Concrete Slump Test Apparatus: Fresh Workability Slump Testers and Cones
Introduction to Concrete Workability
Workability of concrete is a key property that determines how easily a concrete mix can be mixed, transported, placed, and finished on site. It refers to the ability of fresh concrete to flow, fill formwork, and consolidate around reinforcement without segregating or losing homogeneity. Achieving the right workability is essential for ensuring the quality, strength, and durability of the finished structure. Several factors influence the workability of fresh concrete, including the water cement ratio, the size and shape of aggregates, and the use of admixtures. In most cases, a well-designed concrete mix with good workability will allow for smooth placement and compaction, reducing the risk of defects and ensuring optimal performance. The concrete slump test is the most widely used method to evaluate the workability of fresh concrete, providing a quick and reliable measure of how the concrete will behave during placement. Other methods, such as the flow table test, are also used to assess cement mortars. By performing a slump test, construction teams can assess the consistency and flow of the concrete mix, making adjustments as needed to achieve the desired quality and performance for any project. Tools for testing fresh concrete—such as the Deslauriers Fresh Concrete Field Test Starter Kit—can help ensure field measurements meet industry standards.
Concrete Slump Test in Fresh Concrete Testing
The concrete slump test is the most popular method to test the consistency and workability of fresh concrete. In this test, a concrete sample, known as the specimen, is evaluated to determine how well it will flow, settle, and hold its shape after placement so the material will perform optimally for the project. Concrete slumps can indicate many things in the concrete mix, whether the batch is too wet, too dry or just right. These are important when building pavements, hard standing slabs, trench filled foundations and other critical parts of modern infrastructure.
In simple terms the slump test is used to measure the workability or consistency of hydraulic cement concrete. A concrete slump is a measure how much a pile of concrete mixture settles after a slump cone is filled and then removed. This simple test gives how much a pile of concrete’s ease of handling, placement and ability to consolidate around reinforcement like steel.
Types of Slump in Concrete Testing
There are several types of slump in a slump test which indicates the consistency of the concrete:
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True Slump: In a true slump the concrete settles evenly, maintains its original shape but with a decrease in height. This means the mix has a good balance of cohesion which is ideal for normal reinforced concrete structures like foundations.
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Shear Slump: This type of slump occurs when part of the batch shears off and slips sideways. A shear slump means the mix is not well balanced, either due to poorly mixed batch or too much water which can lead to poor performance in the final structure.
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Collapse Slump: A collapse slump occurs when the concrete collapses completely when the cone is removed. This is usually due to excess water in the mix which can reduce the strength and durability of the slabs or foundations being built. A collapse slump is not desirable for most projects but may be acceptable for specialist applications that require very fluid material.
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Zero: If it does not collapse or settle at all when the cone is removed this is called a slump at zero. This means the mix is very dry and lacks and is not suitable for most projects unless used in specific conditions like strip footings or pipework bedding. Zero slump concrete is too stiff to be workable under field conditions without extensive vibration or water reducing admixtures.
Equipment Used for Slump Testing
Accurate slump testing relies on a set of specialized equipment designed to measure under real-world conditions. The core of the slump cone test set is the slump cone itself, also known as the Abrams cone—a sturdy, hollow steel mold with a flat base and a convenient carrying handle for easy transport. The cone is engineered for rust resistance and durability, ensuring reliable performance even in harsh site environments. During the test, the cone is placed on a robust base plate, which is often fitted with clamps to hold the mold securely in place throughout the procedure.
The graduated tamping rod not only helps consolidate but also serves as a measuring tool to ensure each layer is properly filled. After the cone is filled and leveled, it is carefully lifted, allowing it to slump under its own weight. The difference in height is measured using a graduated scale, which is an essential part of the slump test set. For consistent and accurate results, using a Slump Tamping Rod allows precise consolidation during the test.
Additional components such as a funnel and scoop are used to help fill the cone evenly and efficiently, while a brush is often included for cleaning the equipment after each test to maintain accuracy and prevent contamination. All parts of the slump cone test set are constructed from high-quality, corrosion-resistant materials to withstand repeated use on site or in the lab. This comprehensive set of equipment ensures that every slump test provides a reliable measure, helping construction professionals maintain quality and consistency in every batch.
How to Measure Slump
Measuring slump is a simple but important procedure. Once the cone is removed, measure the height of the slumped using a ruler or straightedge placed horizontally across the top of the mold. The difference between the height of the original cone and the slumped is the slump value which is usually measured in inches or millimeters. The average slump value will give an idea of the consistency of the mix and whether the mix is suitable for the application. The testing equipment is designed as a single, integrated unit, combining all necessary components to facilitate efficient and accurate measurement.
The slump value can vary depending on many factors such as water cement ratio, admixtures, presence of reinforcement, shape and size of aggregate used. For example low values means stiff dry material and high slump values means wet workable mix. In most cases the right consistency for a batch is between true slump and moderate slump value depending on the project requirement. It is also important that all improperly mixed batch be discarded. And improperly mixed batch can lead to confusion in the results.
Slump in Different Applications
The slump value required for a project will depend on the application and condition. The slump between 2-4 inches (50-100 mm) is typical for light reinforcement structures like walls, strip footings or pipework bedding. Higher slump value is required for projects that need more fluidity like placing it in tight spacing or complex reinforcement grids. Dry mixes with zero slump is rarely used except for trench foundations or where vibration is used to settle.
To accommodate different project requirements, slump cone test sets are available in various configurations, allowing for adaptability in measuring.
