SELF-COMPACTING CONCRETE

Dr. M.L.V.PRASADDepartment of Civil Engineering

NIT Silchar

SELF-COMPACTING CONCRETE

SELF-COMPACTING CONCRETE

SELF-COMPACTING CONCRETE

Threats to future of Concrete •Shortage & availability of natural Aggregate

•Increasing quantity of steel (Cost & Possibility of corrosion)

•Perceived lack of concrete durability

•Increased Labour Cost

•Availability of Skilled Labour

•Reluctance to change methods and practices

•Reluctant to specify and use new materials and new methods

•Gross delays in revision of Indian standards to match the global research and development

Defined as a concrete, which can be placed and compacted in to every corner of form work, purely by means of its self-weight without any compacting effort.

Also referred as Self Consolidating Concrete, Super workable concrete, Non-Vibrating concrete.

SCC is highly flowable, non segregating concrete that can spread into place, fill the frame work and encapsulate the reinforcement without any mechanical consolidation-ACI 237

Self Compacting Concrete

Historical Development Intention behind developing this was the concerns regarding the homogeneity and compaction of cast-in-place concrete within congested reinforcement sections.And also improvement of over all durability due to lack of skilled labor.Originated from research into in-situ concrete piling, filling of inaccessible areas and under water concrete technology.

CASTING PROBLEMS WITH CONVENTIONAL DRILL-SHAFT CONCRETE

CASTING PROBLEMS WITH CONVENTIONAL DRILL-SHAFT CONCRETE

The Important PropertiesSelf-compactabilityAvoidance of bleeding and segregationLow shrinkageLow permeabilityStrength as needed

The Benefits Faster Construction Reduction in site manpower Better appearance Easier Placing Improved durability Thinner concrete sections Reduced noise levels, absence of vibration Safer working environment

What’s Different?

Segregation resistance from mortar viscosity, not aggregate grading

Workability through admixtures, not water content

What’s The Snag?

Higher cost – especially if high strength not needed

Plant control has to be better

What is the secret?Paste Viscosity! Attained by one of three

means:High cement contentHigh content of Fly Ash, Silica Fume etcUse of Viscosity Modifying Admixture

Plus low water content using HRWR

Constituent Materials of SCCCement +Additions +Aggregate +Admixture +Fibers +Water

Self compacted concrete

•Additions : Stone Powder,Mineral Filler, Fly ash, Silica Fume, Ground Blast furnace Slag (GGBS), Other additions (i.e Metakaolin,natural pozzolana, ground glass etc.,)•Aggregate : Coarse & Fine Aggregate•Admixture : Super plasticiser/ High range water reducing admixtures (HRWR), Viscosity modifying admixtures (VMA), Air entaining admixtures•Fibres : Metallic and polymer fibres

How to Check Suitability?

There are some important tests: V-funnel, L-box, U-box, Slump Flow and J-ring

While several of these may be used in mix development, mainly the slump test will find site use

WORKABILITY TESTS ON VIBRATED CONCRETE

Tests on SCC

H-FLOW TEST

J-RING TEST

Tests on SCC

L-BOX TEST

V-FLOW TEST

Tests on SCC

U-BOX TEST

SCC WORK IN PROGRESS

Traditional Concrete •Vibration required •Skill dependent •Labour intensive•Quality varies

Self Compacted Concrete•No Vibration needed• Faster Construction • Less Noise• Improved quality and durability

Why Does It Look Better?

Perfect compaction

No bleeding

S.No Method Unit Typical range of values

Minimum Maximum

1 Slump flow by Abrams cone mm 650 800

2 T50cm Slump flow sec 2 5

3 J-ring mm 0 104 V-funnel sec 6 125 Time increase, V-funnel at T-5 min sec 0 +3

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

EFNARC SPECIFICATIONS

For SCC, the powder content is in between 160 and 240 litres/m3.

Flyash is to be added in addition with the cement content obtained.Extra volume of fly ash added is replaced to coarse aggregate.Some quantity of cement is also replaced by fly ash. The fly ash replacement is varying from 5 to 20 %.

MIX DESIGN

After obtaining the quantity of cement and fly ash for different grades, the optimum dosage of super plasticizer for each grade has been arrived by conducting basic tests on SCC.The total aggregate content obtained is distributed to the ratio of 50: 50 for sand and coarse aggregate.The water content obtained is taken as it is and the check is to be made that the maximum water should not exceed 210 litres/m3.

MIX DESIGN

Grade Normal Concrete by ACI

SCC by ACI

Normal Concrete by IS

SCC by IS

M20 1:2.38:2.65:0.51 1:2.65:2.20:0.53 1:1.48:3.36:0.49 1:2.67:2.19:0.54

M25 1:2.26:2.55:0.49 1:2.49::2.18:0.52 1:1.30:2.96:0.44 1:2.51:2.15:0.51

M30 1:2.02:2.39:0.45 1:2.36:2.14:0.49 1:1.17:2.65:0.42 1:2.35:2.07:0.49

M35 1:1.74:2.12:0.4 1:2.15:1.97:0.46 1:1.09:2.48:0.40 1:2.21:2.03:0.47M40 1:1.46:1.89:0.36 1:1.97:1.82:0.43 1:1.03:2.32:0.36 1:1.97:1.85:0.44

MIXES DEVELOPED

S.No Method Unit With out Fiber

With PPF

With GF

EFNARC Specifications

1. Slump flow by Abrams cone mm 725 723 720 650-800

2. T50cmslumpflow sec 4.00 4.10 4.15 2-5

3. V-funnel sec 4.11 4.13 4.17 Upto 12

4. Time increase,V-funnel at T5minutes sec 1.00 1.24 1.30 0-3

5. J-ring mm 8.0 8.9 8.6 0-10

6. U-box mm 23 34 28 0-30

SCC Properties

Applications of SCC

AKASHI KAIKYO BRIDGE KAIGA PROJECT

Will it happen?My guess is that 50% of concrete will be

self-compacting within 10 years

In USA and Japan and many European Countries a very large proportion of precast concrete is already SCC

CONCLUSIONWe are going to expect concrete that is a little

more expensive per cubic metre to buyBUT It will require less skill and effort to place It will look better with no appearance defects It will be more durable It will require a little more skill at the batching

plant

THANK YOU