Self compacting concrete

  Self compacting concerete  

Self compacting concrete (SCC) is concerete which is able to flow under its own weight, completely filling formwork & Achieving full compaction, even in the congested places 

The scc mixes  have these attributes beacuse of their good deformabilty enabling them to maintain homogeneity at a fresh state.

It can be placed and compacted under its self weight with little or no vibration Effort & which is at the same time is cohesive enough to be handled without segregation and bleeding.

Viscosity modifiers admixture added to fresh concrete to increase cohesion and segregation resistance.

Viscosity modifiers admixture increase the plastic viscosity and improve the stability of the mixture  at a constant fluidity. 

Admixture added during the mixing process of concrete in small quantities related to the mass of the cementious binder to modify the properties of fresh  or hardened concrete.

Material for SCC 

 1- Cement 

2- Aggregate 

• The maximum size of aggregate is generally limited to 20 mm 
• An aggregate of size 10 to 12 mm is desirable for the structures having congested reinforcement.
• Particles smaller than 0.125mm i.e 125 micron size are considered as a fines which contribute to the powder content.

Sufficient amount of fines should be range somewhere between 400kg/cm3 to 600 kg/cm3. The best approach to Achieving this is by increasing the sand content to 38% and using mineral 25% to 50% by mass of the cement content. 

3- mixing water 

4- chemical admixture 

 Slump flow for self compacting concrete

Slump flow value describes the flowabilty of a fresh mix in unconfined condition.It is a sensitive test that will normally be specified for all SCC, as the primary check that the fresh concrete consistency meet the specifications.

A value atleast 650 mm is required for SCC.in case of severe segregation, most coarse aggregate will remain in the centre of the pool of concrete and mortar and paste at the periphery of concrete. 

The followings are the applications of self-consolidating/compacting concrete.

Areas of congested reinforcements.

Bridges and precast sections.

Drilled shaft columns, earth retaining structures.

High concentration rebars where normal tempering or vibrating is difficult.

Manufacturers of concrete pipes.

Flow in closed spaces-pipes (during pumping).