Self-compacting concrete compacts on its own, without the need for additional compaction. Vibration-free construction of concrete structures has been achieved in the past. For example, the use of “tremie” facilitates the placement of concrete under water without vibrations. Placing concrete in mass and in pits can also be carried out successfully without vibrations. But the fact is that all the instances of concrete mentioned above have minimal strength and consistent quality might be difficult to obtain. Modern applications related to self-consolidating concrete are mainly focused on more reliable and uniform quality as well as high performance.
Researchers at the University of Tokyo began developing self-compacting concrete in the late 1980s, after recognizing the scarcity of complete compaction and uniformity of concrete by vibration. Japan developed and used SSC that did not need vibration in the early 1990s. SSC gained popularity in Japan in the year 2000, for precast and ready-mix concrete products. With this, the use of self-compacting concrete began to grow rapidly.
Self-compacting concrete has been defined as the most radical advance in the area of concrete construction over a period of several decades. It was originally developed in Japan in order to balance the shortage of skilled labor that was prevalent at the time. Over time, it has proven to be remarkably beneficial due to the following advantages:
- Quick build.
- Improved durability.
- Site labor is reduced.
- The surface finish is better.
- Installation is easier.
- The work environment is also safer.
Materials used for self-compacting concrete
• Ordinary Portland cement is used.
• The maximum size of aggregate is limited to 20 mm. For structures with congested reinforcement, a size of 10 to 12 mm is preferred. Whenever possible, aggregate size greater than 20mm can also be used. Round and cubic aggregates that are well graded are also preferred. The quality of the aggregate must be uniform, in terms of granulometry and shape.
The fine aggregates can be manufactured or natural and the granulometry must be uniform throughout the work. Close monitoring of moisture content and absorption aspects is necessary to avoid compromising the quality of self-consolidating concrete. FINES are particles smaller than 0.125 mm. These particles have a say in the dust content.
• Mixing water: The quality of the water must be established in similar lines while it is used for reinforced or prestressed concrete.
• Chemical Additives: A vital component of self-consolidating concrete that is required for the necessary workability is super plasticizers.
Polycarboxylated ethers, the new generation plasticizer, are used especially for self-compacting concrete.
All other types of chemical additives can be incorporated as required, such as Viscosity Modifying Agents (VMAs), retarders for fit control, and air-entraining agents to improve freeze-thaw resistance.
Self-consolidating concrete has gained great popularity in recent years for placement in highly congested reinforced concrete structures that have difficult casting conditions. Therefore, there must be good cohesion and high fluidity in the fresh concrete. Fine materials such as fly ash can ensure that concrete has such properties.