What can be the result when concrete is allowed to drop freely (or drop over 5 feet) over reinforcing bar and ties?

What can be the result when concrete is allowed to drop freely (or drop over 5 feet) over reinforcing bar and ties?

• A. Nothing
• B. The aggregate can separate causing poor consolidation
• C. Reinforcing bars will move
• D. Ties will loosen

Answer: (B)

When fresh concrete is dropped from a height onto reinforcing bars and ties, the mix can separate into its components—coarse aggregate and cement paste. The heavier aggregates tend to settle out and separate from the paste, especially with a free fall of several feet, because the impact and velocity disrupt the mix and prevent proper compaction around the steel. This segregation around the reinforcement leads to poor consolidation, creating voids and honeycombing and resulting in a weaker bond between concrete and steel. So the key outcome is that the aggregate can separate, causing poor consolidation around the reinforcement. The other options aren’t typical results of a free fall onto rebar and ties, since the steel itself doesn’t move and the ties don’t loosen simply from the concrete drop.

When fresh concrete is dropped from a height onto reinforcing bars and ties, the mix can separate into its components—coarse aggregate and cement paste. The heavier aggregates tend to settle out and separate from the paste, especially with a free fall of several feet, because the impact and velocity disrupt the mix and prevent proper compaction around the steel. This segregation around the reinforcement leads to poor consolidation, creating voids and honeycombing and resulting in a weaker bond between concrete and steel.

So the key outcome is that the aggregate can separate, causing poor consolidation around the reinforcement. The other options aren’t typical results of a free fall onto rebar and ties, since the steel itself doesn’t move and the ties don’t loosen simply from the concrete drop.