The mix design self compacted concrete, advantages and disadvantages

The mix design system can be summarized as follows:
  1. Course aggregate content is fixed at a maximum of 50% of the solid volume.
  2. Fine aggregate content is fixed at a limit of 40% of the mortar volume.
  3. Water to powder ratio in volume depends on the properties of the powder, it's assumed as 0.9 to 1.0
  4. Superplasticizers dosage and the final water-powder ratio are determined so as to ensure the self-compatibility.
SCC gives the perfect surface

Typical mix of SCC contains:

Cement 10%
Water 18%
Air 2%   
Fines 8%
Fine aggregate 26%
Course aggregate 36%

Where typical mix of regular concrete contains:

Cement 10%
Water 18%
Air 2%   
Fines 0% (fines aren't used in regular concrete mix) 
Fine aggregate 25%
Course aggregate 45%

Advantages and disadvantages of SCC:

The SSC had been suggested to give a quite concrete mixture, and because conventional concrete tends to present a problem with regard to inadequate consolidation in thin sections or areas of congested reinforcements, since the major disadvantages of concrete is the segregation, the segregation is happen due to many reasons, such as:

  ➧  Rolling of concrete which occur during transport and handling.
  ➧  Falling of concrete from high heights.
  ➧  The increasing of compaction, where: 
When there is a high density of steel bars and the water content is low, we need to compact the concrete in order to ensure that the concrete is infiltrate between steel bars, but that leads to the deposition of sand and gravel at the bottom, and raise the cement mortar at the top.

The (SSC) provide a larger time for handling and transport of concrete, in addition to decrease the opportunity of segregation happen, since it is behave as a liquid which had no need to compaction.

Advantages of SCC:

  1. Casting without compaction, and giving no opportunities to increase water content since of its high liquidity.
  2. Remain homogeneous before and after solidification and the granular separation not taking place, and can penetrate through steel bars.
  3. Improved quality of concrete in shorter time and higher durability compared to normal concrete.
  4. Less labor involved and labor savings.
  5. Eliminated problems associated with vibration.
  6. Faster construction.
  7. Easy for pump to high heights.
  8. No need for leveling of its surface after casting.
  9. Increase the strength of adhesion between the concrete and steel bars, where tests proved that self-compacting concrete gives the highest rate of (50-70) % compared with traditional concrete.
  10. SCC reach it's early strength early so that formwork removal can be performed more quickly.

Disadvantages of SCC:

  1. Although the use of SCC has many technical, social, and overall economic advantages, its supply cost is two of three times higher than that of normal concrete depending on the composition of the mixture and quality control of concrete producer.SCC is specified only to areas where it is most needed. These include places where access to conventional vibration is difficult, or where there are congested reinforcement.
  2. The main difficulty which was faced in SCC was that the concrete should be without bleeding or segregation because it's workability very high and it shoulb be flowable as well. So, the cement mortar of the SCC mush have high viscosity.
  3. It requires quality control of paste and mortar prior to SCC mixing, because the occurrence of separation may take place, and this is more dangerous than in regular concrete.

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