Table 1. Example sealant formulations, percentages by weight. (After Panek and Cook 1984.)
Urethane sealant: urethane polymer, 3545%; fillers, 3040%; colorants, 23%; thixotropic agents, 12%;
adhesion additives, 13%; plasticizers, 1525%; solvent, 04%
Silicone sealant, structural grade: silicone polymer, 6575%; silicone oil plasticizer, 515%; silica filler, 15
25%; curing agent, 35%; adhesive additive, 13% (lower modulus silicone sealants would have a higher
amount of silicone oil plasticizer and less cross-linking trifunctional silane complex)
Polysulfide sealant: polysulfide polymer, 3040%; various fillers, 3040%; plasticizers, 2025%; curing agents, 2
5%; adhesion additives, 13%; miscellaneous, 13%; solvent, 35%
Hot-poured rubber asphalt sealant: ground rubber (e.g., styrene-butadiene rubber ground to a 30-mesh
size), at least 25%; asphalt, remainder
Hot-poured polyvinyl chloride (PVC) and coal tar: PVC powder dispersed in a coal tar base
in which additives are blended and reacted with
sealant behavior in the context of the behavior of
the base elastomer(s) and cured to form the final
rubbers and elastomers since the material response
product, the asphalt and coal tar in such products
features of practical interest for sealing joints and
can be categorically regarded as fillers or plasti-
cracks are clearly revealed, and since the elasto-
cizers and adhesive agents, and the chemical and
meric qualities that a seal displays when subjected
physical reactions between these materials and the
to field loadings and conditions can be used to
rubber polymer can be viewed as a typical curing
judge the effectiveness of the sealant. In addition,
process that yields an elastomeric material. Indeed,
if a seal formed by an elastomeric-based sealant
it would be advantageous to consider all elasto-
does not behave elastically, e.g., if the seal deforms
meric-based sealants, including asphalt and coal
plastically or if it behaves with excessive viscous
tar rubbers, in a single context with respect to form-
behavior, the deviation from ideal elastomeric be-
ulation, so that engineers who select and use these
havior could be quantified and an assessment of
materials will have a mechanical framework that
the sealant could be made. This section describes
can be utilized to compare and contrast them.
the mechanical behavior of rubber-like materials
Different elastomers and elastomeric formula-
and low modulus sealants from a phenomenologi-
tions can attain their application configuration,
cal perspective. The section also describes the
cross-linking and mechanical properties through
hyperelastic material model, which is convention-
a variety of curing reactions and mechanisms. Seal-
ally used as a constitutive model for elastomeric
ants can be formulated to cure by chemical and
materials, and its potential application to sealants.
physical reactions and solvent release. The reac-
tions can be triggered, for example, by heat, as in
Phenomenological behavior of
the case of the hot-poured sealants, or by catalysts,
rubbers and elastomers
as in the case of moisture-induced cure of silicone
In unconfined loading configurations the de-
sealants.
formations of a rubber structure will generally be
dominated by shear distortions. This is because
the volume compressibility of elastomers and
elastomeric formulations of rubber-like materials
MECHANICAL BEHAVIOR
is, relative to the shear deformability, very low.
OF SEALANTS
Typically a rubber will have a bulk modulus that
In general, the commercially available, low
is orders of magnitude greater than its shear mod-
modulus sealants that are used for sealing joints
ulus. As a result, the material is constrained geo-
and cracks in pavements are formulated to behave
metrically by its own response to deform prima-
with rubber-like characteristics. That is, these mate-
rily by distortions. This is particularly true for the
rials are formulated so that a seal made from a low
base elastomer, and, depending upon the addi-
modulus sealant, loaded to a relatively large de-
tives, is likely to be the case for an elastomeric for-
formation, will return to its original shape and size
mulation.
upon unloading. For a description of the mechani-
The shear deformability of rubbers has been in-
cal properties of sealants it is helpful to consider
vestigated using different loading and test speci-
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