A typical expansion joint  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. Its presence does not leave any space for  entry/accomodation of dirt and rubbish.

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.