🏗️ Taking and preparing samples of cement — PN-EN 196-7

Construction PN-EN 196-7

Overview

THE SCOPE FROM THE PKN CATALOGUE CARD, IN FULL: "The equipment used, the methods of procedure and of preparation are described for taking samples of cement representing given lots for testing in order to assess the quality of the product, before, during or after deliveries."

THREE MOMENTS OF SAMPLING — AND WHY THAT IS NOT A MATTER OF INDIFFERENCE. The scope names sampling BEFORE delivery, DURING it and AFTER it. These are not equivalent variants: cement changes with time and with the conditions of storage. It absorbs moisture from the air, which leads to pre-hydration and to a change in setting time and strength; in a silo it may also segregate. A sample taken after a week in storage at the recipient’s therefore describes a different material from the same lot sampled at loading — and a dispute about the quality of a delivery usually turns on exactly this: at what moment the cement ceased to meet the requirements.

REPRESENTATIVENESS AS THE HEART OF THE MATTER. A lot of cement is tens or hundreds of tonnes; a test sample is of the order of kilograms. The ratio is therefore extreme, and no amount of careful measurement repairs an error made in sampling. The standard describes the equipment — among other things probes for sampling from bags and from silos — and the procedures, so that the sample represents the lot and not the place one happened to be able to reach.

PREPARATION OF THE SAMPLE IS PART OF THE PROCEDURE, NOT HOUSEKEEPING. The title speaks of taking AND preparing. Cement once taken must be properly packed, labelled and stored until testing — in a tight container, because contact with humid air changes the sample just as it changed the material in the silo. A sample kept in a leaky container gives a result worse than the truth, and the laboratory has no way of detecting this from the result alone.

PLACE IN THE EN 196 SERIES. The series covers methods of testing cement: strength, setting time and soundness, chemical analysis, heat of hydration. Part 7 stands before them all — without it each of them tests a sample of unknown representativeness. The requirements for the cement itself are given by separate product standards, PN-EN 197-1 and PN-EN 197-2, invoked in this knowledge base by other entries.

THE POLISH VERSION IS NEWER THAN THE ENGLISH ONE. The edition in force, PN-EN 196-7:2009, is in the POLISH version and superseded the ENGLISH version of 2008. This is the OPPOSITE direction to the one seen with PN-EN 932-5, PN-EN ISO 9612, PN-EN 12390-4, PN-EN 482 and PN-EN 933-2, described in this knowledge base — there, newer editions ceased to be translated. We have not measured how often each direction occurs.

WHAT WE DO NOT GIVE. We do not have the text of the standard — PKN supplies it for a fee (TC 196, Cement and Lime). We therefore DO NOT GIVE sample masses, the number of increments making up a bulk sample, the dimensions of probes, or the permissible times and conditions of storage.

Method principle

A bulk sample is formed from increments taken from different places in the lot and is then prepared for testing: reduced, packed tightly and labelled. Cement is a material that reacts with the moisture of the air, so both the moment of sampling and the way the sample is stored affect the result — a sample correctly taken but kept in a leaky container ceases to represent the lot.

Applications

• Sampling cement to assess the conformity of a lot with the requirements of the product standard
• Control of cement deliveries — sampling before, during and after delivery
• Factory production control in cement works
• Settling disputes about the quality of a delivery — the moment of sampling is often the heart of the case

Key parameters

Standard

Standard number

PN-EN 196-7:2009 (wersja polska; wprowadza EN 196-7:2007 [IDT])

Title (PL)

Metody badania cementu -- Część 7: Metody pobierania i przygotowania próbek cementu

Title (EN)

Methods of testing cement — Part 7: Methods of taking and preparing samples of cement

Step-by-step procedure

1. Establish the moment of sampling

   Before, during or after delivery — record it, because what the result describes depends on it. In quality disputes this record is often decisive.

2. Take the increments

   From different places in the lot, with the equipment provided for in the standard. WE DO NOT GIVE NUMBERS OR MASSES — they are in its text.

3. Form the bulk sample

   Combine the increments, then reduce to a laboratory sample.

4. Pack and label

   The container must be airtight. Cement in contact with humid air hydrates — the sample loses representativeness in a way invisible in the result.

5. Store until testing

   Under the conditions and for the time provided for by the standard. Long storage changes the result even in a tight container.

6. Record in the report

   Give the moment and place of sampling, the way the bulk sample was formed, and the full designation of the standard with its year.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Cement is strongly alkaline — contact with the skin causes irritation and burns, and the dust damages the conjunctiva; gloves, goggles and respiratory protection are required
• Sampling from silos involves work at height and in confined spaces — separate safety procedures apply
• TECHNICAL NOTE: a sample kept in a leaky container understates the strength and lengthens the setting time — the error cannot be recognised from the result alone

Frequently asked questions