self compacting concrete
TRANSCRIPT
“smart dynamic concrete”
Engr.Arivusudar Nagarajan
INTRODUCTION By the early 1990's, Japan has developed and used SCC.
Self compacted concrete is highly engineered concrete with much higher fluidity without segregation and is capable of filling every corner of formwork under its self weight .
Thus SCC eliminates the vibration for the compaction of concrete without affecting its engineering properties.
As of the year 2000, SCC used for prefabricated products (precast members) and ready-mixed concrete (cast-in-place) in the Japan, USA, etc….
Development of SCC In 1983, the problem of the durability of the concrete structures
was a major topic of interest in Japan. The creation of durable concrete structures requires adequate
compaction by skilled workers. Solution for the achievement of durable concrete structures
independent of the quality construction work is the use of SCC. The necessity of this type of concrete was proposed by
Okamura in 1986. Studies to develop SCC have been carried out by Ozawa and
Maekawa at the university of Tokyo. Present-day SCC can be classified as an advanced construction
material.
The Important Properties• Self-compactability• Avoidance of bleeding and segregation• Low shrinkage• Low permeability• Strength as needed
What’s Different?• Segregation resistance from mortar viscosity & not
due to aggregate grading.
• Workability through admixtures, not water content.
• Self compacting due to own weight and not vibrators.
What is the secret?Paste Viscosity! Attained by one of three means:• High cement content• High content of Fly Ash, Silica Fume etc• Use of Viscosity Modifying Admixture
Also low water content using HRWR
Basic requirementsFor successful casting of SCC :A. Excellent deformability 1. Increase deformability of paste by a) use of HRWR b) balanced water
2. Reduce inter-particle friction by a) low coarse aggregate volume
( high paste volume)
Continued….B. Good Stability 1. Reduce separation of solids by a) limiting aggregate content b) increasing cohesion and viscosity
2. Minimize bleeding (free water) by a) low water content b) superplastisizers
Continued…. C. Low risk of blockage by:
1. Enhanced cohesiveness 2.Sufficient spacing between reinforcement and
coarse aggregate
Benefits of SCCFor Contractors:
• Reduced vibration effort and noise during placing.• Ability to fill complex forms with limited accessibility.• More uniform distribution in areas of closely bunched
reinforcement.• Rapid pumping of concrete.• Uniform and compact surface.• Less surface voids and need for rubbing and patching.• Improved aesthetics of flatwork for less effort.
Benefits of SCCFor Ready-Mix Producers: Better perception from customers by offering a technically
advanced, higher value concrete mixture.• Offers a product that saves customers time and money.• More efficient use of mixing equipment and delivery.• Can easily expand variety of products offered without
adding more equipment.• Improved aesthetics of final product.
limitations of SCC• Limited bleeding characteristics and plastic shrinkage may
cause if not properly protected and cured.
• Higher admixtures content can also lead to plastic shrinkage if not properly cured.
• SCC requires a higher level of quality control than conventional slump concrete.
Key items to monitor are:• Coarse and fine aggregate grading• Coarse aggregate void volume• Aggregate moistures
Technical advantages of SCC
• Simple even in complicated formwork and tight reinforcement.
• Higher installation performance since no compaction work is necessary.
• Reduced construction times, especially at large construction sites
• Reduced noise pollution since vibrators are not necessary.• Higher and more homogenous concrete quality across the
entire concrete cross-section, especially around the reinforcement
• Improved concrete surfaces (visible concrete quality) • Typically higher early strength of the concrete so that
formwork removal can be performed more quickly.
Cost criteria• The increased cost of the concrete of SCC balances against labor savings
and aesthetic benefits.• Contractors, producers and owners are under great pressure to produce
better quality construction at lower costs of labor, materials and equipment.
Reduced in-place cost: • SCC can increase the speed of construction, improve surface finish and
thus reduce repair, patching costs & reduce maintenance costs on equipment.
Reduced labor costs: • Reduces labor demands of skilled labour for quality concrete works.Improved work environment and safety:• minimizing noise exposures & also It reduces fall hazards, as workers do
not have to stand on forms to consolidate concrete.Improved aesthetics • Provides finished surfaces thus reduces the finishing costs .
Factors affecting SCC1. Aggregate volume2. Size distribution & shape of aggregate3. Ratio between fine and coarse aggregate4. Density of paste of aggregate5. Surface property of aggregate6. Void content of aggregate
Material required• CEMENT • FINE AGGREGATE• COARSE AGGREGATE• FLYASH• WATER• HIGH RANGE WATER RETARDERS• VISCOSITY MODIFYING ADMIXTURES
Principals of SCC mix designSmall size & limited coarse agg.
