🛣️ Sampling of bituminous mixtures — PN-EN 12697-27

Construction PN-EN 12697-27

Overview

THIS IS AN ENTRY ABOUT SAMPLING, THAT IS, ABOUT AN ACTIVITY — AND THAT IS ALSO HOW THIS STANDARD IS CITED IN ACCREDITATION SCOPES. The scope line then reads "Pobieranie próbek" [sampling], not "Oznaczanie…" [determination of…], and there is no measuring range or unit with it, because there is nothing to measure. This is not a lack of data, but a different role of the document.

SCOPE, QUOTED FROM THE TEXT OF THE STANDARD (clause 1): "This European Standard specifies test methods for sampling bituminous mixtures for roads and other paved areas to determine their physical properties and composition."

A CHANGE THAT IS VISIBLE IN THE TITLE ITSELF BUT EASY TO OVERLOOK. The PN-EN 12697-27:2005 edition bore the title "Mieszanki mineralno-asfaltowe — Metody badań mieszanek mineralno-asfaltowych NA GORĄCO — Część 27: Pobieranie próbek" [Bituminous mixtures — Test methods for HOT mix asphalt — Part 27: Sampling]. The 2017-07 edition bears the title without this element: "Mieszanki mineralno-asfaltowe — Metody badań — Część 27: Pobieranie próbek" [Bituminous mixtures — Test methods — Part 27: Sampling]. The standard itself lists this as the first of the significant changes: "the title no longer makes the method exclusively for hot mix asphalt". The document has therefore ceased to be limited to hot mixes — and a laboratory that copies the title from an old accreditation scope narrows it contrary to the standard.

THE SECOND CHANGE OF THE 2017 EDITION IS NUMERICAL AND CONCERNS DAILY WORK: THE INCREMENTS HAVE BEEN REDUCED. When sampling from a truck and from a stockpile — for material with a nominal aggregate size not greater than 16 mm from 3 kg to 2 kg, and for aggregate larger than 16 mm from 7 kg to 3 kg. When sampling from beneath the paver augers — from 7 kg to 3 kg. A laboratory working according to the 2005 edition therefore takes up to more than twice as much material as the edition in force requires. The 2017 edition also added a tool: a stainless steel sampling tube, together with its own procedure, and a new method of sampling — from the paver material hopper (new clause 4.10).

FOUR SAMPLE NAMES THAT DO NOT MEAN THE SAME THING. The standard defines them separately, and this distinction is its core: • INCREMENT — a single quantity of material taken from a larger mass of the material being sampled. • BULK SAMPLE — a sample formed by COMBINING increments, in a quantity sufficient for all intended purposes. • REPRESENTATIVE SAMPLE — a sample consisting of a SPECIFIED NUMBER of increments, taken deliberately so that it represents a specified quantity or a specified area of material. The standard adds that it is assumed to have the same composition as the material being sampled — within the precision associated with the method of sampling. • SPOT SAMPLE — a sample taken in one operation, at one place and time. Here the standard makes a reservation that decides the value of such a sample: if the homogeneity of the material can be assumed, a spot sample may be regarded as representative; if the material is not homogeneous, it is representative only of a limited area around the sampling point. • LABORATORY SAMPLE — a sample sent to the laboratory; it may be the whole or part of a bulk or representative sample and is assumed to be sufficient for all the required tests. A PRACTICAL CONSEQUENCE OF THIS: a report saying "sample taken according to PN-EN 12697-27" does not yet say whether the sample is representative. That depends on the number and distribution of the increments, not on citing the standard.

THE NUMBER OF INCREMENTS IS A MINIMUM, NOT A SET VALUE. The standard repeats this for successive methods: "The number of increments specified is a minimum and more may be necessary in some circumstances." Going below the given number is a deviation from the standard; exceeding it is not.

WHAT WE DO NOT GIVE IN THIS ENTRY. The standard describes ten methods of sampling materials other than coated chippings (clause 4) and, separately, the sampling of chippings from stockpiles (clause 5) and the marking and packing of laboratory samples together with the sampling report (clause 6). The text we read covers clauses 1–4.4; the details of the methods from 4.5 (sampling from a laid but uncompacted layer — using trays and using a shovel or scoop), 4.7 (cores), 4.8 (cutting slabs), 4.9 (drag-slat conveyor of a continuous mixing plant), 4.10 (paver hopper), as well as of clauses 5 and 6, including the content of the sampling report, WE DO NOT GIVE — we know only their names from the table of contents of the standard.

