prEN 679

• Abstract:

  This document specifies the procedure for the determination of the compressive strength of autoclaved aerated concrete.

• Status: Not Published
• Publication Date: 03-Feb-2027
• ICS: 91.100.30 - Concrete and concrete products
• Technical Committee: CEN/TC 177 - Prefabricated reinforced components of autoclaved aerated concrete or light-weight aggregate concret
• Drafting Committee: CEN/TC 177/WG 3 - Test methods
• Current Stage: 4599 - Dispatch of FV draft to CMC - Finalization for Vote
• Start Date: 13-Oct-2026
• Due Date: 23-Dec-2026
• Completion Date: 13-Oct-2026
• Mandate: M/100 - Mandate to CEN/CENELEC concerning the execution of standardization work for harmonized standards on precast concrete products
• Ref Project: oSIST prEN 679:2026 - Determination of the compressive strength of autoclaved aerated concrete

• Revises: EN 679:2005 - Determination of the compressive strength of autoclaved aerated concrete
• Effective Date: 09-Jul-2025

prEN 679 is a CEN draft European Standard for autoclaved aerated concrete (AAC). It specifies the procedure for determining compressive strength, so laboratories and manufacturers can test AAC specimens in a consistent way and report comparable results. The document is submitted for enquiry and is intended to supersede EN 679:2005.

What does prEN 679 specify?

prEN 679 specifies the procedure for determining the compressive strength of autoclaved aerated concrete. The document is organized into clauses 1 to 9, covering scope, normative references, terms and definitions, principle, apparatus, test specimens, testing procedure, test results and the test report.

What are the key requirements of prEN 679?

Sampling and test set-up

prEN 679 requires the sample to be representative of the product being checked. Test specimens may be taken from prefabricated reinforced components or from prefabricated unreinforced components of the same mould, so the results reflect the material actually supplied.

A test set consists of three specimens. Whenever possible, one specimen is taken from the upper third, one from the middle and one from the lower third in the direction of rise of the mass during manufacture, and the direction of rise is marked on the specimens. In practice, this helps show whether the material varies through the component thickness.

Specimen size and preparation

prEN 679 uses cubes with an edge length of 100 mm as the reference specimen. Other shapes or sizes may be used only if their compressive strength can be directly related to the result for 100 mm cubes.

Specimens are cut with a rotating carborundum blade or similar equipment, must contain no reinforcement, and must have plane, clean surfaces. The planeness and squareness limits matter because uneven surfaces can distort the load and change the measured strength.

Measurement and conditioning

prEN 679 requires specimen dimensions to be measured to 0.1 mm, and the loaded cross-sectional area and volume to be calculated from those measurements. The volume is needed for the moisture-content conditioning route.

The standard gives two conditioning procedures. The reference regime is conditioning to (6 ± 2) % by mass moisture content at a temperature not exceeding 60 °C, followed by at least 2 h protected storage for thermal equilibrium before testing. The alternative is drying at (70 ± 5) °C to constant mass, then storing the specimens at (20 ± 2) °C and testing within 24 h; results from this route are adjusted by a factor of 0.8 to match the reference regime.

Compression testing

prEN 679 requires a compression testing machine meeting EN 12390-4, machine class 1 or 2, together with the specified cutting, measuring, drying and weighing equipment. The specimen is centered in the machine and loaded axially, perpendicular to the direction of rise, at a constant stress increase of (0.1 ± 0.05) MPa per second until rupture.

This controlled loading rate matters because compressive strength results are sensitive to how fast the load is applied. The maximum load at failure is recorded for each specimen.

Result calculation and reporting

prEN 679 defines individual compressive strength as the failure load divided by the loaded area, and the product compressive strength as the mean of the three specimen results. Individual results are expressed to the nearest 0.05 MPa and the product result to the nearest 0.1 MPa.

For specimens conditioned by the reference moisture-content route, the post-test moisture content and dry density are determined using EN 1353 and EN 678. The test report must identify the product, specimen shape and position, conditioning method, test results, and any observations on specimen appearance.

What terms does prEN 679 use?

• Autoclaved aerated concrete (AAC) - the lightweight concrete material for which compressive strength is determined.
• Test specimen - the prepared cube or other approved shape that is loaded in compression.
• Test set - the group of three specimens used to represent one result for the product.
• Direction of rise - the direction in which the mass rose during manufacture, used to place and load specimens consistently.
• Moisture content - the amount of water in the specimen by mass, used to define the reference conditioning state.
• Dry density - the density after drying, used to support conditioning control and reporting.
• Compressive strength - the failure load divided by the loaded cross-sectional area.
• Constant mass - the drying condition reached when further mass loss becomes negligible under the specified weighing interval.

