kSIST FprEN 12390-12:2026

• Abstract:

  This document describes a method for evaluating the carbonation resistance of concrete using test conditions that accelerate carbonation. After a defined period of curing and a period of preconditioning, the test is carried out under controlled exposure conditions using an increased level of carbon dioxide.; NOTE The test performed under reference conditions takes a minimum of 112 days comprising a minimum age of the specimen prior to curing under water of 28 days, a minimum preconditioning period of 14 days and an exposure period to increased carbon dioxide level of 70 days.; This procedure is not a method for the determination of carbonation depths in existing concrete structures.

• Status: Not Published
• Public Enquiry End Date: 21-Dec-2025
• ICS: 91.100.30 - Concrete and concrete products
• Technical Committee: BBB - Concrete, reinforced concrete and prestressed concrete
• Current Stage: 5020 - Formal vote (FV) (Adopted Project)
• Start Date: 27-Aug-2026
• Due Date: 15-Oct-2026
• Ref Project: FprEN 12390-12 - Testing of hardened concrete - Part 12: Determination of the carbonation resistance of concrete - Accelerated carbonation method

• Revises: SIST EN 12390-12:2020 - Testing hardened concrete - Part 12: Determination of the carbonation resistance of concrete - Accelerated carbonation method
• Effective Date: 09-Feb-2021

kSIST FprEN 12390-12:2026 is a SIST standard for testing hardened concrete. It specifies an accelerated carbonation method for evaluating the carbonation resistance of concrete test specimens under controlled carbon dioxide, temperature and humidity conditions. The method is intended for cast concrete specimens used to compare mixes or assess durability performance, not for measuring carbonation depths in existing concrete structures.

What does kSIST FprEN 12390-12:2026 specify?

kSIST FprEN 12390-12:2026 specifies a laboratory method for accelerated carbonation testing of hardened concrete. It sets out how to make, cure, condition, expose, cut or split, and measure concrete specimens so the carbonation rate can be calculated from the measured depths.

The document is organized into clauses 1 to 10, covering scope, normative references, terms, principle, reagents and apparatus, specimen production, carbonation depth measurements, calculation of carbonation depth and rate, test reporting, and precision estimate. Annex A gives guidance on storage chambers used for the carbonation exposure.

Annex	What it covers
Annex A (informative)	Guidance on storage chambers, including control of carbon dioxide, temperature, humidity and air circulation

In practice, the scope matters because the method is for a controlled test on cast specimens. It is not a field method for diagnosing carbonated zones in service structures.

What are the key requirements of kSIST FprEN 12390-12:2026?

kSIST FprEN 12390-12:2026 requires specimens to be made from a single batch and then exposed under tightly controlled conditions so the carbonation front can be compared between mixes. The main output is the carbonation rate, expressed as mm/√d, derived from measured depths at fixed exposure times.

Specimen preparation and curing

Clause 6 requires representative constituents and a single concrete batch for each test. A test uses at least two prisms, eight cubes, or five cylinders, with specimen dimensions linked to EN 12390-1 and large enough relative to the maximum aggregate size. This matters because specimen size and batch consistency affect how representative the test result is.

Clause 6.2.1 requires the consistence class or target value to be measured with EN 12350-2, EN 12350-3, EN 12350-4, or EN 12350-5 as appropriate. The document also expects the casting and initial storage of specimens to follow EN 12390-2. For users, this means the fresh concrete record belongs with the carbonation result, so a poor result can be related back to the mix and its handling.

Curing and conditioning options

Clause 6.2 sets out a default 90-day wet-curing route, with the early-age curing step protected in the mould and then stored in water or a chamber at controlled temperature and humidity. The document also allows 28-day curing or accelerated curing where specified, provided the chosen route is declared in the report. This is important when a laboratory needs to test mixes with different binder types or maturity rates.

After curing, the default conditioning is 14 days in a laboratory air-drying environment. An alternative conditioning route is also allowed: oven drying at 45 ± 5 °C for 14 days, followed by 7 days at 20 ± 2 °C and 65 ± 5 % relative humidity. The report has to state which conditioning route was used, because drying history influences carbonation results.

