Cold joints in concrete generally refers to an area in the concrete that is weak due to a delay or interruption in the concreting process. It refers to the gap that was created between the two batches of concrete. The first batch of concrete started setting before the second batch was applied, this ultimately results in the two batches failing to mix. This is referred to as cold joint concrete. This happens due to various reasons such as accidental delays and interruptions, at the day end because of work stoppage, and also due to poor consolidation.
Cold Joint Concrete Effects
Cold Joints in concrete are types of cracks in concrete. A cold joint is bonded, closely joined, and linear. It does not create gaps but has no substantial void structure. However, a small void area is a possibility in the place where the concrete is not compacted fully. It happens in the places that lack the full concrete pour and such voids result in crack development.
A cold joint at times may be a weak point. If concrete is already placed, but the vertical bar is sticking for later attachment out of the concrete, then it is not a weak point. It is a must to have a good joint at the concrete interruption place. But it is more important to place the concrete before an unfinished order so that it bonds mechanically to the surface.
5 Tips to Avoid Cold Joint Concrete:
Avoid cold joint concrete in beam, column, and slab by laying the concrete in 18 inches layers and intermixing each layer using a vibrator with the previous one.
Pouring concrete should start from the corners and work towards the center.
For the rafts and stairs, the work should go in an uphill process.
With slab casting, the concrete should not be dumped as an individual pile. It should be placed against the earlier batch.
In hot weather, while concreting retarding admixture should be needed to decelerate the setting time. In case, the concrete is harder, remove it easily as the concrete is in a loose state, try your best not to disturb the setting process in this phase. Take care while placing concrete for the first time to place it quickly. The concrete filling must have 12mm rich mortar layer in thickness on the cold joint to be effective.
If the concrete is placed before it becomes stiff or hard to remold or does not rise with extensive vibration, the joint should be left for 12 to 24 hours to harden. This cold joint type should be used in regular construction joint.