Abrams Cone Test (Slump Test): Assessing the workability of fresh concrete in accordance with NF EN 12350-2

On any concrete-pouring site, as soon as the concrete mixer truck arrives, testing the fresh concrete is a crucial step in ensuring that the material delivered meets the requirements of the mix design. Among the various consistency tests, the Abrams cone slump test (or slump test) remains the essential benchmark method, governed by the European standard NF EN 12350-2.

Simple, quick and requiring no external power, this test enables the workability of the concrete to be verified before it is poured and compacted in the formwork.

Why measure the slump of fresh concrete?

The workability of concrete refers to its ability to flow, fill the formwork and coat the reinforcement perfectly without the risk of segregation. Concrete that is too dry will be difficult to compact and will contain pockets of stones, whilst concrete that is too fluid due to excess water will result in a significant reduction in its final mechanical strength at 28 days.

According to the NF EN 206 standard, the consistency of concrete is classified into five slump categories (S1 to S5):

• Class S1 (Compact): 10 to 40 mm (road concrete, kerbs, specialised industrial paving).
• Class S2 (Plastic): 50 to 90 mm (shallow foundations, foundation slabs, standard floor slabs).
• Class S3 (Highly ductile): 100 to 150 mm (shear walls, beams, traditional columns).
• Class S4 (Fluid): 160 to 210 mm (heavily reinforced elements, floor slabs, easy pumping).
• Class S5 (Highly fluid): 220 mm (for self-compacting concrete, or SCC, the cone spread test in accordance with NF EN 12350-8 is recommended).

The equipment required (Abrams Cone Kit)

In order to carry out the test on site or in the laboratory under standardised conditions, the operator must have the following equipment:

• Abrams cone: Made of galvanised steel or stainless steel (height 300 mm, lower base Ø 200 mm, upper base Ø 100 mm), fitted with handles and mounting brackets.
• Support plate: Metal, rigid, flat and non-absorbent, with flanges or a cone-holding system.
• Probing rod: Smooth, cylindrical steel rod, 16 mm in diameter, 600 mm long, with rounded ends.
• Filling hopper: Made from galvanised sheet steel to facilitate the pouring of concrete.
• Measuring ruler: For measuring settlement to the nearest millimetre.
• Hand shovel or trowel.

Standard Operating Procedure (Step-by-step)

1. Preparation: Moisten the inside of the cone and the surface of the support plate, taking care not to leave any standing water. Place the cone on the plate and hold it firmly in place using the clamps or by standing on the anchoring lugs.
2. Filling in three layers: Fill the cone in three layers of equal thickness (approximately one-third of the cone’s height after each layer has been compacted).
3. Standard compaction: Compact each layer by applying 25 blows with the rammer, evenly distributed across the entire section. For layers 2 and 3, the rammer must penetrate slightly into the underlying layer.
4. Levelling: After trowelling the third layer, add a small amount of extra concrete, then level the surface to the top of the cone using a sawing motion with a straight edge or trowel.
5. Removing from the mould: Clean away any excess concrete around the base of the cone. Lift the cone vertically and gently within 2 to 5 seconds, without any twisting motion or lateral impact.
6. Measuring slump: Place the inverted cone next to the slumped specimen, position the ruler across the top of the cone and measure, using a feeler gauge or a ruler, the vertical distance between the bottom of the ruler and the highest point of the slumped concrete mass. The entire test must be carried out in less than 150 seconds.

Interpretation of subsidence patterns

The standard distinguishes between three possible behaviours after demoulding:

• True slump: The concrete slumps uniformly and symmetrically without breaking. The test is perfectly valid.
• Shear failure: Part of the concrete slips or breaks away along an inclined plane. The test is not representative; it must be repeated on another specimen. If the shear failure persists, the concrete lacks cohesion.
• Complete collapse: The concrete spreads out completely without retaining any shape (often a sign of a critical excess of water or an incompatibility between admixtures).