Which method of transportation of concrete is useful for transporting concrete to a relatively greater distance from the batching plant?
Correct Answer: C. Transit mixer
📚 Detailed Explanation: Transit Mixer for Long-Distance Concrete Transport
Why C (Transit mixer) is correct: A transit mixer is specifically designed to transport plastic concrete over long distances (typically 5–20 km) without allowing it to set. The rotating drum continuously agitates the concrete, preventing premature hydration while maintaining workability during transport.
Concrete Transportation Methods Compared
| Method | Distance | Application | Notes |
|---|---|---|---|
| Pans / head loads | Very short (<50 m) | Small, simple works | Labour-intensive |
| Wheel barrow | Short (<100 m) | Small projects | Manual; risk of segregation on rough ground |
| Dumper / tipper | Medium (100–500 m) | Roads, dams | Fast but no agitation |
| Pump & pipeline | Up to 400 m horizontal, 80 m vertical | High-rise, tunnels | Requires slump 80–100 mm; continuous flow |
| Crane & bucket | Vertical lifts | High-rise columns, piers | Slow; good for large isolated pours |
| Transit mixer | 5–20 km on roads | RMC plants, large projects | Drum rotates at 2–6 rpm; capacity 4–7 m³ |
Transit Mixer — Key Specifications
| Parameter | Value |
|---|---|
| Drum rotation during transport (agitation) | 2–4 rpm |
| Drum rotation during mixing | 6–18 rpm |
| Typical drum capacity | 4–7 m³ |
| Maximum transport time (IS 4926) | 90 minutes after water addition |
| Maximum drum revolutions before discharge | 300 |
- Transit mixer = best for long-distance (5–20 km) concrete transport; used universally in RMC operations.
- Drum agitation at 2–4 rpm during transport prevents segregation and premature setting.
- Discharge must occur within 90 minutes of water addition per IS 4926.