Rebound Hammer

What is Rebound Hammer Test?

Rebound Hammer test is a Non-destructive testing method of concrete which provide a convenient and rapid indication of the compressive strength of the concrete. 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 operation of rebound hammer is shown in fig. 1. When the plunger of rebound hammer is pressed against the surface of concrete, a spring controlled mass with a constant energy is made to hit concrete surface to rebound back. The extent of rebound, which is a measure of surface hardness, is measured on a graduated scale. This measured value is designated as Rebound Number (rebound index). A concrete with low strength and low stiffness will absorb more energy to yield in a lower rebound value.

Objective of Rebound Hammer Test

As per the Indian code IS: 13311(2)-1992, the rebound hammer test have the following objectives:

  1. To determine the compressive strength of the concrete by relating the rebound index and the compressive strength
  2. To assess the uniformity of the concrete
  3. To assess the quality of the concrete based on the standard specifications
  4. To relate one concrete element with other in terms of quality

Rebound hammer test method can be used to differentiate the acceptable and questionable parts of the structure or to compare two different structures based on strength.

Principle of Rebound Hammer Test

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. The operation of the rebound hammer is shown in figure-1. When the plunger of 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 concrete surface.

Thus, the hardness of concrete and rebound hammer reading can be correlated with 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.

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