The terms F1, F2, and F3 refer to formwork classifications based on their maximum permissible pressure resistance when containing fresh concrete. This system stems from German standards (DIN 18218) but is widely adopted globally to ensure safety and efficiency in concrete construction.
Here’s a breakdown of each type:
Key Differences: F1 vs. F2 vs. F3 Formwork
| Feature | F1 Formwork | F2 Formwork | F3 Formwork |
|---|---|---|---|
| Max Pressure | ≤ 30 kN/m² (≈ 4,350 psf) | ≤ 60 kN/m² (≈ 8,700 psf) | ≤ 100 kN/m² (≈ 14,500 psf) |
| Fresh Concrete Pressure | Low pressure | Medium pressure | High pressure |
| Pour Rate & Height | Slow pours (e.g., walls < 2m/hour) |
Moderate pours (e.g., walls 2–4m/hour) |
Fast pours (e.g., walls > 4m/hour) |
| Temperature Sensitivity | Critical (slow setting) | Moderate | Low (rapid setting) |
| Typical Use Cases | Thin walls, small columns, low-budget projects | Standard walls, beams, medium-rise columns | High-rise cores, silos, rapid-construction projects |
| Engineering Focus | Minimize pour speed | Balance speed & safety | Optimize cycle times |
Critical Factors Influencing F-Class Selection
- Pour Rate:
- Faster pouring → higher fluid pressure → requires higher F-class.
- Temperature:
- Cold weather slows concrete setting → pressure builds longer → demands higher F-class.
- Concrete Mix:
- Fluid mixes (high slump) exert more pressure than stiff mixes.
- Element Geometry:
- Tall, thin walls (e.g., elevator cores) require F2/F3; slabs may only need F1.
Practical Examples
- F1: Used for shallow foundations, slabs, or small residential walls poured slowly.
- F2: Standard for most walls/columns in commercial buildings.
- F3: Essential for high-rise tower cores, bridge piers, or industrial silos with rapid concrete placement.
Safety & Compliance
- F-class ratings prevent formwork failure (a major safety risk) by matching formwork strength to expected concrete pressure.
- Structural engineers calculate required F-class based on pour plans, ambient temperature, and concrete properties.
💡 Pro Tip: Always specify F-class requirements in construction drawings. Using underrated formwork (e.g., F1 for an F3 job) risks catastrophic collapse!
Modern modular systems (e.g., PERI, Doka) often carry F2/F3 ratings to support fast-paced projects, while traditional timber formwork may be limited to F1.
