Concrete that is able to flow and consolidate under its own weight, entirely fills the formwork even in the presence of dense reinforcement, maintaining uniformity and without the requirement for any additional compaction is called self-compacting concrete.
It is the most desirable form of concrete, which has very few voids and requires no vibrator or compactor during the construction.
Here we will learn about self-compacting concrete, properties & uses of self-compacting concrete.
Introduction to Self Compacting Concrete:
This technology was first discovered in Japan in 1980, nowadays widely used all around the world, the material of the concrete is super dense with increased compressive strength.
The flow ability and workability of concrete are super high that no extra plastering is required after the removal of the formwork.
Properties of Self-compacting Concrete:
The properties that describe the concrete as self-compacting concrete are:
Flowing ability: The ability to entirely fill all areas and corners of the formwork in which it is placed.
Passing ability: Ability to undergo congested reinforcement without separation or blockage of the constituent.
Resistance to segregation: The ability to retain coarse components of a mixture in suspension to maintain a homogeneous material.
Types of SCC:
Self-compacting concrete is made by increasing the powder content in it.
Self-compacting concrete is made using a viscosity modified mixture.
Self-compacting concrete is made by increasing the powder content and adding VMA.
Material for Self Compacting Concrete:
Cement: Ordinary portland cement, 43 or 53 grades may be used.
Aggregates: The maximum size of the aggregates is generally limited to 20 mm & set of size from 10 to 12 mm is desirable for structures with crowded reinforcement.
The total size of more than 20 mm can also be used.
Fine aggregates can be natural or manufactured; the grading should be the same for the entire work.
Chemical Mixtures: Super plasers is essential component of SCC to provide the required functionality.
New generation superplastics have identified poly-carboxylated ether (PCE) to be particularly useful for SCC.
Other types includes viscosity modifying agent (VMA) for stability, air-entraining agent (AEA) to improve freeze-thaw resistance and diluent for control.
Fly ash: Fly ash in an appropriate quantity may be added to improve the quality and durability of SCC.
Ground Granulated Blast Furnace Slag (GGBFS): In GBBFS, both the cementations and pozzolanic material can be added to improve the rheological properties.
Silica Fume: Silica fume may be added to improve the mechanical properties of SCC.
Stone Powder: Finely crushed limestone, dolomite, or granite may be added to increase the powder content, the fraction should be less than 125 microns.
Fibers: It may be used to enhance the properties of SCC in the same way as for standard concrete.
Advantages of Self Compacting Concrete:
- The labor charges on compaction and vibration can be saved, as the concrete is very dense and highly flow-able.
- As there is more cement content along with admixtures, the bond with reinforced steel is enhanced due to reduction of voids and high density of SCC.
- It provides lesser dimensions for the structure with a high ratio of steel, offers better construct-ability.
- It provides superior strength and durability when compared with the same grade of RCC.
- Also, provides absorbent noise design since the material is genuinely dense and robust.
- It requires no surfaces finishing as the concrete is super workable and acquires the shape of formwork.
- It reduces equipment wear and tears as they are used less, also saves the cost of procuring such equipment.
- Also, has an improved pumping feature can be transported to remote areas with considerable setting time.
- It provides flexibility in adding admixture and mending the properties of concrete.
Disadvantages of Self-Compacting Concrete:
- SCC is mixed with certain admixtures like Water Retaining Admixture (WRA), superplasticizer to enhanced the workability.
- SCC requires batch mixing that cannot be done at the site, hence it takes a full capacity mixer which is not appropriate for small residential works.
- The individual formwork needs to be used as the density of SCC is nearly double that of traditional concrete.
- SCC will have a nominal excellent aggregate size of around 9 mm or less and will not have any coarse aggregates.
- Viscosity-modifying agents are pseudo polymers are used with SCC to reduce aggregate segregation with that amount of fluidity.
Uses of Self-Compacting Concrete:
The main uses of concrete are the following:
- It is extensively used for the industrial building where a high quantity of reinforcement is used, i.e. metro columns, industrial slabs, large columns, and many others.
- The building of raft and pile foundations.
- In retrofitting and repairing constructions.
- It is used in constructions with complex reinforcement distributions.
- In construction of earth retaining techniques.
- Used in drilled shafts.
There are several special considerations to get the best results using this concrete.
The production of self-compacting concrete requires more experience and care than regular vibrating concrete.