chapter 3 rigid pavement - DOT On-Line Publications - Department ...

TECRWICAL PAPER 89-04 -- PREFORMED COMPRBBSIO# SEALS FOR PCC
PAVEMENT JOIRTS
Joint sealants for jointed concrete pavements are intended to
prevent, or at least deter, the intrusion of water and
incompressibles into the joint and pavement structure. Water
entering a joint can lead to pumping and faulting, while
incompressibles in a joint can cause spalling and blow-ups. A
joint sealant must be capable of remaining in firm contact with
the concrete at the faces of the joint while withstanding
repeated expansion and contraction of the pavement slabs due to
thermal variations. There are two types of joint sealants which
are currently recognized as having the potential for satisfactory
long-term performance. These are the preformed compression seals
and the low-modulus silicones. The purpose of this technical
paper is to discuss key factors in the design and installation of
the preformed compression seals.
DESIGN: Preformed compression seals should be designed so that
the sealant will be in compression at all times. These seals are
typically manufactured from a neoprene compound and factory
molded into a web design. The seal is compressed and inserted
into the pavement joint. These compressed webs exert an outward
force which keeps the seal tightly pressed against the joint
faces, thus effectively sealing the joint. As long as these
seals are in compression,
they will generally be effective. If
compression is lost, they will fail. It is essential to maintain
a good uniform seal between the joint faces and the compression
seal.
Generally, compression seals function best when compressed
between 20 percent and 50 percent of their nominal width. This
range will vary slightly with manufacturer and the seal
dimensions. Compressive forces less than 20 percent may not be
sufficient to hold the sealant in place. If the seal is exposed
to compressive forces greater than 50 percent for an extended
period of time, it may undergo a compression set. Compression
set occurs when the seal doesn't recover to its initial position.
Once it undergoes compression set, the seal will not expand as
the joint opens, resulting in a total loss of compression and
joint sealant failure.
When designing joints using compression seals, the anticipated
joint movement, the uncompressed width of the compression seal,
and the joint width must all be determined. The first step is to
determine the anticipated joint movement, using the following
equation:
where:
. A= = CL * (aAT+r)
AL is the anticipated amount of joint movement.
3.3.2