SELF COMPACTING CONCRETE

INTRODUCTION

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 superplasticizer powder ratio.

Coarse aggregate content-50% of solid volume.

Fine aggregate content-40% of mortar volume.

ROLE OF SUPERPLASTICIZERS.

FLOW DIAGRAM OF MIXDESIGN SYSTEM.

METHODS OF SCC:

PROF. Okamura broadly classified it in 1997.

They are two types Powder based. Viscosity enhancing agent based.

Typical scc mixes in Japan.Ingredients Powder type VEA type

Water kg/m3 175 165

Cement kg/m3 530 220

F.A kg/m3 751 870

C.A kg/m3 789 825

Fly ash kg/m3 70 0

Silica fumes kg/m3

0 0

HRWR kg/m3 9.0 4.4

VEA kg/m3 0 4.1

PROPORTIONING OF SCC RECOMMENDATIONS.constituents Powder type VEA Type

Coarse aggregate

0.28-0.35m3/m3 0.28-0.35m3/m3

Water content 155-175kg m3 -

W / p 28-37% -

Powder content 0.16-0.19m3/m3 >0.13m3/m3

Air content 4.5% -

PROPERTIES OF HARDENED SCC.

Items SCC

1.Water-binder ratio 0.25 to 0.40

2. Air content(%) 4.5-6.0

Compressive strength (age: 28 days) (MPa)

40 to 80

Compressive strength (age: 91 days) (MPa)

55 to 100

5. Splitting tensile strength (age: 28 days) (MPa)

2.4 to 4.8

6. Elastic modulus (GPa) 30 to 36

7. Shrinkage strain (x 10-6) 600 to 800

TEST METHODS FOR SCC:

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

TEST METHOD PROPERTY

Slump flow Filling ability, segregation.

T50cmSlump flow Consistency, cohesiveness.

V funnel Filling ability, viscosity.

J-ring Flowing ability, passing ability.

L box Passing ability, blocking effect.

U box Passing ability.

Fill box Filling ability.

Sr. no

Methods Acceptance criteria

unit min max

1. Slump flow mm 650 800

2. slump flow (T 50 cm)

Sec 2 5

3. V funnel Sec 6 12

4. J-ring mm 0 10

5. L-box (h2/h1) 0.8 1.00

6. U-box (h2-h1) 0 30

7. Fill box % 90 100

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.

SELECTED CASE STUDY

Akashi-Straits Bridge

SCC was used in the construction of the two anchorages of the bridge.

concrete was transported 200 meters through pipes, with out segregation to the actual casting site. In the final analysis self-compacting concrete shortened the anchorage construction period by 20%.

CONCLUSION.

Self-Compacting Concrete is considered to be the most promising building material for the expected revolutionary changes on the job site.

We can create durable and reliable concrete structures using SCC

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