Air entrainment

Air Entrainment

Air entrainment refers to the intentional creation of tiny air bubbles in concrete. The process is typically achieved by adding an air-entraining admixture to the mix. The primary purpose of air entrainment is to increase the durability of the hardened concrete, especially in climates subject to freeze-thaw; the secondary purpose is to increase workability of the concrete while in a plastic state.

Process

The process of air entrainment involves the incorporation of air in the form of tiny, discrete bubbles into the concrete mix. This is typically achieved by adding an air-entraining admixture to the mix during the batching process. The admixture creates a film around the fine aggregates which traps air bubbles, allowing them to be evenly distributed throughout the concrete.

Benefits

Air entrainment provides several benefits to the concrete. The primary benefit is increased durability, especially in climates subject to freeze-thaw cycles. The entrained air bubbles act as tiny reservoirs, allowing water to expand into them when it freezes, thereby reducing the internal pressure on the concrete and preventing cracking and spalling.

In addition to increased durability, air entrainment also improves the workability of the concrete while in a plastic state. The entrained air bubbles act as a sort of ball bearing, reducing friction between the aggregates and making the mix easier to place and finish.

Limitations

While air entrainment provides several benefits, it also has some limitations. The primary limitation is that it reduces the strength of the concrete. For this reason, air entrainment is typically not used in high-strength concrete applications. Additionally, the amount of air entrainment must be carefully controlled, as too much or too little air can lead to problems.

See Also

• Concrete
• Admixture
• Freeze-thaw durability

References

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