What is self-compacting concrete?
Self-compacting concrete (SCC, also called self-consolidating concrete) is a fresh concrete mix that is so fluid it fills the formwork completely under its own weight, flows around the reinforcement and releases trapped air, without any vibration. The difference from ordinary concrete lies in the mix design: a modern superplasticizer (based on polycarboxylate ethers) makes the mix flow, while extra fine fillers keep it stable so the coarse aggregate does not sink.
How is it tested?
Ordinary concrete is checked with the slump test. SCC slumps far too much for that, so its consistency is measured as slump flow: the diameter of the spread after the Abrams cone is lifted. The European concrete standard EN 206 defines the classes SF1 (550-650 mm), SF2 (660-750 mm) and SF3 (760-850 mm).
| SF1 | Slump flow 550-650 mm |
|---|---|
| SF2 | Slump flow 660-750 mm |
| SF3 | Slump flow 760-850 mm |
Application
- Heavily reinforced members with tight bar spacing, where a poker vibrator cannot reach.
- Fair-faced concrete and complex shapes: corners and details fill well, with less honeycombing and fewer blowholes on the surface.
- Precast elements and ready-mixed concrete, and floors that need little finishing.
- Sites where the noise or vibration of compaction must be avoided.
Practical tips
- Formwork: SCC exerts a higher fluid pressure on the formwork than stiff concrete. Have the formwork designed for it and seal joints well, or the cement paste will leak out.
- Do not vibrate: vibration can cause segregation. Follow the supplier’s placing instructions.
- Check stability: on delivery, watch for coarse aggregate settling out or water separating on the surface (bleeding).
- Cost: the admixtures and fillers make SCC more expensive per m³, but you save on labour and compaction.
- Curing: protect it from drying out, as with any concrete.
Related terms
- Superplasticizer
- Slump flow
- Consistency class
- Fair-faced concrete
- Honeycombing in concrete
- Formwork
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