For a constant water cement ratio, decrease in aggregate cement ratio causes
Correct Answer: A. Increase in workability
📚 Detailed Explanation: Decreasing A/C Ratio Increases Workability
Why A (Increase in workability) is correct: The aggregate-to-cement ratio (A/C) is the volume of aggregate relative to cement. At constant w/c:
• Low A/C ratio = more cement per unit aggregate = more paste volume = better workability.
• High A/C ratio = less cement per unit aggregate = less paste = aggregate particles less lubricated = lower workability.
Physically: cement paste coats aggregate particles. A decreasing A/C ratio means each aggregate particle gets a thicker paste coating, reducing inter-particle friction and enabling easier flow. This is why rich mixes (low A/C) are more workable than lean mixes (high A/C) at the same w/c.
• Low A/C ratio = more cement per unit aggregate = more paste volume = better workability.
• High A/C ratio = less cement per unit aggregate = less paste = aggregate particles less lubricated = lower workability.
Physically: cement paste coats aggregate particles. A decreasing A/C ratio means each aggregate particle gets a thicker paste coating, reducing inter-particle friction and enabling easier flow. This is why rich mixes (low A/C) are more workable than lean mixes (high A/C) at the same w/c.
A/C Ratio vs. Workability
| A/C Ratio | Workability (at const. w/c) |
|---|---|
| Decreasing A/C | Increases (more paste = more lubricant) |
| Increasing A/C | Decreases (less paste per aggregate) |
- Decreasing A/C ratio at constant w/c → more paste → increased workability.
- However, rich mixes (low A/C) may be prone to shrinkage and are more expensive.