The concrete slump test is the simplest and most widely used field check of fresh concrete consistency and workability.
What the Test Measures
Slump is the vertical drop of a freshly moulded concrete cone after the mould is lifted. It is an indirect measure of water content and workability, used for routine quality control and to confirm batch-to-batch consistency.
Apparatus Required
- Slump cone (300 mm high, 100/200 mm diameters) and base plate
- Tamping rod (16 mm diameter, rounded end)
- Steel rule or measuring tape
- Scoop and cleaning tools
NL Scientific manufactures the Slump Cone Set and the full concrete testing range, built to ASTM, EN, BS and AASHTO requirements with ISO/IEC 17025 accredited calibration.
Test Procedure
- Dampen the cone and place it on a level, non-absorbent base plate, holding it down with the foot pieces.
- Fill in three equal layers, rodding each layer 25 times uniformly.
- Strike off the top level with the rod.
- Lift the cone vertically in 5–10 seconds without lateral movement.
- Measure the slump as the difference between the cone height and the highest point of the slumped concrete.
Calculation & Reporting
Report the slump in millimetres. EN 12350-2 also classifies slump into classes S1–S5; record the class where required.
Acceptance Criteria
The target slump is set by the specification and placement method (e.g. 50–100 mm for normal reinforced concrete). A slump outside tolerance signals a change in water content or admixture and should be investigated before placing.
Frequently Asked Questions
What causes a shear or collapse slump?
A shear or collapse slump indicates a harsh or over-wet, non-cohesive mix. Only a true (even) slump is valid; repeat the test if shear occurs.
How soon must the test be done?
Begin within a few minutes of sampling and complete the measurement promptly, as slump decreases as the concrete stiffens.
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