Self Compacting Concrete

 INTRODUCTION

Self compacting concrete is a type of concrete that needs no mechanical vibration or any external source for vibration for its compaction. It can be placed under its own weight and it is cohesive much to be handled without bleeding or segregation. However, the circumstances under which it is made should be free from any kind of noise or any kind of vibration that may damage or alter the property of such concrete. Such concrete is used specially in places where compacting is difficult. Hence it has been gaining traction since its discovery and is more used in important works to ensure structural performance and safety. It is widely used in various important project sites, drilled shafts, retaining systems, pipes, conduits, columns, floor finishing and many more.

Fig 1: Flooring Finish done by self compacting concrete
COURTESY: DESIGN FLOOR

ADVANTAGES
Some of the advantages of having such concrete for construction purpose are-
1. Such concrete reduces the construction time as it needs no vibration for compacting.
2. It has own setting property by virtue of its own weight and so not much labours are required.
3. It modifies and enhances the filling capacity of highly sophisticated structural elements.

4. It reduces noise pollution. Noises crossing decibels will cause vibration in the concrete and it will interfere with the matrix of it. So, no noise is encouraged nearby and quiet environment is maintained in construction.
5. It provides good structural performance and is more capable of producing durable structural members.
6. It reduces wearing of equipment which are resulted from vibration as no vibration is needed here.
7. It allows easy pumping of concrete.
8. It opens up spaces for innovative ideas to bring in aesthecity in structural elements.
9. It enables to produce superior finishes on surfaces.
10. It bonds to reinforcements better than ordinary concrete.
11. Safety of labourers are ensured as no heavy equipment are used that will induce vibration.

PROPERTIES
A concrete mix has to undergo three abilities for it to become self compacting concrete. These are –
• Filling ability
• Passing ability and
• Resistance to segregation.

Filling ability is that ability of self compacting concrete to cover all spaces when it is poured in formwork by virtue of its own weight without undergoing vibration and without keeping entrapped air inside or at the surface of concrete. Whereas passing ability is the ability of self compacting concrete to flow freely through congested openings under its own weight like in case of the spaces between reinforcements. This property indicates the concrete’s ability to have homogeneous distribution near the obstacles where it is poured. Lastly, the resistance to segregation is the resistance offered by the concrete against separation and the mixture remains uniform from transporting to placing.

TESTS AS PER EFNARC SPECIFICATIONS
Some tests are recommended for testing the passing ability, filling ability and resistance to segregation. These are –
• Slump Flow Test
• J-Ring Test
• V-Funnel Test
• U box test

Slump Flow Test – This test is used to ascertain the filling ability of self compacting concrete. This test also determines the durability of concrete and ability of concrete to flow freely without any obstructions. T50 is a secondary flow indication and this gives better indication of flowability. Here, minimum slump value should be 650 mm and maximum slump value should be 800 mm.

J-Ring Test – This test is used to ascertain the passing ability of self compacting concrete. It consists of an equipment of rectangular section of size 30 mm x 25 mm.

V-Funnel Test – This test is used to ascertain the filling ability of self compacting concrete. Here maximum size of aggregate used is 20 mm. This test comprises of funnel and concrete of about 12 litres is filled into it. The time taken for it to flow through the apparatus is measured. Then the funnel is refilled with concrete and it is left for 5 minutes to settle under its own weight. The flow time is related to segregation as when flow time increases then the segregation will also increase. The minimum and maximum time for filling ability is 6 sec and 12 sec respectively.

U box test – This test is used to ascertain the filling ability of self compacting concrete. The height of the concrete that is filled in the compartment is measured in two places and them mean is calculated. The whole test is to be performed in 5 minutes. One of the limitations of this test is that the difference in height should be between 0-30 mm.

CONCLUSION
Although advancements in researches are being made in producing more well modified self compacting concrete, the construction industry is somehow still stuck with ordinary concrete. The absence of industrial standard for self compacting concrete allows more room for creativity in producing a custom mix for specific job requirement. This advancement in technology has paved the way for more advanced self compacting concrete to replace ordinary concrete. Furthermore, fly ash or other high range water reducing admixtures can contribute more towards producing a well-advanced concrete that will be cheaper as well as more reliable. Cost is the main deciding factor in the construction industry and so self compacting concrete has to be cheap in order to make its used widespread throughout the world.