What is Concrete Slumping?
Concrete slump can be defined as the measure of the amount of fresh concrete that will settle or collapse after a slump test. It is a reflection of the concrete mixture’s flow—whether it is wet and fluid or a combination of stiff mixes or dry mixes—and its ability to retain its shape after being placed.
Slumped concrete can take various forms based on the concrete mixture composition, air content in the mixture, temperature, and several other factors related to site conditions. There are four types of slump concrete. They include true slump, shear slump, collapse slump, and zero slump.
They cover a standard slump test range, from stiff mixtures with low flowability to highly workable mixtures with high flowability. These results are all based on the concrete mixture composition and the desired slump test for the construction project.
Why is Concrete Slump Important?
Measuring slump is a critical step in the on-site quality control of ready mix concrete and any further concrete supplied to construction projects. It gives information on whether the average slump or average slump value results meet the desired level of slump for placement, compaction, and finishing in real-world field conditions.
Perfect Concrete Mix
When the slump test results are within the standard slump range, the concrete flows freely into moulds, around the reinforcement, and fills walls, trench-filled foundations, and hard-standing slabs without separating. This ensures that the concrete maintains its structural integrity without depending on unrestrained concrete or excess water to hold it together.
High Slump
If a high slump occurs due to excess water or an improperly mixed batch, the mixture may separate or lose its strength.
Low Slump
In contrast, a low or medium slump indicates stiffer mixes, which can make it difficult to place, particularly in areas such as pavements, foundations, or pipework bedding, where a workable but controlled consistency is required.
Identifying the difference early allows you to make any necessary adjustments to the concrete mix before pouring, ensuring the right consistency, strength, durability and overall performance.
What is a Concrete Slump Test?
A concrete slump test is a simple on-site method used to check whether the consistency and concrete’s workability of each batch meet the required standards.
When The Cone Is Filled
The test uses a steel cone (also known as a slump cone) placed upside down on a base plate. The cone is then filled in layers, with each layer compacted using a steel rod. Once the cone is filled and excess material is smoothed off, the cone is carefully lifted upwards, allowing gravity to act on the concrete sample.
The slump measurement is determined by comparing the height difference between the original height of the steel cone and the slumped concrete.
This difference indicates the concrete’s flowability, showing whether the mix is stiff with a small aperture (low mobility) or more fluid with high flowability.
A concrete slump test highlights any potential problems in fluidity, cohesion, or aggregate balance before the concrete is poured.
What is The Ideal Slump Value for Concrete?
The ideal slump value depends on what you’re using the concrete for and what the requirement is for that specific job. In the UK, concrete slump is classified under BS EN 206, which defines five classes based on an acceptable slump range.
These classes ensure the concrete refers to a suitable balance between strength, stability, and workability for its intended use, including walls, structural elements, kerb and pipework bedding applications.
| Slump Class | Slump Value (mm) | Typical Use | Performance Characteristics |
| S1 | 10-40 mm | Pavements, strip foundations | Low slump provides good shape retention and stability |
| S2 | 50-90 mm | Foundations, ground beams | Moderate workability with controlled flow |
| S3 | 100-150 mm | Normal reinforced concrete | Balanced flow and stability for most structural work |
| S4 | 160-210 mm | Piles, heavily reinforced sections | High slump improves flow in congested areas |
| S5 | ≥ 220 mm | Specialist applications only | Very high flow, strict control required to avoid a collapse slump |
Get Professional Help With Your Concrete Slumping
Have confidence that your mixed concrete performs exactly as expected with professional concrete slump testing from STS. Our fast, accurate testing helps ensure your concrete meets the required workability and quality standards on every pour.
Book your slump test today and keep your project moving with confidence.
