According to Caltrans recommendations, air entraining admixtures are used in concrete in the climate zone _______________.

• A. Zone II
• B. Zone III
• C. Zone I
• D. Zone IV

Answer: (B)

Air-entraining admixtures create a controlled system of microscopic air voids in concrete, which provides space for water to expand when it freezes and prevents internal cracking. Caltrans uses climate zones to tailor these durability measures; in climate zone that experiences regular freeze–thaw cycles, using an air-entraining admixture is recommended to ensure the concrete can withstand those cycles. Zone III represents areas with moderate freezing exposure, so the use of an air-entraining admixture is advised there. This helps maintain durability and prevent damage in conditions where freezing and thawing occur.