Being a weak section in concrete, the cold joint is considered as the interruption or somewhat delay in the proper functioning of concreting.
It takes place when the first batch of poured Concrete begins to set before another batch gets poured to prevent intermixing of two batches.
However, sometimes, cold joints happen because of accidental delays and interruptions or if the work stops at the end of the day.
Besides, they may also occur due to improper consolidation. Therefore, the article brings a detailed guide on concrete cold joints discussing whether they are good or bad with their prevention, if necessary.
What Are Concrete Cold Joints?
A cold joint is a naturally occurring phenomenon because of the lack of intermixing or bonding of the two different layers of concrete with each other.
This happens when the already poured concrete has already set and hardened before another batch of concrete is laid on top of it.
It reduces the strength of the concrete as well as its energy efficiency by decreasing its performance. Cold joints increase the chances of cracks, shrinkage, and other issues in the concrete structure.
Usually, the cold joints are visible as a thin line on the concrete surface.
This can happen due to accidental interruption or delays during the construction, improper consolidation, stoppage of work at the end of the day, sudden changes in temperature and humidity level or any other unexpected events.
In What Conditions Do Cold Joints Occur In Concrete?
There are a few cases where you may find cold joints occurring in the concrete. The primary reason is when the already poured concrete starts to set before another batch of concrete is laid on top of it.
Besides, if the cement paste that binds the aggregate particles together gets dried due to high temperature, humidity, or any other environmental factors, then cold joints can also take place. This mainly happens in cases where an extended time gap exists between two successive pours.
Here are some situations where cold joint issues are most likely to happen in concrete:
- The first batch of poured Concrete begins to set.
- Any delay between the pouring of concrete layers.
- Some interruptions in the delivery of concrete or concreting tasks
- If experts try to pour concrete from a certain height and then stop, cold joints may take place.
- Sometimes, after a day, week, or month, another top layer of concrete is poured on the previously poured one.
Do These Cold Joints Give Good Results Anywhere?
Fortunately, some of these cold joints may also provide some good results:
No Gaps Left In The Concrete
We all know cold joints appear when the previously poured concreteatch started to set before another batch is laid on it. However, if the gaps are filled properly using cold joints, then no further gap can be seen in the concrete. This makes the structure more robust and dependable for any load or pressure.
No Structural Issue
Usually observed, cold joints present in concrete do not create any structural issues if the joints are in compression.
But the placement location of cold joints formation, the structural functioning of the element, and the appearance, cold joints may occur due to various reasons and improper temperature, humidity, or any other environmental factors.
It’s Not A Weak Point
Cold joints are often considered to be weak points, but most of the time, they aren’t. If concrete isn’t placed before, but the vertical bar sticks out of the concrete for attachment later on, then in reality, you can’t consider this as a weak point.
Besides, it is sometimes vital to have a good joint in place of concrete interruption. The concrete must then be cut off and then properly joined with cold joint to make the concrete solid and secure.
However, if there is no bar left out of old poured Concrete, a cold joint can become a weak point.
Are There Any Bad Effects Of Cold Joint Concrete?
Yes there are, and here are some:
Chances Of Small Void Space
Though there are no gaps left in the Concrete, there is a slight chance of having a small void space where the concrete is not compacted entirely with the concrete pouring.
Such small voids can result in cracks within a few months or in the upcoming time.
Deterioration Of The Steel Reinforcement
Cold joints present in the concrete can lead to steel reinforcement deterioration. Besides, they also decrease the durability and strength of the structure.
Apart from deterioration in the steel rebars, you may also observe weakness in the building and it will get weak with time quickly.
Affects the Aesthetic Appearance Of Concrete Surface
Known as a weak point, cold joints formed in the Concrete also affect its aesthetic appearance.
It may cause many issues with it, including water leakage. Even if it does not impact the structural elements of the structure, it affects the appearance in one way or another.
May Cause Structural Problems
If the concrete is in the compression phase, there will not be any structural issue, but if your concrete is in the phase of tension, it may result in concrete failure.
How To Prevent Cold Joints on Concrete Surfaces?
Although it has its benefits, the disadvantages usually outweigh the pros. Here are some ways on how you can prevent cold joints from occurring on concrete surfaces:
- From the corners, pour the concrete and move towards the center.
- Place the concrete in layers and around 18 inches deep. Intermix every layer with the prior one to prevent cold join in structural elements such as slab, column, and beam by using a vibrator.
- Place the concrete against the continued batch during the casting of the slab. Do not dump it in a single pile
- Keep retarding admixture with you to slow down the curing time. This is applicable if you’re pouring concrete in hot weather conditions. Although the admixture slows down the drying procedure, it is still vulnerable and time is of the essence. Try to pour and mix the second batch as quickly as possible. Otherwise, it’ll be too late to stop the cold joint even when using a vibrator.
- Lay down the concrete. It should have a rough and unfinished surface.
- Try to use your tools to roughen it so you can connect the layers perfectly.
- Pour concrete layers in stages to intermix efficiently with the previous layer by using a vibrator.
- Retarding admixtures are particularly useful for extending the time it takes to set the concrete.
- You can then create the shape of the concrete on slope operations like staircases and rafts. When doing so, start from the bottom, working your way up.
Concrete Cold Joints: Final Thoughts
Cold joint Concrete is an issue that can be prevented with the right techniques.
A little bit of extra care and awareness will go a long way in preventing this type of issue from occurring on your concrete structures.
Make sure to use the tips above when pouring concrete, and you’ll be able to drastically reduce your chances of cold joints forming.