Method principle

Several increments of a specified mass are taken from the mass of material, from places distributed as widely as possible and from beneath the surface layer, and then combined into a bulk sample. The method of sampling is chosen according to the place and state of the material: transport, paver, stockpile, laid but uncompacted layer, compacted layer (core or cut slab), plant conveyor. The number and distribution of the increments decide whether the sample is representative.

Applications

• Sampling for testing the composition and physical properties of bituminous mixtures
• Control of mix deliveries on site — sampling from a truck load
• Control of laying — sampling from beneath the paver augers and from a laid but uncompacted layer
• Assessment of the finished layer — taking cores or cutting slabs from the compacted pavement
• Factory production control at an asphalt mixing plant — sampling from the drag-slat conveyor of a continuous plant
• Mastic asphalt — sampling during discharge from the transport mixer, with the forming of a pat
• Coated chippings — sampling from stockpiles (a separate clause of the standard)

Key parameters

Standard

Standard number

PN-EN 12697-27:2017-07 (wersja angielska; wprowadza EN 12697-27:2017 [IDT])

Title (PL)

Mieszanki mineralno-asfaltowe — Metody badań — Część 27: Pobieranie próbek

Title (EN)

Bituminous mixtures — Test methods — Part 27: Sampling

Step-by-step procedure

1. Choice of the method of sampling

   The method is chosen according to the place and state of the material: truck load, discharge of mastic asphalt, paver augers, stockpile, laid but uncompacted layer, compacted layer, plant conveyor, paver hopper. Clause 5 deals separately with coated chippings.

2. Choice of tool

   The scoop is used for materials with a nominal size of up to 16 mm, the shovel more widely, the sampling tube — with size M limited to aggregate not larger than 16 mm.

3. Determining the number and mass of increments

   For sampling from a truck and from a stockpile: minimum four increments of approximately 2 kg each (aggregate ≤ 16 mm) or approximately 3 kg each (aggregate > 16 mm); for mixtures with aggregate ≥ 32 mm, eight increments are recommended. With the tube — minimum three increments of approximately 4 kg each. From beneath the paver augers — two increments of approximately 3 kg each from each side.

4. Removal of surface material

   Before sampling, the material is removed from the surface together with coarse particles that could fall into the hole. For less cohesive materials, pushing in a metal plate is recommended to make digging to a depth of 100 mm easier.

5. Taking the increments

   Increments are taken from places distributed as widely as possible: from a truck — approximately 100 mm below the surface and not closer than 300 mm to the side (and with the tube not closer than 0.5 m); from a stockpile — at least 100 mm from its surface; from beneath the augers — only when they are covered along their entire length, pushing the shovel into the material in front of the auger.

6. Combining into a bulk sample

   The increments obtained are combined to form a bulk sample. The number of increments given is a minimum — in some circumstances more are needed.

7. Special procedure for mastic asphalt

   Two increments are taken at the outlet of the mixer after one third of the contents has been discharged, and a pat of a size meeting the requirements of EN 12697-20 is formed from them immediately. Sampling the material discharged first and last is avoided — unless the aim is to test precisely that part of the discharge.

8. Marking, packing and sampling report

   Laboratory samples are marked and packed in accordance with clause 6 of the standard, which also covers the sampling report. WE DO NOT QUOTE THE CONTENT OF THIS CLAUSE IN THIS ENTRY — we did not have it in the text we read.

Required equipment and apparatus

Health and safety (OHS)

• Hot bituminous mixture has a temperature of the order of 140–180 °C — sampling requires heat-resistant gloves and clothing, and contact with the binder risks severe burns, because bitumen sticks to the skin
• Sampling from beneath the paver augers takes place with the machine running — coordination with the operator and keeping a distance from moving parts are mandatory
• Sampling from a truck load requires climbing onto the body or reaching over it — risk of falling from a height and of being crushed when the vehicle moves off
• Work on an active road construction site — traffic of machines and vehicles; high-visibility clothing and securing of the sampling place are required
• Hot bitumen fumes irritate the respiratory tract and the eyes; discharge of mastic asphalt from the transport mixer is a separate source of fumes
• Core drilling and cutting of the pavement — hazards from silica dust, noise and hand-transmitted vibration

Frequently asked questions