Flow table test of concrete
The flow table test is a method used to determine the workability and consistency of fresh concrete, particularly for mixes with high fluidity. This test is crucial for evaluating concrete mix designs, ensuring construction quality, and verifying ease of placement and compaction. Unlike other tests, such as the slump test, the flow table test is particularly adept at characterizing concrete mixes that are too fluid to retain their shape when the slump cone is removed, thus providing valuable data in a range where the slump test becomes less reliable. The test’s widespread adoption in construction underscores its significance in ensuring that concrete meets the required performance criteria for various applications.
The increasing prevalence of self-compacting concrete (SCC) in modern construction practices has further amplified the importance of the flow table test. SCC, by its very nature, requires a high degree of fluidity to flow and consolidate under its own weight, filling intricate formwork and congested reinforcement without the need for mechanical vibration. The flow table test provides a direct measure of this essential characteristic, making it an indispensable tool for quality control in projects utilizing SCC. Understanding the principles and procedures of this test is therefore essential for anyone involved in the design, production, and placement of concrete, especially in scenarios demanding high workability.
Significance
The waft table take a look at is a standard method used to determine the workability and consistency of fresh concrete. It gives treasured information for concrete blend layout, construction quality manage, and ensures that the concrete may be without problems placed and compacted. This experiment ambitions to assess the flowability of concrete by measuring the spread diameter and evaluating its consistency.
Standards
The flow table test is described in, EN 12350-5: Testing fresh concrete. Flow table test”
While ASTM C143/C143M is the standard for the slump test, ASTM C1437 is for the flow table for hydraulic cement mortar. AASHTO T 222 refers to the slump test.”
Australian Standards such as AS 1012.3.5 cover the slump flow test for highly flowable concrete, which is similar in principle to the flow table test.
IS 1199: 1959 – Methods of Sampling and Analysis of Concrete and IS 516: 1959 – Method of Tests for Strength of Concrete are relevant Indian standards that cover various aspects of concrete testing. IS 9103: 1999 – Concrete Admixtures – Specification also indirectly relates to flow properties as admixtures can significantly influence workability. Additionally, IS: 6932 (PART VIII) specifically addresses the flow test table, detailing a 30 cm diameter polished steel plate with engraved annular circles and a free fall mechanism. The mold specified in this part has different dimensions compared to the EN standard. IS:4031(Part-7):1988 details methods for physical tests for hydraulic cement and includes the flow table test for mortar
Scope
The experiment makes a speciality of evaluating the float properties of concrete mixtures with varying water-cement ratios and combination sizes. It ambitions to decide the most reliable mix proportions that offer good enough workability and consistency for construction functions.
Aim
The intention of this test is to degree the drift of concrete the use of the glide table take a look at and analyze its workability and consistency houses. The experiment will also assess how factors like the water-cement ratio and aggregate size affect concrete flow
Objectives
- To determine the flowability of concrete using the flow table test.
- To measure the spread diameter of concrete on the flow table.
- To assess the consistency of concrete based on the flow results.
- To examine the have an impact on of water-cement ratio and mixture length at the float properties of concrete.
Apparatus
- Flow table apparatus with a table pinnacle measuring 700mm x 700mm.
- Mold for shaping the concrete sample (e.g., slump cone).
- Steel tamping rod (16mm in diameter and 600mm in duration).
- Stopwatch or timer.
- Weighing balance.
- Graduated cylinder or measuring container.
- Mixing equipment (e.G., concrete mixer).
- Materials: cement, aggregates (coarse and pleasant), water.
Theory
The glide desk check measures the consistency and workability of sparkling concrete. The concrete sample is placed in a mold on the flow table, and the table is lifted and dropped repeatedly through a specified height of 15mm using a mechanical device. The spread diameter of the concrete after a specific number of drops is measured as an indicator of workability and consistency. A higher spread diameter indicates better flow and workability.
Detailed Step-by-Step Procedure for Conducting the Flow Table Test
The procedure for conducting the flow table test involves a series of carefully controlled steps to ensure accurate and reproducible results. While minor variations may exist depending on the specific standard being followed, the general methodology remains consistent.
Sample Preparation: The initial step involves preparing the concrete mixture according to the desired mix design, ensuring that the proportions of cement, aggregates (both coarse and fine), and water comply with the project specifications. Thorough mixing is crucial until a uniform texture is achieved throughout the batch.
Conducting the Flow Table Test:
- The flow table, typically a flat, level surface, often a 700mm square metal plate hinged to a rigid base, is placed on a stable, horizontal surface, free from any external vibrations or shocks. The table surface and the inside of the mold, usually a frustum of a cone (similar to a slump cone but sometimes with slightly different dimensions), are cleaned to remove any debris or moisture and then dampened, taking care to avoid any standing water.
- The mold is placed centrally on the flow table, often positioned within marked guidelines (e.g., a 200 mm diameter circle). The mold is then filled with freshly mixed concrete in two or three equal layers, depending on the standard. Each layer is compacted using a tamping rod, with a specified number of blows (typically 10 or 25) distributed evenly across the surface to remove entrapped air and ensure proper consolidation. The tamping rod is usually a cylindrical steel rod of specific dimensions, or in some standards, a wooden bar.
- After the final layer is compacted, any excess concrete is carefully removed from the top of the mold using a trowel or scoop, ensuring the surface is level with the rim of the mold.
- The mold is then gently lifted vertically in a smooth, upward motion, allowing the concrete to flow out and spread freely on the surface of the flow table. The lifting should be done without any jerking or twisting to avoid disturbing the concrete mass prematurely. Some standards specify a waiting period (e.g., 30 seconds) before lifting the cone.
