TM 5-822-11/AFP 88-6, Chap. 7
sealant and the joint face. The sealant peels away
bond between the compression seal and the joint is
from the joint face leading to a loss of bond.
provided by the use of a lubricant/adhesive during
Excessive movement of the joint, horizontal or
installation of the preformed seal. The lubricant/
vertical, may produce this stress.
adhesive acts as a lubricant during installation of
(4) Tensile stress on the joint face material is
the seal and then cures to become a weak adhe-
the tensile stress between the sealant and face of
sive. The adhesive is easily damaged if the joint
the joint reservoir. When the joint faces have not
opens wider than the seal. If the joint does open
been properly cleaned or when the concrete is
wider than the seal, the compressive force will be
weak, deteriorated, or damaged during joint
lost, and the seal will either fall down into the
preparation, the sealant will pull the weaker
joint or be pulled out by traffic. It is very critical
material apart as the joint opens.
that the correct seal size be selected and that the
(5) Compressive stress is the stress occurring
seal maintains its elastic properties. The proce-
in the sealant when the joint closes. When under
dural guide for selecting the proper seal size is
excessive stress, the sealant may be pushed above
given in appendix C. Figure 2-5 illustrates the
the pavement surface and tracked onto the pave-
stresses that develop the preformed compression
ment or abraded by traffic, or enough of the
seal as the joint opens and closes. A brief descrip-
sealant may be pushed above the pavement surface
tion of the stresses are as follows:
so that the sealant is pulled completely out of the
(1) The seal remains in compression by trans-
joint reservoir.
mitting forces to the joint face through compres-
b. The preformed compression seals rely more
sion of the webs, which act similar to springs.
heavily on the joint size, shape, and condition for
This is known as the web stress of a seal.
good performance than do the field-poured seal-
Compression set is when the joint becomes too
ants. Compression seals must remain in compres-
narrow and the compression stress becomes too
sion even when the joint is open to its maximum
large causing the webs to lose their elasticity. As
width. This is necessary to maintain the contact
a result, the webs are no longer able to transmit
pressure required between the seal and the joint
the required force to the joint face as the joint
face to hold the seal in place. There is essentially
opens. When compression set occurs, the seal
no bond between the compression seal and the
either falls to the bottom of the joint or is pulled
joint faces except as provided by the friction
out when the joint reopens.
induced by compressive forces. Only a very weak
2-7
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