Kelly Ball Test

This is a simple field test consisting of the measurement of the indentation made by 15 cm diameter metal hemisphere weighing 13.6 kg connected to a handle with a ruler, when freely placed on fresh concrete. ASTM C360 covers the Kelly ball penetration test. The hammer is fixed on a box container through a pin. When taking measurements, the box is placed on the top of the concrete to be tested with the surface of the hammer touching the concrete. When the pin is removed, the hammer will sink into the fresh concrete by its own weight. The depth of the hammer penetration can be read from the ruler and is used as an index of workability. A concrete with higher consistency leads to a deeper ball penetration. The penetration test is usually very quick and can be done on site, right in the formwork, provided it is wide enough. The ratio of slump value to penetration depth is from 1.3 to 2.0.

The test has been devised by Kelly and hence known as Kelly Ball Test. This has not been covered by Indian Standards Specification. The advantages of this test is that it can be performed on the concrete placed in site and it is claimed that this test can be performed faster with a greater precision than slump test. The disadvantages are that it requires a large sample of concrete and it cannot be used when the concrete is placed in thin section. The minimum depth of concrete must be at least 20 cm and the minimum distance from the centre of the ball to nearest edge of the concrete is 23 cm. The surface of the concrete is struck off level, avoiding excess working, the ball is lowered gradually on the surface of the concrete. The depth of penetration is read immediately on the stem to the nearest 6 mm. The test can be performed in about 15 seconds and it gives much more consistent results than Slump Test.

Fig. 1 Kelly Ball Apparatus

Test Procedure

• The concrete which is presumed to be tested should be poured into a container such as a buggy or actually in the form which should be up to a depth of 200mm (20cm). Then once the concrete is poured the top surface should be levelled.
• On the surface of the concrete the Kelly ball apparatus should be placed. The handles of the hemisphere (ball) should be placed in such a way that the frame touches the surface of the concrete. Away from the containers end the minimum lateral dimension of frame should be around 230 mm (23 cm).
• Then once it is done, the handle should be released slowly and the ball should be allowed to penetrate through the concrete by its own weight.
• Once the ball (hemisphere) is relieved, the penetration depth of the ball will be signified on the scale.
• Then the reading of the graduated scale should be noted down. (in which the penetration is showed).

The same procedure should be repeated at different portions for at least three times in the container and the then the average values of these readings should be taken down.