Chapter: Concrete Structures Civel engineering engineer doubt problem guide and intrview questions and answer
What are the functions of different components of a typical expansion joint?
What are the functions of different components of a typical expansion joint?
In a typical expansion joint, it normally contains the following
components: joint sealant, joint filler, dowel bar, PVC dowel sleeve, bond
breaker tape and cradle bent.
Joint sealant: it seals the joint width and prevents water and
dirt from entering the joint and causing dowel bar corrosion and unexpected
joint stress resulting from restrained movement.
Joint filler: it is compressible so that the joint can expand
freely without constraint. Someone may doubt that even without its presence,
the joint can still expand freely. In fact, its presence is necessary because
it serves the purpose of space occupation such that even if dirt and rubbish
are intruded in the joint, there is no space left for their accommodation.
Dowel bar: This is a major component of the joint. It serves to
guide the direction of movement of concrete expansion. Therefore, incorrect direction
of placement of dowel bar will induce stresses in the joint during thermal
expansion. On the other hand, it links the two adjacent structures by
transferring loads across the joints.
PVC dowel sleeve: It serves to facilitate the movement of dowel
bar. On one side of the joint, the dowel bar is encased in concrete. On the
other side, however, the PVC dowel sleeve is bonded directly to concrete so
that movement of dowel bar can take place. One may notice that the detailing of
normal expansion joints in Highways Standard Drawing is in such a way that part
of PVC dowel sleeve is also extended to the other part of the joint where the
dowel bar is directly adhered to concrete. In this case, it appears that this
arrangement prevents the movement of joint. If this is the case, why should
designers purposely put up such arrangement? In fact, the rationale behind this
is to avoid water from getting into contact with dowel bar in case the joint
sealant fails. As PVC is a flexible material, it only minutely hinders the
movement of joint only under this design.
Bond breaker tape: As the majority of joint sealant is applied
in liquid form during construction, the bond breaker tape helps to prevent
flowing of sealant liquid inside the joint .
Cradle bar: It helps to uphold
the dowel bar in position during construction.
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