Looking for advantages of self-compacting concrete or disadvantages of self-compacting concrete? Then you came to the right place.
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.
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.
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.
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.
- 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.
- L Box Experiment : It is the observation of concrete’s settling, filling, transition ability and resistance to segregation in an L box.
- U Box Test : It provides measurement of the setting ability of concrete.
- Fill Box Test : It involves observing the flow movement of the concrete and its ability to rise in a special transparent box.
Performance Characteristics Of Self-Compacting Concrete
The specific performance characteristics provided by self-compactability are:
- Great ease of placement that allows the concrete to reach hard-to-reach places and completely fill sections with high reinforcement density.
- Eliminates compaction means, saving the corresponding energy and avoiding the high level of noise generated by vibration.
- Improves safety and health at the construction site by avoiding, during the concrete laying process, the use of electrically conductive hoses, the generation of noise and the performance of a non-ergonomic activity such as internal vibration concrete section.
- Improves environmental conditions around the works by avoiding noise and reducing execution times.
- It is a suitable material to be placed by pumping.
- Saves the cost of compaction equipment and that corresponding to their conservation and maintenance, as well as the fixed assets in the spare parts list.
- Saves energy consumption, generally electrical, used in the concrete laying process.
- Improves the quality of finished surfaces seen, increasing their uniformity as a consequence of eliminating the heterogeneity produced by vibrating.
- Shorten lead times.
- Increase the number of layouts of the formwork in the same amount of time.
- Reduces the overall cost of the work.
- Increases the productivity of the concrete laying process.