Information of Cold Joint Concrete
Concreting is a critical process which required a strict supervision during placing and compaction of the concrete so as to achieve the desired strength. The improper compaction and bonding between the concrete may leads to various defects which affects the strength and durability of the concrete structure.
Cold joint in the concrete is a defect which occurs in the concrete due to improper or delayed placing of the concrete layers.
To know the answers to all these questions read the complete article where you will get a clear idea about the cold Joint concrete and its effects on the structures how the concrete joint is repaired.
What Is Cold Joint Concrete?
Cold joint concrete is a phenomenon that occurs due to the lack of the bonding or intermixing of the two concrete layers with each other.
The cold concrete joint is a crack that is found in the hardened concrete due to improper intermixing and bonding between the two consecutive layers of the concrete.
Cold joints in the concrete are one type of damage that is developed in the concrete due to an improper concreting operation which may lead to the reduction in the strength and durability of the concrete.
The cold joint presence badly impacts the performance of the concrete. The cold joints are formed between the two layers of the concrete when the second layer is placed after the vibration limit of the first concrete. The cold joints are generally linear, closely joined, and bonded.
How Cold Joints Are Formed in Concrete?
The concreting work is a very complex and time-consuming process that requires strict supervision. The concreting is done layer by layer and the concrete layers must form a good bond with each other to achieve the desired strength of the concrete.
During the concreting work, the first batch of the concrete which is placed and compacted starts setting before the second batch has arrived on the site.
Due to the delay in the placing of the second layer of the concrete on the underlying layer cold concrete joints are formed.
Cold joints are formed because the two layers of the concrete are not get intermixed with each other due to which a concrete gets cracked.
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Effect of the Cold Joint Concrete
- The Cold joint in the concrete will cause the deterioration of the steel reinforcement in the concrete.
- The cold concrete joints reduce the strength and durability of the structure.
- The aesthetic appearance of the surface of the concrete gets affected due to the presence of the cold joint concrete.
- The cold concrete joints may cause various problems in the concrete such as reduction in the strength of concrete and water leakage.
- The cold joints in the concrete do not affect the structural ability of the structure but it affects the appearance of the building.
- The cold concrete joints are considered weak joints but the cold concrete joints are not always weak. For this, it is necessary to provide the extra length of steel reinforcement in the concrete so that another reinforcement should be attached to it to makes it structurally stable.
- If the concrete is in the compression phase, then there will not be any structural problem occurs but if the concrete is in the tension phase, then it may lead to the failure of the concrete.
How to Avoid Concrete Cold Joint?
There are various precautions that should be taken on the construction site during the concreting work to avoids the problem of cold concrete joints in the concrete which are as follows
- While placing the layer of the concrete the concrete which is placed before must have a rough unfinished surface.
- If the previous surface is hardened and not rough enough then make the surface rough with the help of tools so that there will be a good bonding between the two consecutive layers. This will avoid the formation of cold concrete joints in the concrete.
- The concreting should be done in layers and intermix each layer properly with the previous layer with the help of a vibrator.
- The pouring of the concreting should start from the end corners and then move forward towards the center.
- While executing the concreting operations at extremely high temperatures use retarding admixtures which increases the setting time of the concrete.
- The construction of the sloping elements such as rafts and stairs the concreting should be started from the bottom and then move towards the top.
These are the methods which will help to avoid concrete cold joint
Concrete Cold Joint Repair
It is very important to repair cold joint concrete and there are some remedial measures to avoid the concrete joints in concrete which we have to discuss below.
- When the Concrete Which Is Placed Is in the Plastic Stage
- When the Placed Concrete Layer Starts Hardening
- When the Cold Joint Gets Hardened
Case 1: When the Concrete Which Is Placed Is in the Plastic Stage
If the concrete first layer is in the plastic stage so that it can be removed manually and the vibrators can penetrate the surface of the concrete without applying too much effort then the second layer of the fresh concrete can be placed directly on the first layer.
In this case, the second layer of the concrete should be placed quickly and the joint between the two consecutive layers should be compacted and effectively vibrated so that they properly get intermixed with each other.
Case 2: When the Placed Concrete Layer Starts Hardening
In this stage, the concrete is starts hardening but still, it can be removed easily by applying a little bit of effort then the surface of this concrete should be raked and the loose concrete layer should be removed.
The rich mortar layer of about 12 mm thickness should be placed on the cold joint. The layer of fresh concrete should be placed on the cold joint. The concrete at the joint should be systematically vibrated with the help of a vibrator penetrating deep into the previously placed layer of the concrete.
Case 3: When the Cold Joint Gets Hardened
In this case, if the concrete placed at the joint is hardened and cannot be remoulded and mortar or slurry will not rise in spite of the vibration. This joint is left to harden for 12 to 24 hours.
The cold joints in the concrete do not create any integrity problems but it may weaken the bonding between the two layers of the concrete which may create a weak zone with the presence of the voids. This can be evaluated with the help of Non-Destructive Testing which will help to evaluate the strength and defects in the concrete.
Also, read: Procedure For Rcc Concrete