What Is a Concrete Slump Test?
A Concrete Slump Test is used to measure the consistency and workability of fresh concrete. In simple terms, it explains how easily the concrete can be mixed, transported, placed, and compacted.
Concrete Slump Test
This field test has been utilized since 1922, and it remains common because of its simplicity, economy, and speed.
The test is carried out with a cone-shaped mold (which is commonly referred to as a slump cone) that is filled with fresh concrete and then placed in three or four layers, with a steel rod used to tamp the concrete in each layer.
After the cone is removed, the concrete “slumps” or settles down by the weight itself. The distance between the top of the original cone and the height of the slumped concrete is recorded, therefore the “slump.”
The IS code that governs this test in India is IS 1199.
Reasons for Carrying Out a Slump Test
Quick Quality Check: Helps identify if the concrete mix is too dry or too wet.
Check for Uniformity: Indicates consistency between batches of concrete.
Early Detection of Potential Failures: Catch an improper mix before it is poured and cracks the concrete or has other structural weaknesses.
Types of Slump in Concrete
When the cone is lifted, the concrete can assume different shapes. These shapes can be used to distinguish the type of slump:
1. True Slump
The concrete settles evenly.
This indicates a well-mixed concrete mixture that is cohesive.
2. Shear Slump
There is a side slip of concrete.
This indicates a lack of cohesive properties of the concrete mixture, which can lead to segregation.
3. Collapse Slump
The concrete breaks down completely.
This indicates too much water leading to a weak, too-flowy mix.
4. Zero Slump
The concrete keeps its shape.
Usually, the case for very dry mix typically found in road pavements and precast elements.
How It Works?
The Concrete Slump Test works on a simple principle. When a cone of concrete is inverted and released, how it slumps in relationship to gravity indicates its consistency.
A consistent, well-compacted mix will slump moderately. A watery or weak mix will collapse and a stiff mix will barely slump at all.
This principle is very useful for construction crews to understand how concrete will perform once it is poured.
The Process
To test for concrete slump, we can break down the process as follows:
Gather Equipment:
Slump Cone: Made of steel, 200 mm base, 100 mm top, and 300 mm height.
Tamping Rod: steel rod with 16 mm diameter, 600 mm long rounded end rod.
Measuring Scale:
Base Plate: non-absorbent flat surface.
Preparation:
Clean the cone and make sure the base is a stable surface.
Filling the cone:
Fill in three lifts of concrete to roughly one third of the height.
Tamp each lift 25 times with the tamping rod.
Level the Top:
When full, strike off the top surface with the rod to obtain a level surface.
Remove the cone:
Lift the cone up vertically and slowly.
Measure slump:
Get the difference in height between the top of the cone and the height of the slumped concrete.
Apparatus Description
Slump cone: Can be steel, plastic, or polymer. The cone needs to be 12″ tall and can be 8″ or 4″ at the bottom.
Base plate: Can have feet and/or a holder.
Tamping rod: Steel, at least 24″ long and 5/8″ diameter.
Tape measure: A tape measure will be useful for getting exact height measurements.
IS Code
The test process is described in IS 1199:1959. It shows consistency and accuracy. It describes everything from specimen preparation to interpretation of results.
It is important to follow the standards when you are being inspected and/or performing a large job to ensure consistency from batch to batch.
Standards from Around the World
Each region has its own testing codes.
ASTM C143 / C143M – USA.
AASHTO T119 – State transportation standards in the USA.
BS EN 12350-2 – British and European standards.
IS 1199:1959 – Indian standard.
Interpreting Slump Test Results
The amount the concrete slumps tells you about its workability:
| Slump Value | Workability |
| 0-25 mm | Very low |
| 25-50 mm | Low |
| 50-100 mm | Medium |
| 100-175 mm | High |
If you observe either a Shear Slump or Collapse Slump it is best to do another test, only a True Slump produces a reliable result.
