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.
Different concrete construction joint types :-
1. Concrete Construction Joints
Type 1:-
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.
2. Expansion Joints
Type 2:- Joints in Construction: Expansion Joints
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.
3. Contraction Joints
Type 3:- Joints in Construction: Contraction Joints
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.
4. Isolation Joints
Type 4:- Joints in Construction: Isolation Joints
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.
5. Decorative Concrete Joints
Type 5:- Joints in Construction: Decorative Concrete Joints
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.
Why Do We Need To Place Joints in Concrete?
Need To Place Joints in Concrete
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.
