Question
Explain components of a typical expansion joint?
Answer
Dowel bar-This is major component of joint. It serves to guide direction of movement of concrete growth. Therefore, wrong direction of placement of dowel bar determination induces stresses in joint during thermal expansion. On other hand, it links two adjacent structures by transferring loads across joints.
PVC dowel sleeve-It serves to help movement of dowel bar. On one side of joint, dowel bar is encased in concrete. On other side, however, PVC dowel sleeve is bonded straight to concrete so movement of dowel bar can take place. One may notice that detailing of normal expansion joints in Highways Standard Drawing is in such a way that part of PVC dowel sleeve is also extended to previous part of joint where dowel bar is directly stick on to concrete. In this case, it shows that this arrangement prevents movement of joint. If this is a case, why must designers purposely put up this arrangement? In fact, rationale behind this is to avoid water from getting into contact with dowel bar in case joint sealant fails. As PVC is bendable material, it only minutely hinders movement of joint only under this design.
Bond breaker tape-As majority of joint sealant is applied in liquid form during construction, bond breaker tape assists to prevent flowing of sealant liquid inside joint.
Cradle bar- It helps to support dowel bar in location throughout construction.