capability of a sealant to form a seal, independent
Regarding the performance testing of model seal
of the workmanship and other conditions pecu-
structures as the conventional technique for speci-
liar to a given application of the sealant, such an
fying the behavior of the corresponding sealant
isolation of variables is required to improve the
material, Catsiff et al. (1970a) state
degree of control of the experiment. Beech stated
that the long-duration exposure and seasonal cy-
Relevance of the measurements obtained to actual
cling tests noted above (Karpati et al. 1977) are the
use is likely to require an almost intuitive appre-
ciation of past experience. Special-purpose tests may
"closest practicable approach" to in-service tests.
be devised, but the multiplicity of end-use require-
There is confusion in the sealant literature re-
ments can be expected to yield an equal multiplic-
garding the nature of tests on model seals, how-
ity of such tests. In any case, correlation of field
ever. In particular, although the block-shaped seal
failures or successes with numerous laboratory tests
specimens do not respond with a true plane-strain
and controlled field tests is bound to be a tedious
response because of their typically short length, the
and time consuming operation.
models are often assumed to represent long joint
seal structures. Additionally, research test results
Their remarks underscore the need for more engi-
of the model structure are often reported as if a
neering mechanics-based specifications of sealant
homogeneous material response rather than an in-
behavior, such that practical decisions can be made
homogeneous structural response has been mea-
competently by an engineer who does not have
sured. For example, when model seals are tested in
years of experience with special-purpose perfor-
material testing apparatuses, the nominal stress
mance tests.
and strain are often used to calculate the apparent
In addition to movement capability experi-
modulus exhibited by the structure, yet the value
ments, other load and deformation response tests
is typically reported simply as a "modulus" as if
are incorporated in standard test methods to mimic
the structural response could be considered as ho-
the load associated with indentation of hard ob-
mogeneous. Indeed, a leading textbook for seal-
jects. For example, in ASTM D 3407 (1991e), which
ants (Panek and Cook 1984) has incorrectly sug-
is a standard for testing joint sealants for concrete
gested that the modulus of elasticity of the sealant
and asphalt pavements, these tests are penetration
can be calculated from experiments on bonded
index tests of cured sealant specimens.
model seals with 1.3- 1.3-cm cross sections, with-
out alerting the reader that the result is the apparent
Response of seals to
joint movements: Results from
modulus of the structural system rather than the
analyses and experiments
material modulus. Furthermore, "creep" and
In the field of building and pavement sealants,
"stress-relaxation" tests have been conducted using
the most widely used and referenced technique
model seal specimens, without following the con-
for the analysis of the response of seals to joint
ventional approach of using a structural solution
movements is the nominal strain calculation ap-
to calculate the corresponding material response
proach of Tons (1959). Tons used observations of
(Cook 1965a, Sandberg and Rintala 1990), even
elastomer-based seals to suggest that the deformed
though creep and stress-relaxation refer to ma-
top and bottom surfaces of a long butt joint seal
terial responses and not system responses. The
are constrained to have a parabolic shape, and to
implication is that, in general, researchers in this
assume that the material of the seal is incompress-
field do not distinguish between the response of
ible. His analysis consisted of calculating an ap-
the material and the response of the structure
parent, nominal strain along "the parabolic curve-
formed from the material. Evidently this lack of
in line" so that the movement capability of seals
distinction has led to a conventional practice in
with different shape factors could be compared.
which butt joint seal structures are tested not only
He used his observations, constraint assumptions
to ascertain the behavior of a particular structure,
and calculations to suggest guidelines for shape
but also to specify the behavior of the sealant ma-
factor design, stating that "for like conditions, the
terial, and to do so without suggesting that the
greater the width of the joint, the less the sealer
behavior is the apparent material behavior for the
will be strained for the same percentage of joint
particular structure. For the practicing engineer
opening," and that "the shallower the joint is
this distinction may not be of concern, but it is
sealed, the less the sealer will be strained when
important that the researchers who establish de-
the joint opens, other conditions being the same."
sign criteria do so with a firm understanding and
Tons observed that at large deformations the de-
clear communication of such basic mechanics.
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