Selecting the correct poker vibrator diameter is essential to ensure proper concrete compaction, structural strength, and surface quality. This decision affects efficiency, operator fatigue, and overall project outcomes.
- Why diameter matters?
- How to match poker size to project conditions
- Influence radius and spacing
- Trade-offs between diameter, weight, and power
- Practical tables and recommendations
- Case-study style examples
Why Poker Diameter Matters
The diameter of a poker (needle vibrator) directly influences:
Diameter of Influence – The radius within which concrete is fluidized.
Depth of Vibration – How deep into the slab the vibration effectively reaches.
Operator Effort – Heavier, larger diameter pokers require more power and can lead to operator fatigue.
Work Efficiency – Larger diameter means fewer insertion points, speeding up compaction.
Commercial practice suggests that diameter of influence ≈ 10× poker diameter
Some standards note a conservative radius of 4× diameter. Typically, spacing is chosen between 1.0 to 1.5× radius
Popular Diameter Sizes & Typical Uses
Various diameters are commonly available: 25 mm, 35 mm, 40 mm, 60 mm, 75 mm, 90 mm .
- 25–35 mm: Roof slabs, thin walls, small patches—tight spaces, light reinforcement.
- 35–40 mm: General slab work, medium beams, light columns.
- 40–60 mm: Standard beams, slabs, moderate reinforcement areas.
- 60–90 mm: Large footings, mass pours, heavy beams or pile caps.
Common Available Diameters & Specs
Manufacturers usually offer poker heads from 25 mm up to 60–75 mm. Here’s a summary of typical options and product data for reference:
| Diameter (mm) | Typical Frequency (vpm) | Amplitude (mm) | Centrifugal Force (N) | Application Notes |
| 25 | ~12,000–13,000 | 0.65 | ~800 N | Thin formwork, dense rebar zones |
| 35 | ~12,000 | ~0.8 | ~1,500 N | Medium slump mixes, small slabs |
| 38–45 | ~10,000–12,000 | ~1.0–1.3 | ~3,000–5,600 N | General concrete pours in foundations, columns |
| 50–60 | ~10,000–12,000+ | ~1.6 | ~5,600–7,000 N | Heavy pours, large section, high slump mixes |
| 75 (pneumatic) | ~16,000 | – | high | Pneumatic, easier to handle vs. heavy electric head |
Influence Radius & Spacing Guidance
Concrete around the vibrator head is fluidized within a zone called the influence diameter:
- Standard rule: influence ≈ 10× head diameter
- Conservative: influence ≈ 4× diameter in some guidelines
To ensure complete coverage, insertions should overlap so spacing ≈ 1.0–1.5× radius:
For example:
A 50 mm head → radius ~250 mm → spacing ~250–375 mm per insertion.
Matching Poker Diameter to Project Conditions
Rebar density & formwork width
Dense rebar or narrow sections → use 25–35 mm diameter to navigate between bars.
Wide forms (≥ 500 mm) and lighter reinforcement → 50–60 mm.
Concrete workability (slump) & aggregate size
Stiff mixes / large aggregate: avoid small heads like 25 mm—they’ll clog. Use at least 35 mm or larger
High-slump, flowable mixes: larger heads (50 mm+) perform well.
Layer depth & thickness
Recommended layer depth ≤ length of head, or ≤ 1.5× for eccentric-electric types
For depths > 300–500 mm, pour in layers with overlapping vibration to ensure full consolidation
Operator fatigue & power source
Larger heads weigh more and demand more power. For sustained work choose pneumatic for ≥ 60 mm, or engine-driven 50 mm systems with harness support.
Electric high-frequency systems may be heavy in larger diameters—consider operator endurance.
Recommended Poker Diameter by Scenario
| Project Type / Conditions | Typical Concrete Slump/MM | Rebar Density | Thickness (mm) | Recommended Poker Diameter |
| Thin wall / precast moulds | Low (50–75) | High | <300 | 25 mm |
| Dense rebar columns or walls | Medium (75–100) | Very high | 300–500 | 25–35 mm |
| Small footings, decks, slabs | Medium (75–125) | Moderate | 350–500 | 35–38 mm |
| Large slab, foundation, mass concrete pours | Medium-high (100–150) | Low to medium | 400–600 | 45–50 mm |
| High-slump mixes, coarse aggregate heavy pours | High (>150) | Low | >500 (layered) | 50–60 mm |
| Large structural pours, wide forms, spaced reinforcement | Varies | Low | >500 (layered) | 60–75 mm (pneumatic) |
Practical Example: Footing vs Column vs Slab
Example A: Column with dense rebar
- Dimensions: 400 mm width
- Concrete: stiff mix, low slump (˜75 mm), small 20–25 mm aggregate
- Choice: 25 mm poker head allows insertion between bars, avoids flashing and blockage. Insert every ~200 mm, hold 10–15 s.
Example B: Medium slab / footing
- Slab: 500 mm thickness, moderate slump (~100 mm), medium aggregate
- Choice: 38 mm poker head. Influence radius ~380 mm; spacing ~350 mm. Depth ok if head length ~400 mm.
Example C: Highway slab
- Pour: 600 mm deep, high-slump concrete (>150 mm), coarse aggregate
- Choice: 50 or 60 mm hole head gives ~500–600 mm influence radius. Use engine driven or pneumatic unit. Insert in grid with 400–600 mm spacing.
Trade-Offs: Diameter vs Power, Weight, Speed
Larger diameter = fewer insertions → faster job completion.
But greater weight may lead to operator fatigue and slower rhythm; more power is needed.
Small diameter = lighter, easier to handle, better for tight spots—but more dips and slower progress.
From Vibrotechnniques guidance: “A bigger diameter head means more concrete fluidized per dip… but if operator is slowed by extra weight, productivity suffers. In some cases, a smaller head gives higher quality production.”
Operational Best Practices With Chosen Diameter
Once diameter is selected, proper technique ensures consistent results:
Insert vertically, not side to side, to allow air to escape and avoid damage to formwork or rebar.
Hold for 5–20 seconds, enough that bubbles stop, surface sheen appears. Lift slowly (~2.5–7.5 cm/s).
Spacing equal to ≤1.5× radius to maintain overlapping zones.
Use grid (square or offset) patterns for coverage consistency.
Avoid over vibration—it causes segregation, heavy aggregate sinking, water rise. Withdraw too fast leaves voids. Proper overlap or reinsertion solves holes.
Maintenance & Reliability Considerations
Larger diameter pokers generate higher centrifugal force and require more torque. Choose trusted brands and robust designs.
Pneumatic pokers (e.g. 75 mm diameter) can be easier on the operator than heavy electric heads.
Regular inspection: check shaft, needle, coupling; clean after every use.
Backup units are wise—equipment failure during concrete placement is costly.
Practical Recommendations
- Identify your project conditions: slab thickness, slump, aggregate size, rebar density, layer depth.
- Estimate appropriate diameter via table above.
- Confirm influence radius (~10× diameter) and set spacing accordingly.
- Balance operator load with productivity — avoid oversized heads that slow pacing.
- Apply standard technique: vertical insert, time holding, slow withdrawal, controlled spacing.
- Maintain and test equipment, have backups.
Choosing the right poker vibrator diameter is a strategic decision combining engineering judgment, practical jobsite conditions, and operator capability. Too small a head leads to slow compaction; too large increases fatigue, cost, and potential damage.
The diameter range from 25 mm to 75 mm accommodates nearly all field requirements—each has its optimal scenario. By matching poker diameter to mix slump, thickness, rebar configuration, and operator resources, you can maximize compaction quality and operational efficiency.
