The flow table test is a well established method for determining the consistency and workability of fresh concrete, particularly for mixes where the nominal maximum size of aggregate does not exceed 38 mm. Governed by IS 1199 1959, this test measures the spread of concrete under a standardised jolting action, providing a quantitative value that helps engineers assess whether the mix possesses the required degree of workability for a given application. Understanding flow characteristics is essential because workability directly influences placing, compaction, and ultimately the strength and durability of hardened concrete. For an alternative method, see our article on the Vee Bee Test To Determine Workability Of Concrete Using Consistometer, which measures the time required to remould a sample under vibration.
Understanding The Flow Table Test For Concrete Workability
The flow table test belongs to a family of workability assessment techniques that evaluate how easily fresh concrete can fill formwork under its own weight or under mild external energy. Unlike the slump test which relies on gravity alone, the flow table applies a controlled jolting action that simulates the dynamic conditions concrete experiences during compaction and placing. This makes it especially useful for mixes with low to medium workability where the slump test alone may not provide sufficient discrimination between batches.
The principle is straightforward. Fresh concrete is placed inside a truncated cone mould at the centre of a metal flow table. After removing the mould, the table is raised and dropped repeatedly from a fixed height of 12.5 mm, causing the concrete to spread outward. The increase in diameter of the concrete patty, expressed as a percentage of the original base diameter, is known as the flow value. This value correlates directly with the consistency and cohesiveness of the mix. The test is particularly sensitive to changes in water cement ratio, aggregate gradation, and the presence of admixtures. For a related method, refer to the Slump Flow Test On Self Compacting Concrete For Workability, which evaluates the free flow capacity of highly workable concrete mixes.
Equipment Required For The Flow Table Test
Conducting the test in accordance with IS 1199 1959 requires specific equipment, each component playing a vital role in obtaining accurate results.
- Flow table A rigid metal table with a smooth, plane top surface mounted on a sturdy frame, designed to be raised and dropped from a height of 12.5 mm.
- Mould A truncated conical mould made of metal, with an internal base diameter of 250 mm, a top diameter of 170 mm, and a height of 120 mm, open at both ends with handles for easy removal.
- Tamping rod A standard steel rod 16 mm in diameter and 600 mm long, with one end rounded, used to compact concrete in two uniform layers.
- Measuring equipment A caliper or graduated scale capable of measuring the spread diameter to the nearest 5 mm.
- Trowel and rubber squeezer For striking off excess concrete and removing excess water from the table top and mould surfaces.
All equipment must be kept clean and dry. The vertical shaft and cam mechanism must be lubricated and maintained so the drop height of 12.5 mm remains consistent. Even a small deviation introduces variability in the measured flow value. When concrete compression results are questioned on site, some engineers explore alternative evaluation techniques. One such method is discussed at If Concrete Compression Test Fails Should Schmidt Hammer Test Be Adopted As An Alternative Test To Prove The Concrete Strength.Html, which examines non destructive testing for hardened concrete.
Step By Step Procedure For The Flow Table Test
The procedure consists of six clearly defined steps that must be followed methodically to obtain reliable results.
- Prepare the equipment Wet the table top and inside of the mould. Remove all gritty material and excess water using a rubber squeezer to ensure consistent friction conditions.
- Fill the mould Hold the mould firmly at the centre of the table. Fill it in two layers, each approximately half the volume, and rod each layer with 25 strokes of the tamping rod distributed uniformly over the cross section.
- Strike off the surface After rodding the top layer, strike off excess concrete with a trowel so the mould is exactly filled and the surface is level with the top.
- Remove the mould Lift the mould off by a steady upward pull. The concrete patty should remain in the shape of a truncated cone on the centre of the table.
- Execute the jolting action Raise the table and drop it freely from 12.5 mm height. Repeat 15 times within about 15 seconds, maintaining a steady rhythm. The jolting causes the concrete to spread radially outward.
- Measure the spread Measure the diameter of the spread concrete using a caliper. Take six symmetrically distributed measurements and calculate the average, recording each to the nearest 5 mm.
The entire process should be completed without interruption to prevent stiffening. For a broader overview of how different workability tests compare, read Slump And Compacting Factor Test Values And Uses In Concrete Workability, which explains when each test is most appropriate.
Calculating And Interpreting The Flow Value
The flow of concrete is expressed as the percentage increase in the average spread diameter compared to the base diameter of the mould.
Flow (%) = [(D avg – D0) / D0] x 100
D avg is the average diameter of the spread concrete in mm, and D0 is the base diameter of the mould which is 250 mm. For example, if the average spread diameter is 400 mm, the flow value is [(400 – 250) / 250] x 100 = 60%. This value is reported as a percentage to the nearest whole number, accompanied by the reference standard and details of the concrete mix.
| Flow Value Range (%) | Workability Classification | Typical Application |
|---|---|---|
| 0 to 25 | Very Low | Vibrated concrete in heavy sections |
| 25 to 50 | Low | Mass concrete, pavements |
| 50 to 75 | Medium | Reinforced concrete sections |
| 75 to 100 | High | Thin sections, heavily reinforced members |
| Above 100 | Very High | Self compacting concrete with admixtures |
The flow table test is most powerful when interpreted alongside other workability tests. To study how workability classifications relate to concrete strength and durability, refer to Workability Of Concrete Types And Effects On Concrete Strength, which explains the trade off between workability and compressive strength.
Safety Precautions And Equipment Maintenance
Working with fresh concrete and mechanical equipment requires attention to both personal safety and instrument maintenance.
- Personal protective equipment Wear hand gloves and safety shoes during the test. Concrete is alkaline and can cause skin irritation upon prolonged contact.
- Cleanliness of equipment Keep the mould and flow table clean, dry, and free from hardened concrete between tests. Residual concrete alters the friction coefficient and affects spread behaviour.
- Lubrication Keep the vertical shaft lubricated with light oil for smooth operation. Oil the contact faces of the flow table top and supporting frame to prevent rust.
- Inspect the cam mechanism Check the adjustable shaft, hand wheel, and universal joint for wear. Misalignment produces inconsistent jolting energy and unreliable results.
- Calibration Verify the drop height is exactly 12.5 mm using a feeler gauge or calibrated block. Record calibration dates in the laboratory logbook.
Proper maintenance ensures repeatable results across batches tested weeks apart. For another standardised method of measuring concrete workability, see Compaction Factor Test For Concrete Workability Method And Procedure, which uses the degree of compaction achieved by free fall of concrete.
Conclusion
The flow table test as specified in IS 1199 1959 remains a practical and reliable method for evaluating the consistency of concrete where the nominal maximum aggregate size does not exceed 38 mm. The test offers several advantages: sensitivity to mix variations, a quantitative percentage output for quality control, simulation of vibration compaction energy, and good repeatability within plus or minus 5 percent when conducted with well maintained equipment. However, it is limited to aggregate sizes below 38 mm, has some operator dependence in the jolting and rodding technique, and is not ideal for very high workability mixes such as self compacting concrete.
By measuring the percentage increase in diameter after a standardised jolting sequence, engineers obtain a quantitative flow value that reflects the workability of the fresh mix. The test is simple to perform, requires inexpensive equipment, and provides results that correlate well with concrete behaviour under vibration on site. When combined with other methods such as the slump test, the compaction factor test, and specialised tests for high workability concrete, the flow table test forms an important part of a comprehensive quality control programme. For evaluating self compacting concrete in particular, the L Box Test On Self Compacting Concrete For Workability provides additional data about the passing ability through congested reinforcement. Selecting the right workability test and interpreting its results correctly is essential for producing durable, high quality concrete structures that perform as intended throughout their service life.