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Air bubbles in concrete: Why and How to deal with it?

Since the beginning of this year, people around the world have felt the pressure of rising prices. Not only the rise in oil prices but also different industries have seen soaring prices. According to the latest data, from August 2021 to the present, the inflation rate in the United States has risen for 6 consecutive months, and this data has soared from the previous 5.3% to 7.9% today. Inflation in the United States, the global Many countries have been affected.
According to experts' forecasts, the inflation rate in the United States may exceed 10% this year, which will face the danger of collapse, which has a great impact on global inflation, including concrete foaming agent.

The bubbles in concrete above 100μm are called large harmful bubbles, 100 ~ 50μm are called harmful bubbles, 50 ~ 20μm are called low harmful bubbles or harmless bubbles, and those below 20μm are called beneficial bubbles.

 

When the air content in concrete is appropriate, micro-bubbles have a certain stability in the process of concrete construction under the condition of uniform distribution and airtight independence. In terms of concrete structure theory, the voids formed by these tiny bubbles belong to the range of capillary pores or harmless pores or less harmful pores, which not only will not reduce the strength, but also greatly improve the durability of concrete.

 

Causes of bubbles:

1. Raw materials

Effect of cement on Bubble formation

When grinding aids are used in cement production, there are usually too many bubbles, and the alkali content in cement is too high, the fineness of cement is too fine, and the air content will increase. The amount of cement and water consumption is also an important cause of bubbles. In the trial blending of concrete, the amount of cement is mainly considered for the strength of concrete. if the amount of cement is increased on the premise of meeting the strength of concrete, thus the water-cement ratio is reduced, the amount of air bubbles will be greatly reduced. Its function is to use excess mortar to fill the remaining space, so as to block the bubble formation space.

 

Effect of coarse and fine aggregate on bubble formation

According to the grain gradation compaction principle, in the process of construction, the material gradation is unreasonable, the coarse aggregate is too much and the size is inappropriate, the content of needle-like particles is too much, and the actual sand rate used in the production process is smaller than that provided by the laboratory. Such fine particles are not enough to fill the coarse material voids, resulting in uncompacted particles and forming free voids, which provides conditions for the generation of air bubbles.

 

2. Construction technology

Effect of stirring time on Bubble formation

The mixing time also has different effects on the bubbles produced in the concrete. In the process of concrete mixing, if the concrete is mixed unevenly, the same water-cement ratio will make the admixture not be uniformly distributed, and there will be more air bubbles in the surplus part of the admixture, while the part that has not been mixed to the admixture will appear the phenomena of uneven slump, large slump, segregation and so on, but excessive mixing will make more and more air bubbles formed in the mixing process of concrete, thus producing negative effects.

 

Effect of release Agent on Bubble formation

The pure oil release agent will still be used by some construction units, often using the waste oil recovered from the machinery factory, which has a strong adsorption to air bubbles. Once there are air bubbles in the concrete, it will be adsorbed on the formwork and formed on the surface of the concrete structure. There is to pay attention to the selection of release agent should be combined with the type of template for adaptive selection, so that the use of combination can reduce the amount of bubbles.

 

Effect of Vibration on Bubble formation

Due to the different vibration environment in the construction, the operation of the vibrator has different effects on the number of air bubbles on the concrete surface. As a concrete structure, the better the vibration, the denser the internal structure of the concrete. from the two aspects of the height and time of the layered vibration, the higher the height of the layered vibration, the less likely the air bubbles inside the concrete will be discharged. The insertion speed of the vibrator will also affect the discharge of air bubbles, requiring "quick insertion and slow pull-out", that is, the insertion speed should be fast, so that the upper and lower concrete will be vibrated almost at the same time, and it will be slow when pulled out, otherwise the position of the vibrator is not easy to be filled and form a gap, which is not conducive to the discharge of air bubbles. However, with the emergence of overvibration, undervibration and leakage vibration, there will be more and more air bubble defects on the surface of concrete. Supervibration will cause the tiny air bubbles in the concrete to break up and recombine under the mechanical action, from small to large. Both undervibration and leakage vibration will lead to uncompacted concrete natural voids or air-type irregular bubbles.

 

How to deal with the bubbles?

1. It is suggested that priority should be given to the use of cement with few bubbles and low alkali content.

2. For aggregates, the aggregate size gradation and needle-like particle content should be strictly controlled, and the unqualified materials should be carefully screened when preparing materials. Choose reasonable aggregate gradation and sand ratio.

3. Pay attention to the mixing time, so that the admixture can be fully and evenly mixed with other raw materials.

4 It is recommended to use high quality mold release agent, and check whether the template and release agent match. The template should be kept smooth and clean, and the release agent should be applied evenly but not too much or too thick.

 

Concrete Additives Supplier

TRUNNANO is a reliable concrete additives manufacturer with over 12-year experience in nano-building energy conservation and nanotechnology development.

If you are looking for high-quality concrete additives, please feel free to contact us and send an inquiry. (sales@cabr-concrete.com)

We accept payment via Credit Card, T/T, West Union, and Paypal. TRUNNANO will ship the goods to customers overseas through FedEx, DHL, by air, or by sea.


Gas prices in European countries are expected to triple if Russian supplies are restricted, according to a press release from Rystad Energy, a Norwegian Energy consultancy.  

The price of natural gas in Europe was $1,200 per 1,000 cubic meters on Tuesday. The benchmark price is already 300 percent higher than a year ago. European gas prices are expected to continue to soar to $3,500 per 1,000 cubic meters if Russian supplies are restricted, according to Analysis by Monitor.

In 2021, Russia delivered 155 billion cubic meters of gas to Europe, accounting for 31 percent of its gas supply, according to an analysis by Monitor Advisors. It would be difficult for Europe to replace Russian gas, which would also destabilize the global LNG market and have a profound impact on Europe's population and economy.

The analysis also said that if Russia stopped supplies now, Europe's current gas reserves would be exhausted by the end of the year, setting in for a cold winter.

In addition, affected by the geopolitical factors, the supply of the concrete foaming agent is erratic and thus its prices are expected to go higher in the future.

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