Study the following statements: I. For constant w/c ratio, finer sand decreases the workability. II. Creep is the deformation of concrete under sustained loading. Which is/are correct?
Correct Answer: C. Both I and II
📚 Detailed Explanation: Finer Sand, Workability, and Creep
This question tests two separate concepts: how sand fineness affects workability at constant w/c, and the definition of creep in concrete.
Why C (Both I and II) is correct:
Statement I — Finer sand decreases workability at constant w/c: Finer sand (Zone III or IV) has a much higher specific surface area than coarser sand. At a constant w/c ratio, the available water is the same. But finer sand needs more water to wet all its surfaces; with the same water amount spread over a larger surface, there is less free water to lubricate flow. Result: workability decreases despite the same w/c ratio.
Statement I — Finer sand decreases workability at constant w/c: Finer sand (Zone III or IV) has a much higher specific surface area than coarser sand. At a constant w/c ratio, the available water is the same. But finer sand needs more water to wet all its surfaces; with the same water amount spread over a larger surface, there is less free water to lubricate flow. Result: workability decreases despite the same w/c ratio.
Statement II — Creep is deformation under sustained loading: Creep is the long-term, time-dependent increase in strain (deformation) that occurs when concrete is subjected to a constant sustained stress. Unlike elastic deformation (immediate), creep develops over months to years.
Quick Reference
| Concept | Definition / Effect |
|---|---|
| Finer sand at constant w/c | Decreases workability (more surface to wet) |
| Creep | Time-dependent deformation under sustained load |
| Shrinkage | Volume change due to moisture loss (no load needed) |
Key Concepts for Students
- Finer sand + constant w/c = lower workability — to restore workability with finer sand, either raise w/c or add admixture.
- Creep = deformation under sustained load (time-dependent); elastic deformation = instantaneous recovery.
- Shrinkage and creep both contribute to long-term deflections in concrete structures — IS 456 accounts for both in serviceability checks.