What is the purpose of air entrainment in concrete?

What is the purpose of air entrainment in concrete?

• A. Introduce microscopic air bubbles into concrete, enhancing its resistance to freeze-thaw cycles, improving workability, and reducing permeability, thereby increasing overall durability and longevity.
• B. Increase density and thermal mass.
• C. Accelerate curing.
• D. Decrease porosity by making the matrix denser.

Answer: (A)

Air entrainment deliberately adds microscopic air bubbles to concrete to create a controlled air void system. These tiny bubbles give space for water to expand during freezing, relieving internal pressure and preventing cracking, which greatly improves resistance to freeze-thaw damage. The air voids also disrupt continuous capillary paths, reducing permeability and slowing moisture ingress, while they can improve workability by acting like tiny lubricants at the paste-aggregate interface. This approach does not aim to increase density or accelerate curing, and it doesn't simply make the matrix denser or less porous—rather, it creates a pore structure that enhances durability by protecting against freeze-thaw and reducing water permeability.

Air entrainment deliberately adds microscopic air bubbles to concrete to create a controlled air void system. These tiny bubbles give space for water to expand during freezing, relieving internal pressure and preventing cracking, which greatly improves resistance to freeze-thaw damage. The air voids also disrupt continuous capillary paths, reducing permeability and slowing moisture ingress, while they can improve workability by acting like tiny lubricants at the paste-aggregate interface. This approach does not aim to increase density or accelerate curing, and it doesn't simply make the matrix denser or less porous—rather, it creates a pore structure that enhances durability by protecting against freeze-thaw and reducing water permeability.