The entrained air in concrete ………………
Correct Answer: A. Increases workability
📚 Detailed Explanation: Effect of Entrained Air on Workability
Why A (Increases workability) is correct: Air-entraining agents (e.g., vinsol resin, AEA surfactants) produce millions of tiny stable air bubbles (<0.3 mm diameter) uniformly distributed in the cement paste. These bubbles:
1. Act as microscopic ball-bearings between aggregate particles, reducing friction.
2. Increase the paste volume (each bubble displaces an equal volume of denser material).
Both effects increase workability. Note: entrained air is NOT the same as entrapped air (large, harmful voids). Each 1% of entrained air adds approximately 25 mm slump but also reduces strength by 3–5%.
1. Act as microscopic ball-bearings between aggregate particles, reducing friction.
2. Increase the paste volume (each bubble displaces an equal volume of denser material).
Both effects increase workability. Note: entrained air is NOT the same as entrapped air (large, harmful voids). Each 1% of entrained air adds approximately 25 mm slump but also reduces strength by 3–5%.
Entrained Air vs. Workability vs. Strength
| Parameter | Effect of Entrained Air |
|---|---|
| Workability | Increases (~25 mm slump per 1% air) |
| Compressive strength | Decreases (~3–5% per 1% air) |
| Freeze-thaw resistance | Greatly increases |
| Bleeding / Segregation | Decreases (more cohesive mix) |
- Entrained air increases workability but reduces strength.
- Primarily used for frost-resistant concrete (roads, bridges in cold climates), not for strength-critical applications.