- Immediately after lifting the mold, the flow table is subjected to a series of jolts by lifting one side of the hinged table to a specified height (e.g., 40 mm in some standards, 15 mm in others) and allowing it to drop freely onto a stop. This lifting and dropping cycle is repeated a specific number of times (e.g., 15 or 25 times) within a defined time period (e.g., 15 seconds). Motorized flow tables are also available to ensure a controlled and consistent rate of jolting, which is particularly important for strict compliance with standards. The interval between drops should be relatively consistent, typically between 1 to 3 seconds per cycle.
- Once the jolting is complete, the diameter of the concrete spread is measured at two perpendicular directions, parallel to the edges of the table. The average of these two measurements represents the flow diameter. This measurement should be recorded to the nearest millimeter or 10 mm, depending on the standard. In some cases, if the spread is not stabilized after the jolting, a short waiting period before measurement and the time of measurement should be recorded. Additionally, the pattern of the spread is visually inspected for any signs of segregation or bleeding, which should also be noted in the report.
Adherence to each step of this procedure, including the precise dimensions of the apparatus, the number of tamping blows, the lifting height and number of jolts, and the timing of these actions, is crucial for obtaining reliable and comparable results. Variations in these parameters can significantly influence the measured flow diameter and the overall assessment of the concrete’s workability.
Calculation
To calculate the flow value of the concrete, you should follow the formula used in the Flow Table test.
value = (Diameter of spread / Diameter of the flow table) x 100
Flow Value = (Average Diameter of Spread / Initial Diameter of Concrete) x 100
Here, the “Initial Diameter of Concrete” refers to the base diameter of the mold used, which is typically 200 mm in many standards. The “Average Diameter of Spread” is the average of the two measurements taken at perpendicular directions after the jolting process. For example, if the average spread diameter is measured as 260 mm, the flow value would be (260 / 200) x 100 = 130%
Another approach, as outlined in EN 12350-5, involves simply measuring the maximum spread diameter in two perpendicular directions (d1 and d2) and reporting the mean value, F = (d1 + d2) / 2. This mean spread diameter is then used to classify the consistency of the concrete according to predefined classes.
Example
Suppose the average diameter of the circular spread of concrete is measured as 260 mm, and the diameter of the flow table is 700 mm.
Flow value = (260 / 700) x 100 = 37.14
Standard Limits for Flow table Test
The flow value obtained from the flow table test should meet certain standard limits to ensure the workability of concrete. The specific limits may vary depending on the project requirements or specifications.
As a general guideline, it is advisable for the flow value to typically fall within the range of 25% to 130%. If the flow value is below 25%, the concrete may be too stiff and difficult to place or compact effectively. If the flow value exceeds 130%, the concrete may be excessively fluid and prone to segregation or bleeding.
According to EN 12350-5, the consistency of fresh concrete can be classified based on the mean spread diameter (F) as follows :
| Class | Spread (Diameter in mm) | Description of Consistency |
|---|---|---|
| F1 | ≤ 340 | Stiff |
| F2 | 350…410 | Plastic |
| F3 | 420…480 | Soft |
| F4 | 490…550 | Very Soft |
| F5 | 560…620 | Very Soft |
| F6 | ≥ 630 | Very Soft |
It is also noted that the flow test might not be suitable for flow values below 340 mm (34 cm) or greater than 620 mm (62 cm) . In such cases, alternative methods for determining consistency should be considered
Practical Applications of the Flow Table Test in Real-World Construction Scenarios
The flow table test finds numerous practical applications in various stages of construction projects, serving as a crucial tool for ensuring the quality and consistency of concrete, especially when high workability is required.
One significant application is in projects utilizing self-compacting concrete (SCC). The high fluidity of SCC is essential for its ability to flow and fill intricate formwork without vibration. The flow table test provides a direct and reliable measure of this fluidity, allowing engineers to verify that the SCC mix meets the required flow characteristics for proper placement and consolidation. This is particularly important in complex structural elements with congested reinforcement where traditional vibration methods might be ineffective or impossible.
The flow table test is also valuable in evaluating concrete mixes intended for high-performance structures, such as bridges and dams. These structures often require concrete with specific workability characteristics to ensure proper placement and compaction, leading to the desired strength and durability. The flow table test helps in optimizing the mix design to achieve these requirements and in verifying the consistency of the concrete during construction.
Ready-mix concrete suppliers often use the flow table test as a quality control measure to ensure that the concrete delivered to construction sites meets the specified workability requirements. Upon arrival at the site, a quick flow table test can confirm that the concrete has the correct consistency before it is poured into the formwork, preventing potential issues related to placement and compaction.
In situations where limited vibration or compaction is possible, such as in thin sections or areas with difficult access, highly workable concrete is often preferred. The flow table test helps in assessing the suitability of such mixes by quantifying their flowability. Similarly, in hot weather concreting, where concrete tends to lose workability more rapidly due to increased evaporation, the flow table test can be used to monitor the consistency of the mix over time and make necessary adjustments.
Furthermore, the test can be used in laboratory settings to investigate the effects of different mix design parameters (e.g., water-cement ratio, aggregate type and size, admixtures) on the workability of concrete, aiding in the development of optimized concrete mixes for specific applications. By conducting flow table tests on trial mixes with varying proportions, researchers and engineers can determine the most reliable mix proportions that provide adequate workability and consistency for construction purposes.
Recommendations
- Optimize the water-cement ratio and aggregate size based on the desired flow and workability requirements.
- Additional investigation is warranted to assess how factors like admixtures and curing conditions impact concrete flow.
- To thoroughly validate the results, it’s vital to closely correlate the flow table test outcomes with those from related tests, notably the slump test. This comparison is critical to ensuring data accuracy and reliability.
- Conduct additional experiments to evaluate the long-term effects of flow properties on the strength and durability of concrete structures.
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