TM 5-822-11/AFP 88-6, Chap. 7
sealant or filler in the lower portion of the joint
or cold applied, depends in part upon the joint
reservoir. Separating materials are typically adhe-
size, shape, and cleanliness for good performance.
sive backed tapes or low strength plastic strips.
These sealants rely on a strong bond forming
The material must be low strength to deform with
between the sealant and the joint sidewalls or
the sealant as the pavement moves. These materi-
faces. As the joint opens or closes under the
als should have a melting point at least 5 degrees
effects of daily temperature changes, the sealant is
Fahrenheit higher than the pouring temperature of
stretched or compressed. An adequate bond is
the sealant and should be approximately 1/8 inch
necessary to prevent the sealant from pulling away
wider than the nominal width of the joint
from the joint face or being forced out of the joint
reservoir. The additional width will help the sepa-
during these movements. Figure 2-4 illustrates the
rating material stay in position as the sealant is
stresses a field-poured sealant undergoes as the
being installed, and will prevent the separating
joint opens and closes. A brief description of the
material from floating up into the sealant. The
stresses which develop are as follows:
separating material should be flexible and non-
(1) Adhesive stress is the bond stress between
reactive with the sealant in the same manner as the
the sealant and joint face caused by tension as the
backer material. If there is any doubt about the
joint expands. The sealant will separate from the
compatibility of the separating material or the
joint face if the bond strength is too weak or the
backer material and the sealant, a trial joint may
tensile stress created by the movement is too
be sealed during the equipment evaluation to
large.
ensure the material will perform as desired. Fig-
(2) Cohesive stress results from the tensile
ure 2-3 illustrates the function of the separating
load within the sealant material itself. The sealant
and backer materials.
will split under this stress if the sealant is not
sufficiently elastic or the interparticle bond within
2-6.
Shape Factor.
the sealant is too weak.
(3) Peeling stress results from load concentra-
a. The performance of field-poured sealants, hot
tion at the edge of the contact surface between the
2-6
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