What is flowing concrete?
Flowing concrete is ordinary fresh concrete to which a superplasticiser is added shortly before placing, making the mix temporarily much more fluid without adding extra water. This makes the concrete easier to place, pump and spread, even between dense reinforcement and in hard-to-reach corners. In Dutch it is called vloeibeton.
Why not just add water?
Making concrete more fluid by adding water raises the water-cement ratio. The result is weaker, more porous and less durable concrete with more shrinkage. A superplasticiser makes the cement particles repel each other so they slide past one another more easily. The consistency becomes softer while the amount of water stays the same.
Properties
- Good workability: the mix flows out and fills the formwork better.
- Less entrapped air: with the same compaction you get denser concrete with fewer honeycombs.
- Watertightness and homogeneity: thanks to the higher density, flowing concrete generally performs better on these points than a stiffer mix.
- Temporary effect: the superplasticiser loses its effect over time. That is why it is often added on site or shortly before placing.
Self-compacting concrete is a further development: a mix so fluid that it de-aerates without vibration and fills the formwork completely without segregating.
Applications
Flowing concrete is used for heavily reinforced structures, walls and columns, floors that need to level out quickly and places where vibrating is difficult. Consistency is checked with tests such as the flow table test or, for very fluid mixes, the slump flow test.
Tips and points of attention
- Never add water on site to make the mix “a bit softer”. It reduces strength and durability.
- Seal the formwork well: fluid concrete finds every gap. Seal joints, or the cement paste will leak away.
- Formwork pressure: fluid concrete exerts higher pressure on the formwork, especially with tall walls. Have the formwork designed for it.
- Watch for segregation: if the coarse aggregate sinks and water or cement paste collects on top, the mix is too fluid or poorly designed.
Related terms
- Fresh concrete
- Superplasticiser
- Plasticiser
- Consistency class
- Flow table test
- Slump flow
- Compaction
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