Identifying the strength of the concrete is essential for building a strong and sturdy structure. This can be easily achieved by doing a rebound hammer test. This test helps to determine the strength and stiffness of the concrete in the structure. Without causing any damage to the structure, you can easily find the strength of the concrete.
In this Brick & Bolt’s blog, we will explain how the rebound hammer test is taken to identify the structural strength on site for quality construction in detail.
What is the Rebound Hammer Test?
The rebound hammer test is used to determine the strength of the concrete of the structure that you have built. It is a non-destructive test of the concrete, also called the Schmidt hammer and Swiss hammer, which has a spring-controlled mass that moves along a plunger inside the tube. If you press the plunger against the concrete surface, this spring-controlled mass hits the surface and bounces back. The distance at which it is rebounced shows how hard the concrete is. The rebound distance measured on the scale is called the rebound number or the rebound index. The harder the concrete, the higher the rebound number. If the concrete is weak and not stiff, the rebound number will be low.
Principle of the Rebound Hammer Test
The rebound hammer test works on the basic principle that the bounce of a mass depends on how hard the concrete surface is. A spring-controlled mass inside the hammer impacts the concrete and bounces back when the plunger is pressed on it. The concrete’s hardness affects the rebound distance.
The rebound index is a scale-based measure of this rebound value. A chart on the body of the hammer can be used to determine the concrete’s strength.
Equipment Used in the Rebound Hammer Test
A rebound hammer is a piece of equipment used to measure the rebound strength of concrete. The specifications of the rebound hammer are as follows:
Plunger:
The component that makes direct contact with the concrete surface is called a plunger.
Impact Spring:
The hammer mass is pushed forward to strike the concrete by the impact spring.
Hammer Mass:
The moving component that strikes and bounces off the concrete is called the hammer mass.
Housing:
The external structure keeps everything together.
Window & Scale:
Shows the rebound number or rebound value.
Rider on Guide Rod:
The rider on the guide rod aids in directing the movement of the hammer mass.
Hammer Guide:
Assures that the hammer mass moves smoothly.
Release Catch:
Regulates the hammer mass’s release during testing. After impact, the compression spring aids in resetting the hammer. Before using the gadget, press the locking button to lock and reset it.
What is the Procedure for a Rebound Hammer Test?
The rebound hammer test starts with checking the hammer for accuracy. It should first be tested against a test anvil made of steel with a Brinell hardness of approximately 5000 N/mm2. This step ensures that the hammer gives correct readings.
Steps for Rebound Hammer Test
Step 1: Calibration
Test the hammer on a steel anvil with a hardness of 5000 N/mm². If the hammer gives correct results, move to the next step. If not, send it for recalibration.
Step 2: Clear the surface to be tested.
The concrete surface must be dry, clean, and smooth. Use a stone or grinding wheel to clear loose particles. Avoid testing on rough, spalled, or damaged surfaces. Keep at least 20 mm distance from edges or corners.
Step 3: Rebound Testing
Hold the hammer at a right angle to the concrete surface. Press the plunger against the concrete until the hammer releases and makes an impact.
Step 4: Interpretation of Results
The results show the quality and strength of the concrete or rock.
The above test can also be done in three ways:
- Horizontal Position – The hammer is placed against a vertical surface.
- Vertical Downward Position – The hammer is placed on a flat surface, facing downward.
- Vertical Upward Position – The hammer is placed on a flat surface, facing upward.
If the hammer is used at an angled position, the rebound number may change, even for the same concrete.
The rebound hammer requires varied amounts of impact energy depending on the application. The table below shows approximate impact energy values for various applications.
| S. No | Application | Impact Energy (Nm) |
| 1 | For normal concrete | 2.25 |
| 2 | For light concrete or small parts | 0.75 |
| 3 | For large concrete structures (e.g., roads, dams, pavements) | 30 |
Applications of the Rebound Hammer Test in Construction
The rebound hammer is a useful tool in construction. It helps check the strength of concrete using non-destructive techniques (NDT techniques). Below are its important uses.
1. Quality Control
- It evaluates the concrete quality of structures.
- Construction workers ensure that the concrete mix is strong and consistent by testing freshly mixed or freshly cured concrete.
2. Checking the Condition of Structures
- Engineers use it to monitor concrete strength over time.
- It helps check for damage caused by weather, aging, or other structural problems.
3. Checking Repair Work
- It helps test repaired concrete in buildings.
- Engineers compare before and after readings to check if the repair work is strong enough.
4. Testing in Laboratories
- It helps test small concrete samples in labs.
- It ensures that the concrete meets quality standards and gives accurate test results.
5. Finding Weak Areas in Concrete
- It helps find weak spots in concrete structures.
- Engineers test different areas to locate voids, poor compaction, or low-strength zones.
- This helps in planning repairs and improving the structure.
Advantages of the Rebound Hammer Test
The several benefits of using the rebound hammer test for measuring the strength of concrete are as follows:
- It is a fast and easy test.
- It helps to check concrete strength.
- It does not damage the concrete.
- It can be used on existing concrete structures.
- It is cheaper than some other tests.
- It needs little surface preparation.
Disadvantages of the Rebound Hammer Test
Some limitations of using the rebound hammer test are as follows:
- Surface condition affects the results.
- Results depend on the operator’s skill.
- Concrete quality differences can change the results.
- It does not work well for thin or soft concrete layers.
Conclusion
In summary, the rebound hammer test is a reliable and non-destructive method to assess the compressive strength of concrete in various types of structures. Evaluating the concrete strength helps ensure the use of a standard and durable concrete mix, contributing to the construction of long-lasting, structurally sound buildings.
At Brick & Bolt, we ensure quality checks for every step in constructing your dream home. Our professional experts provide 100% quality construction work with advanced home construction techniques and methods. Our Brick & Bolt team is always there to resolve your queries at any time of the day.