TM 5-822-11/AFP 88-6, Chap. 7
technique has proven very successful in removing
amount of debris that blows back into the joints.
foreign debris. When using the multiple pass
e. Backer or Separating Material. The backer
technique, the nozzle is directed at one of the joint
rod or separating material is installed after the
faces, and that face is sandblasted the entire length
joint is air blown. The backer materials should not
of the slab. After one face has been completed, the
be left in the joint for an extended period of time
nozzle is directed at the other joint face, and it is
before sealing. The materials may work loose and
sandblasted for the entire length of the slab. The
move up or down in the joint or may even come
pavement surface adjacent to the joint is then
completely out yielding results similar to that
sandblasted to remove all surface debris. If
shown in figure 4-13. These materials must not be
waterblasting is used instead of sand-blasting, a
twisted, stretched, or otherwise damaged when
multiple pass technique should still be employed
they are installed in the joint. Damaging the
and the joints will have to dry before the sealing
backer material can cause sealant failure or a poor
operation continues. Cleaning the joint is one of
sealing job. The backer or separating material
the most important steps in obtaining a high-
should be inspected after installation to ensure that
quality sealing project. If the joints are not clean
it has been placed at the proper depth and that it
and dry before the sealant is installed, the sealant
has not been damaged. After installation of the
will usually fail prematurely. An example of a
backer or separating material, the joint is ready
sandblasted joint is shown in figure 4-12. After
for the sealant material. However, the joint should
the joint has been sandblasted, it must be airblown
be sealed only if all steps have been performed
to remove any remaining sand or dust. However,
properly. Detailed inspection guidelines are
the final air blowing of the joint should be
presented later in this manual.
completed immediately before sealing to prevent
4-3.
Preparing Old Joints in PCC.
more sand and dust from blowing back into the
joint. A vacuum sweeper can be used to clean
a. General. Joints that have been previously
around the joints, which will help reduce the
sealed require additional work to remove the old
4-5
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