6.7 : Vebe Test

The Vebe test is a method used to measure the workability of concrete, particularly effective for dry concrete mixes. This test employs a specific apparatus that includes a cylindrical chamber, a standard slump cone, and a transparent disc-shaped rider, all mounted on a vibrating table. The cylindrical chamber has dimensions of nine and a half inches in diameter and eight inches in height.

To conduct the test, concrete is placed into the slump cone. The concrete is filled in layers and compacted in a standard manner. Once filled, the slump cone is removed, leaving the concrete in the shape of a truncated cone within the cylinder. Subsequently, a 6-pound transparent disc-shaped rider, supported by the apparatus, is placed on top of the concrete cone.

The vibrating table is then activated at a frequency of 50 Hertz to induce vertical movements that compact the concrete. The completion of compaction is determined when the transparent rider becomes fully obscured by the concrete, indicating that there are no visible voids on the surface of the concrete.

The workability of the concrete is quantified in terms of Vebe seconds, which is the time it takes for the concrete to transition from the initial slump cone shape to a fully compacted cylindrical shape under vibration. This duration reflects the energy required to achieve full compaction, providing a measure of the concrete's workability. Higher Vebe seconds indicate lower workability, making the concrete stiffer and harder to compact. Lower Vebe seconds suggest higher workability, with the concrete being more fluid and easier to handle and compact.