What Is Construction Joint?
The Construction Joint in concrete is used to prevent any crack during its life period. Concrete has the property of expansion and contraction due to temperature changes, which is resulting in a change in the volume of concrete.
This change in the volume of concrete can be a cause of concrete cracking. Therefore, to prevent concrete cracks construction joints are provided in concrete.
Construction joint is essential if the size or length of concrete members exceeds some specified limit.
Generally for short-length concrete member construction joints are not required, because, for expansion and contraction of concrete, there is the end of the concrete is too close.
But when the length of the concrete member has exceeded a certain limit there is no endpoint where this volume change can take place.
In such a case, the concrete member will crack.
Importance of Different Types of Construction
These different types of construction joints used for enhancing the structural integrity and structural durability.
The contraction joint is crucial to control cracking which caused by dry shrinkage of concrete and it help to prevent random cracking by creating predetermined weak points, where cracks can occur in a controlled manner.
On other side, the expansion joint is accommodating the natural contraction and natural expansion of concrete due to temperature variations and it reduce the risk of uncontrolled cracking.
The construction joint at intersection and corner provide stability and prevent structural discontinuities and each types of construction joints play a vital role in ensuring the long term performance and reliability of concrete structure, and minimizing the damage and preserving their overall strength.
Types of Construction Joints In Concrete
The following are the common concrete joint,
- Concrete Construction joints
- Expansion joints
- Contraction joints
- Isolation joints
- Decorative concrete joints
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1. Concrete Construction Joints
Construction joints are generally placed in the concrete slab to determine the extent of the individual placements. It is generally in conformity with a predetermined joint layout.
Construction joints are designed in order to allow the displacement between each (both) sides of the slab but, they also transfer the flexural stresses produced in the slab by the external loads at the same time.
Construction joints allow only horizontal displacement which is right-angled to the joint surface that is normally caused by thermal or shrinkage movement. Vertical or rotational displacement is not allowed by the joint at the same time.
2. Expansion Joints
Sometimes due to many reasons, the volume of the concrete change. For these reasons, we provide the joint to relieve stress. The building that’s length is more than 45m provided one or more expansion joints. In India, it is recommended in the building that the c/c distance is 30m.
An expansion joint means a GAP is provided between the parts of the building.
3. Contraction Joints
A contraction joint is made in the concrete slab with help of the sawed or it should be created as or groove which creates a weakened vertical plane. Cracks in the slab due to dimensional changes are resisted by the contraction joint.
Due to the unregulated cracks that can grow or the water is infiltrated in the base, sub-base, or subgrade of pavement creates other types of distress in the pavement.
It is the most common type of joint in pavements, so the term “joint” refers to a contraction joint. Contraction joints are defined by their spacing and their method of load transfer. In the slab, contraction is provided at 1/4 – 1/3 the depth of the slab or is typically spaced every 3.1 to 15m.
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4. Isolation joints
An isolation joint is used for a special purpose it completely isolates the slab from the wall or a column or drains pipes.
The walls or the columns that have their own footing or are deeper than the slab subgrade are not easily joined to move the same way as a slab it shrinks or expands due to drying or temperature changes or as the subgrade compresses a little.
If the slab is connected to these types of walls or columns or the drain pipes as they contract or settle there will be resistance but the cracks shown on the slab.
Joint material is placed next to the column or wall or drain pipes for the formation of the isolation joint. The material used for the isolation joint is generally asphalt-impregnated fibreboard or plastic, croc, rubber, or neoprene. The isolation material should go all the way through the slab from start to end but not on the top surface.
At columns, in all four directions, the contraction joint is provided with an isolation joint ending. Generally shaped in a circular or a diamond-shaped column. Until the column is not carrying its full dead load does not install the isolation material around the column.
5. Decorative Concrete Joints
The decorative concrete construction of joints requires a little more planning and execution. The decorative stamping is not sunk deep in the concrete slab because the stability of the slab is needed.
The joints are generally penetrated 1/4th of the surface. So, the cracks are carefully controlled. We just need to cut the concrete along with the pattern of the stamped design so the joints are not visible from the surface.
Conclusion
In conclusion the different types of construction joint in concrete and play a vital role in ensuring the structural longevity of concrete and integrity of concrete structure.
The expansion joints accommodate the natural movement of concrete, and minimizing the risk of cracking due to temperature variation.
The construction joint at intersection or corner provide continuity and stability ensuring a seamless and robust structure.
By considering some factors like material, maintenance practices, joint location, engineers and construction professionals and it can create strong, resilient concrete structure which can withstand the test of time.
FAQs
What is a construction joint in concrete?
A construction joint in concrete is a deliberate separation or discontinuity created between two successive concrete placements, usually in different construction stages. It allows for controlled cracking and provides a location for future connection or expansion.
Why are construction joints used in concrete construction?
Construction joints are used to divide large concrete placements into manageable sections. They help accommodate construction sequencing, facilitate formwork removal, control cracking, and allow for expansion or contraction of the concrete due to temperature changes or other factors.
How are construction joints created in concrete?
Construction joints are created by intentionally interrupting the concrete placement at a predetermined location. This interruption can be achieved by using construction joint formwork, keyways, dowels, or by cleaning and roughening the surface before placing additional concrete.
What are the common types of construction joints used in concrete construction?
The common types of construction joints include butt joints (plain joint), keyway joints (formed by removing a portion of concrete), dowel joints (using steel dowels for load transfer), and construction joints with tie bars or connectors.
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Nicely explained, for expansion and contraction joints in concrete pvc water stops are recommended, these prevent seepage across joints