Rebound Hammer

1. Most common NDT method.
2. Developed in 1948.
3. Measures rebound hardness of concrete.
4. No theoretical relationship available for assessment of strength.
5. Empirical relationship between rebound hardness and strength developed.

Average rebound number	Quality of concrete
> 40 30 to 40 20 to 30 < 20 0	Very good hard layer Good layer Fair Poor concrete Delaminated