Carbonation exposure

Clause 4 and clause 5 require exposure in a storage chamber at an increased carbon dioxide level of 3.0 ± 0.5 % by volume, with temperature at 20 ± 2 °C and relative humidity at 57 ± 3 %. The chamber needs active control of carbon dioxide, humidity and temperature, plus air circulation. In practice, this is the core of the accelerated method, because it drives a measurable carbonation front in a shorter time.

The note in the scope states that the reference procedure takes a minimum of 112 days: 28 days minimum specimen age before water curing, 14 days minimum preconditioning, and 70 days exposure. That timing helps users plan test programmes and compare results on the same basis.

Measurement of carbonation depth

Clause 7 requires carbonation depth measurements at 7, 28 and 70 days of storage in the chamber. The specimen is split or broken to expose a fresh surface, the indicator solution is applied, and the depth of the colour change is measured. The document allows phenolphthalein or a suitable alternative indicator with a colour change in the pH 8 to 11 range.

Clause 8 then defines how to average the readings. The method measures 3 to 5 points on each face, handles dense aggregates by using the theoretical front across the particle, and limits the influence of pores or porous particles and extreme values. This matters because a single void or dense aggregate can distort a local reading if the rules are not applied consistently.

Calculation and reporting

Clause 8 calculates mean carbonation depths for the face, the specimen, and the test age, then plots average depth against the square root of exposure time. A linear regression gives the carbonation rate, KAC, and the coefficient of determination R should be at least 0.95. If the fit is poor, the reasons should be investigated and the test repeated where possible.

Clause 9 lists the reporting items, including specimen details, curing and conditioning history, test ages, individual and mean depths, rejected extreme values, KAC, the regression plot, any deviation from the procedure, and relevant photographs. For a buyer or quality manager, the report section shows exactly what evidence should be on file to support a stated carbonation resistance result.

What terms does kSIST FprEN 12390-12:2026 define?

kSIST FprEN 12390-12:2026 defines the terms that control how results are reported and compared.

• Carbonation rate - the average rate at which the carbonation front moves into concrete, expressed in mm/√d; the document uses KAC for the rate obtained under its test conditions.
• Depth of carbonation - the depth measured on a freshly split concrete surface using phenolphthalein or a similar indicator that changes colour in the pH 8 to 11 range.
• Effective time - the number of days the specimens spend in the storage chamber while continuously exposed to carbon dioxide.
• Mean carbonation depth - the average depth of carbonation of two specimens.
• Single point carbonation depth - the carbonation depth measured at one point on a specimen, after applying the rules for dense particles, porous particles, or voids.
• Specimen carbonation depth - the mean depth of carbonation of one specimen.
• Specimen face carbonation depth - the mean depth of carbonation on one exposed face of one specimen.

Who uses kSIST FprEN 12390-12:2026?

kSIST FprEN 12390-12:2026 is used by testing laboratories, concrete producers, and technical teams that need to compare the carbonation resistance of mixes. It is also relevant to quality managers, engineers, and specifiers who need a documented durability test for hardened concrete specimens.

The method supports product development, mix approval, internal quality control, and technical documentation for concrete used in reinforced structures. It is especially useful when carbonation resistance is part of a durability assessment and the same test conditions must be repeated consistently.

What changed in kSIST FprEN 12390-12:2026 from the previous edition?

kSIST FprEN 12390-12:2026 will supersede EN 12390-12:2020. The foreword states these significant technical changes:

• the scope has been updated;
• alternatives for adapted curing times and procedures have been included;
• an alternative preconditioning procedure has been included;
• the revisions take account of slowly reacting binders.

These changes matter because they widen the procedures that can be used while still keeping the test result tied to declared curing and conditioning conditions.

Which standards are used with kSIST FprEN 12390-12:2026?

kSIST FprEN 12390-12:2026 refers to these standards and related parts:

Standard	What it contributes
EN 12350-2	Slump test for measuring consistence
EN 12350-3	Vebe test for consistence
EN 12350-4	Degree of compactability test
EN 12350-5	Flow table test
EN 12390-1	Specimen shape, dimensions and other requirements, including designated size d
EN 12390-2	Making and curing specimens for strength tests
EN 12390-10	Related hardened-concrete carbonation resistance method at atmospheric carbon dioxide levels
EN 206	General concrete specification, performance, production and conformity, listed in the bibliography
EN 12350-8	Self-compacting concrete slump-flow test, listed in the bibliography

What does the kSIST FprEN 12390-12:2026 document contain?

kSIST FprEN 12390-12:2026 contains the test principle, specimen production rules, curing and conditioning regimes, chamber requirements, measurement instructions, calculation steps, reporting items, and precision estimates. It also includes figures showing how to treat dense aggregates, pores and voids when a measurement point falls on them.

