What are the functions of different components of a typical expansion joint? - Civil Engineer Blog

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 alsoextended 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.