TM 5-822-11/AFP 88-6, Chap. 7
f. Some joint sealing projects may require that
manufacturers recommend a primer to be used to
a sealant be compatible with liquid oxygen (LOX),
improve the sealant's bond to concrete. If a
for example LOX storage areas. Sealants that are
primer is recommended, it should be used during
not LOX compatible could possibly create an
the acceptance testing and must be applied to the
explosion when they come in contact with LOX.
joints in the field. Full compliance with material
Some sealants are more resistant to LOX than
specification test requirements does not guarantee
others; therefore, the major command engineer
the desired sealant performance in the field. The
must be consulted to determine if a sealant is
requirements involving joint and crack preparation
acceptable before using any sealant material in a
and sealant installation play a significant role in
LOX area. In new construction projects, LOX
sealant field performance. Poor workmanship will
areas should be designed using continually
result in poor sealant field performance regardless
reinforced concrete.
of the quality of the sealant material. Laboratory
g. Fillers. Joint and crack fillers are materials
tests only indicate the expected relative behavior
that are used to fill joints and cracks, but the
of sealants that are properly installed.
material is not pliable or elastic enough to with-
c. The series of tests conducted on each type of
stand pavement movement. The most common
sealant are provided in table 2-1. ASTM tests are
included in table 2-1 for reference between federal
cements, asphalt or emulsion sand mixtures, and
specifications and the ASTM specifications. The
for large cracks, asphalt cement pavement mix-
important features of the more critical tests are
tures. Choosing which of these materials should be
listed below.
used for the crack sealing project is based upon
2-5.
Backer and Separating Material.
the expected future use of the pavement and the
size of the cracks. If the pavement is to be
a. Backer Material. The backer material, which
overlaid within 2 years, then emulsion or sand
is often termed "backer rod," provides support to
emulsion mixture could be used. If the pavement
the sealant material to prevent field-poured seal-
is not expected to be overlaid or abandoned in the
ants from sagging into joint reservoirs deeper than
near future, a high-quality sealant should be used.
the desired sealant depth. The backer material
Some crumb rubber modified asphalt formulations
provides the proper shape factor for the sealant
have worked very well as crack sealants; however,
and prevents bonding between the new sealant and
they may not meet current federal specifications.
any old sealant remaining in the lower portion of
Therefore, their use should be thoroughly investi-
the joint reservoir or between the sealant and the
gated and approval obtained before they are in-
lower portion of the joint reservoir, which is
stalled in the pavement.
known as three-sided adhesion. The backer
h. To perform properly, the sealant must prevent
material must be flexible, compressible, non-
intrusion of water and incompressibles. To accom-
shrinkable, nonreactive, and nonmoisture absorp-
plish this, the sealant must bond to the pavement,
tive
material
such
as
a
closed-cell
remain resilient, and reject incompressibles. It
polychloroprene, polyurethane, polystyrene or
should not harden, crack, split, or separate from
polyethylene rod. Paper rods, ropes, or cords and
the joint or crack faces. Tests used to evaluate
some open-cell foam rods should not be used
these properties are presented in the following
because of the amount of water they can absorb.
section. Normally fillers do not possess sealing
The absorption of the backer material should be
abilities which would allow them to fulfill these
tested if there is any doubt. The backer material
requirements.
should have a melting temperature of at least 5
degrees Fahrenheit higher than the pouring
2-4.
Sealant Properties.
temperature of the sealant. The uncompressed
backer material should be approximately 25
a. The sealant must be resistant to aging or
percent wider in diameter than the nominal width
ultraviolet deterioration, which is evident by a
of the joint to keep it in position during the
hardening of the sealant or loss of resiliency.
installation of the sealant. Different types of
Additional properties such as jet ("eat) blast resis-
backer rod materials are illustrated in figure 2-2.
tance or fuel resistance are related to specific
b. Separating Material. When the joint seal res-
conditions that the sealant will encounter.
ervoir is sawed or formed to the desired sealant
b. The properties of a sealant are indicated by
depth, a separating material should be used be-
the tests that are required for specification compli-
neath the sealant. The separating material pre-
ance. Different tests are required of different
vents field-poured sealants from bonding to the
sealant types to emphasize the particular properties
bottom of the reservoir or contacting any old
each sealant should possess. Some sealant
2-4
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