Self-Compacting concrete

Self-compacting concrete is a type of concrete in construction that uniformly and completely fills every corner with the formwork by its own weight, without the need for any vibration application and without segregation, all while maintaining homogeneity.

Exploring the History of Self compacting concrete

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In the year 1983, during construction projects in Japan, issues arose regarding premature deterioration and incomplete compaction or vibration of the concrete. Additionally, there was a shortage of skilled construction labour in Japan at that time. This challenge led to the development of a new technology to address these issues.

In 1986, as previously mentioned in the table above, Prof. Hajime Okamura at the University of Tokyo introduced the concept of self-compacting concrete (SCC). Utilizing self-compacting concrete made it easier to place in congested areas and access difficult locations. After two years of research, they launched the prototype in 1988. However, the prototype showed signs of segregation in the concrete. But it can be placed without vibration and it was a fully compacted concrete. Following this, in 1989, self-compacting concrete (SCC) was made available for experimentation. The University of Tokyo collaborated with various companies and organizations to achieve success in the research.

Finally, in 1993, the concept of self-compacting concrete was accepted, and the focus shifted towards high-performance concrete.

The development of SCC quickly spread to other countries, and it is now used in construction projects all over the world. SCC is particularly popular in Japan, Europe, and North America.

One of the most notable examples of Self compacting concrete (SCC) use is the Burj Khalifa in Dubai, which is the tallest building in the world. The Burj Khalifa was constructed using Self compacting concrete (SCC) because it was the only way to place concrete in the building’s complex and congested formwork. Below are some common examples of self compacting concrete structures.

Indian History and structure of self compacting concrete

In India, self-compacting concrete has been utilized in various construction projects. For instance, it was employed in about 5000 cubic meters in the Kaiga Nuclear Power Project in Karnataka. Additionally, it was also used in the Kota Atomic Power Project in Rajasthan.

Here are some other examples of self-compacting concrete.

Important Definitions

Segregation: Segregation occurs due to:

a. Separation of Coarse Aggregates from Fine Aggregates: When coarse aggregates separate from fine aggregates within the mix, causing an uneven distribution.

b. Paste Separation from Coarse Aggregate or Water: Separation of paste from coarse aggregate or water, resulting in non-uniform distribution of ingredients in fresh concrete.

Bleeding:  

The flow of mixing water within and its emergence on the surface of freshly placed concrete is usually due to excessive vibration aimed at achieving full compaction.

Bleeding can be reduced through the use of uniformly graded aggregates, pozzolans (to break the continuous water channel), or by incorporating entraining agents, finer cement, and a rich mix.

Applications of Self compacting concrete

Self-compacting concrete can be utilized in precast concrete applications or for concrete placed on-site. It can be manufactured at a site batching plant or at a ready-mixed concrete plant, and then transported to the site via a truck mixer. It can be placed using pumping, pouring, or vertical forms.

Features of Fresh Self-Compacting Concrete According to IS 456-2000

• Minimum Slump Flow: 600 mm.
• Adequate amount of fines (<0.125 mm), preferably in the range of 400 kg/m³ to 600 kg/m³, This can be achieved by having sand content more than 38 percent and using mineral admixtures constituting 25 to 50 percent by mass of the cementitious material.
• Usage of High-Range Water-Reducing (HRWR) admixture and appropriate dosages of Viscosity Modifying Agent (VMA).

Advantages of Self compacting concrete

Flow and Compaction:

SCC flows and compacts under its own weight, achieving full compaction even in congested areas.

Maintains homogeneity in the fresh state due to good deformability.

Construction Efficiency:

Facilitates faster construction with rapid concrete placement.

Easy flow around congested reinforcement, reducing construction time.

Eco-Friendly and Heat Control:

Use of fly ash in SCC is eco-friendly and controls excess heat of hydration.

Enhances homogeneity, permeability, and durability of the concrete.

Performance and Stability:

SCC’s self-compacting property ensures consistent performance regardless of compaction degree.

Reduces noise at the construction site, improving health and safety for workers.

Manpower and Complex Designs:

Requires reduced manpower compared to traditional vibrated concrete.

Enables innovative designs and complex shapes, including thinner sections.

Improved Concrete Properties:

Exhibits greater stability, reduced internal bleeding, and denser microstructure.

Forms a stronger interfacial transition zone (ITZ), resulting in a more durable concrete.

Optimized Microstructure:

The denser microstructure of ITZ contributes to lower plastic settlement, higher steel-concrete bond, and lower permeability.

Limitations of Self Compacting Concrete

Higher cost: SCC is typically more expensive than conventional concrete due to the specialized admixtures that are required.

Potential for segregation: SCC is more prone to segregation than conventional concrete, so it is important to carefully design the mix and to place the concrete carefully.

Difficulty in controlling flow: It can be difficult to control the flow of SCC, especially in complex shapes or in congested areas.

Need for specialized equipment: Some specialized equipment, such as self-compacting pumps and formwork, may be required to place SCC.

What is the necessity to choose (SCC) Self compacting concrete

The choice of Self-Compacting Concrete (SCC) is necessitated by several important reasons:

Flowability and Pass ability:

SCC is chosen due to its well-known properties of flowability and ability to easily pass through openings. It can flow effortlessly and fill complex moulds, ensuring complete compaction without the need for excessive vibration.

Compatibility:

SCC is a preferred option due to its compatibility with various construction materials and reinforcement types, making it suitable for a wide range of applications.

Repair Material:

SCC is commonly used as a repair material for concrete encasement, especially for its ability to flow through narrow openings. However, it is crucial to take care to ensure proper bonding between the new SCC and the existing concrete, which is a requirement in repair work.

The presence of congested reinforcement, secondary gate slots, and complicated shapes in concrete structures necessitates the use of SCC. Its ability to flow and self-compact is especially advantageous in such scenarios, ensuring that all spaces are adequately filled without the need for manual intervention.