What is the range of air entrainment required in concrete that is subject to thawing and freezing?

Concrete that is subjected to cycles of freezing and thawing must contain enough air entrainment to improve its resistance to these conditions. The correct range for air entrainment in this scenario is between 5% and 7%. This air content provides microscopic air bubbles within the concrete matrix, which act as shock absorbers during freeze-thaw cycles. When water in the concrete freezes, it expands; these air bubbles give the expanding water a place to go, which helps to prevent cracking and spalling.

The selection of 5% to 7% as the appropriate range reflects established guidelines and standards in the concrete industry, especially for outdoor concrete exposed to the elements. Insufficient air entrainment could lead to significant durability issues in colder climates, where freeze-thaw cycles are a common occurrence.

The other options suggest higher or lower percentages that do not align with the standards necessary for ensuring concrete durability under these specific conditions. While various factors may influence the exact air content needed, those percentages listed outside of this range are not sufficient to provide the necessary freeze-thaw protection.