Vee-Bee Test to Determine Workability of Concrete using Consistometer

The Vee-Bee test, also known as the Vee-Bee consistometer test, is a method used to determine the workability of concrete. It measures the time taken by concrete to reach a certain degree of compaction when subjected to vibration. The test is conducted using a Vee-Bee consistometer, which consists of a vibrating table, a slump cone, and a standard shape mold.

Vee-Bee Test on Concrete

Here is the theory and objective of Vee-Bee test. The Vee-Bee test is primarily used to assess the workability of freshly mixed concrete. It provides information about the concrete’s mobility and compatibility. The test involves measuring the relative effort required to change the shape of the concrete from a conical form to a cylindrical form through vibration.

The measurement is performed by timing how long it takes for the complete remolding to occur, which is known as the remolding effort and is expressed in Vee-Bee seconds. The test was named after its developer, V. Bahrmer from Sweden. It can also be used for dry concrete. However, when the slump value of the concrete exceeds 50mm, the remolding activity happens so rapidly that time measurement becomes impractical.

Vee-Bee test Apparatus

The Vee-Bee test apparatus, based on the IS: 119 – 1959 standard, comprises a Vee-Bee consistometer and accompanying equipment shown in figure-1. This equipment includes a vibrating table that is supported and mounted on elastic supports. Additionally, it includes a sheet metal slump cone, a weighing balance, a cylindrical container, a standard iron tamping rod, and trowels.

The vibrating table shown in Figure-1 has dimensions of 380mm length and 260mm width. It is supported at a height of 305mm above the floor by a rubber shock absorber. An electrically operated vibrator is installed beneath the table. The entire assembly is mounted on a base that rests on three rubber supports.

The setup includes a sheet metal slump cone mold with openings at both ends, placed inside a cylindrical container as depicted in Figure-1. The cylinder container is attached to the vibration table using wing nuts. The cone used in this arrangement has a height of 300mm, with top and bottom diameters of 200mm and 100mm respectively.

The base of the assembly features a swivel arm holder, which is equipped with another fixed swivel arm that includes a funnel and a guide sleeve. The swivel arm can be detached from the vibrating table. A graduated rod is affixed to the swivel arm through the guide sleeve, with a provision for screwing a transparent disc. The divisions on the rod’s scale are used to measure the slump of the concrete cone. Additionally, a 20mm diameter standard iron tamping rod with a length of 500mm is used in the setup.

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Procedure of Vee-Bee Test on Concrete

To conduct the Vee-Bee test, the following procedure is followed.

Step 1:

The process begins by placing a sheet metal slump cone inside a cylinder container within a consistometer. The cone is then filled with four layers of concrete, each layer being one-fourth the height of the cone. After pouring each layer, it undergoes twenty-five tamping actions using a standard tamping rod with its rounded end.

The tamping strokes are evenly distributed to ensure that the second and subsequent layers penetrate the underlying layers. Once the final layer of concrete is placed and compacted, the surface is leveled by striking it off with a trowel. This ensures that the cone is completely filled with concrete.

Step 2:

After preparing the concrete cone, the glass disc is attached to a swivel arm and positioned on top of the slump cone within a cylindrical container. The glass disc is carefully placed to ensure it makes contact with the highest point of the concrete surface. Subsequently, the measurement is taken from the graduated rod to determine the slump value of the concrete.

Step 3:

The cylindrical cone is now lifted vertically, removing it from the concrete. A transparent disc is then placed on top of the concrete in its new position, and a reading is taken. By subtracting the value obtained in step 4 from the value measured in step 3, the slump of the concrete can be determined.

Step 5:

The electrical vibrator is activated while simultaneously starting the stopwatch. The concrete is then poured into the cylindrical container, and the vibration process continues until the concrete is thoroughly compacted. During this stage, the concrete surface levels out and adheres uniformly to the transparent disc, creating a smooth and even surface.

Step 6:

The duration for complete remolding, measured in seconds, serves as an indicator of the workability of fresh concrete. This measurement, known as Vee-Bee seconds, provides a quantitative assessment of the ease with which the concrete can be manipulated and shaped.

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Vee-Bee Test Observation and Calculations

Before unmolding, the initial reading on the graduated rod is measured in millimeters as ‘a’. After removing the mold, the final reading on the graduated rod is measured in millimeters as ‘b’. The slump of the concrete can be determined by subtracting ‘b’ from ‘a’.

The time required for complete remolding of the concrete is measured in seconds.

The consistency of the concrete is assessed using the vee-bee seconds measurement.

Vee-Bee Test Necessary Precautions

Before adding the concrete mix, it is important to clean the mold and ensure that it is free from moisture internally. This step helps in achieving better results. When applying strokes over the layers, it is crucial to do so uniformly throughout the layers. This ensures that the strokes have the desired impact and penetrate the concrete fully.

When removing the slump cone, it should be lifted upward carefully without disturbing the concrete cone in any way. This precaution helps in maintaining the integrity of the concrete structure. During vee-bee tests, it is essential to conduct them at a distance from any other source of vibration, apart from the designated vibration procedure provided in the test. This ensures accurate and reliable test results.

The remolding of concrete is considered complete when the transparent disc rider completely covers the concrete surface, and all voids and cavities in the concrete disappear. This indicates that the concrete has achieved the desired state.

How to Compare Vee-Bee Test with Other Workability Tests?

The Vee-Bee test is advantageous because it simulates the behavior of freshly mixed concrete in its actual state. This sets it apart from other tests like the slump test and the compaction factor test. However, visually determining the completion of remolding can be challenging and may introduce measurement errors, particularly in concrete mixes with high workability.

Such mixes tend to have lower Vee-Bee times. For concrete mixes with a slump value exceeding 125mm, the remolding process happens so quickly that it becomes difficult to measure the time accurately. Consequently, the Vee-Bee test is not suitable for measuring the mobility of highly workable concrete.

To address this issue, an automatic operating device that records movement time can be used in some cases. Generally, the Vee-Bee test is best suited for concrete mixes with low or very low workability. Among the three recommended workability tests (slump test, compaction factor test, and Vee-Bee test), the slump test is the most popular method for measuring concrete workability. The table below presents Vee-Bee times in seconds for various workability levels based on the American Concrete Institute 211 (ACI Committee 211) guidelines.

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FAQs about Vee-Bee Test