SELF COMPACTING CONCRETE
- WHAT IS SELF COMPACTING CONCRETE?
- MECHANISM OF ACHIEVING SELF COMPACTION
- PROPERTIES OF SELF COMPACTING CONCRETE
- ADVANTAGES & DISADVANTAGES OF SELF COMPACTING CONCRETE
- TEST METHODS FOR SELF COMPACTING CONCRETE
- EMPLOYABILITY OF SCC IN EARTHQUAKE RESISTANT STRUCTURE
- PRECAUTIONS OF SCC IN EARTHQUAKE RESISTANT STRUCTURE
WHAT IS SELF COMPACTING CONCRETE?
Self-compacting concrete (SCC) describes a concrete with the ability to compact itself only by means of its own weight without the requirement of vibration. Self-compacting concrete also known as self-consolidating concrete or self-leveling concrete.
Self-compacting concrete is used for:
•Heavily congested reinforced members
•Delays and additional cost in the projects
•Under water concreting
•Lack of skilled labor
HISTORY OF SCC
- FIRST DEVELOPED IN JAPAN IN the LATE 1980s where the lack of uniform and complete compaction had been identified as the primary factor responsible for the poor performance of concrete structures.
- This led to the development of the first practicable SCC by researchers (Okamura, Ozawa, et al.) at the University of Tokyo and the large Japanese contractors (e.g. Kajima, Maeda, Taisei, etc.) quickly took up the idea.
- Self-compacting concrete has been successfully used in France, Denmark, the Netherlands, the UK, the USA, and Germany apart from Japan.
MATERIAL USED IN SELF COMPACTING CONCRETE
- The material used in SCC are the same as in conventional concrete except that an excess of fine material and the chemical admixture is used
- Fly ash, silica, limestone powder, glass filler.
- A high-range water-reducing admixture (HRWRA) such as Acrylic Poly-carboxylated-ethers (PCE) & polyacrylates
- Viscosity- modifying agents (VMA) and ultra-fine materials are used to reduce bleeding and segregation.
Comparison of SCC over Normal Concrete
|INGREDIENTS||NORMAL CONCRETE||SELF COMPACTING CONCRETE|
Mechanism of Achieving Self Compaction
PROPERTIES OF SELF COMPACTING CONCRETE
Properties of fresh concrete:-
1. Filling ability:- Flows easily at suitable speed into the formwork.
2. Passing ability:- Passes through reinforcements without blocking.
3. High resistance to segregation:- The distribution of aggregate particles remains homogeneous in both vertical and horizontal directions.
Properties of hardened concrete:-
Development of compressive strength with time.
Isolated cases, however, showed that at the same water-cement ratios slightly higher compressive strengths were reached for SCC.
After 28 days the reached compressive strength of SCC and normal vibrated concrete of similar composition does not differ significantly in the majority of the published test results.
At the current time, there is insufficient research to result in generalized conclusions with this fact.
ADVANTAGES OF SCC
- Simple inclusion even in complicated formwork and tight reinforcement.
- Less skilled manpower. Since no compaction work is necessary, it leads to reduced construction times, especially at large construction sites.
- Reduces 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 surface. Typically higher early strength of the concrete so that formwork removal can be performed more quickly.
- Strict quality control required to ensure the required properties.
- Increased plastic shrinkage potential.
- Elaborate testing arrangements required to ensure quality control.
- Highly skilled workers are required for the production of SCC.
- Higher material costs & production expenses.
- More stringent requirements on the selection of materials. ØRequire more Trial Batches at the lab as well as at RMC plants.
- More precise measurement and monitoring of constituent materials.
DIFFERENT TEST FOR SCC
|FILLING ABILITY TESTS||PASSING ABILITY TEST||SEGREGATION RESISTANCE TEST|
|Slump Flow Test||J-Ring Test||V-Funnel At T5minutes|
|T50cm Slump Flow||L-Box Test||GTM Screen stability Test|
|V- Funnel Test||U-Box Test|
|Orimet||Fill- Box Test|
TEST METHODS FOR SCC
ACCEPTANCE CRITERIA FOR SCC
|METHOD||UNIT||TYPICAL RANGE OF VALUE|
|Slump flow by Abrams cone||mm||650||800|
|T 50cm Slump flow||sec||2||5|
|Time increase, V- funnel at T5min||sec||0||+3|
|GTM Screen stability test||%||0||15|
Employability of SCC in Earthquake Resistant Structure
Precautions of SCC in Earthquake Resistant Structure
APPLICATIONS OF SCC
- Pipe roof
- Precast section
- Drilled shaft column
- Earth retaining structure
- The high concentration of rebar
- Manufacture of concrete pipe
- Congested reinforced column
- Self Consolidating Concrete, as well as Conventional Slump Concrete, require proper mix proportion to become a durable concrete.
- Even though the initial cost of SCC is comparatively higher than the conventional concrete.
- Considering the long service of the structure, maximum maintenance, labor cost, cost due to the vibrators required, the benefit-cost ratio is very much in favor in the case of SCC.
- The use of pozzolanic materials, such as slag, fly ash, silica fume, etc. will help SCC more durable, otherwise these are waste products demanding with no practical applications and which are costly to dispose of.
- In countries like Japan, Sweden, Thailand, U.K., and the U.S.A, etc. the knowledge of SCC has moved from the domain of research to application. But in India, this Knowledge is to be widespread.
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