oSIST prEN 679:2026

• Abstract:

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

• Status: Not Published
• Public Enquiry End Date: 23-Jul-2026
• ICS: 91.100.30 - Concrete and concrete products
• Technical Committee: BBB - Concrete, reinforced concrete and prestressed concrete
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 08-Jun-2026
• Due Date: 26-Oct-2026
• Mandate: M/100 - Mandate to CEN/CENELEC concerning the execution of standardization work for harmonized standards on precast concrete products
• Ref Project: prEN 679 - Determination of the compressive strength of autoclaved aerated concrete

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

oSIST prEN 679:2026 is SIST’s Slovenian version of draft European Standard prEN 679, prepared by CEN. It specifies the procedure for determining the compressive strength of autoclaved aerated concrete, so laboratories, manufacturers and other users can test AAC specimens in a consistent way.

What does oSIST prEN 679:2026 specify?

oSIST prEN 679:2026 specifies one test method for autoclaved aerated concrete (AAC): how to prepare specimens, condition them, load them in compression, calculate compressive strength and report the result. The document is organized in Clauses 1 to 9, covering scope, normative references, terms and definitions, principle, apparatus, test specimens, testing procedure, test results and test report.

Clause 6 is the most detailed part of the document because specimen selection and conditioning strongly affect the result in practice. Clause 7 then sets the actual compression test, and Clause 8 shows how to convert the failure load into specimen strength and a product mean value.

What are the key requirements of oSIST prEN 679:2026?

Specimens and apparatus

• Clause 5 requires a compression testing machine that meets EN 12390-4, machine class 1 or 2, together with cutting, measuring, drying and weighing equipment. In practice, this means the test is only valid when the laboratory can control specimen dimensions, mass and loading conditions.
• Clause 6.1 requires a representative sample, and specimens may be taken from prefabricated reinforced components or from prefabricated unreinforced components of the same mould. This matters because the test result must reflect the product actually being assessed.
• Clause 6.2 states that the usual test specimen is a 100 mm cube. Other shapes or sizes are allowed only if their compressive strength can be directly related to the result for a 100 mm cube.

Sampling and preparation

• Clause 6.3 requires a test set of three specimens, and whenever possible they should come from the upper, middle and lower thirds of the component in the direction of rise of the mass during manufacture. This helps capture variation within the product.
• Clause 6.4 requires specimens to be cut without reinforcement, with plane and clean surfaces, and with checked limits for flatness and squareness. In practice, damaged or poorly prepared faces can change the load distribution and distort the result.
• Clause 6.5 requires the specimen dimensions to be measured to 0.1 mm, and the loaded area and volume to be calculated from those measurements when needed. Accurate geometry is important because strength is calculated from load divided by area.

Conditioning and test loading

• Clause 6.6 gives two conditioning routes. The reference conditioning regime is to (6 ± 2) % by mass moisture content, while the alternative route is oven drying at (70 ± 5) °C to constant mass. This choice affects the result and must be recorded.
• Clause 7.1 requires axial loading perpendicular to the direction of rise, at a constant stress increase of (0.1 ± 0.05) MPa per second until rupture. This keeps the test comparable between laboratories.
• Clause 7.2 requires actual moisture content and dry density to be determined after testing when the reference moisture-conditioning route is used. When specimens are oven-dried under the alternative route, that post-test moisture and density check is not required.

Results and reporting

• Clause 8 defines compressive strength as the maximum load at failure divided by the loaded area, and the product strength as the mean of the three specimen results. When oven-dried specimens are used, the mean result is multiplied by 0.8 to relate it to the reference conditioning regime.
• Clause 9 requires the report to identify the product, specimen origin, conditioning method, individual and mean strength results, and observations on specimen appearance. That record is what allows the test to be reviewed or compared later.

What terms does oSIST prEN 679:2026 define?

oSIST prEN 679:2026 uses the following key terms in the test method.

• Autoclaved aerated concrete (AAC) - a lightweight concrete product whose compressive strength is being measured by this procedure.
• Compressive strength - the failure load in axial compression divided by the loaded cross-sectional area.
• Reference conditioning regime - the specimen conditioning route to (6 ± 2) % by mass moisture content used as the comparison basis for results.
• Constant mass - the condition reached when repeated weighings show only a very small mass loss during drying.
• Dry density - the density determined after drying, used here together with moisture content calculations.
• Moisture content - the amount of water in the specimen, needed because specimen condition affects the measured strength.
• Direction of rise - the manufacturing direction marked on specimens so that the load direction and specimen position are known.

Who uses oSIST prEN 679:2026?

oSIST prEN 679:2026 is used by AAC manufacturers, test laboratories, and quality control teams that need to measure product compressive strength in a repeatable way. It is also relevant to certification, inspection and conformity assessment work where test reports must be compared against a product specification. Engineers, buyers and specifiers use it when they need a defined laboratory method behind a declared AAC strength value.

What changed in oSIST prEN 679:2026 from the previous edition?

oSIST prEN 679:2026 supersedes EN 679:2005. The foreword states two significant changes:

• it adds a conditioning procedure based on drying specimens to constant mass at (70 ± 5) °C before testing;
• it supports the use of standardized test methods needed to meet the performance requirements for prefabricated AAC components.

Which standards are used with oSIST prEN 679:2026?

Standard	What it contributes
EN 678	Method for determining the dry density of autoclaved aerated concrete.
EN 1353	Method for determining the moisture content of autoclaved aerated concrete.
EN 12390-4	Specification for the compression testing machine used in the test.

These references connect the compressive strength test to the companion measurements and machine requirements needed to make the result usable.

What does the oSIST prEN 679:2026 document contain?

oSIST prEN 679:2026 contains the test principle, apparatus list, specimen preparation rules, conditioning procedures, loading procedure, calculation of strength and the reporting checklist. Figure 1 shows the recommended sampling scheme relative to the direction of rise in manufacture, so the specimens represent the component more reliably. Clause 6.6.2 includes a calculation note for estimating expected moisture content, and Clause 8 includes the equations for specimen strength and product mean strength. Clause 9 gives the information that must be recorded so the test can support product testing, laboratory comparison and conformity work.

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
...