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Air entrainment is a step in the concrete mixing process that introduces very small and regularly spaced air bubbles into the mixture. This is distinct from air entrapment, when air bubbles become accidentally trapped in the concrete while it is being mixed and poured. Air entrainment is used in concrete mixing for many different settings and it enhances durability.
To trap entrained air in concrete, surfactants are added during the mixing process. Surfactants lower surface tension at the air-water barrier, allowing very small bubbles to form. As the concrete sets, the surfactant protects the bubbles, allowing them to set into the concrete. One immediate advantage of air entrainment is that it makes the concrete easier to work and reduces the amount of water needed to make the concrete workable.
In the long term, air entrainment reduces internal pressures on the concrete, allowing it to last longer. In harsh climates where freeze-thaw cycles are common, regular concrete can start to crack and split as a result of pressure. Air entrained concrete, on the other hand, will be able to resist the pressure and maintain its structural integrity. This makes it especially useful for applications like bridges and buildings, where it is critical that the concrete retain its strength and durability over time.
In addition, air entrained concrete tends to resist flaking more effectively than other types of concrete mixtures. This prevents concrete spalling, or chipping, and other problems that can develop over time as a result of environmental exposure. Aesthetically, flaking and cracked concrete is not desirable, but it can also compromise the strength of the concrete, making it a concern structurally as well. This is a special concern in corrosive settings like coastal areas where salt spray will be routinely hitting the concrete, which would cause regular concrete to be prone to flaking and cracking.
Air entrainment may be recommended for concrete used in a variety of settings. The concrete needs to be specially mixed, making it necessary to place an order for air entrained concrete ahead of time to ensure that the needed surfactants will also be added. There may be other special considerations that have to be taken into account when placing an order for a concrete pour, such as the materials used as filler, the need for dyes or stains to color the concrete, and so forth. The more advance notice a company has, the more likely it will be able to meet the needs of an order on time.
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