Use Of Rebound Hammer In Testing Strength Of Concrete

Rebound hammer as you may know is used for checking strength of concrete. It is also called Schmidt Hammer in honor of Ernst O. Schmidt, who invented it in 1950s. This test depends on a principle according to which the way any elastic mass rebounds is dependent on hardness of surface on which elastic mass gets impinged.

Importance of Rebound Hammer Test

These hammers help to judge concrete’s compressive strength and such tests are additionally used to check whether any concrete mixture is as per defined standards or not. It could be catastrophic if any concrete mix is weaker than required and could lead to structural failures. Therefore, such kind of quality check using these hammers is very important for construction companies to perform. NDT or non-destructive testing such as these on samples are also economical for companies to undertake compared to destructive testing.

How Rebound Hammer Works?

At the time of test rebound hammer’s impact-bolt hits concrete surface with a specified force and after such impact the hammer rebounds. Total rebound distance is measured and recorded with the help of a sensor & shown on the display screen. Let us now look at the steps to check strength of concrete with the help of this test.

Checking Concrete’s Strength

  1. First of all the test surface is made smooth with the help of grinding stone.
  2. Some test impacts are performed using these prior to final measurement & evaluation.
  3. Checking is done to make sure that all the settings are in place.
  4. Hammer is kept totally perpendicular to test surface and is pushed towards the surface.
  5. The surface is tested with about twelve impacts & the average used. Additionally, impact points are kept apart by around 25 mm.
  6. Test results are then checked.

Types of Rebound Hammer Tests

There are two basic types of these tests, the first is mechanical and the second is electronic rebound hammer.

  1. Mechanical Rebound Hammer: It measures how much mechanical travel is completed by impact mass on rebound. Things affecting it include guide rod friction, scale’s drag pointer friction, gravitational pull and velocity between mechanical & unit parts.
  2. Electronic Rebound Hammer: This makes use of actual rebound coefficient which represents correct coefficient of physical rebound.

Conclusion

Thus we can clearly figure out that these tests are quite important to know whether concrete mix used is as per standards or not. These are an integral part of NDT and help construction companies spend less as compared to destructive testing.