Special types of concrete have been invented to be used for conditions that require specific considerations. Self-compacting concrete is one such type of concrete. Self-compacting concrete is new concrete that flows under its weight and does not require external vibration to compact.
It is utilized in construction where vibrators cannot be used for concrete consolidation. In this article, we will understand in detail about self-compacting concrete, the materials used to make it, its properties, advantages and disadvantages, and its applications in construction.
What Is Self-compacting Concrete?
Self-compacting concrete (SCC), sometimes known as self-consolidating concrete, is one of the most popular forms of concrete. SCC has outstanding flow ability in its fresh state, performing self-compaction and material consolidation without segregation concerns.
Self-compacting concrete is a type of non-segregating concrete that can settle into formwork and envelop heavily reinforced, narrow, and deep portions with its weight.
Unlike typical concrete, which employs mechanical equipment such as immersion vibrators, self-compacting concrete does not require external force or vibration to compact. When it is impossible to consolidate concrete with vibrators, self-compacting concrete is used.
To decrease bleeding and segregation, certain self-compacting concrete mixtures use admixtures such as superplasticizers and viscosity modifiers. Concrete loses strength when it segregates, resulting in honeycombed regions on the surface. However, due to its plasticity and stability, well-designed self-compacting concrete will not segregate.
Materials Used to Make Self-compacting Concrete:
The following are the primary ingredients utilized in the production of self-compacting concrete:
1. Cement
Self-compacting concrete can be made with ordinary/regular Portland cement in grades 43 or 53.
2. Aggregates
The aggregate size utilized in SCC design is limited to 20mm. If the structure’s reinforcement is crowded, the aggregate size can be 10 to 12mm. The optimum choice is well-graded aggregates in round or cubical shapes.
Fine aggregates used in SCC can be either natural aggregates or uniformly graded manufactured aggregates (M- Sand). Fine aggregates with particle sizes less than 0.125mm are commonly used.
3. Water
The water quality is the same as in reinforced concrete and prestressed concrete construction.
4. Mineral Compounds
The mineral admixtures utilized can vary depending on the mix design and needed qualities. Many mineral admixtures can be used, and the properties they provide are listed below.
• GGBS (Ground Granulated Blast Furnace Slag): The addition of GGBS improves the flowing properties of self-compacting concrete.
• Fly ash: The fine fly ash particles aid in filling the interior concrete matrix, resulting in fewer pores. This increases the quality and durability of structures made from self-compacting concrete.
• Silica Fumes: The addition of silica fumes to the self-compacting concrete structure improves its mechanical qualities.
• Stone Powder: Stone powder is used in SCC to increase the powder content of the mix.
5. Chemical Compounds
New-generation superplasticizers are often employed in the design of self-compacting concrete mixes. Air-entraining agents are used to strengthen the freezing and thawing resistance of the concrete construction. Retarders are used to control the timing of the setting.
Properties of Self-compacting Concrete:
Self-compacting concrete and traditional vibrated concrete with comparable compressive strengths have comparable qualities. Hence SCC can be utilized in most applications where traditional vibrated concrete is employed.
However, the composition of SCC differs from that of conventional concrete, and the difference exists in the performance during the fresh state; not much in terms of hardened state attributes.
Self-compacting concrete with the same water cement or cement binder ratio has a little higher strength than typical vibrated concrete, owing to an improved interface between the aggregate and solidified paste due to the absence of vibrations.
SCC varies from normal concrete in that its fresh qualities are critical in determining whether or not it can be successfully laid. To guarantee that its ability to be placed stays satisfactory, the aspects of workability that affect its filling ability, passing ability, and Segregation resistance must all be properly regulated.
Filling Ability: This attribute of concrete refers to its ability to flow under its weight without any purposeful vibration.
Passing Ability: The ability of the concrete to preserve its homogeneity is referred to as its passing ability. SCC is flexible enough to flow through dense reinforced areas of buildings without honeycombing.
Segregation resistance: This is the concrete’s resistance to segregation as it flows throughout the self-compaction process. Because of its particular admixtures and mineral fillers, self-compacting concrete (SCC) is resistant to segregation.
The above-mentioned properties of self-compacting concrete must be handled when pouring it.
Advantages of Self-compacting Concrete:
The primary advantages of self-compacting concrete are as follows:
• The permeability of the concrete structure is reduced, as self-compacting concrete has a high filling ability.
• SCC allows for greater flexibility when developing concrete structures due to its high flowability.
• The SCC construction is more rapid as compared to traditional concrete.
• The vibration-related issues have been resolved. Vibrational noise is decreased.
• SCC is easily laid, which results in significant cost savings.
• The construction’s quality is improving.
• In comparison to standard concrete constructions, the concrete structure has high durability and reliability.
• It can create creative architectural concrete constructions.
• SCC produces smoother and more aesthetically attractive surface finishes.
• The cost of manpower is reduced as there is no requirement for laborers to vibrate the concrete.
• Using SCC reduces cavities in heavily reinforced sections of the structure.
• It allows for easier pumping and a wide range of positioning methods. SCC necessitates lower pumping pressures. As a result, compared to standard concrete, SCC can be pumped more efficiently across greater distances and heights.
Disadvantages Of Self Compacting Concrete:
• Self-compacting concrete, like any other building material, has the following limitations:
• The materials used for making SCC have to be selected very carefully. Hence the material selection process becomes more stringent.
• Using a planned blend necessitates multiple trial batches and laboratory tests.
• The greater flow velocity of SCC, in contrast to ordinary concrete, may result in a dynamic pressure in addition to the hydrostatic pressure of poured concrete for formwork design.
• There is no internationally recognized test standard for self-compacting concrete mix. Hence maintaining quality standards can be challenging while using SCC.
Applications:
The following are the primary applications of self-compacting concrete:
• SCC is often used in construction where intricate reinforcing is required.
• SCC is used in construction for repairs, restoration, and rejuvenation.
• It is used to build highly sturdy and long-lasting retaining walls.
• SCC is used in the fabrication of raft and pile foundations.
• It also finds its application in drilled shafts and columns.
Special Considerations while Using Self-Compacting Concrete:
Self-compacting concrete has advantages and speeds up construction. There are various unique considerations to make while utilizing this type of concrete to attain the best results:
• The production of self-compacting concrete necessitates more experience and attention than normal vibrated concrete.
• Formwork must be constructed to withstand the pressure of the fluid concrete, which will be greater than the pressure of conventional concrete.
• Because of the great fluidity of self-compacting concrete, utilizing mixers at maximum capacity is not suggested since it may flow along the road, creating contamination.
• Self-consolidating concrete may need to be poured in and lifted in taller elements.
• SCC manufacturing takes more skill and care than regular concrete.
Conclusion:
It’s important to note that the design and production of self-compacting concrete require careful consideration of the mix proportions, including the selection of suitable cementitious materials, aggregates, and chemical admixtures.
Proper testing and quality control procedures are necessary to ensure consistent performance and meet the specific requirements of the project.
Overall, self-compacting concrete offers significant advantages in terms of workability, durability, structural integrity, and aesthetics, making it a preferred choice in various construction applications.