Components of a an Expansion joint

Components of a an Expansion joint

An Expansion joint has the following components:

·         Joint filler

·         Joint sealant

·         Expansion Cap/PVC dowel sleeve

·         Joint sealant

·         Bond breaker tape

·         Cradle bar

1. Joint filler: 

This material is compressible so that the joint can freely expand without any constraint. Some people are of opinion that even in absence of filler, the joint can still expand freely. But its presence is needed because it serves the purpose of space occupation such that there is no space for dirt and rubbish to accommodate.

2. Joint sealant:

 Main function of a sealant is to cover up the joint width and prevents seepage of water and dirt into the joint. Sealants also prevent corrosion of dowel bars and unexpected joint stress resulting from restrained movement.

3. Expansion Cap/ PVC dowel sleeve: 

It provides to space for the movements of the dowel bar. On one side of the joint, the dowel bar is encased in concrete & on the other side, the PVC dowel Sleeve is bonded directly to concrete so as to allow movement of dowel bar. As seen in the detailing of normal expansion joints in Highways Standard Drawing, a part of PVC dowel sleeve is also extended to the other part of the joint where the dowel bar is directly bonded to concrete. The reason 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.

4. Dowel bar: 

This is a one of the major component of the expansion joint. It guides the direction of movement of concrete expansion. If dowel bars are incorrectly placed, it will induce stresses in the joint during thermal expansion. On the other hand, it connects the two adjacent structures by transferring loads across the joints.

5. Bond breaker tape: 

The main function of the bond breaker tape is to prevent the flowing of  liquid sealant at the time of construction since the majority of joint sealant is applied in liquid form.

6. Cradle bar: 

These bars are supporting bars used to hold the dowel bar in position at the time of construction.