Contraction Joint In concrete
Expansion and contraction joints: These joints are provided in all the concrete structures of length exceeding 12 meters, mainly for two purposes:
1. To allow for changes in volume of concrete due to temperature, and
2. To preserve the appearance and the original shape of the concrete structures.
These joints generally consist of some elastic material, known as the joint filler and dowels or keys. The joint filler should be compressible, rigid, cellular and resillent.
In cold weather, it should not become brittle and it should be easy to handle. the usual joint filers are built-in strips of metal, bitumen-treated felt, cane fibre-board, cork bound with rubber or resin, dehydrated cork, natural cork, soft wood free knots, etc.
The dowels or keys are provided in these joints to transfer the load.
Types of Joints in Concrete | What is Construction Joints in Concrete
The contraction joints are installed to allow for shrinkage movement in the structure. It may either be a complete contraction joint or a partial contraction joint.
In former case, there is complete discontinuity of both concrete and steel. In the latter case, there is discontinuity of concrete, but the reinforcements continue across the joint.
But only complete or partial separation of the adjacent sections is made.It is also knows as dummy Joint and in this case, a groove of about 3 mm width is created in the concrete member to act as a joint.
The groove is filled with joint filler and its depth is about one-third to one- fifth of the total thickness of the member.
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