What is a poker vibrator?
A poker vibrator, also called an internal vibrator, immersion vibrator or needle vibrator, is a rod-shaped tool that you push into freshly placed concrete to compact it. A rotating eccentric weight inside the head makes it vibrate rapidly. The concrete temporarily becomes more fluid, the aggregate settles more closely and trapped air bubbles rise to the surface. The result is dense, strong concrete that fully surrounds the reinforcement.
Uses
- Compacting cast-in-place footings, walls, columns, beams and slabs.
- Especially useful for deep pours and congested reinforcement where a vibrating table or screed cannot reach.
- Not needed for self-compacting concrete, which is designed to be placed without vibration.
Rules of thumb
- Insert vertically: let the poker drop quickly to depth, then withdraw it slowly while running so the hole closes behind it.
- Work in layers: push the poker through into the previous layer (about 150 mm, or 6 in, is a commonly cited figure) so the layers knit together.
- Overlap: space the insertion points so the zones of influence overlap. A common guideline is a spacing of about one and a half times the radius of influence of your vibrator.
- Know when to stop: a spot is done when air bubbles stop rising and the surface looks even and glossy.
Common mistakes
- Too little vibration: air stays trapped and you get honeycombing.
- Over-vibration: vibrating too long in one place causes segregation; coarse aggregate sinks while water and fines rise.
- Moving concrete with the poker: this also causes segregation. Place concrete as close as possible to its final position.
- Touching reinforcement or formwork: this can damage the formwork, displace bars and leave marks on the finished surface.
- Pulling out too fast: a void is left behind.
Related terms
- Honeycombing in concrete
- Segregation of concrete
- Formwork
- Fresh concrete
- Bleeding in concrete
- Soil compaction
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