Self Compacting Concrete

A special type of concrete of flowing consistency.

Developed initially in Japan in 1980s to offset the growing shortage of skilled labour.

The composition in addition to cement and water, consists of high amount of super plasticizer, high powder content and a viscosity modifying agent.

Requirements

For a mixture to have self compatibility, it should have

• Filling ability
• Passing ability
• Segregation resistance

Requirements of constituent Materials

Cement

Type depends on the overall requirements for concrete such as strength, durability, etc.

C3A content higher than 10% may cause poor workability retention.

Typical cement content – 350 to 450 kg/m3.

Cement > 500kg/m3 cause increase in shrinkage.

Cement < 350kg/m3 demands other fine fillers such as flyash, pozzolan, etc.,

Aggregate

Sands

All normal sands are suitable for SCC,

Fines less than 0.125mm – powder, very important for SCC.

Coarse Aggregate

All types of aggregates are suitable for SCC,

Normal maximum size is generally 16 – 20mm,

Crushed aggregates improve strength while rounded aggregate improve flow.

Fly ash:

In appropriate quantity may be the added the quality.

Silica fumes:

Added to improve the mechanical properties of scc.

Stone powder:

Finely crushed lime stone, dolomite or granite added to increase the powder content.

Fibres:

Fibres may be used to enhance the properties of scc as same as normal concrete.

Mix Proportioning for achieving Self Compaction

Changes in the coarse aggregate content.

Changes in the fine aggregate content.

Use of super plasticizers.

Combination of most suitable water cement ratio and super plasticizer powder ratio.

Methods Of SCC:

• PROF. Okamura broadly classified it in1997.
• They are two types
  • Powder based.
  • Viscosity enhancing agent based.

Test Methods For SCC:

• Slump flow test
• Slump flow (T 50 cm)
• J-ring
• V- Funnel
• L box
• U box
• Fill box

Advantages of SCC

• Faster construction.
• Reduction in site manpower.
• Better surface finishes.
• Easier placing.
• Improved durability.
• Greater freedom in design.
• Thinner concrete sections.
• Reduced noise levels, absence of vibration.
• Safer working environment.