Joints in Concrete Pavements:
Concrete pavements in India are of the jointed plain (unreinforced type). The following types of joints are needed in them :
(a) Transverse Contraction Joints
(b) Longitudinal Joints
(c) Expansion Joints
Transverse contractions are provided at 3.5-5.0 m spacing for relieving the tensile stress induced when the temperature of the concrete falls below the laying temperature. The modern practice is to lay the slab continuously and cut the transverse joints to a depth of 1/3rd the slab thickness by a joint cutting saw, and allow the crack to travel downwards in due course. A dowel bar is provided to transfer the load. For low volume roads, the dowel bars are omitted and the load transfer takes place by aggregate interlock. A sketch of a contraction joint is given in Figure. The joint is sealed with a sealant.
Figure: Contraction Joint
Longitudinal joints are provided on pavements which are wider than one lane to relieve warping stresses. They are also cut by joint cutting saws. Tie rods are provided to prevent the adjoining slabs from separating. The joints also need to be sealed. A sketch of a longitudinal joint is given in Figure.
Figure: Expansion Joint
Expansion joints are provided to allow for the expansion of slabs. The current practice is to provide expansion joints only at culverts and bridges. A typical expansion joint is shown in Figure.
Figure: Longitudinal Joint with Tie Bar