Which non-destructive method uses a hammer to estimate the surface hardness of concrete?

• A. Rebound Hammer
• B. Ultrasonic pulse velocity
• C. Chloride penetration test
• D. Pull-out test

Answer: (A)

The rebound hammer test is used to estimate surface hardness of concrete with a quick, nondestructive approach. A small mass inside the hammer is released to strike the concrete surface, and the device measures how far the mass rebounds. That rebound value, often called a rebound number, correlates with the hardness of the surface and, to some extent, with the local compressive strength. It’s fast, portable, and good for screening large areas or checking consistency between pours.

However, readings come with caveats. The surface condition matters a lot—moisture, laitance, roughness, and carbonation can affect results, and the test only assesses the outermost layer, not the core. For accurate strength assessment, use rebound hammer readings alongside other tests and calibration with cylinder tests.

Other non-destructive methods mentioned involve different principles: ultrasonic pulse velocity uses sound waves through the concrete to infer properties, not a hammer strike; chloride penetration tests measure chemical diffusion rather than hardness; and pull-out tests are destructive, pulling a rod or anchor to fail the concrete.