Principle
The Schmidt
rebound hammer is used to find the surface hardness of the concrete. It works
on the principle that the rebound of an elastic mass depends on the hardness of
the surface against which it strikes. Empirical correlations have been
established between strength
Equipment
In 1948, a Swiss Engineer,
Schmidts Ernst developed a test hammer for measuring hardness of concrete known
as Schmidts Rebound Hammer 1.8 kg
and is suitable for both field and laboratory use. Fig.2 shows a schematic view
of the rebound hammer. The main components of Rebound Hammer are the outer
body, the Plunger, the main spring
Fig.1
Schmidt rebound hammer
Procedure
The method of
using the hammer is explained using Fig.2. The hammer is pushed hard against
the concrete. Then the body is allowed to move away from the concrete until the
hammer mass is connected to the plunger by the latch. Then hold the plunger
perpendicular to the concrete surface and the body is pushed towards the
concrete.
This movement
causes the extension of the spring holding the mass to by rebound
Fig.2
Schematic view of the Schmidt Rebound Hammer
Range and Limitations
Although the
rebound hammer test is a quick and inexpensive method of finding the surface
hardness of concrete, it has some serious limitations. The result will be affected
by the following factors:
·
Smoothness of the test surface
·
Size, shape and rigidity of the specimen
·
Age of the specimen
·
Surface and internal moisture conditions of
concrete
·
Type of coarse aggregate
·
Type of cement
·
Carbonation of the concrete
surface
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