Who uses prEN 679?

prEN 679 is used by testing laboratories that measure compressive strength of AAC. It is also used by manufacturers of AAC components, quality control teams, and product assessment or certification bodies that need repeatable strength data for incoming materials, production control, or conformity checks. Buyers and specifiers use it indirectly when they want test results that are based on the same procedure.

What changed in prEN 679 from the previous edition?

prEN 679 will supersede EN 679:2005. The document states two significant technical changes: it adds a procedure for additional conditioning by drying specimens to constant mass at (70 ± 5) °C before testing, and it supports the set of standardized test methods needed to meet the performance requirements in the product standard for prefabricated components of autoclaved aerated concrete.

Which standards are used with prEN 679?

• EN 678 - used to determine dry density, including the dry density of a companion specimen and, after reference conditioning, the dry density of test specimens.
• EN 1353 - used to determine moisture content after testing when specimens are conditioned to the reference moisture-content regime.
• EN 12390-4 - sets the requirements for the compression testing machine, including machine class 1 or 2.

What does the prEN 679 document contain?

prEN 679 contains the full test procedure, from sampling and specimen preparation to reporting. It gives the apparatus list, the required specimen geometry, the two conditioning routes, the compression test procedure, and the calculation method for individual and mean strength results. The document also includes Figure 1, which shows the sampling scheme relative to the direction of rise, and it specifies the information that must appear in the test report.

SLOVENSKI STANDARD
01-julij-2026
Ugotavljanje tlačne trdnosti avtoklaviranega celičastega betona
Determination of the compressive strength of autoclaved aerated concrete
Bestimmung der Druckfestigkeit von dampfgehärtetem Porenbeton
Détermination de la résistance à la compression du béton cellulaire autoclavé
Ta slovenski standard je istoveten z: prEN 679
ICS:
91.100.30 Beton in betonski izdelki Concrete and concrete
products
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2026
ICS 91.100.30 Will supersede EN 679:2005
English Version
Determination of the compressive strength of autoclaved
aerated concrete
Détermination de la résistance à la compression du Bestimmung der Druckfestigkeit von dampfgehärtetem
béton cellulaire autoclavé Porenbeton
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 177.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 679:2026 E
worldwide for CEN national Members.

Contents Page
European foreword . 3
1 Scope . 4
2 Normative references . 4
3 Terms and definitions . 4
4 Principle . 4
5 Test apparatus . 4
6 Test specimens . 4
6.1 Sample . 4
6.2 Shape and size of test specimens . 5
6.3 Number of specimens . 5
6.4 Preparation of test specimens . 5
6.5 Measurement of test specimens and determination of their volume . 5
6.6 Conditioning of the test specimens . 6
6.6.1 General. 6
6.6.2 Procedure a) Conditioning to (6 ± 2) % by mass moisture content . 6
6.6.3 Procedure b) Conditioning to the oven dry condition (70 ± 5) °C . 6
7 Testing procedure . 7
7.1 Compression test . 7
7.2 Determination of actual moisture content and dry density of test specimens . 7
8 Test results . 7
9 Test report . 8

European foreword
This document (prEN 679:2026) has been prepared by Technical Committee CEN/TC 177 “Prefabricated
reinforced components of autoclaved aerated concrete or light-weight aggregate concrete with open
structure”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 679:2005.
This document includes the following significant technical changes with respect to EN 679:2005:
— incorporation of procedure for additional conditioning [drying to constant mass at temperature of
(70 ± 5) °C of specimens before testing as stated in the test standard for masonry units
(EN 772-1:2016, 7.3.3 b))];
— in order to meet the performance requirements as laid down in the product standard for
prefabricated components of autoclaved aerated concrete, a number of standardized test methods
are necessary.
1 Scope
This document specifies the procedure for the determination of the compressive strength of autoclaved
aerated concrete.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 678, Determination of the dry density of autoclaved aerated concrete
EN 1353, Determination of moisture content of autoclaved aerated concrete
EN 12390-4, Testing hardened concrete — Part 4: Compressive strength — Specification for testing
machines
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
4 Principle
The compressive strength is determined on test specimens as the ratio between the rupture load in axial
compression and the cross-sectional area of the test specimen perpendicular to the loading direction.
5 Test apparatus
a) Saw for cutting test specimens;
b) compression testing machine, which meets the requirements of EN 12390-4, machine class 1 or 2;
c) calipers, capable of reading the dimensions of the test specimens to an accuracy of 0,1 mm;
d) ventilated drying ovens, capable of maintaining required temperatures for conditioning and drying
test specimens: (≤60 °C), (70 ± 5) °C and (105 ± 5) °C;
e) straight edge, at least 200 mm long, a 0,1 mm-feeler gauge, a 1 mm-feeler gauge, and a square;
f) balance, capable of determining the mass of the test specimens to an accuracy of 0,1 %.
6 Test specimens
6.1 Sa
...