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However, all good things have a downside. In the case of concrete, it’s the fact that it is not a ductile material; it cannot bend or stretch without breaking. This ability is both an upside and a downside.
But this brittle feature of concrete doesn’t prohibit it from moving at all. Concrete can shrink and expand, causing the building to move in different ways. Yet, it needs something to make these movements smoother and ensure that the concrete does not break or crack.
This is where construction joints come into the picture.
Changes in temperature cause concrete to shrink and expand, which in turn changes the volume of the material. This volume change can be a cause of cracking or breaking.
So, to avoid this, construction joints are used as a crack prevention tool. If the size and length of the concrete exceed a specified limit, using construction joints becomes vital. Usually, joints are not needed for short-length concrete members.
This is because in the expansion of short-length concrete, the endpoint is close and the probability of cracking is low. This probability increases if the concrete member crosses the specified limit.
If you’re wondering what a construction joint is used for, it is used for designing and building multiple building elements. Mostly, they are placed in concrete slabs and pavements at regular intervals to prevent cracking.
Having said that, let’s take a look at the different concrete construction joint types :
Different types of joints can be installed in construction based on the requirement of the project. You can place different construction joints in a particular concrete slab for better resistance and safety.
Here are the different concrete joint types that you can install :
Construction joints are normally installed in concrete slabs to figure out the extent of the individual placements. They are generally designed to permit displacement between both sides of the slab and also transfer flexural stresses produced by external loads in the slab.
Normally, these joints are designed in accordance with an already fixed joint layout.
In situations where the volume of the concrete changes, joints are required to relieve stress. Expansion joints are placed to create a gap between parts of a building in such cases.
A building longer than 45m is generally provided with more than one expansion joint. A c/c spacing of 30m is recommended in India.
Concrete contraction joints are sawed, formed, or tooled grooves in concrete slabs that intend to create a weakened spot, normally in a straight line. This is the most common type of joint used in pavements.
Through dimensional changes in the slab, it regularises the location of the cracks. Uncontrolled cracks can grow and cause a rough surface, water infiltration, and stress on the surface. To avoid this, contraction joints are placed in slabs.
The name itself is self-explanatory: they are used to completely isolate the concrete slab from something else. Be it a wall, a column, or a drain pipe, concrete isolation joints are useful in isolating the slab from all.
These joints are installed by placing previously decided joint material adjacent to the wall, standpipe, or column before pouring the slab.
A higher amount of planning and execution is required while installing these joints. The joints penetrate only 1/4th of the slab’s surface. The decorative stamping doesn’t go any deeper as stability of the slab is required.
All you have to do is cut along the pattern of the stamped design, so the cracking is controlled and the joints turn invisible.
The weakest area cracks the first under pressure in a situation where the concrete’s surface is on the verge of cracking. Using building joints or construction joints gets rid of the concrete’s onus of surface cracking by transferring the pressure on the joints instead.
Concrete joints enable horizontal movement while restricting vertical and rotational movements, successfully preventing the untimely failure of concrete construction.
Also Read : Types of Cracks in Concrete.
Knowing what a construction joint is as well as what types of joints there are in construction, and good planning will go a long way in ensuring cracks only happen where you want them, giving your concrete structure a long life.
It is best advised to have a structural engineer on board for designing and specifying the construction joints.