The rebound (Schmidt) hammer is one of the oldest and best known methods of comparing the concrete in various parts of a structure and indirectly assessing concrete strength.Â The hammer weighs about 1.8 kg and is suitable for use both in a laboratory and in the field. The rebound of an elastic mass depends on the hardness of the surface against which its mass strikes.
- Finding the elastic properties like compressive strength
- Assessing – the uniformity of concrete.
- Determining variations of strength within a structure
- IS 13311, IS 516: 1959
- BS EN 12504-2
- ASTM C805
- Before commencement of a test, the rebound hammer should be tested against the test anvil, to get reliable results,
- Apply light pressure on the plunger. it will release it from the locked position and allow it to extend to the ready position for the test.
- Press the plunger against the surface of the concrete, keeping the instrument perpendicular to the test surface. Apply a gradual increase in pressure until the hammer impacts
- Take the average of about 15 readings.
- Hammer has to be used against a smooth surface, preferably a formed one.
- If the concrete does not form part of a large mass any movement caused by the impact of the hammer will result in a reduction in the rebound number
- Not a very good test for old concrete and low strength concrete.
- Moisture content affects the readings significantly.
- Type of cement also affects the readings.
- Surface Carbonation increases the hammer reading significantly than it actually is.