Self Compacting Concrete With Marble Powder

Concrete is a very important construction material that contributed immensely to the development of the civilization. The material has seen tremendous development from High performance concrete, High Early Strength Concrete, High Strength Concrete, Self Compacting concrete.

With increase in demand in the rate of construction and demand to decrease different type of pollution, including sound pollution, Self Compacting Concrete or SCC was developed. This type of concrete has more mortar in it by increase in the amount of fly ash, Sand/Aggregate ratio, etc. As a result concrete behaves as a solution with Coarse Aggregate floating in it. This type of concrete has great potential in future as this type of concrete does not require vibration.

Present-day self-compacting concrete can be classified as an advanced construction material. As the name suggests, it does not require to be vibrated to achieve full compaction. This offers many benefits and advantages over conventional concrete. These include an improved quality of concrete and reduction of on-site repairs, faster construction times, lower overall costs, facilitation of introduction of automation into concrete construction. An important improvement of health and safety is also achieved through elimination of handling of vibrators and a substantial reduction of environmental noise loading on and around a site.

Valeria et al. mentions that high fineness of marble powder is proved to be very effective in assuring very good cohesiveness of mortar and concrete, even in the presence of super plasticizing admixture, provided that water to cement ratio was adequately low. Marble powder has a very high Blaine fineness value of about 1.5 m2/g, with 90% of particles passing 50?m-sieves and 50% under 7?m.

Similar work has been reported by the research work led by Dr. Supratic Gupta. They have found that with an increase in the mortar density, the segregation index increases irrespective of other parameters. Also increase in volume of fines (cement and fly ash) at the cost of decrease in sand, the segregation index decreases.

Hence, sand plays a more crucial role than the fines towards improving segregation resistance. Since Marble powder has higher density, it is assumed that this would improve the segregation resistance of the Self Compacting Concrete.

Hanifi Binici et al. found that Marble dust concretes had higher compressive strength than that of the corresponding Lime stone dust and control concrete with equivalent w/c and mix proportion, the results indicate that the Marble dust concrete would probably have lower water permeability than the lime stone and control concrete. It is in this respect that marble powder is expected to play an important role in Concrete, and SCC in particular.

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Self Compacting Concrete

Self compacting concrete compacts on its own, without any need for further compaction. Building concrete structures sans vibration has been accomplished in the past. For instance, the use of "tremie" facilitates the placement of concrete underwater without vibration. The placement of shaft and mass concretes can also be done successfully without vibration. But the fact is all the above mentioned instances of concrete are of minimized strength and consistent quality could be difficult to obtain. Modern applications pertaining to self compacting concrete are primarily focused on reliable and better uniform quality as well as high performance.

Researchers at Tokyo University began to develop self compacting concrete during the late 1980's, after recognizing the shortage of complete compaction and uniformity of concrete by vibration. Japan developed and utilized SSC that did not need vibration, by the early nineties. The SSC gained popularity in Japan by 2000, for ready mixed concrete and prefabricated products. With this, the use of self compacting concrete began to grow rapidly.

Self compacting concrete has been defined as the most radical advancement in the area of concrete construction for a period of several decades. It was originally developed in Japan for the purpose of balancing skilled labor shortage that was prevalent then. Over time, it has proved to be remarkably beneficial owing to the following advantages:

Quick construction.
Enhanced durability.
Site manpower is reduced.
The surface finish is better.
Placing is easier.
The working environment is safer too.

Materials Used for Self Compacting Concrete

• Ordinary Portland cement is used.
• The maximum aggregate size is limited to 20mm. For structures with congested reinforcement, a size of 10 to 12 mm is preferred. Aggregate size greater than 20mm can also be used whenever possible. Rounded and cubical aggregates that are well graded are also preferred. The quality of the aggregate has to be uniform, with regard to grading and shape.

Fine aggregates can either be manufactured or natural and the grading has to be uniform during the complete work. Close monitoring of the content of moisture and the aspects of absorption is necessary to avoid compromising on the quality of self compacting concrete. FINES are particles that are smaller than 0.125 mm. These particles have a say in the powder content.

• Mixing water: The quality of water has to be established on similar lines while using for prestressed or reinforced concrete.
• Chemical admixtures: One vital component of Self Compacting concrete that is required for necessary workability is super plasticizers.

Poly-carboxylated ethers, the new generation plasticizer, is specially used for self compacting concrete.
All other type of chemical admixtures can be incorporated as per the requirements, like Viscosity Modifying Agents (VMA), retarders for settings control and air entraining agents to enhance the resistance to freeze-thaw.

Self compacting concrete has won wide popularity in the past few years to be used for placement in highly congested reinforced concrete structures possessing difficult casting conditions. Hence, there must be good cohesiveness and high fluidity in the fresh concrete. Fine materials on the likes of fly ash can make sure that the concrete possesses such properties.

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