Which admixture is used to improve workability of concrete?
Correct Answer: A. Plasticizers
📚 Detailed Explanation: Plasticizers as Workability Improvers
Why A (Plasticizers) is correct: Plasticizers (water-reducing admixtures) work by adsorbing onto cement particle surfaces and creating electrostatic repulsion, dispersing cement flocs and releasing entrapped water. Result: same workability with 5–15% less water, OR better workability at the same w/c. Metakaolin (B) is a pozzolanic material that can actually reduce workability. Reducers (C) is not a standard admixture category. Accelerators (D) speed up hydration — which can actually reduce workability faster.
Workability-Related Admixtures
| Admixture | Effect on Workability |
|---|---|
| Plasticiser (water reducer) | Increases workability |
| Superplasticiser (high-range water reducer) | Greatly increases workability |
| Air-entraining agent | Slightly increases workability |
| Accelerator | No improvement; may reduce |
| Retarder | Maintains workability longer |
- Plasticisers = primary admixtures for improving workability without raising w/c.
- Examples: hydroxylated carboxylic acids, lignosulphonates, modified lignosulphonates.