by Most of the air entraining agents are anionic surfactants.
At the water vapor interface, the hydrophobic group adsorbs directionally towards the air side.
At the cement water interface, the cement or its hydrated ions adsorb towards the hydrophilic group.
The hydrophobic group deviates from the cement and its hydrated ions, forming a hydrophobic adsorption layer and striving to approach the air surface.
Due to the proximity of these ions to the air surface and the adsorption effect of the air entraining agent molecules at the air water interface, the surface tension of water is significantly reduced, resulting in the generation of a large number of fine bubbles in the concrete during the mixing process.
These bubbles carry directional adsorption layers with the same charge, so they repel each other and can be evenly distributed; On the other hand, many anionic air entraining agents have calcium salt precipitation in cement aqueous solutions with high calcium content, which adsorbs onto the bubble membrane and can effectively prevent bubble bursting.
The small and uniform bubbles introduced can exist stably for a certain period of time.
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