Entrained Air – Chemical admixture that increases the air in the concrete.
Entrapped Air – Natural air in concrete.
What is Air Entrained Concrete?
Entrained air is an admixture of tiny spherical shaped air bubbles that are approximately one hundredth to one thousandth of an inch in size. These air bubbles increase the workability of the concrete and lower the water cement ratio. Most importantly, they create air voids that are evenly distributed throughout the concrete which are essential in colder climates due to freeze thaw cycles.
Freeze Thaw Effects on Concrete:
Concrete contains a network of capillaries. Every time water penetrates the concrete into these capillaries, it ends up freezing and expanding in size. Have you ever left a soda in the freezer? When you go to grab it the next day, the can is deformed right? The same thing happens with concrete. These extra air voids in the concrete create a cushion for the concrete through freeze thaw cycles. Entrained air is specifically designed for exterior concrete mix designs, such as, driveways, patios, or sidewalks.
What is Entrapped Air in Concrete?
There will always be air in concrete. This natural air is known as entrapped air. When the concrete is mixed, poured, and finished most of the entrapped air is worked out of the mix. The entrapped air that remains in the mix creates an air void. Most mix designs that do not have entrained air, are for interior applications that are unexposed to freeze-thaw cycles.
What Percentage of Air is in Each Mix Design?
Entrained Air: 4-8%
Entrapped Air: 1-4%