Table 1 gives precision estimates from a validation exercise, and Annex A describes a suitable storage chamber with carbon dioxide injection and monitoring. Those parts are useful when a laboratory is setting up the test or checking that its chamber and reporting practice match the method.

SLOVENSKI STANDARD
oSIST prEN 12390-12:2025
01-december-2025
Preskušanje strjenega betona - 12. del: Določanje odpornosti proti karbonatizaciji
betona - Metoda pospešene karbonatizacije
Testing of hardened concrete - Part 12: Determination of the carbonation resistance of
concrete - Accelerated carbonation method
Prüfung von Festbeton - Teil 12: Bestimmung des Karbonatisierungswiderstandes von
Beton - Beschleunigtes Karbonatisierungsverfahren
Essais pour béton durci - Partie 12 : Détermination de la résistance à la carbonatation du
béton - Méthode de la carbonatation accélérée
Ta slovenski standard je istoveten z: prEN 12390-12
ICS:
91.100.30 Beton in betonski izdelki Concrete and concrete
products
oSIST prEN 12390-12:2025 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN 12390-12:2025
oSIST prEN 12390-12:2025
DRAFT
EUROPEAN STANDARD
prEN 12390-12
NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2025
ICS 91.100.30 Will supersede EN 12390-12:2020
English Version
Testing of hardened concrete - Part 12: Determination of
the carbonation resistance of concrete - Accelerated
carbonation method
Essais pour béton durci - Partie 12 : Détermination de Prüfung von Festbeton - Teil 12: Bestimmung des
la résistance à la carbonatation du béton - Méthode de Karbonatisierungswiderstandes von Beton -
la carbonatation accélérée Beschleunigtes Karbonatisierungsverfahren
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 104.
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
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 12390-12:2025 E
worldwide for CEN national Members.

oSIST prEN 12390-12:2025
prEN 12390-12:2025 (E)
Contents Page
European foreword . 3
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Principle and general procedure. 7
5 Reagents and apparatus . 8
6 Production of concrete specimens . 9
6.1 General . 9
6.2 Making, curing and testing concrete specimens . 9
6.2.1 General . 9
6.2.2 First 7 days curing . 9
6.2.3 Curing from 7 to 90 days. 10
6.2.4 Default 90 day curing . 10
6.2.5 Standard 28 day curing . 10
6.2.6 Accelerated curing . 10
6.2.7 Specimen conditioning . 10
6.2.8 Exposure to accelerated carbonation . 11
7 Carbonation depth measurements . 11
8 Determination of the carbonation depth . 12
8.1 General . 12
8.2 Measuring the depth of carbonation on each test specimen . 12
8.3 Appreciation of dense aggregates . 12
8.4 Appreciation of pores and porous aggregates and extreme values . 12
8.5 Expression of the results . 12
9 Test report . 13
10 Precision estimate . 14
Annex A (informative) Guidance on storage chambers . 16
Bibliography . 19

