To determine the workability of fresh concrete by flow table test method.

To Determine the Workability of Fresh Concrete by Flow Table Test Method.

REFERENCE STANDARD:

IS: 1199–1959—Method of sampling and analysis of concrete.

APPARATUS REQUIRED:

• Metal Cone or Mould: Mould is in the form of a frustum of a cone with a base diameter of 250 mm, an upper surface diameter of 170 mm, and a height of 120 mm. The mould comes with handles for support.
• Flow Table, having a diameter of 76 cm.
• Trowel
• Scale
• Tamping Rod

THEORY:

As we are already familiar with, workability is a purely physical property of freshly mixed concrete. The workability of concrete simply means the ability to work with concrete. Fresh concrete is said to be workable if it can be easily transported, placed, compacted, and finished without any segregation. The ease of placing, compacting, and finishing concrete in the desired manner is called its workability. Concrete must be workable so that it achieves maximum density with a reasonable amount of compaction effort. If concrete is not workable or relatively less workable, it will not be compacted to its desired density, resulting in less strength and porosity ultimately. If concrete is not workable, one will not be able to place it well.

The flow A table test is performed to measure the workability of concrete. As the name suggests, in this test the workability of concrete is measured by examining the flowing property of concrete. This test is used primarily for assessing concrete that is too fluid (workable) to be measured using the slump test because the concrete will not retain its shape when the cone is removed. It gives an idea about the quality of the concrete with respect to the consistency and cohesiveness. It is usually best for concrete, which has a nominal maximum size of aggregate less than 38 mm.

PROCEDURE:

• Before commencing the test, the tabletop and inside of the mould are to be wetted and cleaned of all gritty material, and the excess water is to be removed with a rubber squeezer.
• The mould is to be firmly held on the center of the table and filled with concrete in two layers, each approximately one-half the volume of the mould, and rodded with 25 strokes with a tamping rod uniformly over the cross-section of the mould.
• After the top layer has been rodded, the surface of the concrete is to be level with the help of a trowel, and excess concrete should be removed from the table.
• The mould is then removed from the concrete by a steady upward pull.
• The table is then raised and dropped from a height of 12.5 mm 15 times in about 15 seconds with the handle of the apparatus.
• Next, measure the diameter of the spread of concrete in about 6 directions and note down the average.
• A close look at the pattern of the spread of concrete can also give a good indication of the characteristics of concrete, such as the tendency for segregation.

CALCULATIONS:

The flow of concrete:The percentage increase in the average diameter of the spreading concrete over the base diameter of the mould is called the flow of concrete. It is calculated by:

RECOMMENDED RESULTS:

The value could range anything from 0 to 150 percent.

RESULT:

The flow percent of the concrete is __________%, and the consistency of the concrete is _____________.

SAFTEY AND PRECAUTIONS

• Use hand gloves and shoes at the time of the test.
• Keep the mold and flow table clean, dry, & free from sticking concrete.
• Keep the vertical shaft lubricated with light oil.
• Keep the contact faces of the flow tabletop and supporting frame oiled.
• Keep the hand wheel, the adjustable shaft & universal joint.

Fig. 10.1 Flow Table Apparatus

Fig. 10.2 Mold and Tamping Rod