Which of the following conditions followed in making concrete reduces the workability of concrete?
Correct Answer: B. Higher aggregate-cement ratio in concrete
📚 Detailed Explanation: Aggregate-Cement Ratio and Workability
Workability of concrete depends on the ease with which cement paste can lubricate the aggregate skeleton. A higher aggregate-cement ratio (A/C) directly reduces the volume of paste available per unit of aggregate surface area.
Why B (Higher A/C ratio) is correct: When A/C rises, there is less cement paste per unit of aggregate. The paste must cover a greater aggregate surface area — so the paste film becomes thinner, increasing friction between aggregate particles. This makes the mix harsher and less workable. Options A (superplasticisers), C (round aggregates), and D (higher w/c) all increase workability, not decrease it.
Effect on Workability
| Factor | Effect on Workability |
|---|---|
| Higher A/C ratio | Decreases (less paste to lubricate) |
| Superplasticisers | Increases |
| Round aggregates | Increases (ball-bearing effect) |
| Higher w/c ratio | Increases |
- Higher A/C = leaner mix = less paste = more friction = lower workability.
- At constant w/c, increasing A/C simultaneously reduces workability and potentially reduces strength.