Self compacting concrete (SCC), also known as self consolidating concrete, is a fluid type of concrete that can be placed and consolidated by means of its own weight without needing mechanical vibration. One of the important characteristics of self compacting concrete is that it maintains durability and characteristics of concrete, while being cohesive enough to be handled without segregation.
Some self compacting concrete mixtures include admixtures like superplasticizer and viscosity modifiers for reducing segregation and bleeding. Segregation of concrete leads to loss in strength and results in honeycombed area throughout the concrete. A well-designed self compacting concrete will not segregate due to its excellent deformability.
Now that you know about what SCC is, let’s take a look at the Materials, Properties, Application, Advantages and Disadvantages of SCC.
SCC Materials
The following at the materials used to create SCC mixture:
- Portland Cement
Common Portland cement grade 43 or 53 is commonly used.
- Aggregates
Coarse aggregates are normally limited to the size of 20 mm, but in some cases where congested reinforcement is required, the aggregate size can range between 10 mm to 12 mm. Fine aggregates, of size smaller than 0.125 mm, can be natural or manufactured. Well graded round aggregates or cubical aggregates are recommended for optimal performance.
- Water
Water is treated the same way as with regular concrete.
- Mineral Admixtures
It varies depending upon the mix design and properties required. Below are the minerals used along with the properties they add to the concrete mixture:
- Fly Ash – Improves internal concrete matrix, reduces permeability, and improves structure quality.
- Ground Granulated Blast Furnace Slag (GGBS) – Improves the rheological, also known as deformation, properties of concrete.
- Stone Powder – Improves powder content of the mixture.
- Silica Fumes – Improves mechanical properties of the structure.
- Chemical Admixtures
Superplasticizers are commonly used in SSC. Air entraining, intentional creation of air bubbles, agents are used to improve the freezing and thawing resistance. Setting time of concrete is controlled by using Retarders.
SCC Properties
Due to the presence of mineral fillers and special admixtures, SCC is resistant to segregation. It is also fluid enough to pass around congested reinforced areas withing structures, while avoiding any honeycombing. The fluidity can be varied based on the SCC design. With a properly designed SCC, the concrete can be placed at above 5 meters height without any segregation whatsoever.
SSC having similar water-cement ratio as of the traditional vibrated concrete will result in higher strength, due to lack of vibration. This significantly improves the interface between the aggregate and the hardened paste. However, it is important to remember that SCC must be poured faster than regular concrete.
SCC Applications
- Construction of raft and pile foundations
- Retrofitting and repairing constructions
- Structures with complex reinforcement distributions
- Construction of earth retaining systems
- Drilled shafts
- Columns
Advantages
- Fast placement without mechanical consolidation.
- Improved constructability.
- Reduces permeability in concrete structures.
- Minimizes voids in highly-reinforced areas.
- Eliminates problems associated with concrete vibration.
- Creates high quality structures with improved structural integrity.
- High durability, strength and reliability.
- Reduces labor costs.
- Allows for innovative architectural features, since it can be used in complex forms.
- Creates smoother and more aesthetic surface finishes.
- Allows easier pumping, and there are many placement techniques available.
Disadvantages
- Material selection is stricter.
- Construction costs increase, compared with regular concrete.
- Many trial batches and laboratory tests are required to use a designed mixture.
- Higher precision is required when measuring and monitoring.
- There is no internationally accepted test standard for self-compacting concrete mix.
BONUS
To achieve the optimal results when using this type concrete, there are many special considerations. Firstly, the production of SCC requires a lot of experience and care, more than regular vibrated concrete. Secondly, the formwork must be designed to withstand pressure higher than with regular concrete. Finally, using mixers at full capacity is not recommended as the concrete might spill along the road and cause contamination due to its high fluidity.
