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.
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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