Air Entrained Concrete: What is it. When to use it. When not to use it.
When exposed to the elements, concrete will retain some moisture. When the temperatures dip below freezing that moisture will expand as it freezes. As the moisture freezes and expands it creates internal pressure on the concrete, potentially leading to cracks.
To help prevent this Air-Entrained concrete mix was created. It is sometimes referred to simply as “exterior mix”. In really simple terms an exterior mix uses an admixture during the batching process to create billions of microscopic bubbles in the concrete. When the concrete cures the bubbles harden and form tiny chambers. During the winter months when the temperature dips below freezing and moisture in the concrete freezes, these tiny pockets allow space for that freezing moisture to expand, relieving the internal pressure on the concrete and lowering the risk of cracking.
Image of Air Entrained Concrete
An air-entrained mix is best to use for concrete projects where the surface will be exposed to the freeze-thaw cycle during the winter months. Even in climates where the winters aren’t as harsh, but still reach occasional temperatures below freezing, using air-entrained concrete is a safe idea.
Air entrained mixes are not all-purpose! It is not recommended to slick-finish air-entrained concrete. A slick finish is achieved by repeatedly passing a steel trowel over the surface, like a basement slab, garage slab, or warehouse floor. Finishers can finish a surface to a mirror-like sheen. The process of slick finishing can be detrimental to air-entrained mixes for two reasons. One, repeatedly working the surface can lower the density of the air bubbles, they are physically worked out of the mix. But worse, the air bubbles can get pushed down and together, creating a void just below the surface. Over time, that void has the potential to give way to blistering or delaminating the surface.
Deciding on an air entrained or non-air concrete mix can usually be answered with two easy questions.
Is the surface of the concrete going to be exposed to the elements and getting a broom finish? If so, use an air-entrained exterior mix.
Is the surface going to be indoors and/or getting a slick finish? Use a “non-air” interior mix.
As always, we are available for ready-mix concrete deliveries in Mooresville, Statesville, Davidson, Cornelius, Huntersville, Kannapolis, China Grove, and other towns around the Lake Norman, North Carolina area. Call or text to schedule your pour, 980-281-3131
