Slump Test
vs Slump Flow —
When Each Is Right.

Codes & standards referenced

Why this matters

Workability is a multi-dimensional property. A concrete that flows under vibration may not flow under its own weight; a concrete that flows under its own weight may segregate under vibration. Two different concrete families answer two different questions about workability, and the test apparatus is the only thing the two have in common. Operators who have internalised one test default to it when the other is required; the result looks familiar and reads as wrong only on the second pour, the cube report, or the slab. The test you pick is upstream of every acceptance decision on the truck.

The cost of the wrong test is rarely on the testing day. It surfaces in the cube report two weeks later, in a pour rejected at the pump, or in a slab whose 28-day strength has been quietly compromised. The QC log carries a number; the QC log does not always carry the procedure used to get the number. By the time the cube report tells you the number was meaningless, the truck, the slab and the decision have all moved on.

The slump test (IS 1199)

The Abrams cone is a frustum (a truncated cone) of 1.6 mm galvanised steel, 300 mm tall, 100 mm inside diameter at the top, 200 mm inside diameter at the base. The cone has two foot-pieces welded to the rim at the base for the operator to stand on, and two handles at the top for the lift. The tamping rod is a 16 mm-diameter, 600 mm-long steel rod, bullet-nosed at the tamping end. The base plate is a flat, non-absorbent, rigid plate. The scoop is a round-nosed scoop suitable for placing concrete without segregation. The whole test, from fill to lift, runs in about five minutes.

Procedure — five steps

1. Position the cone. Place the cone on the base plate, centred, small opening up. Hold it steady by standing on the two foot-pieces throughout the filling operation.
2. Fill in three equal layers. Fill the cone with concrete in three layers of approximately equal volume. Rod each layer 25 times with the bullet-nosed rod, distributing the rodding uniformly over the cross-section. Each rodding stroke must penetrate into the layer below.
3. Strike off. Strike off the top of the concrete flush with the rim of the cone using a sawing and rolling motion of the tamping rod. Clean any spilled concrete from around the base of the cone.
4. Lift vertically. Lift the cone straight up, vertically, in three to seven seconds. The lift is the test's moment of truth — a sideways lift shears the sample; a slow lift lets the concrete sag and over-reads. Place the lifted cone upside-down on the base plate next to the displaced concrete.
5. Measure and record. Measure the slump as the vertical distance between the top of the cone (now used as a reference) and the highest point of the displaced concrete. Record the reading in millimetres, the visual outcome (true / shear / collapse), the time from batching, and the ambient and concrete temperatures.

Reading the slump

The reading is in millimetres. Typical targets for vibrated concrete in India, depending on member type and reinforcement density: 75–100 mm for beams, columns and walls; 100–125 mm for slabs, foundations and lightly reinforced members; 50–75 mm for heavily reinforced members, pavements, and mass-concrete work where a stiffer mix is required. Outside these bands, the mix is either too wet or too stiff for the member — and each failure mode has a different downstream consequence. A wet mix segregates and is porous; a stiff mix is hard to compact and leaves voids.

The visual interpretation is part of the test, not a footnote. A true slump is the only valid outcome. A shear slump means the mix is too wet for the grading, or under-sanded, or both — re-test, do not record the number. A collapse means too much water, too much fines, or both — re-test; if it collapses again, reject the batch. A technician who records "slump = 180 mm" on a sheared sample has lost the diagnostic value of the test and reported a number that will mislead every downstream decision.

The slump-flow test (EFNARC)

The apparatus is the same Abrams cone, plus a base plate marked with a 500 mm circle (so the operator can read the spread against the markings rather than measure with a tape), plus a stopwatch. No tamping rod is required for the standard EFNARC slump-flow test — the rod belongs to the slump test, not this one.

Procedure — four steps

1. Position the cone. Moisten the base plate. Place the cone centrally, small opening up. Hold it steady during filling — do not stand on the foot-pieces for this test (it changes the lift geometry).
2. Fill in a single layer. Fill the cone in one layer, with no rodding or minimal tamping if required by the mix design. Strike off flush.
3. Lift vertically. Lift the cone vertically in under three seconds — quicker than the slump test, because SCC keeps moving on its own.
4. Measure the spread. Wait until the concrete stops flowing, then measure the spread diameter in two perpendicular directions. The slump-flow value is the average of the two measurements, in millimetres.

Reading the slump flow

The reading is in millimetres of spread. Typical EFNARC targets for SCC: 500–700 mm for normal SCC applications; outside this band, the mix is either too stiff (poor filling ability, risk of voids behind reinforcement) or too fluid (segregation risk, aggregate pile-up at the centre). The visual stability index — observation of bleed water, aggregate pile-up, or paste migration — is recorded alongside the number, because the number alone does not capture segregation.

The slump-flow test is one of four EFNARC SCC tests. The other three — J-ring (passing ability around reinforcement), V-funnel (viscosity / filling rate), and L-box (filling and passing ability through reinforcement) — characterise the mix from different angles. For site acceptance, the slump-flow test is the most common single check because it is fast, repeatable, and the apparatus is already on the truck.

Side-by-side — when each is right

The visual rule: vibrated concrete → slump test; SCC → slump-flow test. The table below captures the dimensions along which the two tests diverge — and the one dimension (apparatus) along which they look deceptively similar.

