 
Schmidt Concrete Test Hammer
Surface Hardness and Penetration Resistance
Introduction
BS1881: Part 202 ;ASTM C805
The concrete hammer is a hand held
instrument used for testing the quality
of hardened concrete in a structure.
On new structures, once the concrete
has hardened, the instrument can be
used to give an indication of the gain in
concrete strength.
On existing structures, it can be used to
gain an estimate of the uniformity of
the concrete.
Description
The instrument works on the principle
that the rebound of an elastic mass
impacting on a surface is a function of
the hardness of the surface itself.
Hence the harder the surface, the
greater is the rebound distance.
The test sequence consists of:
1. prior to using the hammer, the
surface of the concrete is first abraded
with the carborundum stone to remove
surface irregularities.
2. the hammer is then pushed firmly
against the concrete until the the trigger
button is automatically released
3. hand pressure is then reduced, to
allow the plunger to fully emerge from
the instrument.
4. extra hand pressure is then applied
to push the plunger back into the
instrument, compressing the internal
spring to a point where the trigger
mechanism over-rides and causes the
impact force to be applied to the
surface.
5. still applying hand pressure, the push
button is pressed to lock the plunger in
place, retaining the reading on the
graduated scale.
6. the strength corresponding to the
reading on the scale is then noted.
7. if concrete test cubes from the
structure are available, then using the
hammer on these will allow a more
accurate answer to be established.
Specification
Measures concrete strengths of:
10 to 70 N/mm (100 to 700 kgf/cm)
Supplied in a carrying case complete
with carborundum stone.
Total Weight 1.7kg.
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