Self Compacting Concrete

Self-compacting concrete (SCC) is a flowing concrete mixture that is able to consolidate under its own weight. The highly fluid nature of SCC makes it suitable for placing in difficult conditions and in sections with congested reinforcement. Use of SCC can also help minimize hearing-related damages on the worksite that are induced by vibration of concrete. Another advantage of SCC is that the time required to place large sections is considerably reduced. When large quantity of heavy reinforcement is to be placed in a reinforced concrete (RC) member, it is difficult to ensure that the formwork gets completely filled with concrete, that is, fully compacted without voids or honeycombs. Compaction by manual or by mechanical vibrators is very difficult in this situation. The typical method of compaction, vibration, generates delays and additional cost in the projects. Underwater concreting always required fresh concrete, which could be placed without the need to compaction; in such circumstances vibration had been simply impossible. This problem can now be solved with self-compacting concrete. This type of concrete flows easily around the reinforcement and into all corners of the formwork. 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.

The Materials used in SCC are the same as in conventional concrete except that an excess of fine material and chemical admixtures are used. Also, a viscosity-modifying agent(VMA) will be required because slight variations in the amount of water or in the proportions of aggregate and sand will make the SCC unstable, that is, water or slurry may separate from the remaining material. The powdered materials are fly ash, silica fume, lime stone powder, glass filler and quartzite filler. The use of pozzolanic materials helps the SCC to flow better. The pozzolanic reaction in SCC, as well as in Conventional Slump Concrete (CSC), provides more durable concrete to permeability and chemical attacks.

To achieve a high workability and avoid obstruction by closely spaced reinforcing, SCC is designed with limits on the nominal maximum size (NMS) of the aggregate, the amount of aggregate, and aggregate grading. However, when the workability is high, the potential for segregation and loss of entrained air voids increases. These problems can be alleviated by designing a concrete with a high fine-to-coarse-aggregate ratio, a low water–cementitious material ratio (w/cm), good aggregate grading, and a high-range water-reducing admixture (HRWRA).
Following are bases which are commonly used as superplasticizers.
• Modified Lignosulfonates(MLS).
• Sulfonated Melamine Formaldehyde (SMF)
• Sulfonated Naphthalene Formaldehyde(SNF)
• Acrylic Polymer based(AP)
•Coplymer of Carboxilic Acrylic
•Acid with Acrylic Ester(CAE)
•Cross Linked Acrylic Ploymer(CLAP)
•Polycarboxylatethers(PCE)
•Multicarboxylatethers(MCE)
•Polyacrylates
   

   Combination of above Different bases of New Generation super Plasticizers or High Water reducing agents(HRWRA) have different water reduction capacities. The advantage of this water reduction can be taken either to increase the strength as in high strength concrete or to obtain a better flowability as in case of self compacting concrete.