Which of the following conditions followed in making concrete reduces the workability of concrete?
- AHigher water-cement ratio in concrete
- BUse of superplasticisers
- CUse of round aggregates
- DHigher aggregate-cement ratio in concreteCorrect
Solution
Concept
A lean mix (more aggregate per unit cement) has less cement paste, so it is less workable.
Step-by-step solution
1. Check each option for its effect on workability. 2. Higher w/c ratio means more water, so workability increases. 3. Superplasticisers increase workability. 4. Round aggregates have less surface area and friction, so workability increases. 5. Higher aggregate-cement ratio means less paste to coat and lubricate the aggregates, so workability decreases. 6. Answer is (D).
Explanation
When the aggregate-cement ratio is high, the mix is lean. There is less cement paste to coat the aggregate particles and reduce friction. So the concrete becomes harsh and less workable.
Why the other options are wrong
A: More water makes concrete more workable. B: Superplasticisers are used to increase workability. C: Round aggregates give less friction and better workability than angular ones.
Shortcut
Less paste (lean mix) means less workability.
Common mistake
Thinking that more aggregate gives a stronger and easier mix. In fact, it reduces the lubricating paste.
Correct answer: D) Higher aggregate-cement ratio in concrete