Match List-I (Aggregate) with List-II (Effect) and select the correct answer using the codes given below the lists.
| List-I | List-II |
|---|---|
| a.Rounded aggregates | 1.Reduce workability appreciably because of a high ratio of surface area to volume |
| b.Crushed aggregates | 2.Require more water than rounded aggregates and give strength lesser than crushed aggregates |
| c.Flaky aggregates | 3.Give concrete of higher compressive strength due to development of stronger aggregate-mortar bond |
| d.Irregular aggregates | 4.Require lesser amount of water and cement paste for a given workability |
Codes:
- Aa – 1, b – 2, c – 4, d – 3
- Ba – 1, b – 3, c – 4, d – 2
- Ca – 4, b – 3, c – 1, d – 2Correct
- Da – 4, b – 2, c – 1, d – 3
Solution
Concept
Effect of Aggregate Shape on Concrete Properties
Formula
No
Step-by-step solution
- Rounded aggregates (a): Minimum surface area requires less water for workability (4) - Crushed aggregates (b): Angular shape provides a stronger bond and higher compressive strength (3) - Flaky aggregates (c): High surface area significantly reduces workability (1) - Irregular aggregates (d): Requires more water than rounded and yields lower strength than crushed (2) - Combine matches to get a–4, b–3, c–1, d–2 (Option C)
Explanation
Option C is correct because each aggregate shape affects concrete properties as follows: - Rounded aggregates (a–4): Have minimum surface area and smooth surfaces, requiring less water and cement paste to achieve workability. - Crushed aggregates (b–3): Have sharp, angular edges that create a stronger bond with the mortar, increasing compressive strength. - Flaky aggregates (c–1): Have a high surface-area-to-volume ratio, which greatly reduces workability. - Irregular aggregates (d–2): Require more water than smooth rounded aggregates and offer less strength than fully angular crushed aggregates.
Shortcut
Remember the key keywords for each aggregate shape: - Rounded = Least water needed (a - 4) - Crushed = Highest strength/bond (b - 3) - Flaky = Reduced workability (c - 1) - Irregular = Intermediate performance (d - 2)Shortcut rule: Matching just "Rounded -> Least Water (4)" or "Crushed -> Best Strength (3)" immediately isolates the correct code option (a-4, b-3, c-1, d-2).
Common mistake
Students often confuse rounded aggregates with flaky or irregular aggregates, leading them to incorrectly match rounded aggregates with high surface area or poor workability (item 1) instead of low water demand (item 4). Another common error is confusing the workability reduction of flaky aggregates with that of irregular aggregates.
Correct answer: C) a – 4, b – 3, c – 1, d – 2