oSIST prEN 12390-12:2025
prEN 12390-12:2025 (E)
European foreword
This document (prEN 12390-12:2025) has been prepared by Technical Committee CEN/TC 104
“Concrete and related products”, the secretariat of which is held by SN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 12390-12:2020.
prEN 12390-12:2025 includes the following significant technical changes with respect to
EN 12390-12:2020:
— the scope has been updated;
— alternatives for adapted curing times/procedures have been included;
— alternative for preconditioning procedures has been included;
— in order to account for slowly reacting binders.
The EN 12390 series, under the general title Testing hardened concrete, consists of the following parts:
— Part 1: Shape, dimensions and other requirements for specimens and moulds
— Part 2: Making and curing specimens for strength tests
— Part 3: Compressive strength of test specimens
— Part 4: Compressive strength - Specification for testing machines
— Part 5: Flexural strength of test specimens
— Part 6: Tensile splitting strength of test specimens
— Part 7: Density of hardened concrete
— Part 8: Depth of penetration of water under pressure
— Part 9: Freeze–thaw resistance with de-icing salts - Scaling (Technical Specification)
— Part 10: Determination of the carbonation resistance of concrete at atmospheric levels of carbon
dioxide
— Part 11: Determination of the chloride resistance of concrete, unidirectional diffusion
— Pert 12: Determination of the carbonation resistance of concrete – Accelerated carbonation method
— Part 13: Determination of the secant modulus of elasticity in compression
— Part 14: Semi-adiabatic method for the determination of heat released by concrete during its
hardening process
oSIST prEN 12390-12:2025
prEN 12390-12:2025 (E)
— Part 15: Adiabatic method for the determination of heat released by concrete during its hardening
process
— Part 16: Determination of the shrinkage of concrete
— Part 17: Determination of creep of concrete in compression
— Part 18: Determination of the chloride migration coefficient
— Part 19: Determination of electrical resistivity
oSIST prEN 12390-12:2025
prEN 12390-12:2025 (E)
Introduction
Reinforced concrete structures need to be durable to ensure that the intended working life is achieved.
The resistance to corrosion of reinforcement induced by carbonation plays a significant role in a
structure’s serviceability and consequently carbonation behaviour of concrete is an important property
to measure. This document specifies an accelerated test method applicable to cast test specimens, in
order to assess the carbonation behaviour of a concrete mix.
oSIST prEN 12390-12:2025
prEN 12390-12:2025 (E)
1 Scope
This document describes a method for evaluating the carbonation resistance of concrete using test
conditions that accelerate carbonation. After a defined period of curing and a period of preconditioning,
the test is carried out under controlled exposure conditions using an increased level of carbon dioxide.
NOTE The test performed under reference conditions takes a minimum of 112 days comprising a minimum
age of the specimen prior to curing under water of 28 days, a minimum preconditioning period of 14 days and an
exposure period to increased carbon dioxide level of 70 days.
This procedure is not a method for the determination of carbonation depths in existing concrete
structures.
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 12350-2, Testing fresh concrete — Part 2: Slump test
EN 12350-3, Testing fresh concrete — Part 3: Vebe test
EN 12350-4, Testing fresh concrete — Part 4: Degree of compactability
EN 12350-5, Testing fresh concrete — Part 5: Flow table test
EN 12390-2, Testing hardened concrete — Part 2: Making and curing specimens for strength tests
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1
carbonation rate
average rate at which the carbonation front penetrates concrete expressed as mm/√d (days)
Note 1 to entry: The carbonation rate varies depending upon the test curing, preconditioning or exposure
conditions. The carbonation rate is strictly associated with the conditions under which it was obtained. The
abbreviation ‘KAC’ is the carbonation rate under the test conditions specified in this document.
3.2
depth of carbonation
depth as measured using a phenolphthalein solution or an alternative indicator that results in a colour
change in the range of pH 8 to pH 11 on the freshly-split concrete surface
3.3
effective time
time in days spent in the storage chamber with the concrete specimens continually exposed to carbon
dioxide
oSIST prEN 12390-12:2025
prEN 12390-12:2025 (E)
3.4
mean carbonation depth
d
k
mean depth of carbonation of two specimens
3.5
single point carbonation depth
d
k, point
depth of carbonation recorded for a single point on a specimen
Note 1 to entry: This is the measured depth of carbonation except where the measurement point coincides with
a dense particle, porous particle or void, see 8.3 and 8.4.
3.6
specimen carbonation depth
d
k, spec
mean depth of carbonation of a single specimen
3.7
specimen face carbonation depth
d
k, face
mean depth of carbonation of a single exposed face of a single specimen
4 Principle and general procedure
2 concrete prisms, 8 concrete cubes or 5 concrete cylinders are cast and thereupon after a defined
period of curing and conditioning, and then placed in a storage chamber with a carbon dioxide
concentration within the storage chamber in percent by volume of (3,0 ± 0,5) % when the storage
chamber is at normal conditions (1 013 mbar at 25 °C) , temperature (20 ± 2) °C and relative humidity
(57 ± 3) % for periods of up to 70 days. Immediately prior to placing specimens in the storage chamber
and after prescribed ages corresponding to 7, 28 and 70 days of storage in the chamber (this gives
approximately equidistant values of √days), 2 of the cubes are split in half; 1 cylinder is split in half
along its vertical axis and a 50 mm slice is split from each of the prisms and the depths of carbonation
measured.
On one half of each cylinder or each slice of prism or on one half of each cube, twelve single point
carbonation depths (d ) are measured after each exposure period and the depth of carbonation d ,
k,point k
at that exposure time is expressed as the mean of the two test specimens. Using measurements taken at
the fixed times, the carbonation rate expressed as mm/√d is determined.

