What is the Function of Air-entraining Agent in Mortar?

The air-entraining agent can bring a large number of uniformly distributed, stable and closed micro-bubbles during the mixing process of the mortar. Adding an air-entraining agent to the mortar can significantly improve the workability of the slurry, and enhance the impermeability and frost resistance of the hardened mortar. Although the amount of air-entraining agent is small, it has a great influence on the performance of mortar. The main functions are:

Improve the Workability of Mortar

After adding the air-entraining agent, a large number of tiny closed air cells will be formed inside the mortar. These micro-bubbles act like rolling balls to reduce the friction between aggregate particles, thereby increasing the fluidity of the mortar mixture. Especially in machine-made sand, coarse grain, poorly graded natural sand, or poor quality cement mortar, the effect is better. At the same time, since the water is evenly distributed on the surface of many air cells, the amount of free flowing water can be reduced, thereby reducing the amount of bleeding of the mortar.

Enhance the Impermeability, Frost Resistance and Durability of Mortar

The air-entraining agent reduces the bleeding performance of the mortar mixture, so the capillary of the bleeding channel is correspondingly reduced. At the same time, the existence of a large number of closed micro-bubbles blocks or cuts off the capillary seepage channels in the mortar, changes the pore structure of the mortar, and improves the impermeability of the mortar. The air bubbles have a large elastic deformation capacity, and have a certain buffering effect on the expansion stress caused by the freezing of water, which enhances the frost resistance and improves the durability.

Reduce the Strength of the Mortar

Due to the existence of a large number of air bubbles, the effective bearing area of the mortar is reduced, and the strength of the mortar is reduced. Generally, for every 1% increase in air content, the strength will decrease by 5%. The air-entraining agent with a certain water-reducing effect will compensate the strength of the mortar due to the reduction of the water-cement ratio. Therefore, during the use of air-entraining agent, the dosage should be strictly controlled to achieve the best effect.

In addition, due to the existence of a large number of air bubbles, the elastic deformation of the mortar increases and the elastic modulus decreases.

Increase Mortar Volume

Because the air-entraining agent brings in a large number of air bubbles, the volume of the mortar increases and the density decreases, thereby saving materials and increasing the construction area.