Why are air-entraining admixtures used in concrete?

• A. To create microscopic air voids that improve freeze-thaw durability and reduce scaling.
• B. To accelerate hydration.
• C. To increase slump.
• D. To decrease curing time.

Answer: (A)

Air-entraining admixtures create microscopic air voids that are evenly distributed throughout hardened concrete. These tiny voids provide space for water to expand when it freezes, relieving internal pressure and preventing cracks from forming or propagating. That relief is what gives concrete better freeze-thaw durability and reduces surface scaling when it’s exposed to freezing temperatures and de-icing salts. The main purpose isn’t to speed up hydration or to make the mix slumpier; it’s to improve durability in cold, freeze-thaw conditions by enabling the concrete to tolerate ice formation inside without cracking.