CO concentration can vary with altitude above the sea level.
oSIST prEN 12390-12:2025
prEN 12390-12:2025 (E)
5 Reagents and apparatus
A solution of 0,8 g of phenolphthalein powder dissolved in a solution of 70 ml ethanol and 30 ml of
deionised water or a suitable alternative indicator giving a colour change in the range pH 8 to 11 that
gives a sufficiently clear colour change in concrete to differentiate the neutralized zone, e.g.
thymolphthalein .
WARNING — Phenolphthalein is listed in REACH appendix 2 and its lists of substances of very high
concern. Phenolphthalein powder should be handled with the greatest care using safety gloves in a
fume cupboard fitted with an extractor.
Where needed, a fixing solution to permanently fix the colour change in the concrete specimen, see
Clause 7.
NOTE 1 Suppliers of some indicator solutions also provide a fixing solution that permanently fixes the colour
change.
A magnifier and a gauge with a precision of 0,5 mm.
A ventilated oven in which the temperature is capable of being controlled to (45 ± 5) °C. The oven is
only used in case of alternative conditioning. The volume of the oven shall be not less than 2,5 times the
volume of all the specimens to be dried at the same time.
A storage chamber with a carbon dioxide concentration within the storage chamber in percent by
volume as indicated in Clause 4, temperature at (20 ± 2) °C and a relative humidity at (57 ± 3) %, see
Annex A for details of a suitable chamber. The carbon dioxide concentration shall be within ± 0,5 % by
volume of the target value with no variation for longer than 4 h outside the target value ± 1,0 %.
NOTE 2 Experience [5] has shown that if saturated surface-dry specimens are placed in the storage chamber
shortly after removal from water curing, the relative humidity can exceed that permitted. Also, without active
control of the carbon dioxide concentration, the levels can drop below the permitted tolerance as the carbonation
process continues. Therefore, it is important that the storage chamber has active control on carbon dioxide
concentration, relative humidity and temperature.
NOTE 3 Relative humidity levels is maintained using methods at the discretion of the laboratory, for example
active humidification/dehumidification.
When the door of the storage chamber is opened, the carbon dioxide concentration within the chamber
can fall rapidly, and therefore, for practical reasons, a short period of low carbon dioxide concentration
is acceptable. The cumulative periods of times of low carbon dioxide concentration cannot exceed 4 %
of the storage time of 63 days. The relative carbon dioxide concentration is expected to be
within ± 0,1 % by volume of the target value during 96 % of the storage time in the carbonation
chamber
Apparatus for recording the relative humidity with a maximum permissible measurement error
of ± 3,0 % and the temperature with a maximum permissible measurement error of ± 0,5 °C.
Apparatus for recording CO concentration with a maximum permissible measurement error of ± 0,1 %
by volume.
The recording apparatus can be fitted with an audio/visual/email or other suitable alarm to alert
breaches of CO concentration within the storage chamber due to possible apparatus malfunction.
Thymolphthalein is not currently classified under REACH as a health or environmental hazard.
oSIST prEN 12390-12:2025
prEN 12390-12:2025 (E)
The accuracy of the sensors shall be higher than the requirements for the CO and humidity content
measurements. The CO and humidity sensors shall be controlled and calibrated regularly
Fans to facilitate steady circulation of air within the storage chamber.
6 Production of concrete specimens
6.1 General
Representative samples of the constituents, e.g. cement, aggregates, shall be used for making the test
specimens. Either a sample of concrete is taken from the concrete production plant or the concrete
mixes shall be produced using the laboratory’s standard procedures. The specimens for one test shall be
cast from a single batch of concrete.
NOTE A minimum batch volume of 50 l is sufficient.
Where the specimens are prepared by the client or their representative, the test laboratory shall be
informed of the day of casting and a confirmation that the specimens were stored as required by this
document.
Each test shall comprise at least two prismatic beams each being at least
...