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Self Compacting Concrete - Basics and how to do flow table test

Dnyan Deshmukh

Knowledgeable Member
Staff member
Sep 7, 2017
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Pune
#1
Self Compacting Concrete - Basics and how to do flow table test
No a days due to increase in demand of housing and shortage of space and also the demand of architect to make structure thin. Self Compacting concrete is widely used from small to a big scale project.


Principle behind self compacting concrete - lets go to soil mechanics.
How we do compaction of soil - there are two ways
by force
or by water

when a soil is fully saturated, there are no voids in it and it get compacted.

Same way the concrete is made flow able to ensure no voids in it.

This ensures settlement of particles and hence the compaction of it.
If the flow of concrete is beyond design - it leads to segregation and bleeding.

To control the flow of concrete and to give a viscus property to concrete to make it like jelly, viscosity modifier additives were used in concrete along with super plasticizers.

It helps to avoid settlement of heavy aggregates down in the direction of gravity and accumulation of fines at top.

The accumulation of finer particle at top is a very severe issue as your wall of height up to 2 feet may be made up of slurry which is weaker and may lead to failure of structure (this happens due to no quality control over raw materials).

In normal concrete the workablity of the concrete is measured by doing slump cone test and recorded in mm for the collapse height.

For self compacting concrete, the workability of concrete is measured by its flow and its measured in mm for the out to out flow of concrete.

For measuring flow of concrete, following equipments are required;

1. Flow table - a flat sheet of metal, plastic anything non absorbent material, roughly more in size by 1 meter.
2. Slump Cone
3. Measuring tape
4. Scoop

Flow table should be placed on level ground or should be place on ground ensuring its level.

In this test, the slump cone is place in revert direction on the flow table.


Then with the help of scoop, it is filled till top without compacting and tamping.

After filling the slump cone to full height, it should be gently lifted upward.

When the slump cone is lifted, self compacting concrete by its property starts to flow out.



When there is no further movement seen in concrete, measure the flow in 3 to 4 direction and record it.

For a good self compacting concrete

Flow should be more than 650 mm

For a good pumpable concrete

Minimum fine content should be more than 450 kg

Difference between good and bad self compacting concrete is only one - good concrete flows uniformly and the spreading is slightly slow due to viscosity modification.

Bad concrete is nothing but a due to bad performing admixture, water is added in concrete at site, which leads to watery concrete which lack in uniform flow and mostly shows segregation and bleeding after placing in location.