The Rebound Hammer Test, also known as the Schmidt Hammer Test, is a
non-destructive test (NDT) used to assess the surface hardness and, indirectly,
the compressive strength of concrete. It is widely used in the field of civil
engineering for quality control and to estimate the uniformity and strength of
in-situ concrete.
Principle of the Rebound Hammer Test
The Rebound Hammer Test is based on the principle that the rebound of an
elastic mass depends on the hardness of the surface it strikes. When the
plunger of the rebound hammer is pressed against the concrete surface, a
spring-controlled mass rebounds. The rebound distance depends on the surface
hardness of the concrete, which is then correlated to the compressive strength
of the concrete.
Procedure of the Rebound Hammer Test
1. Preparation : Ensure that the concrete surface is clean and smooth, free from dust,
loose particles, and any form of coating or surface irregularity that may
affect the reading. The test should be performed on a dry surface for more
accurate results.
2. Calibration : Check and calibrate the rebound hammer as per the manufacturer's
specifications before starting the test.
3. Positioning the Hammer : Hold the hammer firmly and press it perpendicularly against the
concrete surface. The plunger of the hammer should be in contact with the
concrete.
4. Rebound Measurement : Press the plunger firmly until the hammer impacts the surface. The
hammer will rebound, and the rebound number (a dimensionless number indicating
the rebound distance) is displayed on a scale.
5. Recording the Rebound Number : Repeat the test at different points on the concrete surface, typically
at least 10-12 times for a reliable average, spaced uniformly to cover the
entire area.
6. Analysis : The average of the recorded rebound numbers is used to estimate the
compressive strength of the concrete using established correlation charts or
formulas provided by the hammer manufacturer.
Advantages of the Rebound Hammer Test
1. Non-Destructive : The test does not damage the structure being tested, making it suitable
for in-situ testing of finished concrete.
2. Quick and Easy : It is a simple, rapid, and cost-effective method that requires minimal
preparation.
3. Portable Equipment : The rebound hammer is a portable tool that can be easily carried to
different sites for on-site testing.
4. Immediate Results : Provides immediate results that can be used for quick assessments of
concrete quality and uniformity.
5. Wide Application : Suitable for testing large areas of concrete surfaces to detect
variations in surface hardness and potential weaknesses.
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