For compacting plain concrete road surface of thickness less than 20 cm, which vibrator is used?
Correct Answer: B. Screed vibrator
📚 Detailed Explanation: Screed Vibrator for Road Surfaces <20 cm
Why B (Screed vibrator) is correct: A screed vibrator (surface vibrator) is a vibrating screed board moved across the top surface of freshly placed concrete. It is perfectly suited for thin, flat sections like roads, floors, canal linings, and slabs <20 cm thick because the vibration penetrates the full depth of the thin layer uniformly.
Types of Concrete Vibrators
| Type | How It Works | Best Application | Depth |
|---|---|---|---|
| Screed vibrator (surface) | Vibrating screed moved across surface | Roads, slabs, canal linings <20 cm | Up to 20 cm |
| Internal vibrator (immersion) | Probe inserted into concrete | Beams, columns, deep slabs >60 cm | Unlimited with reinsertion |
| Form vibrator (external) | Clamped to formwork; vibrates mould | Precast units, thin walls, hard-to-reach sections | Works through formwork |
| Table vibrator | Concrete mould placed on vibrating table | Laboratory cube/cylinder specimens; small precast | Small specimens |
| Vibrating roller | Rolling compaction on surface | Roller Compacted Concrete (RCC) dams, roads | Layer by layer |
Screed Vibrator Specifications
| Parameter | Value |
|---|---|
| Operating frequency | ≥4000 cycles per minute (4000 cpm) |
| Maximum effective depth | ~15–20 cm |
| Applications | Road pavements, airport runways, floors, slabs, canal linings |
- Screed vibrator = correct choice for road surface (flat, <20 cm thick).
- Internal vibrators become ineffective at such shallow depths (zone of influence too wide).
- Operates at ≥4000 cpm; moved at 0.3–0.6 m/min across the surface.