The 25-blow rodding mistake

This is the single most common cause of incorrect slump-flow readings on Indian sites. The Abrams cone is the same in both tests, and the rodding habit from the slump test carries over to the slump-flow test out of operator muscle memory. Twenty-five rodding blows per layer on an SCC mix collapses the air structure, breaks down the viscosity-modifier network that gives SCC its flow, and produces a misleadingly low slump-flow reading — typically 300–450 mm on a mix that would actually flow 600 mm or more without rodding.

The downstream cascade is predictable. A site that rodding-errors a 620 mm mix down to 380 mm will reject the load as "too stiff". The contractor then adds water or superplasticiser at site to "fix" the mix — losing the SCC's passing ability in the process. The cube from the original (rejected) batch would have been fine; the cube from the doctored batch carries the consequence. The fix is procedural, not chemical: retrain the operator on the difference between the two tests, mark the base plate with the 500 mm circle so the test looks visibly different from the slump test, and keep the rod out of reach during the slump-flow procedure.

Shear slump, collapse — and what they mean

The visual interpretation is part of the test, not a footnote. A true slump is the only valid outcome. The other two outcomes tell you something specific about the mix — and that "something" almost always means the mix, not the test, needs to be re-done.

The two outcomes are diagnostic, not failing. A technician who records "slump = 180 mm" on a sheared sample has lost the diagnostic value of the test and reported a number that will mislead every downstream decision — the cube report, the next-batch comparison, the placement team's expectation. Re-test, look at the mix, then re-test again. The number is downstream of the visual outcome; never the other way round.

What goes wrong — five failures

Five failures show up again and again on fresh-concrete tests in Indian site conditions. None is exotic; all are visible to a careful operator, and most are visible in the QC log alone.

How to apply — QC log template

A printable one-page fresh-concrete acceptance record. The columns cover the data points that the cube report two weeks later will not have — but that the placement decision right now depends on. Print this as a single A4 sheet; the average pour requires two to four entries; multi-truck pours require one row per truck.

The columns — 11 fields

1. Date / time of test. When the sample was taken, not when the form was filled in.
2. Sample ID / batch ticket #. The traceability link to the plant's batch record and the cube register.
3. Mix grade. e.g., M30, with the admixture and SCM notation if relevant.
4. Concrete type. Vibrated / SCC. Determines which test applies.
5. Test type. Slump / slump flow. Note the test, not just the number.
6. Target value (mm). The spec band for the member being poured, taken from the mix-design submittal.
7. Actual value (mm). Recorded in millimetres; if shear or collapse, write "shear" or "collapse" — do not record a number.
8. Visual outcome. True / shear / collapse (slump); spread + segregation indicators (slump flow).
9. Time from batching (min). The column that catches the late-arrival problem. A 90 mm slump that was 110 mm at batching is a different decision than the same 90 mm at 30 minutes.
10. Ambient & concrete temperature (°C). Both — they diverge in hot weather.
11. Sampled by / witnessed by / approved by. Three signatures — the QC technician, the site engineer's witness, and the placement approval.

Printable template — single-truck row

Note the second row: 78 mm at 95 minutes from batching. The reading is in spec — but the margin is gone. Refused at pump placement by RP (resident engineer). The third row's cube will pass; the second row's cube, had it been placed, was almost certain to fail. The number on the form was identical to many an accepted load; the time-from-batch column is what made the decision defensible.

The acceptance decision is not a number; it is a number read against the time-since-batch, the visual outcome, the test type, and the member being poured. Three of those four are not on the form's left side — they are columns 8, 9 and the type field. That is the part of the test the form is there to capture.

References & further reading

1. IS 1199 (Part 2):2018 — Fresh Concrete — Methods of Sampling, Testing and Analysis — Part 2 (First Revision). Bureau of Indian Standards. Apparatus dimensions (300 mm tall × 100 mm top × 200 mm base), the 16 mm bullet-nosed tamping rod, the three-layer filling with 25 rodding blows per layer, the vertical lift in 3–7 s, and the decision rule that shear slump and collapse mean re-test rather than record.
2. EFNARC SCC Guidelines (2002 / 2005) — Specification and Guidelines for Self-Compacting Concrete. European Federation of National Associations of Specialist Contractors for Concrete. Slump-flow test method, target spread diameter (typically 500–700 mm), the visual stability index, and the supporting J-ring, V-funnel and L-box tests. No IS code covers SCC as a single integrated specification; EFNARC is the de facto reference for Indian SCC practitioners.
3. ASTM C143 / C143M — Standard Test Method for Slump of Hydraulic-Cement Concrete. ASTM International. The US counterpart to the IS 1199 slump test method; useful when reading international specifications.
4. ASTM C1611 / C1611M — Standard Test Method for Slump Flow of Self-Consolidating Concrete. ASTM International. The US counterpart to the EFNARC slump-flow test method.
5. IS 456:2000 (Amend. 6:2024) — Plain and Reinforced Concrete — Code of Practice (Fourth Revision). Bureau of Indian Standards. The downstream link: Cl 15 sampling and Cl 16 acceptance of compressive strength confirm whether the fresh-concrete testing regime was tight enough to deliver characteristic strength on the member. The slump and slump-flow tests are upstream of that decision.
6. IS 516:2021 — Hardened Concrete — Methods of Test. Bureau of Indian Standards. The compression-test method referenced from IS 456 Cl 16; the cube result that closes the fresh-concrete → strength loop.

Year notes: IS 1199 (Part 2):2018 is the most recent revision at the time of writing; verify currency against the BIS catalogue before tendering. EFNARC SCC guidelines were published in 2002 with the 2005 update for the European market; the principles (slump-flow target band, supporting tests) are unchanged. ASTM editions should be checked against the current ASTM volume before use.

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