Concrete is one of the most essential materials in modern construction. To achieve durable and high-quality concrete, its workability and consistency must be carefully assessed by selecting the right mix of water, cement, aggregates, and admixtures. Whether for casting slabs, columns, or pavements, concrete must be easy to mix, place, and compact without segregation. To evaluate this property in the laboratory, engineers use the Flow Table Test, a standardized workability test that measures the consistency and flowability of freshly mixed concrete. This simple yet effective test helps determine how well a concrete mix can spread under its own weight, ensuring quality and performance at the construction site.
Read this blog to understand what the flow table test is, the procedure for conducting the test, and the IS codes related to it.
What is the Flow Table Test?
The flow table test is used to measure the workability and flowability of a freshly prepared concrete mix. In this workability test, the concrete is placed in a cone-shaped mould on a flow table. As soon as the cone is lifted upward, the concrete starts to spread. The extent of this spread will be used to calculate the workability of the concrete.
This test is mainly used for concrete with great flowability and small-sized ingredients, like stone sizes less than 38 mm. Based on this test result, engineers and construction workers can make adjustments to the mix ratio to suit the project’s requirements.
What are the Flow Table Test Apparatus?
The flow table test apparatus generally involves the following:
- Flow Table: A square, flat metal table with a hinged base. Commonly used apparatus dimensions are around 700mm x 700mm or smaller.
- Measuring Scale: Used to measure the diameter of the concrete spread on the flow table.
- Trowel: A flat, metal tool used to place concrete into the mould and for smoothing and levelling the concrete surface within the mold, maintaining uniformity.
- Cone-shaped Metal Mold: This mold is used to hold the fresh concrete or mortar sample before the test. Common dimensions are a base diameter of 25 cm, top diameter of 17 cm, and height of 12 cm, as per IS 1199.
- Tamping Rod: A cylindrical steel rod used to compact the material inside the mold evenly, removing air pockets.
Stepwise Flow Table Test Procedure
The Flow Table test on concrete will be conducted following this procedure:
Step 1: Prepare the Equipment: Clean and dry the entire apparatus setup, including the tabletop and the mould, to remove any gritty materials for ease of conducting the test. Place the frustum cone firmly at the center of the flow table.
Step 2: Fill the Cone: Fill the cone with freshly mixed concrete in two layers; each layer should be one-half of the volume of the mould. Tamping each layer 25 times with the tamping rod.
Step 3: Level the Surface: Ensure the top of the cone is level by removing excess concrete using a trowel. Wipe and clean the table surface around the mould.
Step 4: Lift the Mold: Slowly lift the mold up so that the concrete can flow.
Step 5: Measure the Spread Diameter: Measure the diameter of the concrete spread out in at least two perpendicular directions and calculate the average.
Calculation for the Flow Table Test
The flow value of concrete is the ratio of the percentage increase in the average diameter to the base diameter of the mould.
The flow value will be calculated using the formula:
Flow Value = ((Diameter of spread – Diameter of Mold)÷ Diameter of Mold) x 100
Result of Flow Table Test
The value of the flow test varies from 0 to 150%.
IS Code for the Flow Table Test
In India, the Flow Table Test for concrete is governed by the following standards:
- IS 1199: 1959 – Specifies the standard procedure for the Flow Table Test, including other workability tests. It also gives details about the apparatus, test method, and calculation of flow percentage.
- IS 9103: 1999 – Give specifications for chemical admixtures such as plasticizers and superplasticizers to improve the workability of concrete and maintain consistency.
Advantages of the Flow Table Test
- Simple and Time-Efficient: The test procedure is straightforward and operator training is minimal, allowing for rapid assessment of fresh concrete.
- Requires minimal equipment: Only a flow table, mold, and basic hand tools are needed, making it accessible to many labs and field locations.
- Effective for evaluating concrete with high fluidity: It is ideal for mixes like self-compacting concrete or other highly workable concretes that are difficult to measure by slump tests.
- Reliable for checking Workability: The flow spread measurement indicates how well the concrete will perform in placement without segregation.
Limitations of the Flow Table Test
- Not applicable to all Concrete Mixes: This testing method is not suitable for concrete with low fluidity.
- Operator Technique With Variations: Any small variation while performing the test will impact the result, causing inaccuracy.
- Need for Careful Procedure: Requires an experienced lab performer to follow standard procedures with maximum precision to obtain correct results.
Factors Affecting the Workability of Concrete
The following are different factors impacting the workability of concrete:
- Aggregate Cement Ratio: If the cement content is high in the concrete, it reduces the friction, easing the movement of aggregates during mixing, transportation, placement, and compaction. This way, overall workability also increases.
- Water/cement Ratio: A rising water-cement ratio increases the workability of concrete. However, using too little water can hinder proper hydration, resulting in poor strength development, while using too much water can weaken the concrete. The best water-cement ratio for good workability is typically 0.45 to 0.55.
- Aggregate Shape and Size: Aggregates with a rounded or slightly irregular shape improve the flow and workability. Conversely, elongated, angular, and flaky aggregates are harder to mix, have a larger surface area to cover, and thus result in lower workability of concrete.
- Temperature: Elevated temperatures speed up setting and increase viscosity, reducing flow. Below 0°C, the setting halts, impacting workability. The ideal temperature range for flow test accuracy is about 14°C to 18°C.
- Use of Admixtures in Concrete: Admixtures such as plasticizers and superplasticizers considerably improve concrete workability without affecting strength. Also, mineral admixtures such as pozzolanic materials enhance the flow and performance of concrete mixes.
In conclusion, the flow table test is ideal for evaluating the workability and consistency of highly fluid or self-compacting concrete that is difficult to measure by other workability tests. This test will help to ensure that the concrete mix can be easily placed and compacted without segregation, improving the overall quality and durability of the building. Although this test has its own limitations, it is often used and considered essential in current concrete quality control. For professional construction services that prioritise concrete testing and high-quality construction work, consider working with Brick & Bolt, where expert engineering meets reliable construction solutions for your dream home.
Frequently Asked Questions
1. What is the purpose of the Flow Table Test?
The Flow Table Test measures the workability and flowability of fresh concrete, particularly useful for highly fluid or self-compacting mixes to ensure proper consistency and placement.
2. What does the flow value indicate in this test?
The flow value represents the percentage increase in the concrete’s spread diameter from the mould size, indicating its fluidity and workability.
3. How is the Flow Table Test different from the Slump Test?
The Flow Table Test is better suited for high-workability or very fluid concrete mixes that may collapse in a Slump Test, providing a more accurate measure for such mixes.
4. Why is the Flow Table Test important in construction?
It ensures quality control by verifying that concrete has adequate workability for easy placement and compaction, reducing segregation and ensuring uniform strength.