Concrete Testing Hammer
Non Destructive Concrete Testing Hammer
Concrete Testing Hammer – When concrete is in place and has cured but the strength of the concrete is in question a concrete rebound hammer test can be used to determine the strength.
The other method is to take a core sample and crush it to determine the concrete strength. Taking a core is more accurate but also more expensive. The rebound hammer test is very easy and fast for an approximate guide.
The rebound hammer is also called as Schmidt hammer that consist of a spring controlled mass that slides on a plunger within a tubular housing.
The Rebound Hammer Test
Pros and Cons of The Use of a Rebound Hammer Test
The Pros of Rebound Hammer Test
1. Apparatus is easy to use
2. Determines uniformity properties of the surface
3. The equipment used is inexpensive
The Cons of Rebound Hammer Test
1. The results obtained are based on a local point
2. The test results are not directly related to the strength and the deformation property of the surface
3. The probe and spring arrangement will require regular cleaning and maintenance
4. Flaws cannot be detected with accuracy
Principle of The Rebound Concrete Testing Hammer
The Rebound hammer test method is based on the principle that the rebound of an elastic mass depends on the hardness of the concrete surface against which the mass strikes.
When the plunger of the rebound hammer is pressed against the concrete surface, the spring controlled mass in the hammer rebounds. The amount of rebound of the mass depends on the hardness of the concrete surface.
Thus, the hardness of concrete and rebound hammer reading can be correlated with the compressive strength of concrete.
The rebound value is read off along a graduated scale and is designated as the rebound number or rebound index. The compressive strength can be read directly from the graph provided on the body of the hammer.
Procedure for The Rebound Concrete Testing Hammer
Procedure for rebound hammer test on concrete structure starts with the calibration of the rebound hammer. For this, the rebound hammer is tested against the test anvil made of steel having Brinell hardness number of about 5000 N/mm2.
After the rebound hammer is tested for accuracy on the test anvil, the rebound hammer is held at right angles to the surface of the concrete structure for taking the readings.
Interpretation of Rebound Concrete Testing Hammer Results
After obtaining the correlation between compressive strength and rebound number, the strength of the concrete can be assessed. In general, the rebound number increases as the strength increases and is also affected by a number of Parameters i.e. type of cement, type of aggregate, surface condition and moisture content of the concrete, curing and age of concrete, carbonation of concrete surface etc.
As such the estimation of the strength of the concrete by the rebound hammer method cannot be held to be very accurate and probable accuracy of prediction of concrete strength in a structure is ± 25 %
If the relationship between rebound index and compressive strength can be found by tests on core samples obtained from the structure or standard specimens made with the same concrete materials and mix proportion, then the accuracy of results and confidence thereon gets greatly increased.
Hard Concrete Testing Standard BS EN 12504
Hardened concrete testing – Non destructive
Testing of concrete in situ is covered by various parts of BS EN 12504, Testing concrete in structures, including:
Part 1, Cored specimens – Taking, examining and testing in compression
Part 2, Non-destructive testing – Determination of rebound number
Part 3, Determination of pull-out force
Part 4, Determination of ultrasonic pulse velocity
However, various parts of BS 1881, Testing concrete, remain current including:
Part 201, Guide to the use of non-destructive methods of test for hardened concrete
Part 204, Recommendations on the use of electromagnetic cover meters
Part 207, Recommendations for the assessment of concrete strength by near-to-surface tests
Part 208, Recommendations for the determination of the initial surface absorption of concrete
Concrete design is a specialist subject. We would recommend that you speak to a concrete technologist to design your mixes or to adjust your current mixes if you think they can be improved.
You can speak to one of our recommended concrete technologists by request. Either complete the contact us form on our contact us page or text Bob Evans. His details are below.