🏗️ Sampling of fresh concrete — composite and spot samples, PN-EN 12350-1

Construction PN-EN 12350-1

Overview

TWO METHODS, TWO DIFFERENT QUESTIONS. The scope from the PKN catalogue card states: "This document specifies two methods of sampling fresh concrete: composite sampling and spot sampling." The difference is not technical but one of meaning. A COMPOSITE SAMPLE is made up of several increments taken from different places in the batch and mixed — it describes the batch as a whole. A SPOT SAMPLE is a single increment from one place and one moment — it describes what was there and then. Results from the two are not interchangeable: a spot sample can reveal heterogeneity which a composite sample, by definition, cannot see, because it averages it out.

WHY THIS IS CRITICAL PRECISELY FOR FRESH CONCRETE. Fresh concrete is a living, heterogeneous material: it segregates during transport, changes consistence over time as hydration proceeds, and its properties depend on whether it was taken from the beginning, middle or end of discharge. A sample taken incorrectly gives a result that no amount of care in the subsequent testing can repair — and, unlike many other materials, it cannot be taken again, because the same concrete is a different material an hour later.

THREE NOTES FROM THE SCOPE THAT CHANGE THE APPLICATION. The catalogue card quotes them directly. First: "Requirements for the re-mixing of fresh concrete before testing it or before making test specimens are given in the relevant standards" — that is, the manner of re-mixing is not in this standard but in the standards for the individual tests. Second: "Where the mixing and sampling of fresh concrete take place in a laboratory, other procedures may be required", with the note that Clause 6, item g) then applies. Third: "In addition, this standard specifies the common apparatus listed in at least two standards of the EN 12350 series and in EN 12390-2" — which is why it is cited by many entries in this database.

WHY THE EQUIPMENT IS DESCRIBED HERE. Scoops, containers, trowels and base plates would be repeated in each standard of the series. Gathering them in part 1 means that an entry on consistence by the slump test or on air content cites 12350-1 although it tests something else — and that is why this standard appears in accreditation scopes alongside several items at once.

DATE OF PUBLICATION VERSUS DESIGNATION — A DETAIL WORTH NOTING. The designation of the standard reads "PN-EN 12350-1:2019-07", but the "Date of publication" row on the PKN card gives 16-11-2022. The same discrepancy occurs with PN-EN 12390-1, described in this database: designation 2021-12, date of publication 23-06-2023. We do not explain it — we have not verified the PKN convention governing the relation of the two dates in any source. We note it because it is sometimes taken for an error on the card and leads to citing the standard under the non-existent designation "PN-EN 12350-1:2022". In documentation, quote the designation from the card, not the date of publication.

WHAT WE DO NOT GIVE. We do not have the text of the standard — PKN supplies it for a fee. We therefore DO NOT GIVE minimum sample volumes, the number of increments making up a composite sample, the permissible time from sampling to testing, or the dimensions of the equipment. We know from the scope that the standard specifies two methods and the apparatus, and there our statements end.

A note on the edition: the 2019-07 edition replaced PN-EN 12350-1:2011 — the Polish version.

Method principle

A sample is taken so as to answer the question put to the batch. Composite sample: several increments from different places in the batch, combined and re-mixed — it represents the batch as a whole and serves conformity assessment. Spot sample: a single increment from one place and moment — it serves the assessment of that particular location, including the detection of heterogeneity. From the moment of sampling the concrete changes its properties with time, so testing is carried out without delay and the time of sampling is recorded.

Applications

• Sampling for tests on fresh concrete: consistence, air content, density, temperature
• Sampling concrete for making specimens for hardened concrete strength testing (moulding per EN 12390-2)
• Production control of ready-mixed concrete and control on site
• Common apparatus shared by the tests of the EN 12350 series — a document cited by several methods at once

Key parameters

Standard

Standard number

PN-EN 12350-1:2019-07 (wersja polska; wprowadza EN 12350-1:2019 [IDT])

Title (PL)

Badania mieszanki betonowej -- Część 1: Pobieranie próbek i podstawowe wyposażenie

Title (EN)

Testing fresh concrete — Part 1: Sampling and common apparatus

Step-by-step procedure

1. Choose the sampling method

   Decide whether the question concerns the batch as a whole (composite sample) or a particular place and moment (spot sample). The results are not interchangeable — record the choice, as it cannot be reconstructed from the result.

2. Verify the sampling location

   Sampling from the beginning or end of discharge yields material unrepresentative of the batch. For a composite sample, increments are taken from different places.

3. Take the increments

   The equipment and manner are specified by the standard. QUANTITIES ARE NOT GIVEN HERE — volumes and numbers of increments are in its text.

4. Re-mix before testing

   The requirements are given by the STANDARDS FOR THE INDIVIDUAL TESTS — check them in the standard for the test you intend to perform, not in this one.

5. Test without delay

   Fresh concrete changes its properties with time. Record the time of sampling and the time of testing — without them a consistence result cannot be interpreted.

6. Record in the report

   State the sampling method (composite or spot), the location, the time and the full designation of the standard with its year.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Fresh concrete is strongly alkaline — skin contact causes chemical burns and, on prolonged contact, ulceration; gloves and eye protection required
• Work at the discharge of a truck mixer — risk of crushing and splashing; sampling is carried out in agreement with the vehicle crew
• TECHNICAL NOTE: a composite sample by design averages the batch and will not reveal heterogeneity — if the question concerns suspected segregation, a spot sample is the appropriate one

Frequently asked questions