Self-compacting concrete (SCC), which flows under its own weight and doesn’t require any external vibration for compaction, has revolutionized concrete placement. Such concrete should have relatively low yield value to ensure high flow ability, a moderate viscosity to resists segregation and bleeding and must maintain its homogeneity during transportation, placing and curing to ensure adequate structural performance and long term durability.
Self-compacting concrete (SCC) can be defined as a fresh concrete which possesses superior flow ability under maintained stability (i.e. no segregation) thus allowing self-compaction that is, material consolidation without addition of energy. Self-compacting concrete is a fluid mixture suitable for placing in structures with Congested reinforcement without vibration and it helps in achieving higher quality of surface finishes. However utilization of high reactive Metakaolin and Flyash as an admixtures as an effective pozzolan which causes great improvement in the porestructure. The relative proportions of key components are considered by volumerather than by mass. self compacting concrete (SCC) mix design with 29% of coarse aggregate, replacement of cement with Metakaolin and class F flyash, combinations of both and controlled SCC mix with 0.36 water/cementitious ratio(by weight) and 388 litre/m3 of cement paste volume. Crushed granite stones of size 16mm and 12.5mm are used with a blending 60:40 by percentage weight of total coarse aggregate. Self-compacting concrete compactibility is affected by the characteristics of materials and the mix proportions; it becomes necessary to evolve a procedure formix design of SCC. The properties of different constituent materials used in this investigation and its standard tests procedures for acceptance characteristics of self compacting concrete such as slump flow, V-funnel and L-Box are presented.
Who Invented SCC?
In general, the concept of SCC is not new. The history of self- compacting concrete (SCC) dates back to late 1980s. For special applications such as underwater concreting, vibration of placed concrete is simply impossible. In such circumstances, concrete needs to be placed without any compaction. Early self-compacting concrete relied on very high content of cement paste and once superplasticizer was available, it was added in the concrete mixes. The mixes required specialized and perfectly controlled placing methods in order to avoid segregations. The high content of cement paste made concrete prone to shrinkage. The overall cost was very high and application remained limited.
The introduction of SCC was associated with the drive towards the better quality concrete pursued in Japan around 1983, where the lack of uniform and good compaction had been identified as the primary factor responsible for poor performance of concrete structures. Since there was no practical means by which full compaction of concrete in a construction site could be guaranteed, the focus turned on to the elimination of the need to compact by vibration. This reason led to the development of the first practicable form of SCC. The idea of formulating SCC was first proposed by Prof. Okamura in 1986. Nevertheless, SCC was first developed in Japan in 1988 by Prof. Ozawa at the University of Tokyo to ensure homogeneity and compaction of cast-in-situ concrete within thin structuralelements thereby to improve the durability of concrete structures. Many Japanese contractors quickly followed the idea.
An important factor was that each of the large contractors formulated their own testing methods and devices. By 1988, the concept of SCC was developed and ready for the first real scale test. The first prototype of SCC was made using materials available in the market. The prototype performed satisfactorily with regard to drying; hardening shrinkage, heat of hydration and denseness after hardening. The prototype was named as ‘High Performance Concrete’. At the same time, HPC was known as a concrete with high durability due to low water-cement ratio by Professor Aitcin. Since then, the term HPC has been used around the world to refer to high durability concrete, Prof. Okamura has changed the name for the newly invented concrete to ‘self- compacting high performance concrete’ in 1997.
After 1988, European countries started working on SCC. During 1990~2000, very active research was going on in Europe and they published many specifications and guidelines for SCC. Moreover in November 2002, the first North American Conference on design and use of SCC was organized. There have been a large number of researches carried out throughout the world to optimize the fluidity of SCC, enhance its strength and durability in a cost-effective manner. According to Hajime Okamura & Ouchy (1999), the solution for achieving durable concrete structures independent of the quality of construction work, is the use of self-compacting concrete.
The reason for the development of self-compacting concrete was the problems associated with the durability of concrete structures that arose in Japan during 1983. To make durable concrete structures, concrete must be sufficiently compacted by skilled workers during casting. Due to gradual reduction of skilled workers in Japan, the quality of construction work also reduced. The cause for the poor strength & durability performance was inadequate consolidation of concrete. Due to this fact, the only solution available for the achievement of concrete structures with more durability was to use self-compacting concrete in construction.
Self-Compacting Concrete Properties
Self-compacting concrete produces resistance to segregation by using mineral fillers or fines and using special admixtures. Self-consolidating concrete is required to flow and fill special forms under its own weight, it shall be flowable enough to pass through highly reinforced areas, and must be able to avoid aggregate segregation. This type of concrete must meet special project requirements in terms of placement and flow.
Self-compacting concrete with a similar water cement or cement binder ratio will usually have a slightly higher strength compared with traditional vibrated concrete, due to the lack of vibration giving an improved interface between the aggregate and hardened paste. The concrete mix of SCC must be placed at a relatively higher velocity than that of regular concrete. Self-compacting concrete has been placed at heights taller than 5 meters without aggregate segregation. It can also be used in areas with normal and congested reinforcement, with aggregates as large as 2 inches.
Self-Compacting Concrete Uses
Self-compacting concrete has been used in bridges and even on pre-cast sections. One of the most remarkable projects built using self-compacting concrete is the Akashi-Kaikyo Suspension Bridge. In this project, the SCC was mixed on-site and pumped through a piping system to the specified point, located 200 meters away. On this particular project, the construction time was reduced from 2.5 years to 2 years. This type of concrete is ideal to be used in the following applications:
- Drilled shafts
- Earth retaining systems
- Areas with a high concentration of rebar and pipes/conduits
Self Compacting Concrete Benefits
Using self-compacting concrete produce several benefits and advantages over regular concrete. Some of those benefits are:
- Improved constructability.
- Labor reduction.
- Bond to reinforcing steel.
- Improved structural Integrity.
- Accelerates project schedules.
- Reduces skilled labor.
- Flows into complex forms.
- Reduces equipment wear.
- Minimizes voids on highly reinforced areas.
- Produces superior surface finishes.
- Superior strength and durability.
- Allows for easier pumping procedure.
- Fast placement without vibration or mechanical consolidation.
- Lowering noise levels produced by mechanical vibrators.
- Produces a uniform surface.
- Allows for innovative architectural features.
- It is recommended for deep sections or long-span applications.
- Produces a wider variety of placement techniques.
Method of Testing Click Here for Video
Testing Procedure Click Here For Written Procedure
Europe Guideline for SCC