Using Slump Cones in Concrete Testing: Mastering Workability

When assessing concrete workability, a full slump cone test is indispensable. This guide provides you with practical knowledge on correctly employing slump cones to gauge the consistency of your concrete mix and insight into why accurate results are crucial for high-quality construction.

Key Takeaways

Slump cones are a cone-shaped tool used to evaluate the workability and consistency of fresh concrete by measuring the slump after the cone is removed.
The slump test involves filling the cone with concrete in three layers, each tamped 25 times, then lifting the cone and measuring the slump to check for a true slump, shear slump, or collapse slump, each indicating different properties of the concrete.
Various factors like aggregate size, water content, and mixing procedures affect the slump test results, and several standards such as ASTM C143, AASHTO T 119, and EN 12350-2 offer guidelines on how to perform the slump test across different regions.

Understanding Slump Cones: Purpose and Design

Slump cones, or an Abrams cone, is a vital tool in the world of concrete construction. This conical frustum-shaped apparatus aids in assessing the workability of fresh concrete, including zero slump concrete, before it sets.

Purpose of Slump Cones

The bottom diameter of a slump cone is 200 millimeters (8 inches). This feature aids the slump cones primary function: assessing the consistency and workability of fresh concrete on a level surface, which are two key elements in gauging concrete quality during construction.

Slump Cone Design

Standard slump cones are 305 millimeters (12 inches) high with a top diameter of 100 millimeters (4 inches) and top diameter and a bottom diameter of 200 millimeters (8 inches). It’s usually made of steel or plastic to guarantee longevity and maintain precise measurements.

Performing the Concrete Slump Cones

Performing a slump cone test necessitates a specific set of tools and equipment: a slump cone, base, tamping rod, scoop, funnel, measuring tape, and a cleaning brush.

Preparing the Test Site

The initial step is to locate a stable, vibration-free flat surface and prepare a non-porous base plate, as these measures significantly influence the accuracy of the test outcomes, especially when dealing with rotational movement.

Filling Slump Cones

Next, the slump cone is filled with concrete in three equal layers, with each layer being tamped 25 times before the addition of fill to the next.

Measuring Slump Cones

Concrete fill slump cones, gauging the slump by measuring the difference in distance from the top of slumped concrete to the level of the top of the removed slump cone, thus assessing the concrete’s workability.

Interpreting Slump Test Results

Once the slump value is determined, it’s time to interpret what it means. The results can be categorized into one end of three types: true slump, shear slump, and collapse slump.

True Slump

A true slump, characterized by the uniform subsidence of the concrete between slump cones, signifies suitable workability and consistency. It’s measured by calculating the vertical distance between the top of the slump cone and the top of the slumped concrete.

Shear Slump

A shear slump occurs when one side of the concrete shears or falls away from the main portion, indicating a lack of cohesion within the three stages of the mix.

Collapse Slump

A collapse slump signifies that a layer in the mix is excessively wet, leading to compromised structural integrity and potential shrinkage and cracking.

Factors Affecting Slump Test Results

Several variables can influence or determine the outcome of a slump test, including aggregate size, water content, and mixing procedures.

Aggregate Size

Aggregate size plays a significant role in slump test outcomes. Larger aggregates can enhance workability, leading to a higher slump, while smaller aggregates can reduce workability and result in a lower slump.

Water Content

The water-to-cement ratio influences the workability of the concrete. An elevated ratio may result in an increased slump, suggesting a high workability mix. However, it’s essential to avoid excess concrete, as it can compromise the final product’s strength and durability.

Mixing Procedures

Consistent slump test results hinge on correct mixing techniques, as differing durations of mixing can impact concrete workability, especially when using dry mixes and ready mixed concrete.

Comparing Slump Test Methods and Standards

Across the globe, different standards and methods are used for slump testing. The prevailing standards include ASTM C143 in the United States, AASHTO T 119, and EN 12350-2 in the United Kingdom and mainland Europe.

ASTM C143 (United States)

ASTM C143, the American standard for slump testing, outlines the test procedure and equipment specifications, including the use of a specific cone-shaped mold for the test.

AASHTO T 119 (United States)

AASHTO T 119 is another American standard for slump testing, used primarily for transportation-related projects. It outlines specific instructions for determining the slump of hydraulic cement concrete.

European Standard EN 12350-2 (United Kingdom and mainland Europe)

On the other side of the Atlantic, the European Standard EN 12350-2 outlines a procedure for assessing the consistency of fresh concrete using the concrete slump test, employing a cone-shaped mold and demonstrating sensitivity to variations in the concrete mixture’s consistency.

Alternative Workability Tests

Slump testing, while a reliable measure, isn’t the sole method for assessing concrete workability. Alternative tests include the flow table test, K-Slump test, and the Vebe Consistometer.

Flow Table Test

The flow table test measures the flow of concrete on a flat surface. It aids in assessing the consistency and workability of fresh concrete, as well as its transportability.

K-Slump Test

The K-Slump test uses a specialized device to measure the slump of concrete in-situ. It’s conducted by utilizing a K-Slump Tester, which is inserted into the concrete to promptly ascertain the approximate slump and workability.

Vebe Consistometer

The Vebe Consistometer measures the time it takes for a given volume of concrete to be compacted under vibration, thereby evaluating concrete workability.

Summary

In summary, slump tests with slump cones are a crucial aspect of concrete quality control, with different types of slump providing insights into the workability of concrete. Various factors including aggregate size, water content, and mixing procedures can influence the outcome of a slump test. While different standards and methods are used across the globe, they all aim to ensure the reliability of concrete slump test results. Alternatives such as the flow table test, K-Slump test, and the Vebe Consistometer provide additional ways to measure concrete workability.

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Frequently Asked Questions

What is the purpose of slump cones?

The purpose of a slump cone is to measure the workability of a fresh concrete mix according to ASTM and AASHTO standards. It is used for acceptance purposes, recording mixture characteristics, and as an indirect method for determining the water/cement ratio.

What are the 4 types of slump?

There are three types of concrete slump, that may occur in a slump test: true slump, shear slump, and collapse slump. True slump refers to a general drop of the concrete mass evenly without disintegration, while shear slump indicates a lack of cohesion.

What is a good slump for concrete?

A good slump for concrete is 4 inches or less if it’s to be consolidated by vibration, or 5 inches or less if it’s consolidated in any other way.

What do slump cones measure?

The slump test measures the consistency of a concrete mix batch and its flowability, allowing operators to identify mix defects and make adjustments.

What are slump cones used for a slump test?

Slump cones are used for a slump test is a cone-shaped mold, typically made of steel or plastic, measuring 8″ (203mm) in diameter at the base, 4″ (102mm) in diameter at the top, and 12″ (305mm) in height. It should sit on a steel base plate with bolt-on clamps to hold it steady during testing.