Question

Which one of the following is employed to determine the strength of hardened concrete of an existing concrete structure ?

• A. Bullet test
• B. Kelly ball test
• C. Rebound hammer test
• D. cone penetrometer test

Answer 1

The correct option is C Rebound hammer test

The rebound hammer test is one of the non-destructive test used to check the compressive strength of concrete.
The rebound of an elastic mass depends on the hardness of the surface against which its mass strikes.
Average Rebound Number Quality of concrete

>40	Very good hard layer
30 to 40	Good layer
20 to 30	Fair
<20	Poor Concrete
0	Delaminated

To measure the consistency of concrete is the ball penetration test (ASTM 360) which is also known as the Kelly ball test.