Surfaces to Avoid
Avoid testing concrete that is:
• Frozen
• Honeycombed or excessively porous
• Known to have rebar 2cm or less below the surface
• Carbonated on the surface
If you must test a mature concrete surface that is damp from rain or flowing
water, or if you must test new concrete, keep in mind that you will probably get
rebound numbers that are lower than they should be. Using the Rebound Ham-
mer on new concrete may damage it if the strength is less than 1,000 PSI.
If you are testing concrete with a lot of surface carbonation, the rebound read-
ings will be significantly higher than normal. The thicker the layer of carbonated
concrete, the higher the rebound numbers.
Holding the Rebound Hammer against Walls, Ceilings, and Floors
The Rebound Hammer will work against any concrete surface as long as you
keep it perpendicular to that surface. The Rebound Hammer can be used
against a ceiling (upward), a floor (downward), or a wall (forward). You will
need to consider gravity when estimating the compressive strength of concrete.
The rebound number found when pressing up against a ceiling will differ from
the number that appears if you are pressing down against a floor. Please review
the strike angles A, B, and C and the correlation curves in “Reading your
Results” below.
Specialty Concrete
The Rebound Hammer is designed to estimate the compressive strength of
standard concrete. The correlation diagram for standard concrete is printed on
the side of your Concrete Rebound Hammer. It shows the correlation curves
determined when the compressive strength of standard concrete, as measured
with your Rebound Hammer, is directly compared to the compressive strength
from laboratory tests of concrete cylinders or cubes.
This diagram is not designed for use with:
• Light weight concrete
• Concrete using artificial aggregates
• High performance concrete
In order to gain an accurate rebound number for these specialty materials, you
will need to create your own correlation curves diagram intended for this use.
See the standards ACI 228.1R-2010 and ASTM C-805-08.
