Airentraining

Airentraining refers to the use of air-entraining agents (AEAs) in cementitious mixes to introduce and stabilize microscopic air voids in the hardened paste. These admixtures are designed to improve durability and workability, especially for concrete exposed to freezing and thawing cycles.

AEAs are surface-active compounds, often synthetic surfactants or fatty acids, that migrate to air–water interfaces in the cement paste. During mixing, they promote the formation of numerous small air bubbles and stabilize them against coalescence. The resulting micro air voids—typically tens of micrometers in diameter—provide space for ice expansion and reduce internal stresses, improving freeze–thaw resistance and finishing characteristics. They can also reduce bleeding and segregation, aiding consistency.

Applications include concrete used in cold climates, pavements, structural elements subject to freeze–thaw exposure, and decorative or self-consolidating concretes where improved finish is desired. The air void system can cause a modest reduction in early strength, so dosage is adjusted based on materials and performance requirements. Typical dosages are a few hundredths to a few tenths of a percent by mass of cement, depending on the project.

Measurement and standards: fresh concrete air content is usually measured by methods such as the pressure or volumetric air content test (for example, ASTM C231). AEAs are specified under standards like ASTM C260. Proper selection and dosing depend on cement type, aggregates, climate, and desired durability and workability, with excessive air diminishing strength or causing surface defects.