What is Slump of Concrete?
CivilSite.in — tools for Indian construction
Updated
Slump is a simple measure of the workability — the ease of placing and compacting — of fresh concrete, found with the slump cone test. A higher slump means a wetter, more flowable mix; a lower slump means a stiffer one. It is the quickest field check that the concrete arriving is the consistency you asked for.
How the slump test works
A standard cone (300 mm high) is filled with fresh concrete in layers, each rodded, then lifted straight up. The concrete settles under its own weight, and the drop of the top from the cone height, in millimetres, is the slump. The test follows IS 1199.
Typical slump values
| Work | Typical slump |
|---|---|
| Lean / mass concrete, pavements | 25–50 mm |
| Ordinary RCC — footings, slabs | 50–100 mm |
| Columns, thin or congested sections | 75–125 mm |
| Pumped concrete | 100–150 mm (with admixture) |
Very low slump can leave concrete hard to compact (risking honeycomb); very high slump can mean segregation and, if achieved by adding water, weak concrete.
Never raise slump with water
If the concrete is too stiff, the correct fix is a plasticiser or superplasticiser, not more water. Adding water raises the water-cement ratio and permanently cuts strength and durability. A high slump reached with admixture is fine; a high slump reached with a bucket of water is a weak pour.
Frequently asked questions
What is slump in concrete? A measure of the workability of fresh concrete — how far a cone of concrete settles under its own weight in the slump cone test, in millimetres.
What is a good slump value for concrete? About 50–100 mm for ordinary RCC slabs and footings; 100–150 mm for pumped concrete achieved with an admixture; lower for mass concrete and pavements.
How is the slump test done? A standard 300 mm cone is filled and rodded in layers, then lifted; the vertical drop of the concrete is the slump.
Can I increase slump by adding water? No — extra water raises the water-cement ratio and weakens the concrete. Use a plasticiser to increase workability instead.
Related
CivilSite Editorial Team✓ Engineer reviewed
Written and reviewed by practising civil engineers with 10+ years of Indian residential construction experience.