They put air into concrete?
By David Brown P.Eng,
Regina Bypass IMS Director
Concrete is the most widely used construction material worldwide. It is virtually impossible to think of any man-made infrastructure that doesn’t include some form of concrete. When one looks at a concrete bridge or a section of concrete curb, you typically think of a hard and very durable material – but can you imagine that the long term durability of this material is dependent upon something as simple as ‘air’.
The primary components of concrete include stone, sand, cement and water. When mixed together in the proper portions, hard concrete will result. Each of these four components plays a very important role in how the concrete will end up.
- Stone – typically constitutes approximately 50% of the volume of concrete. Hard stone is critical to strong concrete.
- Sand – fills in the larger voids between the pieces of stone.
- Cement and Water – when mixed together these materials start a chemical reaction that results in a paste that coats and connects all the stone and sand particles into a hardened structure. It is the glue that holds everything together.
There are many other additives that can be mixed into the concrete to adjust the material properties but the most important one is actually ‘air’. From years of study and research, it has been determined that the durability of concrete is greatly increased by including 5 to 7% air in the form of small micro-bubbles.
These micro-bubbles are spread throughout the hardened concrete and are there to allow any trapped water a place to expand when exposed to freezing temperatures. If these bubbles are not present, the forces created by the freezing and expanding water will quickly cause the concrete to break apart and crumble. If too many air bubbles are in the concrete, the strength of the concrete to handle the applied loads could be compromised.
So next time you are walking on a hard concrete sidewalk, remember that in a way, you are ‘walking on air’.