What Causes Air Bubbles in Concrete? Explained in Detailed

Air bubbles in concrete are a very critical thing as they can reduce the strength of the concrete slab or structure. It decreases the unit weight of the concrete by increasing porosity and it causes lesser compressive strength.

That’s why it’s important to prevent air bubbles from forming in your concrete slab or structure. To prevent this particular issue, first, you will need to know how air bubbles are formed in concrete. Knowing the reasons will help you to get rid of this thing quite easily.

In today’s article, we have shared the potential reason for forming air bubbles in concrete. So, be with us and learn about how to prevent air bubbles from forming. Let’s begin then!

Reasons for Causing Air Bubbles in Concrete

There are actually two main reasons behind causing air bubbles in concrete. 

• The first one is the construction materials that are being used.
• The other one is the wrong construction way is followed during the casting of concrete.

Now, let’s learn in detail about the aforementioned reasons.

(A) Construction Materials

If you didn’t use the construction materials in a proper way then you will have air bubbles in your concrete floor, slab, or structure. Now, let’s find out how the material creates air bubbles.

1. Effect of Cement

During cement production, grinding aids are used and this is one of the reasons behind forming bubbles in concrete. Also, if the cement has a high amount of alkali content and if the fineness is too fine then air content can be increased in the cement and cause air bubbles in concrete.

2. Too Much Admixture or Release Agent Can Create Air Bubbles

Basically, the admixture is used to improve the workability of concrete. However, using excessive amounts of admixture or releasing agents in the concrete mixture can create air bubbles. When you are using more than the limit, then the releasing agent will trap the air within the concrete mixture and form air bubbles in the concrete.

3. Improper Coarse and Fine Aggregate Size

Using the proper size of coarse and fine aggregate is mandatory. Using improper or unreasonable size aggregates can cause different issues in concrete and air bubble is one of them.

If the coarse aggregate size is improper, the sand has a lot of flaky particles, and the sand ratio is lower than the recommended one then you will have air bubbles in your concrete structure. So, it’s important to use the suggested size and ratio while preparing the mixture.

(B) During Construction

If you are in or visit a construction site, then you will see that the concrete casting is done completing a lot of phases. If the work during concrete casting isn’t done properly then you will have air bubbles in your concrete

1. Using too Much Water with Cement

Using too much water with cement can increase porosity in concrete. And when the porosity is higher, there will be air bubbles.

2. Rough or Uneven Template Surface

If you are using an uneven or rough template at your concrete casting then it will cause air bubbles in the concrete.

3. Inadequate Vibration Process

The vibration process is done to compact the concrete mixture properly. If you do high or low vibration rather than the required limit then the compaction process won’t be fulfilled and there will be a void. Air will enter those voids and create air bubbles in the concrete.

Here are the reasons that cause air bubbles in concrete. You will need to look after the following things while preparing and casting the concrete. However, air bubbles are important too. It helps to improve workability and frost resistance to concrete. But there is a catch, the bubbles need to be smaller and then you can allow them in concrete.

Final Thoughts

If the construction codes aren’t followed properly then you will have issues in your structure. Having large air bubbles can reduce the compressive strength of concrete and make it weaker. That’s why, while preparing and casting concrete, it’s important to follow the codes and proper materials, and the construction technology needs to be maintained properly. 

People Also Asked – PAA

Is it normal for concrete to bubble?

Actually, yes. It is normal for concrete to bubble. During the construction process, air bubbles are formed. And if they are in large size then you will need to prevent them before drying the concrete.

Which size of Air bubbles is acceptable?

There are different air bubbles can be found in concrete. If the size of the air bubble is between 50 to 20μm or less than 20μm, they are acceptable. Moreover, air bubbles that are less than 20μm are known as beneficial bubbles.