Compacting placed concrete is advisable because of:

• A. Higher cured strength
• B. Faster setting
• C. Better air entrainment
• D. Lower permeability

Answer: (A)

Compacting placed concrete densifies the mix, pushing out excess air voids and improving the contact between cement paste and aggregates. This creates a more uniform, tighter microstructure with lower capillary porosity, which translates directly into higher strength once the concrete cures. In practice, the main reason to compact is to achieve stronger hardened concrete, not to speed up setting or to alter air-entrainment behavior. While a denser matrix can also reduce permeability, compaction doesn’t speed up the chemical setting of the cement, and excessive vibration can even disrupt any designed air void system. So the primary benefit driving compaction is higher cured strength.