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Rebound Hammer Concrete Test
Hammer Rebound Test
Schmidt Hammer Test
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REBOUND HAMMER
Rebound hammer test is done to find out the compressive strength of concrete by using rebound hammer as per IS: 13311 (Part 2) - 1992. The underlying principle of the rebound hammer test is :
The rebound of an elastic mass depends on the hardness of the surface against which its mass strikes. When the plunger of the rebound hammer is pressed against the surface of the concrete, the Spring-controlled mass rebounds and the extent of such a rebound depends upon the surface hardness of the concrete. The surface hardness and therefore the rebound is taken to be related to the compressive strength of the concrete. The rebound value is read from 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 to determine strength of hardened concrete by rebound hammer:
Interpretation of Results
The rebound reading on the indicator scale has been calibrated by the manufacturer of the rebound hammer for horizontal impact, that is, on a vertical surface, to indicate the compressive strength. When used in any other position, appropriate correction as given by the manufacturer is to be taken into account.

Hammer test can provide fairly accurate estimate of concrete compressive strength, it performed with precautions and co- relations :
  1. Concrete Age : The concrete should be 14 to 56 days old.
  2. Surface Condition : The surface of the concrete at the point tested must be smooth dry and free of honey combing. Otherwise, rebound readings will be low indicating a weaker concrete than is actually the case .
  3. Location of Test Point : The concrete to be tested must be at least 100 mm thick. Care must be taken that the test points are no closer than 25 mm from the edge.
  4. No. of Readings : Calculate the average of 10 readings and exclude extreme readings (if any) and recalculate average using the remaining readings.
A simple equipment known as Rebound Hammer or Schmidt Hammer is used for this purpose. Surface hardness measured during the test give an idea about the soundness and quality of cover concrete. Locations having very low rebound numbers indicate weak surface concrete and may be affected by corrosion. The quality of concrete may be interpreted as shown in the above table.

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