To remove air bubbles from already laid concrete, what action is best?

• A. Vibrate
• B. Add water
• C. Add cement
• D. Let it dry

Answer: (A)

Vibrating the concrete is the most effective method for removing air bubbles after it has been laid. When concrete is poured, air can become trapped within the mixture, leading to voids that can weaken the finished product. By using a vibrator, the concrete is agitated, which allows the air bubbles to rise to the surface and escape, creating a denser and more durable slab. The vibration helps ensure better compaction of the concrete, improving its overall strength and integrity.

Adding water or cement after the concrete has been poured is not advisable, as these actions can adversely affect the mixture's water-cement ratio, potentially leading to issues such as decreased strength or increased susceptibility to cracking. Allowing the concrete to dry without addressing air bubbles will not resolve the problem, leaving the concrete with potential weak points that could affect performance. Thus, vibrating is indeed the best approach for addressing trapped air in freshly poured concrete.