Introduction:
Air-entraining agents are chemical additives used in concrete to create small, stable air bubbles in the mixture. These air bubbles improve the workability, durability, and freeze-thaw resistance of the concrete. One of the main applications of air-entraining agents is in the production of cellular concrete.

Explanation:
1. Air-tight concrete:
Air-tight concrete refers to a type of concrete that has a low permeability to air. While air-entraining agents can contribute to reducing the permeability of concrete, they are not specifically used to create air-tight concrete. The primary purpose of air-entraining agents is to improve the durability and performance of concrete in various conditions.

2. Cellular concrete:
Cellular concrete, also known as aerated concrete or foam concrete, is a lightweight concrete that contains a high volume of air voids. These air voids are created by the addition of air-entraining agents to the concrete mixture. The air-entraining agents generate small, stable bubbles that remain dispersed throughout the mixture, resulting in a cellular structure.

The production of cellular concrete involves the following steps:

1. Mixing: The air-entraining agent is added to the concrete mix during the mixing process. The agent is typically in the form of a liquid or powder and is mixed with water before being added to the concrete.

2. Foaming: The air-entraining agent creates air bubbles within the concrete mixture, which leads to a foaming effect. The bubbles are evenly distributed throughout the mixture, creating a lightweight and porous material.

3. Curing: After the concrete is poured and shaped, it undergoes a curing process to allow it to harden and gain strength. During this time, the air bubbles remain intact, resulting in the formation of a cellular structure.

Conclusion:
In conclusion, air-entraining agents are primarily used to produce cellular concrete, which is a lightweight and porous material with a high volume of air voids. These agents create small, stable air bubbles within the concrete mixture, improving its workability, durability, and freeze-thaw resistance. While air-entraining agents can contribute to reducing the permeability of concrete, they are not specifically used to create air-tight concrete.