The concrete slump test is a method used to measure the consistency or workability of freshly mixed concrete. It’s a simple and widely used procedure in construction to ensure that the concrete being poured has the desired properties for its intended application.
Different concrete construction projects may require different levels of slump, depending on factors such as the method of placement, weather conditions, and structural requirements.
What is Concrete Slump?
Concrete slump refers to the measure of the consistency or fluidity of freshly mixed concrete. It’s a crucial property because it directly influences the ease with which concrete can be handled, placed, and compacted during construction.
When concrete is freshly mixed, it has a certain degree of plasticity, meaning it can be molded and shaped. The slump test measures how easily the concrete flows or slumps under its own weight when placed in a standard slump cone.
The amount of slump observed in a slump test provides an indication of the workability of the concrete. Higher slumps indicate more workable or fluid concrete, while lower slumps suggest stiffer, less workable concrete.
How to Perform a Concrete Slump Test:
Before performing the test, the equipment needs to be set up. This usually involves a mold in the shape of a truncated cone (often referred to as a slump cone), a base plate, and a tamping rod. Samples of the concrete should be taken at intervals throughout the discharge process from the truck. The metal slump cone used for slump testing is typically made from sheet metal, measuring 4’’ at the top, 8’’ at the bottom, and 12’’ high. The cone should be dampened before use, and place on a non-absorbent surface for the test.
- Fill the cone 1/3 by volume. Fill the slump cone to 1/3 by volume with the sampled concrete. Use the tamping rod to tamp the concrete 25 times, evenly across the entire cross section of the concrete sample.
- Fill the cone 2/3 by volume. Fill the slump cone to 2/3 by volume with the sampled concrete. Use the tamping rod to tamp the second layer 25 times, penetrating into (but not completely through) the first layer.
- Fill the cone to overflowing and clean away the excess. Fill the cone to overflowing. Use the tamping rod to tamp the third layer 25 times, penetrating into (but not completely through) the second layer of the sample. Remove excess concrete from the top of the slump clone. Clean away any concrete overflow from around the base of the cone.
- Lift the cone away. Carefully lift the slump cone away from the concrete sample vertically. Use a slow, even motion and do not jar the concrete or tilt the cone. This action should take no longer than 3–7 seconds.
- Measure the slump. Invert the slump cone and place it next to the slumped concrete sample. Place a straight edge across the top of the cone, and extending over the concrete sample. Measure the amount of slump in inches from the bottom surface of the straight edge to the displaced center of the slumped concrete sample.
Did you know?
The concrete slump test was developed in the 1920s by Duff Abrams, an American researcher in the field of composition and properties of concrete. Abrams was a pioneer in the field of concrete technology and made significant contributions to the understanding of concrete properties and mix design. His work, including the development of the slump test, has had a profound impact on the construction industry by providing a standardized method for assessing the workability of concrete mixes.
Now, over a century later, Duff Abrams’ concrete slump test is used daily in quality control testing of ready-mixed concrete at construction sites all over the country and around the world.
It’s a standard procedure in the construction industry for assessing the workability of concrete mixes before placement. Countries across the globe, regardless of their location or level of industrial development, utilize the slump test as a fundamental tool in quality control during concrete construction projects. The test’s simplicity, effectiveness, and ability to provide valuable insights into the consistency of freshly mixed concrete make it a preferred method for contractors, engineers, and concrete producers worldwide. Additionally, international standards organizations like ASTM International and the International Organization for Standardization (ISO) have established guidelines and specifications for conducting the slump test, further promoting its use on a global scale.
Find helpful information and free educational resources about concrete on our Concrete Resources page at TriangleReadyMix.com/edu. We also have a convenient Glossary of Ready-Mixed Concrete Terms. Triangle Ready Mix is a proud member of L&L Construction Group, along with our sister companies L&L Concrete and East Coast Civil Group.