The air-entraining agent can bring in a lot of evenly distributed, stable and closed tiny bubbles in the process of mortar mixing and stirring. The addition of air-entraining agent into mortar can significantly improve the workability of slurry and enhance the impermeability and frost resistance of hardened mortar. Although the dosage of air-entraining is small, it has an very great impact on the performance of mortar, with main roles including:

•  Improving the workability of mortar

After the addition of air-entraining agent, a large number of tiny closed air bubbles will be formed inside the mortar. These micro-bubbles are like roll balls to reduce the friction between aggregate particles, thus increasing the mobility of mortar mixture. Especially in manufactured sand, natural sand of coarse particles and poor gradation, or poor cement mortar, the use effects are better. Meanwhile, since the moisture is evenly distributed on the surface of the many bubbles, it can reduce the amount of free-moving water, thus reducing the water bleeding amount of mortar.

• Enhancing the impermeability, frost resistance and durability of mortar

The air-entraining agent has decreased the bleeding property of mortar mixture, so the capillary of bleeding channel has also been reduced accordingly. Meanwhile, the existence of a large number of closed tiny bubbles has blocked or cut off the capillary water seepage channel in the mortar, changed the pore structure of mortar, and improved the impermeability of mortar. The bubbles have a greater ability of elastic deformation and a certain buffering effect on the expansion stress generated by water freezing, so the frost resistance has been enhanced and so is the durability.

• Reducing the strength of mortar

Since there are a large number of bubbles, the effective force area of mortar has been reduced, reducing the strength of mortar. Generally, every 1% increase in the air content will lead to 5% decrease in the strength. For the air-entraining agent with a certain water-reducing effect, since it has reduced the water-cement ratio, the strength of mortar will get some compensation. Therefore, during the use of air-entraining agent, the dosage should be strictly controlled in order to achieve the best results.

In addition, due to the presence of a large number of bubbles, the elastic deformation of mortar will be increased and the elastic modulus will get decreased.

•  Increasing the volume of mortar

Since the air-entraining agent has brought in a large number of bubbles, the volume of mortar will increase and the density will decrease, thus saving materials and increasing the construction area.