REBOUND HAMMER
AIM
To assess the likely compresive strength of concrete by using
rebound hammer as per IS: 13311 (Part 2) - 1992.
PRINCIPLE
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.
APPARATUS
REBOUND HAMMER
PROCEDURE
i) Before commencement of a test, the rebound hammer
should be tested against the test anvil, to get reliable
results, for which the manufacturer of the rebound hammer
indicates the range of readings on the anvil suitable for
different types of rebound hammer.
ii) Apply light pressure on the plunger - it will release it from
the locked position and allow it to extend to the ready
position for the test.
iii) Press the plunger against the surface of the concrete,
keeping the instrument perpendicular to the test surface.
Apply a gradual increase in pressure until the hammer
impacts. (Do not touch the button while depressing the
plunger. Press the button after impact, in case it is not
convenient to note the rebound reading in that position.)
iv) Take the average of about 15 readings.
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.