For given water content, workability decreases if the concrete aggregates contain an excess of
Correct Answer: D. All options are correct
📚 Detailed Explanation: Particle Shape and Workability
Why D (All options correct) is correct:
All three particle shapes cause increased internal friction and resistance to flow:
Thin particles: High specific surface area → absorb more water → less free water → lower workability.
Flat particles (flaky): Plate-like shape creates high inter-particle contact area and interlocking. Flakiness index >35% is rejected per IS 383.
Elongated particles: Long needle-like shapes bridge across narrow sections, resist flow, and can snap under stress. Elongation index >45% rejected per IS 383.
All three are “undesirable” aggregate shapes that reduce workability by increasing friction and blocking flow.
All three particle shapes cause increased internal friction and resistance to flow:
Thin particles: High specific surface area → absorb more water → less free water → lower workability.
Flat particles (flaky): Plate-like shape creates high inter-particle contact area and interlocking. Flakiness index >35% is rejected per IS 383.
Elongated particles: Long needle-like shapes bridge across narrow sections, resist flow, and can snap under stress. Elongation index >45% rejected per IS 383.
All three are “undesirable” aggregate shapes that reduce workability by increasing friction and blocking flow.
Undesirable Particle Shapes
| Shape | Problem | IS 383 Limit |
|---|---|---|
| Flaky (flat) | High contact area, interlocking | Flakiness index <35% |
| Elongated (thin, needle) | Bridging, resistance to flow | Elongation index <45% |
| Angular | Surface friction | Use crushed carefully |
- Thin, flat, and elongated particles all reduce workability — all options are correct.
- Cubical/equidimensional aggregates are ideal: maximum volume per unit surface area = least water demand.