What is Self Compacting Concrete (SCC)?
Concrete Technology has advanced over the last three decades, with the use of blended cements and mineral and chemical admixtures producing a wide range of concrete of varying strengths, durability, and suitability to specific construction industry requirements.
Professor Okamura in Japan proposed the development of Self Compacting Concrete (SCC) in the late 1980s to offset a growing labour shortage in the construction industry. “The sedimentation velocity of a particle is inversely proportional to the viscosity of the floating medium in which the particle exists,” according to the guiding principle of Self Compacting Concrete.
Numerous R&D efforts were made with the goal of developing raw material requirements, mix proportions, special materials and properties, and test methods required to manufacture and test SCC.
SCC is a type of concrete that spreads through congested reinforcement, reaches every corner of the formwork, and is solidified under its own weight. It has great filling and passing capabilities, as well as good segregation resistance while being homogeneous.
Several European nations created the “Rational Production and Improved Working Environment through SCC” initiative in 1996 to investigate the relevance of published achievements in SCC and to develop applications to capitalize on SCC’s potentials.
The European Federation for Specialist Construction Chemicals and Concrete Systems (EFNARC) published the European Guidelines for SCC in May 2005, which include test procedures that differ from those used for other forms of cement concrete. Many nations have broadly accepted these.
Although the technology was originated in Japan and widely used in the Middle East, it was not widely used in the United States until much later. In the late 1990s, India swiftly implemented the technique, utilizing indigenous materials, and successfully used SCC in the Mumbai-Pune highway, the J.J. Flyover in Mumbai, the Bangalore International Airport, the Vivekananda Bridge in Kolkata, the Bandra-Worli sea connection, and the Delhi Metro project.
To keep it from falling behind, the amended IRC:SP:70-2016 extended the Guidelines for the Use of High Performance Concrete (HPC) to include Self Compacting Concrete in order to popularize the new concrete.
Self Compacting Concrete is ideal for conditions including reinforcing congestion, complex geometry of a part, and narrow portions of superstructure with no access to vibration. However, it is not widely utilized in bridge construction.
As a result, the most recent IRC:112 for Concrete Road Bridges incorporated Self Compacting Concrete (SSC) paras from IRC:SP:70 and amended the contents therein. Except for their selection and dose, SCC can be produced in concrete of appropriate Grades by employing several standard components as used in High Performance Concrete. The European Federation for Specialist Construction Chemicals and Concrete Systems (EFNARC) introduced SCC guidelines in May 2005, which are largely followed in India.
Flow ability tests, passing ability tests, and segregation tests, which require specialised equipment, are some of the significant tests that differ from standard concrete. The IRC:112-2020 specifies SCC test techniques in addition to transportation, placement, compaction, and curing of concrete. However, SCC requires more strict curing than other forms of concrete, and efforts to develop Self Curing compounds to combine during mixing are ongoing.
Polyethylene Glycol (PEG) has been discovered to assist in self-curing by providing strength comparable to traditional curing. As a result, identifying admixture(s) for Self curing of SCC and developing Self curing Self Compacting Concrete (SCSCC) and determining its Mechanical characteristics is required.
The reason for the low use of Self Compacting Concrete in highway bridge construction in India is a lack of familiarity with the material, which needs specialised knowledge in production and acceptance testing.
While the use of appropriate ingredients in the production of SCC, such as OPC aggregates, fly ash, and VMA, is critical, the use of a new generation superplasticizer based on Poly-Carboxylate Ether (PCE), is more beneficial.
SCC requires a higher level of quality control than standard slump concrete. All production personnel must be more aware of combined aggregate grading, tightly regulated mix water, controlled cement source, and the usage of advanced admixtures.
The following are typical ranges of SCC Constituent Materials:
- Water content: 170 to 210 Kg/m3
- Cement content: 350 to 450 Kg/m3
- Total powder content (i.e., cement + filler): 400 to 600 kg/m3
- Dosage of superplasticizer: 1.5-1.8 % of the total powder content (by mass)
- A W/ P ratio 0.80 to 1.10 (by volume) or in the range of 0.30 to 0.38 (by mass)
- Coarse aggregate content: 28 to 35% by volume of the mix of concrete
Proportions of a Standard Mix Self Compacting Concrete contains the same component elements as Cement Concrete, but their relative proportions differ and must be carefully chosen. To obtain self compacting characteristics, lower coarse aggregate content and larger volumes of additives, cement, and admixtures (especially superplasticizer) are required.
SCC has a higher overall material cost than regular concrete, but it has better mechanical and durability performance as well as a longer service life.
Inadequate concrete compaction and inadequate concrete cover over the reinforcements are the most prevalent causes of corrosion and early degradation in RCC bridges. This is certainly relevant when deep and narrow sections are used in I girders or wing/return walls.
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