An aggregate is known as cyclopean aggregate if its size is more than ………
Correct Answer: D. 75 mm
📚 Detailed Explanation: Cyclopean Aggregate
Cyclopean aggregate (also called plum or boulder aggregate) refers to large rock fragments that are too big to be processed through standard aggregate crushing plants. They are typically placed manually into large-volume pours of mass concrete such as gravity dams and large foundations.
Why D (>75 mm) is correct: Standard coarse aggregate ranges from 4.75 mm to 80 mm. Aggregate exceeding 75–80 mm is classified as cyclopean or plum aggregate. It cannot be handled by conventional batching and mixing plants, so it is embedded by hand into the mass concrete (a practice sometimes called “plum concrete”). These large stones displace cement paste and significantly reduce the heat of hydration in massive pours.
Aggregate Size Classification
| Classification | Size Range | Application |
|---|---|---|
| Fine aggregate | 75 µm – 4.75 mm | All concrete |
| Coarse aggregate | 4.75 mm – 75 mm | Standard structural concrete |
| Cyclopean / Plum | >75 mm (up to 300+ mm) | Mass concrete (gravity dams) |
Key Concepts for Students
- Cyclopean aggregate occupies up to 30–40% of mass concrete volume, drastically reducing cement usage and cost.
- The embedded stones must be clean, non-reactive, and placed at least 150 mm from any form or reinforcement.
- Plum concrete is the mix containing cyclopean aggregate; IS 456 addresses its use in massive plain concrete structures.