What is a consequence of increasing air content in mortar concerning resistance to freeze-thaw conditions?

Increasing the air content in mortar enhances its resistance to freeze-thaw conditions. This improvement is primarily due to the introduction of microscopic air voids created by air-entraining agents in the mortar mix. These air voids provide space for water to expand when it freezes, reducing internal pressure on the mortar.

When water contained within the mortar freezes, it expands, which can create stress and lead to cracking if there is insufficient space for that expansion. By incorporating air voids, the mortar can accommodate this expansion, thus significantly lowering the likelihood of damage during freeze-thaw cycles. As a result, the overall durability and longevity of the masonry structure are improved under varying thermal conditions.

Therefore, the relationship between increased air content and enhanced freeze-thaw resistance is well established in masonry practices, supporting the choice that resistance increases with greater air content in the mortar.