Mechanism of air-entraining agent (1)
There are many factors that affect the air content of mortar. Including the characteristics and dosage of cement and admixture, water-cement ratio (water-binder ratio), type and dosage of air-entraining agent, quality and particle distribution of aggregate, type and capacity of mortar mixer, mixing temperature, mixture Consistency, temperature, etc. Although the amount of air-entraining agent is very small, the air-entraining agent has a great influence on the performance of dry powder mortar.
Its main functions are:

1.Improve the workability of dry powder mortar.

The incorporation of air-entraining agent will form a large number of tiny, closed air cells in the concrete mixture. These microbubbles are like rolling balls. Reduce frictional resistance between aggregate particles. Increase the fluidity of the concrete mixture. If the liquidity remains unchanged. You can reduce water consumption. At the same time, because the moisture is evenly distributed on the surface of a large number of air bubbles. This reduces the amount of water that can move freely. Bleeding of the wet mortar is thus reduced. The water retention and cohesiveness will increase accordingly.

2.Reduce the strength of dry powder mortar.

Due to the presence of a large number of air bubbles. The stress area of the mortar is reduced. reduce the strength of concrete. However, the air-entraining agent has a certain water-reducing effect (especially like the air-entraining water-reducing agent, the water-reducing effect is more significant). The reduction of the water-cement ratio compensates the strength to a certain extent.

However, the addition of air-entraining agent will still reduce the strength of mortar. Especially compressive strength. Therefore, the dosage of air-entraining agent should be strictly controlled. The optimum dosage can be determined by testing the air content, construction performance and relative strength of the mortar.
In addition, due to the presence of a large number of air bubbles. Increase the elastic deformation of mortar. The modulus of elasticity is reduced. This is beneficial to improve the crack resistance of mortar.

3.Improve the impermeability and frost resistance of mortar.

The air-entraining agent reduces the bleeding of the concrete mixture (generally, the amount of bleeding can be reduced by 30% to 40%). Therefore, the capillary of the bleeding channel is correspondingly reduced. At the same time, a large number of closed microbubbles exist. Block or cut off the capillary seepage channel in the mortar. The pore structure of the mortar is changed. Improve the impermeability of mortar.
Bubbles have greater elastic deformation capacity. It has a certain buffering effect on the expansion stress generated by the freezing of water. Therefore, the frost resistance of the mortar is improved, and the durability is also improved. In addition, the addition of air-entraining agent will reduce the density of mortar. Save material. Increase the construction area.

It can be seen that the technical benefits brought by the incorporation of air-entraining agent can be summarized as follows:

(1) The dispersing, lubricating and water-reducing effects of the air-entraining agent significantly improve the workability and workability of concrete.
(2) The ball and lubrication effect of air-entraining agent bubbles improves the pumpability of concrete.
(3) Due to the surface adsorption of the air-entraining agent. Increased viscosity of cement paste. Can significantly reduce concrete bleeding and settlement shrinkage.
(4) The capillary porosity of concrete mixed with air-entraining agent is also significantly reduced due to the reduction of water demand. The capillary channels in the concrete are cut off by tiny air bubbles, and the impermeability of the concrete is improved.
(5) An appropriate amount of air bubbles can buffer the expansion stress caused by freezing and thawing in the concrete. The freeze-thaw resistance of concrete can be improved several times.
(6) The corrosion resistance of concrete largely depends on its own permeability and compactness. Therefore, the corrosion resistance of concrete mixed with air-entraining agent is also significantly improved.