FprEN 12390-12

• 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
• Publication Date: 16-Dec-2026
• ICS: 91.100.30 - Concrete and concrete products
• Technical Committee: CEN/TC 104 - Concrete ( performance, production, placing and compliance criteria )
• Drafting Committee: CEN/TC 104/SC 1 - Revision of ENV 206
• Current Stage: 5020 - Submission to Vote - Formal Approval
• Start Date: 27-Aug-2026
• Due Date: 08-Oct-2026
• Completion Date: 27-Aug-2026
• Ref Project: kSIST FprEN 12390-12:2026 - Testing of hardened concrete - Part 12: Determination of the carbonation resistance of concrete - Accelerated carbonation method

• Revises: EN 12390-12:2020 - Testing hardened concrete - Part 12: Determination of the carbonation resistance of concrete - Accelerated carbonation method
• Effective Date: 18-Jan-2023

FprEN 12390-12 is a CEN draft European Standard for testing hardened concrete. It specifies an accelerated carbonation method for evaluating the carbonation resistance of concrete cast as test specimens, under controlled exposure to increased carbon dioxide. The method is used to compare concrete mixes and assess their carbonation behaviour; it is not a method for measuring carbonation depth in existing concrete structures.

What does FprEN 12390-12 specify?

FprEN 12390-12 specifies the scope, test principle, specimen preparation, exposure conditions, depth measurement method, calculation of carbonation rate, and the required test report for accelerated carbonation testing of hardened concrete. The document is organized into Clauses 1 to 10, with one informative annex and a bibliography.

The document begins with the scope and normative references, then defines key terms before describing the principle and general procedure, reagents and apparatus, specimen production, carbonation depth measurements, determination of carbonation depth, reporting, and a precision estimate. Annex A gives guidance on storage chambers.

Annex	What it covers
Annex A	Guidance on storage chambers for accelerated carbonation exposure

What are the key requirements of FprEN 12390-12?

FprEN 12390-12 requires concrete test specimens to be cast, cured, conditioned, exposed to controlled CO2, and then split so that carbonation depth can be measured on freshly broken surfaces. The measured depths are then used to calculate the carbonation rate, KAC, in mm/√d.

Specimen type and batch preparation

Clause 4 requires either 2 concrete prisms, 8 concrete cubes, or 5 concrete cylinders for a test, all from a single batch of concrete. Clause 6.1 says the specimens should represent the concrete constituents and that the concrete may come from a production plant or be made using laboratory procedures. In practice, this means one test is tied to one batch, so the result reflects one mix rather than a blend of materials.

Fresh concrete record and specimen making

Clause 6.2.1 requires the consistence class or target value to be measured using EN 12350-2, EN 12350-3, EN 12350-4, or EN 12350-5 as appropriate. It also requires casting the specimens from a single batch and protecting them from drying immediately after finishing. This gives traceability for the fresh mix, which matters when comparing mixes or investigating unusual results.

Curing options before carbonation exposure

Clause 6.2.2 gives the first curing period, with the specimen kept in its mould under controlled conditions before demoulding and further curing in water or a high-humidity chamber. Clause 6.2.3 sets the default curing as 90 days, while Clause 6.2.4 permits 28 day curing and Clause 6.2.5 permits accelerated curing where specified. These options matter because curing age changes hydration and therefore the carbonation response.

Conditioning before exposure

Clause 6.2.7 sets the default conditioning as 14 days of laboratory air drying at 18 °C to 25 °C and 50 % to 65 % relative humidity. An alternative conditioning route uses oven drying at (45 ± 5) °C for 14 days, followed by 7 days at 20 °C and 65 % relative humidity. This step matters because specimen moisture strongly affects carbonation, so the drying history must be controlled and reported.

Accelerated carbonation exposure conditions

Clause 4 and Clause 5 require exposure in a storage chamber at (3.0 ± 0.5) % CO2 by volume, 20 ± 2 °C, and 57 ± 3 % relative humidity, with active monitoring and control. Clause 5 also requires temperature, humidity, and CO2 recording instruments, alarms for CO2 breaches, and air circulation fans. In practice, this is the core of the accelerated method: the chamber must hold conditions tightly enough that results from different tests remain comparable.

