Which non-destructive testing method(s) are used for concrete?

• A. Rebound Hammer test method
• B. Pulse velocity method
• C. Both of these
• D. None of these

Answer: (D)

Non-destructive testing methods used on concrete include surface hardness tests and ultrasonic pulse tests. The rebound hammer (Schmidt hammer) measures how much the spring-loaded mass rebounds after striking the concrete surface. That rebound value correlates with compressive strength when properly calibrated for the mix and age. It’s quick, portable, and good for on-site screening, but its accuracy depends on surface condition, moisture, and representative calibration.

The pulse velocity method sends an ultrasonic wave through the concrete and measures how fast it travels from sender to receiver. Faster travel times (higher velocities) generally indicate denser, more uniform material with fewer flaws, while slower speeds can reveal voids, cracks, or highly porous zones. This method provides information about the interior quality of the member and can help locate defects, though results depend on access, geometry, moisture, and material properties.

Because both tests offer non-destructive insight into concrete’s strength and integrity, they are both used in practice.