Flow Table Test

This is a laboratory test, which gives an indication of the quality of concrete with respect to consistency, cohesiveness and the proneness to segregation. This test is as per IS: 5512 – 1983. In this test, a standard mass of concrete is subjected to jolting. The spread or the flow of the concrete is measured and this flow is related to workability.

Flow Table Apparatus

The flow table top is constructed from a flat metal of minimum thickness 1.5 mm. The top is in plan 700 mm x 700 mm. The centre of the table is marked with a cross, the lines which run parallel to and out to the edges of the plate and with a central circle 200 mm in diameter. The front of the flow table top is provided with a lifting handle and the total mass of the flow table top is about 16 ± 1 kg. The flow table top is hinged to a base frame using externally mounted hinges in such a way that no aggregate can become trapped easily between the hinges or hinged surfaces.

Fig.1 Flow Table Apparatus

The front of the base frame shall extend a minimum 120 mm beyond the flow table top in order to provide a top board. An upper stop similar to that is provided on each side of the table so that the lower front edge of the table can only be lifted 40 ± 1mm. The lower front edge of the flow table top is provided with two hard rigid stops which transfer the load to the base frame. The base frame is so constructed that this load is then transferred directly to the surface on which the flow table is placed so that there is minimal tendency for the flow table top to bounce when allowed to fall.

Accessory Apparatus

Mould

The mould is made of metal readily not attacked by cement paste or liable to rust and of minimum thickness 1.5 mm. The interior of the mould is smooth and free from projections, such as protruding rivets and is free from dents. The mould shall be in the form of a hollow frustum of a cone having the internal dimensions as shown in Fig. 2. The base and the top is open and parallel to each other and at right angles to the axis of the cone. The mould is provided with two metal foot pieces at the bottom and two handles above them.

Fig. 2 Mould for Flow Test

Tamping Bar

The tamping bar is made of a suitable hardwood.

The table top is cleaned of all gritty material and is wetted. The mould is kept on the centre of the table, firmly held and is filled in two layers. Each layer is rodded 25 times with a tamping rod 1.6 cm in diameter and 61 cm long rounded at the lower tamping end. After the top layer is rodded evenly, the excess of concrete which has overflowed the mould is removed. The mould is lifted vertically upward and the concrete stands on its own without support. The table is then raised and dropped 12.5 mm 15 times in about 15 seconds. The diameter of the spread concrete is measured in about 6 directions to the nearest 5 mm and the average spread is noted. The flow of concrete is the percentage increase in the average diameter of the spread concrete over the base diameter of the mould.

The value could range anything from 0 to 150 per cent. A close look at the pattern of spread of concrete can also give a good indication of the characteristics of concrete such as tendency for segregation. As well as getting an accurate measurement of the workability of the concrete, the flow test gives an indication of the cohesion. A mix that is prone to segregation will produce a noncircular pool of concrete. Cement paste may be seen separating from the aggregate. If the mix is prone to bleeding, a ring of clear water may form after a few minutes.

Procedure

1. The table is made level and properly supported. Before commencing the test, the table-top and inner surface of the mould is wiped with a damp cloth.
2. The 700 mm square flow table is hinged to a rigid base, provided with a stop that allows the far end to be raised by 40 mm.
3. A cone, similar to that used for slump testing but truncated, is filled with concrete in two layers.
4. Each layer is tamped 10 times with a special wooden bar and the concrete of the upper layer finished off level with the top of the cone. Any excess is cleaned off the outside of the cone.
5. The cone is then raised allowing the concrete to flow out and spread out a little on the flow table.
6. The table top is then raised until it meets the stop and allowed to drop freely 15 times.
7. This causes the concrete to spread further, in a roughly circular shape.
8. The diameter of the concrete spread shall then be measured in two directions, parallel to the table edges.
9. The flow diameter is the average of the maximum diameter of the pool of concrete and the diameter at right angles.