Air-entraining agents are mostly anionic surfactants. On the water-vapor interface, the hydrophobic group adsorbs directionally to the air side. At the cement-water interface, cement or its hydration ions are adsorbed with hydrophilic groups. The hydrophobic group deviates from the cement and its hydration ions to form a hydrophobic adsorption layer. And try to get close to the air surface.
Due to the approach of the ions to the air surface and the adsorption of air-entraining agents molecules on the air-water interface. It will significantly reduce the surface tension of water, so that a large number of fine air bubbles will be generated during the mixing process of concrete. These bubbles carry an oriented adsorption layer of the same charge. So mutually exclusive and can be evenly distributed.
On the other hand, many anionic air-entraining agents precipitate calcium salts in cement solutions with high calcium content. Adsorbed on the bubble film, it can effectively prevent the bubble from bursting. The fine and uniform bubbles introduced can exist stably for a certain period of time.

From the above mechanism, it can be seen that the interfacial activity of the air-entraining agent is similar to that of the water reducing agent, the difference is that the interfacial activity of the water reducing agent mainly occurs at the liquid-solid interface. The interfacial activity of the air-entraining agent mainly occurs at the gas-liquid-solid interface.

It is not difficult to see that the main function of the air-entraining agent is firstly to introduce air bubbles, followed by dispersion and wetting.

When the dry powder mortar containing air-entraining agent is mixed with water. It can significantly reduce the surface tension and interfacial energy of water. It will easily produce many tiny, closed bubbles in the aqueous solution during the stirring process. Most of the bubble diameters are below 200 μm.

Air-entraining agents introduce stable micro-bubbles into the mortar through physical action. This results in a lower density of the wet mortar, better workability and increased yield of the wet mortar. The air trapped in the mortar makes the concrete more insulating, but also reduces its strength. The amount of air-entraining agent varies with the type of dry powder mortar and the type of air-entraining agent. However, the dosage of air-entraining agent is usually very low. Generally, only 0.002%~0.01% of the cement mass. Not more than 0.05% of the cement mass.
Mechanism of air-entraining agent (2)