete to detect and locate embedded or differing materials. For example, this technique allows for the determination of the amount of reinforcement in a concrete column, slab, or foundation when the structural drawings are not available.
Impact-echo is a nondestructive method that uses mechanically generated acoustic waves to assess the concrete. The technique was developed in the mid 1980s at the National Institute of Standards and Technology (NIST, formerly the National Bureau of Standards) and has since been adopted as a standardized test method (ASTM C 1383).
When appropriate, the impact-echo method allows for nondestructively determining the thickness of concrete elements (foundations, slabs, walls, pavements). In addition, the impact-echo technique can be used to locate flaws (cracking, voids, honeycombing, delaminations, etc.) in plain and reinforced concrete. When the thickness of the concrete feature is known, the acoustic wave velocity can be determined. Because wave velocity is related to the mechanical properties of a material (i.e., density, elastic modulus), the velocity can be used as an indicator of a material’s strength. In general, higher velocities will correspond to higher compressive strengths of concrete.