Concrete is among the strongest, most durable building materials on earth. And in many cases, there is something surprising contributing to its strength and durability: Air. That’s right, concrete can be made stronger when it has air in it. Now, it has to be the right kind of air, as not all air voids are created equal. And it is something that the driver and quality control man need to learn how to control. Too much air and the concrete will not be as strong as it needs to be. Not enough of the right kind of air, and the concrete will be more easily damaged. So, let’s talk about the different types of air content in concrete and how to control it to provide the best possible results.
What are the different types of air content in concrete?
When concrete is mixed, it can sometimes generate foam. The bubbles from this foam can get trapped in the mix when it is placed. As the concrete sets up these bubbles pop, leaving behind large voids in the concrete. This is called entrapped air and it is less than ideal for the durability and strength of the concrete.
In order to better control the air content of the concrete, the concrete driver may add an air-entraining admixture. These products produce thousands of microscopic bubbles and disperse them evenly throughout the mix. This is called entrained air and has actually been proven to improve the durability of concrete.
Why is entrained air better than entrapped air?
Air voids in set concrete serve an important purpose in protecting the concrete from freeze-thaw damage. When the water in the concrete freezes, it expands. If there is no room for the water to expand, it will force the expansion and crack the concrete. This can result in spalling and scaling and ultimately lower the durability of the concrete. Air voids provide the room needed for the concrete to expand into.
The thing that makes entrained air voids better for this than entrapped air voids is the distribution of the voids. Entrapped air is very unevenly distributed. So there could be sections of the concrete that don’t have any air voids at all and some that have too many. The section that has no air voids at all will be subject to freeze damage, and the section that has too many air voids may be weaker than the rest of the concrete. Entrained air, however, creates smaller, evenly distributed air voids. So no part of the concrete has too many or too few. This allows for consistent room for water to expand as it freezes across all the concrete.
If you would like to try an air entrainer to see how it will improve the performance of your concrete, order a case or request a sample of our Air Plus or Super Air Plus online today. Don’t forget to follow our social media channels for more information about how our products can improve your concrete.