HRWR’s
Viscosity Modifying agents
Mineral Admixtures
Reduction of internal stress causing blockages
Increase Paste flow
Increase paste viscosity to prevent segregation
Low heat of hydration, Enhances Stability
TYPES OF SCCThere are three ways in which scc can be made• POWDER TYPE
– Scc is made by increasing the powder content • VMA TYPE
– Scc is made by using viscosity modifying admixture• COMBINED TYPE
– Scc is made by increasing the powder content and adding VMA
HIGH RANGE WATER RETARDERS (HRWR) SUPERPLASTICIZER
• Super plasticizer (Master Glenium Sky 8650/CCP XR /CCP VMA ) is used as high range water retarder.
• Super plasticizing action of VMA is different than conventional super plasticizers based on – sulfonated melamine formaldehyde condensate,– sulfonated naphthalene formaldehyde condensate
which create electrostatic repulsion of particles. • VMA is free from chlorides and complies with ASTM C494 G
(retarding super plasticizer).
HRWR CONTD…TYPICAL PROPERTIES• Calcium chloride content: Nil• Specific gravity: 1.08 at 20 C• Air entrainment: Less than 1% additional air is
entrained• Setting time: 1-4 hours retardation depending on
dosage and climatic conditions• Chloride content: Nil
VISCOSITY MODIFYING ADMIXTURE (VMA)
• VMA is an admixture used for enhancing the viscosity and rheological properties (flow of fluids).
• Polyethylen glycol and biopolymers are combined and used as VMA
Flow tests of self compacted concrete
U box test Slum test
V funnel testL box test
Test result in brief
BIS Limiting test Values
M30 Grade of concrete designed & Achieved
CASE STUDIES
1.Shin-Kiba Ohashi bridge in 1991 in Tokyo :
Case study continued…. The use of self-compacting concrete in actual structures has
gradually increased. Self-compacting concrete has been successfully used in France, Denmark, Netherlands,Germany,USA and UK, apart from Japan.
A typical application example of Self-compacting concrete is the two anchorages of Akashi-Kaikyo (Straits) Bridge opened in April 1998, a suspension bridge with the longest span in the world (1,991 meters) . The volume of the cast concrete in the two anchorages amounted to 290,000 m3.
2.Akashi-Kaikyo suspension bridge in Japan
Case study continued….• Self-compacting concrete was used for the wall of a large
LNG tank belonging to the Osaka Gas Company, whose concrete casting was completed in June 1998.
• The volume of the self compacting concrete used in the tank amounted to 12,000 m3. The adoption of self-compacting concrete means that ,
(1) the number of lots decreases from 14 to 10, as the height of one lot of concrete casting was increased.
(2) the number of concrete workers was reduced from 150 to 50.
(3) the construction period of the structure decreased from 22 months to18 months.
3.LNG tank belonging to the Osaka Gas Company, Japan:
4.SCC for Rafts & Retaining Walls for Kesar Solitaire,Navi Mumbai :
INDIAN SCENARIO OF SCC• Current Indian scenario in construction shows increased
construction of large and complex structures, which often leads to difficult concreting conditions.
• In India, during last few years, attempts were made in the laboratories and in the field to develop and use SCC.
• Some efforts have been made in Delhi Metro Projects in association with L&T a large scale SCC for dome construction and tunnel lining, column casting, etc, are used to attain 35 MPa strength.
• The knowledge of SCC has moved from domain of research to application. But in India, this knowledge is to be widespread.
EXAMPLE FOR SCC STRUCTURES
TUNNEL LINING DMRL
EXAMPLE FOR SCC STRUCTURES
DOME CONSTRUCTION IN CENTRAL STATION IN DELHI
Different Codes used For SCC• Annexure J of IS 456 as Amendment no 3.
• BS EN 206-9:2010 • EN 197-1 Cement-Composition, specifications and
conformity criteria• EN 206-1 Concrete – Specification, performance,
production, and conformity• EN 450 Fly ash for concrete – Definitions, requirements
and quality control• EN 934-2 Admixtures for concrete – Definitions and
requirements• EN 1008 Mixing water for concrete• EN 12350-1 Testing fresh concrete: Part 1: Sampling• EN 12350-2 Testing fresh concrete: Part 2: Slump test• EN 12620 Aggregates for concrete
CONCLUSION• We are going to expect concrete that is a little more
expensive per cubic metre to buy• BUT• 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 more skill at the batching plant.
