The essence of the air entrainment process of concrete is that under the action of external forces (such as mechanical mixing or mechanical mixing), the mechanical mixing energy of bubble membrane machine is partly converted into the surface free energy of concrete. As a result of air entrainment, the free energy of rod-concrete system increases, and the air entraining concrete becomes a thermodynamic unstable system. The increase of the free energy of the system is mainly due to the increase of the surface energy of the system due to the attraction of bubbles. Therefore, the size of C is equal to the increase of the surface free energy. The change of surface free energy of air-entrained concrete can be calculated by the following formula:

The role of air entraining agent is to increase the stability of air bubbles in concrete. To achieve this day, air entraining agent is from two aspects.

① Reduce the free branding of the system and improve the stability of the air-entrained concrete system. The enrichment of air entraining agent on the gas-liquid interface reduces the surface tension of the gas-liquid surface, and further reduces the self-d3 energy U of the concrete system caused by the air entrainment process.

②Dynamic barrier of bubble coalescence in Pujia. The formation mechanism of dynamic barrier of bubble coalescence varies with the type of air entraining agent.

For ionic air entraining agent, the mechanism is mainly hidden by electrostatic repulsion. The first way is to concentrate the air entraining agent on the surface of the liquid film which forms bubbles. The polar groups of the adsorbed attractant molecules point to water and form a protective film. If the air entraining agent molecules are charged, the bubbles are charged as a result. In the process of bubble approaching each other under the action of mixing, bubbles are separated because of the influence of electrostatic repulsion. This effect is similar to that of emulsifier in maintaining the stability of the emulsion and preventing demulsification. In concrete without air entraining agent, small bubbles tend to merge into bubbles when bubbles are close to each other under the action of stirring. Then, under the dual action of buoyancy and stirring loosening, bubbles rise to the surface of concrete slurry, where bubbles break down and are consumed, and the air content of concrete slurry decreases.