🏗️ Consistence of fresh concrete by the slump test

Construction PN-EN 12350-2

Overview

Consistence is the degree of fluidity of fresh concrete, showing its capacity to deform under load. The standard PN-EN 12350-2 describes the simplest and most widely used method of determining it: the concrete is compacted in a mould in the shape of a truncated cone, and after the mould is lifted the distance by which the concrete has subsided is measured. The method is sensitive to changes of consistence corresponding to slumps from 10 mm to 210 mm; outside that range the measurement may not be reliable and other methods should be considered (degree of compactability, flow table, Vebe).

The test is not suitable for mixes in which the declared maximum aggregate size D exceeds 40 mm, nor when the slump goes on changing for more than 1 min after the mould is lifted. The 2019 edition introduced a reference to the common apparatus of PN-EN 12350-1, a procedure for testing slump retention over time and the possibility of giving the class or the target value of the slump in the test report.

The consistence classes according to the slump test: S1 (10–40 mm), S2 (50–90 mm), S3 (100–150 mm), S4 (160–210 mm), S5 (≥ 220 mm) — the class S5 already lies outside the range in which the slump test gives meaningful results. The consistence must not be increased by adding water, because that raises the w/c ratio and lowers the durability of the concrete; it is adjusted with plasticising and superplasticising admixtures. In pavements of cement concrete the General Directorate for National Roads and Motorways (GDDKiA) permits a consistence of S1–S2 checked by this method.

Method principle

Fresh concrete is compacted in a conical mould. After the mould has been lifted, the distance by which the concrete has subsided is a measure of its consistence. The slump h is the difference between the height of the mould and the height of the highest point of the demoulded specimen. The result is valid only in the case of a true slump, that is when the concrete remains substantially intact and symmetrical; if the specimen shears (a shear slump), the test is to be repeated on another specimen, and two successive shears mean that the mix does not have the plasticity and cohesion required for this method.

Applications

• Factory production control of ready-mixed concrete and control of deliveries on site
• Classification of a mix into the consistence classes S1–S5
• Control of the mix for pavements of cement concrete (a consistence of S1–S2 is permitted by the WWiORB technical specifications of GDDKiA)
• Testing of slump retention after a prescribed time from mixing
• Proficiency testing of construction laboratories

Key parameters

Standard

Standard number

PN-EN 12350-2:2019-07

Title (PL)

Badania mieszanki betonowej — Część 2: Badanie konsystencji metodą opadu stożka

Title (EN)

Testing fresh concrete — Part 2: Slump test

Step-by-step procedure

1. Sampling and remixing of the sample

   Take the sample of the mix in accordance with PN-EN 12350-1 and remix it on a tray with a shovel or a scoop before the test. In the slump retention test, tip the concrete out of the airtight container onto the tray and remix it.

2. Preparation of the mould

   Dampen the mould and the base plate, remove any excess moisture with a damp cloth, place the mould on the level plate and hold it down during filling (with the clamp or by standing on the foot pieces).

3. Filling in three layers

   Fill in three layers of approximately equal height (each about one third of the height of the cone after compaction). Compact each layer with 25 strokes of the rod distributed evenly over the cross-section; the bottom layer throughout its depth without striking the base plate, the following layers so that the rod penetrates slightly into the layer below.

   ⏱ Time: the whole ≤ 150 s

4. Levelling of the surface

   Before compacting the top layer, heap the concrete above the rim of the mould; if after compaction the concrete falls below the rim, add more of the mix. Level the surface with the trowel or with a sawing and rolling motion of the rod and remove any concrete spilt onto the plate.

5. Lifting of the mould

   Lift the mould vertically and steadily in a time of 2 s to 5 s, without imparting any lateral or torsional movement to the concrete. Carry out the whole operation from the start of filling to the lifting of the mould without interruption and within 150 s.

   ⏱ Time: 2–5 s

6. Measurement of the slump

   Immediately after the mould has been lifted, measure and record the slump h as the difference between the height of the mould and the height of the highest point of the subsided specimen.

7. Assessment of validity

   The test is valid only in the case of a true slump (the specimen substantially intact and symmetrical). In the case of a shear slump, take a fresh sample and repeat; two successive shears mean that the method is not suitable for that mix.

8. Test report

   Give the true slump rounded to 10 mm, the type of slump (true/shear), the identification of the sample, the place and date of the test and, in the slump retention test, the age of the sample from the first contact of the cement with the water. Carry out comparative tests after the same time from mixing, because the consistence changes with time through the hydration of the cement and the loss of moisture.

Required equipment and apparatus

Health and safety (OHS)

• Fresh concrete is alkaline — wear gloves and protective clothing, protect the eyes when tipping the mix
• The mould and the plate must be set up stably; hold the mould down during rodding
• Do not increase the fluidity of the mix by adding water — that changes the composition of the concrete under test

Frequently asked questions