The slump flow test is the simplest and most widely used test for self-compacting concrete — and the first one you should learn. It uses the same Abrams cone as the ordinary slump test, but instead of measuring how far the concrete drops, you measure how far it spreads. That single diameter tells you the mix’s filling ability: whether it will flow under its own weight and fill formwork without vibration.
Every other SCC test — V-funnel, L-box, J-ring — is interpreted against the slump flow. Get this one right first.
What the Slump Flow Test Measures
When the cone is lifted, SCC collapses and spreads into a flat patty. Three things are read from that patty:
- Slump flow (spread diameter) — the average of two perpendicular diameters, in millimetres. This is the headline result and the direct measure of filling ability: bigger spread, more fluid concrete.
- T500 time — the seconds for the spreading concrete to reach the 500 mm diameter circle. This is an index of plastic viscosity: a longer T500 means a stickier, slower mix.
- Visual Stability Index (VSI) — a 0-to-3 visual rating of segregation and bleeding on the patty. This is the quick stability check.
Practical note: Filling ability and viscosity are independent. A mix can spread 750 mm quickly (low viscosity) or spread 750 mm slowly (high viscosity) — both fill the formwork, but they behave very differently around reinforcement and over long flow distances. That is why you record the spread and the T500.
Governing Standards
- ASTM C1611/C1611M — Standard Test Method for Slump Flow of Self-Consolidating Concrete.
- EN 12350-8:2010 — Testing fresh concrete, Part 8: Self-compacting concrete — Slump-flow test.
Both describe the same test: fill the cone in one lift without tamping, lift it, measure the spread. The test is not suitable when the maximum aggregate size exceeds 40 mm.
Apparatus
- Standard Abrams slump cone (300 mm tall, 200 mm bottom diameter, 100 mm top diameter), clean and damp inside
- Rigid, non-absorbent base plate at least 900 × 900 mm, marked with a 200 mm and a 500 mm diameter circle
- Tape or ruler reading to 5 mm
- Stopwatch (for T500)
- Scoop and strike-off bar
Practical note: The base plate must be flat, level, and fully supported. A plate that rocks or flexes lets the concrete run downhill, and your “spread” becomes a measure of the plate, not the mix.
Test Procedure
- Dampen the base plate and the inside of the cone; wipe off surplus water (a wet plate exaggerates the spread and hides bleeding).
- Hold the cone firmly centred on the plate. It may be used upright or inverted — be consistent within a project.
- Fill the cone in one lift with fresh SCC. No tamping, no rodding, no vibration — this is the critical difference from the normal slump test.
- Strike off the top level and clear away any concrete spilled around the base of the cone.
- Lift the cone vertically and steadily — about 225 mm in roughly 3 seconds — with no lateral or twisting motion. Start the stopwatch as lifting begins if recording T500.
- Let the concrete spread until it stops completely.
- Measure the largest diameter (d₁) of the patty to the nearest 5 mm, then a second diameter (d₂) approximately perpendicular to the first.
- Slump flow = (d₁ + d₂) / 2, reported to the nearest 10 mm.
- If recording T500, note the time the outer edge first touches the 500 mm circle.
- Assign the VSI rating by looking at the patty (see below).
Complete the test without interruption — from the start of filling to lifting the cone should take no more than about 2½ minutes. The test is invalid if d₁ and d₂ differ by more than 50 mm; the spread was not circular (the plate wasn’t level or the sample was disturbed) — remix and repeat.
Slump Flow Classes: SF1, SF2, SF3
EFNARC (2005) groups SCC by spread:
| Class | Slump flow | Typical use |
|---|---|---|
| SF1 | 550–650 mm | Unreinforced or lightly reinforced sections, short flow distances — e.g. slabs, trench fill |
| SF2 | 660–750 mm | Normal applications — walls, columns, beams with ordinary reinforcement |
| SF3 | 760–850 mm | Heavily congested reinforcement, long flow distances, or where the surface finish is critical |
Most structural SCC you will meet is SF2.
T500 Viscosity Classes: VS1, VS2
The T500 time is classified alongside the V-funnel time:
| Class | T500 | Meaning |
|---|---|---|
| VS1 | ≤ 2 s | Low viscosity — fast-flowing; watch stability |
| VS2 | > 2 s | Higher viscosity — slower, more cohesive; better segregation resistance |
Typical T500 values run about 2–5 seconds. ACI 237 notes that ≤ 2 s indicates low viscosity and > 5 s indicates a distinctly high-viscosity (sticky) mix.
