Air Entraining Agent

Definition

An air-entraining agent is a substance added to concrete, mortar, or cement that introduces microscopic air bubbles during the mixing process. These air bubbles improve the workability of the mixture and enhance its resistance to damage from frost and freezing temperatures.

Purpose

The primary purpose of an air-entraining agent is to improve the durability and workability of concrete, mortar, and cement. The tiny air bubbles produced by the agent help to:

• Increase the mixture’s resistance to freeze-thaw cycles, which can cause cracking and deterioration.
• Enhance the workability and plasticity of the mixture, making it easier to handle and place.
• Reduce the risk of segregation and bleeding in the mix, leading to a more uniform and stable product.

Examples of Use

1. Concrete Pavements: Air-entrained concrete is used in roadways and airport runways to withstand the stress and damage caused by freeze-thaw cycles and deicing chemicals.
2. Bridge Decks: Bridges are exposed to harsh weather conditions and heavy traffic loads; air-entrained concrete helps maintain their structural integrity over time.
3. Foundations: In regions with cold climates, using air-entraining agents in foundation concrete helps prevent frost heave and other freeze-thaw related damages.
4. Exterior Walls: Mortar containing air-entraining agents is used for bricklaying in exterior walls to improve resistance to weathering and frost.
5. Sidewalks and Driveways: Concrete for sidewalks and driveways often includes air-entraining agents to enhance durability and reduce maintenance needs.

Related Terms

1. Plasticizer: An additive used to increase the plasticity or fluidity of concrete, making it easier to work with, but without adding air bubbles.
2. Superplasticizer: A high-range water reducer that significantly increases the fluidity of the concrete, often used to create highly workable and flowable concrete mixes.
3. Freeze-Thaw Cycle: The process of water freezing and thawing within the concrete, which can cause expansion and contraction, leading to cracks and structural damage.
4. Bleeding: The process where water rises to the surface of freshly placed concrete, which can lead to weaker surfaces and other defects if not controlled.
5. Segregation: The separation of concrete components (aggregates, cement paste) during handling and placement, resulting in non-uniform and weak concrete.

Notes

• The amount of air entrained by the agent typically ranges from 4% to 8% of the concrete volume, depending on the specific application and environmental conditions.
• The introduction of air bubbles does not significantly compromise the strength of the concrete when properly proportioned.
• Air-entraining agents are available in liquid and powder forms and should be added according to manufacturer guidelines to achieve the desired results.
• Regular quality control and testing are important to ensure that the correct amount of air is entrained in the concrete mix.
• The use of air-entraining agents can also reduce the overall density of the concrete, potentially affecting other properties such as thermal conductivity and strength.