🏗️ Methods for reducing laboratory samples of aggregates — PN-EN 932-2

Construction PN-EN 932-2

Overview

WHY SAMPLE REDUCTION IS A SEPARATE STANDARD. Aggregate is an inherently heterogeneous material: particles of different sizes segregate at every transfer, transport and vibration. Fine particles run to the bottom and the centre of a cone, coarse ones roll down its slope. Taking "a handful from the top" of a sample weighing tens of kilograms yields material with a particle size distribution different from that of the whole — and particle size distribution is precisely what is most often tested. An error introduced at this stage is irreversible: no amount of careful sieving will repair it, because the sieve will faithfully measure the composition of a sample that no longer represents the batch.

THE SCOPE FROM THE PKN CATALOGUE CARD, IN FULL: "Methods are given for reducing laboratory samples of aggregates to test portions in the minimum number of division stages. Definitions are given of: laboratory sample, sub-sample, test portion, test specimen, division into 1/2, division into 3/4 and division into 5/8. The apparatus is specified."

FOUR SAMPLE NAMES — AND WHY THE STANDARD DISTINGUISHES THEM. The scope lists four terms: laboratory sample, sub-sample, test portion and test specimen. In everyday use all of them tend to be called "the sample", which makes any description of the path of the material unreadable. The distinction has a practical consequence in the report: the sentence "a 2 kg sample was tested" does not say whether this was the laboratory sample or an already reduced test portion — and on that depends whether the result relates to the batch or only to what reached the sieve.

"THE MINIMUM NUMBER OF DIVISION STAGES" — A SENTENCE FROM THE SCOPE THAT IS A PRINCIPLE. Every division stage introduces its own error. The more successive divisions, the greater the probability that the test portion will depart in composition from the laboratory sample. The standard therefore does not say "divide until you reach the right mass", but requires the route to be planned so that there are as few stages as possible — hence three different division ratios (1/2, 3/4, 5/8) rather than one. With three ratios available, the required mass can be reached by a shorter route than by halving alone.

RELATION TO OTHER DOCUMENTS OF SERIES 932 AND 933. Series PN-EN 932 covers the general properties of aggregates: part 2 is sample reduction, and part 5 (common equipment and calibration) is also cited in this database. Series PN-EN 933 concerns geometrical properties — including part 1 (determination of particle size distribution by sieving) and part 2 (test sieves, nominal size of apertures), to which a separate entry in this database is devoted. The order is therefore: take the sample, reduce it per 932-2, sieve it through sieves sized per 933-2, determine the grading per 933-1.

WHAT WE DO NOT GIVE. We do not have the text of the standard — PKN supplies it for a fee (17 pages, TC 108, ICS 91.100.15). We therefore do not quote the required masses of test portions as a function of grading, the dimensions of divider chutes, or the permitted number of division stages. We know from the scope that the standard specifies the apparatus and defines three division ratios, and that is the limit of what we may say without the text.

WHY THE "LABORATORIES" TAB IS EMPTY HERE (23.09.2026). Measurement (23.09, copy of the scopes; all records of the number counted in the reference-document field, and separately also in the entry description fields): PN-EN 932-2 — zero entries, in each of these fields. Neighbouring parts of the same standard are present in the scopes: PN-EN 932-1 (sampling of aggregates) — 58 entries at 41 laboratories, PN-EN 932-3 (petrographic description) — 7 at 6; part 5 — like part 2 — zero. WHAT THIS ZERO DOES NOT MEAN. It does not result merely from the fact that part 2 describes an auxiliary operation — reducing the sample — and not a test. Another auxiliary standard, PN-ISO 5667-10 on the sampling of waste water, has 309 entries at 247 laboratories in the scopes (the same measure), because sampling is sometimes a separate entry in an accreditation scope. The zero for PN-EN 932-2 therefore says only that no laboratory has entered the reduction of an aggregate sample into its scope — either as a separate entry or as a standard added alongside a test standard. Why this is so, we have not established. FOR THE READER THIS MEANS SOMETHING PRACTICAL: they will not find this entry through the list of laboratories and should not look for that list here. They will find it by searching for the standard DIRECTLY — because the question is not "who does this" but "how may a sample be reduced so that the test remains valid".

Method principle

Reduction is intended to preserve the particle size distribution: the test portion is to be a scaled-down image of the laboratory sample, not an arbitrary fragment of it. The standard provides three division ratios — 1/2, 3/4 and 5/8 — so that the route from the initial mass to the required one can be covered in the fewest stages, since each further stage introduces additional error. The scope of the catalogue card also states that the standard "specifies the apparatus", but we do not hold its text and do not enumerate which methods of division it permits: laboratory practice uses riffle dividers and coning-and-quartering, the latter not being mentioned on the card.

Applications

• Preparing a test portion before every aggregate test — grading, particle shape, density, water absorption, resistance to fragmentation
• Aggregate production control and type testing of the product
• Documenting the path of the material from delivery to the portion on the sieve — distinguishing laboratory sample, test portion and test specimen
• Reviewing another laboratory's report: whether the method of reduction and the mass of the test portion are stated

Key parameters

Standard

Standard number

PN-EN 932-2:2001 (wersja polska; wprowadza EN 932-2:1999 [IDT])

Title (PL)

Badania podstawowych właściwości kruszyw -- Metody pomniejszania próbek laboratoryjnych

Title (EN)

Tests for general properties of aggregates — Methods for reducing laboratory samples

Step-by-step procedure

1. Establish the required mass of the test portion

   Check in the test method what mass it requires for the given grading. That mass is the target of the reduction.

2. Plan the division route

   Choose the division ratios (1/2, 3/4, 5/8) so as to reach the required mass in the MINIMUM number of stages. This is the principle of the standard, not a recommendation.

3. Mix before every division

   Material segregates at every transfer. Dividing segregated material yields two portions of differing composition — and both are then wrong.

4. Carry out the division

   By a method permitted by the standard — the apparatus is specified in its text, which we do not hold. With a riffle divider the chute width is matched to the largest particle: too narrow a chute holds back coarse particles and shifts the composition of the portion.

5. Record the path of the material

   Note the mass of the laboratory sample, the number and type of stages, and the mass of the test portion. Without this it is later impossible to determine what the result relates to.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Dust release when transferring fine aggregates — respiratory protection required for materials containing crystalline silica
• Laboratory samples of coarse aggregates reach tens of kilograms — risk of injury when lifting
• TECHNICAL NOTE: an error in reduction is irreversible and invisible in the result — the sieve faithfully measures the composition of a sample that does not represent the batch

Frequently asked questions