Measurement of carbonation depth

Clause 7 requires the specimen faces to be broken or split, not sawn, and the freshly exposed surfaces to be sprayed with indicator solution such as phenolphthalein or another suitable indicator giving colour change in the pH 8 to 11 range. Measurements are taken after 7, 28, and 70 days of storage, and Clause 8 requires 3 to 5 points on each relevant face with 0.5 mm precision. This means the laboratory measures the coloured front directly rather than inferring carbonation indirectly.

Calculation and result expression

Clause 8 requires the mean carbonation depth to be calculated for each face, specimen, and test age, and the carbonation rate to be obtained from a linear regression of mean depth against the square root of exposure time. The coefficient of determination should be at least 0.95, and the test report must include the intercept, regression plot, and any deviations from the procedure. In practice, the result is not just a depth value - it is a rate that allows comparison between concretes under the same test conditions.

What terms does FprEN 12390-12 define?

• Carbonation rate - The average rate at which the carbonation front moves into concrete, expressed in mm/√d; the standard uses the abbreviation KAC for the rate under its test conditions.
• Depth of carbonation - The depth identified by a colour change on a freshly split concrete surface using phenolphthalein or another suitable indicator.
• Effective time - The time, in days, during which specimens are continuously exposed to carbon dioxide in the storage chamber.
• Mean carbonation depth - The average carbonation depth of two specimens.
• Single point carbonation depth - The carbonation depth measured at one point on one specimen.
• Specimen carbonation depth - The mean depth of carbonation for one specimen.
• Specimen face carbonation depth - The mean depth of carbonation for one exposed face of one specimen.

Who uses FprEN 12390-12?

FprEN 12390-12 is used by concrete laboratories, concrete producers, durability engineers, quality managers, and project clients who need a repeatable way to compare carbonation resistance of concrete mixes. It is relevant in concrete and concrete products work, especially where durability against reinforcement corrosion matters.

In practice, laboratories use it to prepare specimens, run the chamber exposure, measure carbonation depth, and report the carbonation rate. Manufacturers and buyers use it to compare mix designs, check the effect of binder type or curing regime, and document performance for product development or specification.

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

FprEN 12390-12 will supersede EN 12390-12:2020. The foreword states that the significant technical changes are:

• the scope has been updated;
• alternatives for adapted curing times and procedures have been included;
• an alternative preconditioning procedure has been included;
• the changes were made to account for slowly reacting binders.

Which standards are used with FprEN 12390-12?

FprEN 12390-12 cites these standards in its normative references:

• EN 12350-2 - slump test for fresh concrete, used to record consistence.
• EN 12350-3 - Vebe test, used to record consistence where appropriate.
• EN 12350-4 - degree of compactability, used to record consistence where appropriate.
• EN 12350-5 - flow table test, used to record consistence where appropriate.
• EN 12390-2 - making and curing specimens for strength tests, used for specimen preparation and curing.

The foreword also places this document within the EN 12390 series, alongside parts covering specimen geometry, strength, density, water penetration, chloride resistance, modulus of elasticity, shrinkage, creep, resistivity, and carbonation at atmospheric CO2. EN 12390-10 is also cited in the bibliography and in the reporting notes for comparison of carbonation resistance at atmospheric carbon dioxide.

What does the FprEN 12390-12 document contain?

The document contains the test principle, specimen preparation routes, exposure chamber conditions, measurement rules, calculation method, reporting items, and a precision estimate based on a CEN validation exercise. Clause 7 and Clause 8 include the practical rules for breaking specimens, using indicator solution, handling dense aggregates, pores, and extreme values, and plotting carbonation depth against the square root of time.

It also contains a worked regression approach in Clause 8, plus Figure 1 and Figure 2 to show how to treat points that fall on dense aggregate, porous aggregate, or voids. Annex A describes a suitable storage chamber arrangement, including CO2 control and specimen spacing, and the document includes a table of precision estimates for different concrete mixes.

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
...