Sealants and Cold Regions Pavement Seals
A Review
STEPHEN A. KETCHAM
to the temperature reduction. A seal will also be
INTRODUCTION
subjected to shorter duration loads that may be
ASTM standard C 717 defines a seal as a bar-
critical. For example, joint movements associated
rier against the passage of liquids, solids or gases
with stickslip motions, daily temperature varia-
and defines a sealant as a material that has the
tions and traffic can induce short duration loads
adhesive and cohesive properties to form a seal
that will be superimposed on existing longer
(ASTM 1991a). For applications to buildings and
period loads. For each specific application and
pavements, a field-molded seal can be formed in
loading configuration, the cured sealant must have
a joint or a crack by the curing of a sealant that is
mechanical properties that are appropriate for
applied in liquid, viscous form. The primary me-
the structural response and climatic requirements
chanical requirements of the seal are that it re-
of the seal. In addition, these properties must not
spond elastically or viscoelastically, over a rea-
degrade significantly when the sealant is exposed
sonable design life, to any thermal- or load-in-
to weathering processes, loading cycles, chemi-
duced movement of the joint or crack without ad-
cal agents and other conditions that are present in
hesive or cohesive failure, and that it cure to a
its working environment.
sufficient hardness and remain sufficiently hard
In recent years elastomeric sealants have been
so that it will not be damaged by indentation of
introduced commercially that are formulated to
harder objects. Such a seal is not meant to transfer
have relatively low resistance to load at low tem-
significant forces of the structure across the joint.
peratures compared to conventional and tradi-
On the contrary, for large joint movements, seal-
tional seal materials. The lower resistance at lower
ants with lower load resistance are most able to
temperatures is a result of a more flexible mate-
deform without failure of the seal or of the struc-
rial formulation and of a lower temperature of the
ture to which it is bonded.
material's transition to harder behavior. This re-
Joints and cracks in building and pavement
port is concerned with the behavior of these elasto-
structures undergo movements that are dominated
meric sealants, which are often simply called "low
in amplitude by the seasonal movements caused
modulus sealants," for sealing joints and cracks
by the thermal expansion and contraction of the
in asphalt and portland cement concrete pave-
structural materials. Expansion at higher tempera-
ments in cold regions and with the specific prob-
tures and contraction at lower temperatures of the
lems and requirements that cold climates create
building or pavement materials are realized at the
for seal performance. Emphasis is placed on the
joint as closure during summer and opening dur-
material response behavior that can lead to fail-
ing winter, respectively. The result is that a seal in
ure of a seal, rather than on strength of sealants
a building or pavement joint must be able to ex-
and failure of seals. Several low modulus elasto-
tend during cold periods and compress during
meric compounds have been marketed as pave-
warm periods. Cold-period loading of a seal is
ment sealants. A significant concern for pave-
recognized as the most critical loading period be-
ment seal designers should be the transition tem-
cause of the possibility that failure stresses will be
peratures below which these sealants in pavement
reached in the seal or at the adhesive interface as
seal configurations perform inadequately because
the joint opens and the sealant hardens in response
of the stiffening of the material. In an attempt to
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