Self-compacting concrete; It is an innovative concrete that has significant fluidity and the ability to settle with its own weight, does not require vibration for compression and placement. It generally provides high strength at an early age.
Self-Compacting Concrete Casting Process
- 1 Advantages of Self-Compacting Concrete
- 2 Disadvantages of Self-Compacting Concrete
- 3 History of Self-Compacting Concrete
- 4 Why is Self-Compacting Concrete Needed?
- 5 How Self-Compacting Concrete Is Created
- 6 Mix Design of Self-Compacting Concrete
- 7 The Most Important Properties of Self-Compacting Concrete
- 8 Usage Areas of Self-Compacting Concrete
- 9 Tests Applied to Self-Compacting Concrete
Advantages of Self-Compacting Concrete
- During concrete casting, the need for vibration is minimal and thus labor and time are saved.
- Creating a smooth concrete surface facilitates the gauging process.
- It shortens the construction period, thus reducing the construction and labor costs.
- It increases the durability by creating a space-free structure between concrete and iron reinforcement.
- By preventing segregation, it provides a homogeneous concrete without air bubbles.
- The permeability of self-compacting concrete is lower than normal concrete, its insulation values are higher.
Disadvantages of Self-Compacting Concrete
- Since its production is not very common, it cannot be found everywhere.
- Its cost is higher than normal concrete today.
- Maintenance is more demanding than curing normal concrete.
- Due to its high fluidity, it may cause problems in mold workmanship due to hydrostatic pressure.
History of Self-Compacting Concrete
Before 1983, durability in concrete structures was a big problem in Japan. Concrete had to be compacted sufficiently to produce durable concrete. As there were not enough qualified personnel, the building quality decreased day by day. One of the solutions achieved to achieve a successful result without the need for a large number of qualified personnel was to use self-compacting concrete. The concrete needed in this way was created in 1986 by Okamura. Important work was done at Tokyo University by Ozawa and Maekawa to improve its workability.
Why is Self-Compacting Concrete Needed?
Lack of vibration under field conditions, poor quality workmanship, tightly reinforced and complex geometry sections, demanding sufficient fluidity and separation resistance in concrete, producing with low water / cement ratio, removing from the mold at an early age and allowing faster use of structures are the reasons to prefer self-settling concrete. It appears before us.
How Self-Compacting Concrete Is Created
- A strong super plasticizer is needed to provide fluidity in KYB.
- In order to reduce the friction effects between the aggregate grains in the concrete, the grains must be removed from each other. For this purpose, the cement paste amount can be increased. Thus, the deformation ability of concrete increases.
- The fine material amount is kept high without changing the water content. Fly ash, slag, silica fume and stone dust can be used as fine materials, but because the use of fine materials increases the cost, viscosity-regulating additives have been developed instead of reducing the fine material.
Comparison of Conventional Concrete and Self-Compacting Concrete
Mix Design of Self-Compacting Concrete
- Coarse aggregate volume should not be more than 45-50% of the total volume.
- Maximum aggregate diameter should be between 10-20mm.
- Generally, the fine aggregate volume should be between 40% and 50% of the total mortar volume.
- A polycarboxylate based chemical additive should be used.
- In order to adjust the viscosity, either a viscosity increasing chemical additive or filler type material should be used.
- The mixing water should never exceed 200 kg / m³.
Self-Compacting Concrete Various Trial Mix Designs
The Most Important Properties of Self-Compacting Concrete
- High Fluidity
- High Stability
- Low Blocking Risk
Fresh concrete must have a fluid consistency, optimum viscosity and cohesion to achieve these properties. In order to achieve these, the mixture design should be done well and suitable materials should be used in appropriate proportions.
Usage Areas of Self-Compacting Concrete
- Places where vibrator cannot be used
- Difficult and inaccessible patterns
- Aesthetic mold designs
- Strongly reinforced elements
- Strengthening projects
- Prefabricated elements, panels and floors
Tests Applied to Self-Compacting Concrete
- Spreading Test: It covers the observation of the deformation rate and the measurement of the diameter that the sample will create by spreading with its own weight.
Propagation Test Setup
- V Funnel Experiment : Gives an idea about viscosity and transition ability. A special funnel is used as an apparatus and it is measured how long the concrete will flow from the mouth of this funnel.
V Funnel Experiment Setup
- L Box Experiment : It is the observation of concrete’s settling, filling, transition ability and resistance to segregation in an L box.
L Box Experiment Setup
- U Box Test : It provides measurement of the setting ability of concrete.
U Box Assembly
- Fill Box Test : It involves observing the flow movement of the concrete and its ability to rise in a special transparent box.