Difference between Control Joint, Construction Joint and Expansion joint

You have probably heard these terms often and wonder what these really mean? Right.

Today we are going to see the difference between Control, Construction, and Expansion Joints.

We know that concrete is strong in compression and weak in tension that’s why we use reinforcement for high tensile strength. The added content of the concrete makes it incredible in strength.

However, due to the temperature and time, the material starts to deteriorate and expand timely. From cement to bars every material will be affected by the temperature and changes its volume. Any structure that comes into direct contact will affect by this.

Read also – Soundness Test of Cement

That’s the reason why we provide different types of construction joints to withstand the volume change (except control joint).

  • Contraction / Control Joint
  • Construction Joint
  • Expansion Joint

What is Contraction/Control Joints?

Once the concrete gets poured and hardened, the water in it starts to evaporate and makes the concrete to shrink and develop shrinkage cracks, especially on longer slabs. Contraction or Control joints are provided to avoid this crack from developing to the entire area.

Purpose of Control Joints

Basically, control joint is the action of making a saw cut groove and weaken the slab where we think the crack may occur due to shrinkage (Mostly at the middle of the slab). Refer the diagram.

Contraction Joint

This way the cracks developed under the slab find its way at the weak point (the point we have grooved) and avoid spreading all over the slab.

What is Construction Joints & Its Purpose?

In a day we only pour a certain amount of concrete and leave the rest to the next day even though it all act as one complete structure for load transfer. Construction joints are used to strengthen the unit and make it as one whole unit.

Construction joint

That means we purposefully make the concrete pour in certain shapes and stages like shown in below. So that the next fresh set of concrete will blend together with the older one and act as one whole unit. This is known as construction joint.

What is Expansion Joint?

Expansion Joint on the other hand, as we told earlier, the materials gets expand due to temperature. If we construct the adjacent structure without providing expansion joint then the volume change will affect the adjacent structure and gets it defigured. Makes the whole structure collapsed.

Expansion Joint

Purpose of Expansion Joints

Providing expansion joints makes room for the structure to allow to move or expand according to their properties. These gaps will be filled by some allowable materials such as bitumen or fiberboard. We can see these mainly at Bridge decks and sometimes in a long set of building units constructed very closely.

 Control Joint in Concrete  Construction Joints  Expansion Joint
Contraction Joint Control Joint Expansion Joint


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