Description
Tapping on a wall with a
dense object, such as a hammer, and listening to the vibrations emitted from
the wall can be useful for identifying voids or delaminations in concrete and
masonry walls. The sound produced from a solid wall will be different from that
from a wall with voids or delaminations close to the surface. In concrete block
masonry walls, sounding can be used to verify that the cells in the blocks have
been grouted.
Equipment
The typical equipment
required for sounding is a hammer. However, any hard, dense object can be used.
Conducting Test
In areas where the visual
observations indicate that the wall may have delaminations, the wall can be
sounded by tapping with a hammer. Delaminations and spalls will generally
produce a hollow sound when compared with solid material. The wall should be
tapped several times in the suspect area and away from the suspect area, and
the sounds compared. It is important to test an area that is undamaged, and of
the same material and thickness to use as a baseline comparison. For a valid
comparison, the force exerted by the tapping should be similar for both the suspect
and baseline areas. In reinforced masonry construction, sounding can be used to
assess whether the cells in the wall have been grouted. Near the ends of a
block, the unit is solid for the full thickness of the wall. For most of the
length of the block, it is relatively thin at the faces. If the sound near the
end of the block is substantially different than at the middle of the cell, the
cell is probably not grouted.
Personal Qualification
Sounding of concrete and
masonry walls should be performed by an engineer or trained technician.
Engineers and technicians should have previous experience in identifying damage
to concrete and masonry structures. Engineers and technicians should also be
able to distinguish between sounds emitted from a hammer strike. Prior
experience is necessary for proper interpretation of results.
Reporting Requirements
The personnel conducting
the tests should provide sketches of the wall indicating the location of the
tests and the findings. The sketch should include the following information:
•
Mark the location of the test on either a
floor plan or wall elevation.
•
Report the results of the test, indicating
the extent of delamination.
•
Report the date of the test.
•
List the responsible engineer overseeing
the test and the name of the company conducting the test.
Limitations
The properties of the
wall can influence the usefulness of sounding. The geometry of the wall and the
thickness of the wall will affect the results. Sounding is best used away from
the perimeter of the wall and on a wall of uniform thickness. The accuracy of
information from sounding with a hammer also depends on the skill of the
engineer or technician performing the test and on the depth of damage within
the thickness of the wall. Delaminations up to the depth of the cover for the
reinforcing bars (usually about 1 to 2 inches) can usually be detected.
Detection of deeper spalls or delamination requires the use of other NDE
techniques. Sounding cannot determine the depth of the spall or
delamination.
Tapping on a loose
section of material can cause the piece to become dislodged and fall. Avoid
sounding overhead. A ladder, scaffold, or other lift device should be used to
reach higher elevations of a wall.
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