Visual Stability Index (VSI)
Rate the patty immediately, 0 to 3:
| VSI | What you see |
|---|---|
| 0 | Homogeneous mass, no bleeding, no segregation |
| 1 | Slight bleeding — a sheen on the surface, but no mortar halo and no aggregate pile |
| 2 | Mortar halo and water sheen at the edge of the patty |
| 3 | Clear segregation — coarse aggregate piled at the centre, mortar halo around it |
VSI 0 or 1 is acceptable; the mix is considered stable. VSI 2 or 3 means segregation potential — adjust the mix (more fines, less water, or a viscosity-modifying admixture) and retest. Because VSI is visual and somewhat subjective, use it as a quality-control flag rather than a pass/fail acceptance criterion on its own.
Practical note: Judge VSI on a dry plate. A wet plate leaves a water sheen everywhere and makes every mix look like VSI 1 — wipe the plate properly before each test.
Worked Example
A trial batch for reinforced columns is tested in the lab:
- d₁ = 720 mm, d₂ = 710 mm → slump flow = (720 + 710) / 2 = 715 mm
- T500 = 3.1 s
- VSI = 1 (slight surface sheen, no halo, no aggregate pile)
Interpretation:
- Filling ability: 715 mm → class SF2 — right for columns with normal reinforcement.
- Viscosity: 3.1 s → class VS2 — a moderately viscous, cohesive mix.
- Stability: VSI 1 → acceptable, no action needed.
The mix is approved for the column pour, with the V-funnel and J-ring run as the companion checks (viscosity confirmation and passing ability through the column ties).
Slump Flow vs the Normal Slump Test
Beginners often confuse the two — they use the same cone, but they are different tests for different concretes:
| Feature | Slump flow (SCC) | Slump test (normal concrete) |
|---|---|---|
| Standard | ASTM C1611 / EN 12350-8 | ASTM C143 / EN 12350-2 |
| Filling | One lift, no tamping | Three layers, 25 rods per layer |
| Measurement | Horizontal spread (mm) | Vertical drop (mm) |
| Concrete type | Self-compacting only | Conventional vibrated concrete |
| Tells you | Filling ability, viscosity, stability | Workability/consistency of ordinary mixes |
Practical note: Never run a “slump flow” on conventional concrete or a “slump” on SCC and compare the numbers — the procedures and the meanings are entirely different. For the conventional test, see the slump test on fresh concrete.
The Full SCC Test Battery
| Test | Property checked | Standard |
|---|---|---|
| Slump flow (+ T500, VSI) | Filling ability, viscosity, stability | ASTM C1611 / EN 12350-8 |
| V-funnel | Viscosity, filling ability, segregation | EN 12350-9 |
| L-box | Passing ability (lab) | EN 12350-10 |
| J-ring | Passing ability (site) | ASTM C1621 / EN 12350-12 |
For the companion tests, see the V-funnel test, the L-box test, and the J-ring test — and the self-compacting concrete introduction for the background on the material itself.
Frequently Asked Questions
What is a good slump flow value for self-compacting concrete?
660–750 mm (class SF2) suits most reinforced structural work. 550–650 mm (SF1) is for lightly reinforced sections; 760–850 mm (SF3) is for congested reinforcement or long flow distances.
What is T500 in the slump flow test?
The time in seconds for the spreading concrete to reach 500 mm diameter. It indicates plastic viscosity: ≤ 2 s is low viscosity (VS1), more than 2 s is higher viscosity (VS2).
What is VSI in concrete testing?
The Visual Stability Index — a 0-to-3 visual rating of segregation and bleeding on the slump flow patty. 0 means homogeneous, 3 means clearly segregated. Ratings of 0 or 1 are acceptable.
Why is my slump flow not circular?
Usually the plate isn’t level, the cone was lifted with a sideways jerk, or the sample was disturbed. If the two diameters differ by more than 50 mm the test is invalid — level the plate and repeat.
Can I do the slump flow test on normal concrete?
No. The slump flow test (no tamping, spread measurement) is only for self-compacting concrete. Conventional concrete is tested with the standard slump test, which uses rodding and measures vertical drop.
The slump flow test takes five minutes and tells you three things — spread, viscosity, and stability — that govern everything else about an SCC mix. Master the plate setup, the single untamped lift, and the VSI reading, and the rest of the SCC test battery falls into place around it.
Written by Mohsin Raza Adil — BSc Civil Engineering Technologist (NTC-registered), Pakistan.