ISO/TR 22861:2025

Guidance on marine environment zonation for steel corrosion embedded in concrete

This document sets out a methodology for the exposure zone division of reinforced concrete structures in marine environments, based on a test procedure that is provided in this document. This document is applicable to the division of coastal and offshore marine environment areas. It is not applicable to typhoon, strong tide and other marine environment areas. Annexes B, C, and D provide examples of marine environment zonation to illustrate the methodology.

Recommandations relatives au zonage de l'environnement marin pour la corrosion de l'acier encastré dans le béton

General Information

• Status: Published
• Publication Date: 12-Oct-2025
• ICS: 77.060 - Corrosion of metals
• Technical Committee: ISO/TC 156 - Corrosion of metals and alloys
• Drafting Committee: ISO/TC 156 - Corrosion of metals and alloys
• Current Stage: 6060 - International Standard published
• Start Date: 13-Oct-2025
• Due Date: 20-Jun-2026
• Completion Date: 13-Oct-2025

Overview - ISO/TR 22861:2025 (Guidance on marine environment zonation for steel corrosion embedded in concrete)

ISO/TR 22861:2025 is a Technical Report that provides a practical methodology for dividing exposure zones of reinforced concrete structures in coastal and offshore marine environments to assess chloride‑induced corrosion risk to embedded steel. The document prescribes an investigation and test‑based workflow for identifying where different environmental actions affect reinforcement durability. It is applicable to coastal and offshore areas but explicitly excludes typhoon, strong tide and other extreme marine conditions. Annexes provide worked examples to illustrate the method.

Key technical topics and requirements

• Scope and purpose: Establish exposure zones to support durability design, corrosion protection decisions and lifecycle planning for marine reinforced concrete.
• Fundamental concepts: Transfer mechanisms (gravity, condensation, drainage), environmental action (chemical/electrochemical/physical) and the definition of an exposure zone (surface area of a concrete element exposed to marine action).
• Investigation requirements (Clause 5):
  • Collect tidal data (design tide level, astronomical tide level).
  • Define high tide and low tide using cumulative frequency (high tide 10 %, low tide 90 %) from multi‑year or at least one year hourly records.
  • Determine coastline limit by long‑term high tide boundaries.
• Exposure zone division (Clause 6):
  • Two approaches: experimental determination (Clause 7) or estimation (Annex A) when tests are not feasible.
  • Recognize uncertainties when using generalized descriptions.
• Specimen‑based determination (Clause 7):
  • Use uniformly fabricated standard specimens (referenced standards include EN 197‑1, ISO 22965‑1/‑2, ISO 6935‑2).
  • Apply a thin organic surface coating (dry thickness ≤ 20 µm is prescribed in the text) leaving controlled exposed areas.
  • Place specimens on horizontal and vertical platforms to capture exposure gradients (distance from coastline, elevation relative to mean sea level); exposure duration minimum 90 days (one year recommended for long‑term properties).
  • Measurement examples in Annexes B–D include reinforcement corrosion potential, surface chloride concentration and concrete electrical resistivity.

Practical applications and users

• Primary users: coastal and offshore structural designers, corrosion engineers, materials scientists, asset owners, inspection teams, and standards bodies.
• Practical uses:
  • Categorize exposure conditions for durability design and specification of corrosion protection (barriers, coatings, concrete cover, cathodic protection).
  • Inform maintenance planning, monitoring strategies and lifecycle cost assessments.
  • Provide test protocols for site‑specific environmental action measurement to reduce over‑ or under‑specification of protective measures.

Related standards

• ISO 13823, ISO 16204 and ISO 12696 are referenced as complementary documents for durability analysis and corrosion protection guidance.
• Annexes B–D illustrate how common field parameters (corrosion potential, chloride content, resistivity) can be used to determine exposure zones.

Keywords: ISO/TR 22861:2025, marine environment zonation, steel corrosion embedded in concrete, exposure zones, chloride‑induced corrosion, reinforced concrete, specimen testing, coastal and offshore durability.

Standards Content (Sample)

Technical
Report
ISO/TR 22861
First edition
Guidance on marine environment
2025-10
zonation for steel corrosion
embedded in concrete
Recommandations relatives au zonage de l'environnement marin
pour la corrosion de l'acier encastré dans le béton
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Fundamental . 2
4.1 Transfer mechanisms .2
4.2 Environmental action .2
4.3 Exposure zone .2
5 Investigation . . 2
5.1 Investigation object .2
5.2 Investigation content .2
6 Exposure zone division . 2
7 Exposure zone determination based on environmental action measurement of standard
specimens . 3
7.1 Specimen fabrication .3
7.2 Specimen placement .3
7.3 Test procedure .4
7.4 Exposure zone determination .4
Annex A (informative) Influence factor of marine environmental action and normative
estimation process of typical exposure zones . 6
Annex B (informative) A case of exposure zone determination with the corrosion potential of
the reinforcement . 8
Annex C (informative) A case of exposure zone determination with the surface chloride ion
concentration .11
Annex D (informative) A case of exposure zone determination with the concrete electrical
resistivity.15
Bibliography . 17

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
Due to the different exposure zones encountered by reinforced concrete structures within marine
environments, the mechanisms of chloride penetration vary, resulting in various levels of steel corrosion.
It is imperative to design the durability of reinforced concrete structures in these distinct exposure zones
to satisfy specific requirements and implement appropriate anti-corrosion strategies. Underestimating the
environmental effects without implementing sufficient protective measures can precipitate premature
degradation of reinforced concrete. Conversely, overestimating environmental effects and adopting excessive
protective measures can incur superfluous construction costs. Therefore, it is essential to accurately identify
the boundaries of exposure zones to categorize the effect of the actual environmental action.
The division of exposure zones is based on the assessment of the durability of marine reinforced concrete
structures. From the outcomes of exposure zone division, the intensity of environmental effects can also
be broadly categorized. However, similar levels of environmental effect can manifest across different
exposure zones, indicating the necessity for a more refined categorization tailored specifically to marine
environments.
This document aims to highlight the main exposure zones that infrastructure services need to consider
when providing corrosion protection for reinforced concrete structures. It provides a general method for
determining the exposure zone of marine reinforced concrete structures. The identified exposure zones
are used for durability analyses of corrosion damage and for making informed decisions about corrosion
protection measures. This document is a supplement to existing specifications, such as ISO 13823, ISO 16204
and ISO 12696.
v
Technical Report ISO/TR 22861:2025(en)
Guidance on marine environment zonation for steel corrosion
embedded in concrete
1 Scope
This document sets out a methodology for the exposure zone division of reinforced concrete structures in
marine environments, based on a test procedure that is provided in this document.
This document is applicable to the division of coastal and offshore marine environment areas. It is not
applicable to typhoon, strong tide and other marine environment areas.
Annexes B, C, and D provide examples of marine environment zonation to illustrate the methodology.
2 Normative references
There are no normative references in this document.
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:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
durability
capability of a structure or any component to satisfy, with planned maintenance, the design performance
requirements over a specified period of time under the influence of environmental action, or as a result of a
self-ageing process
3.2
environmental action
chemical, electrochemical, biological, physical and/or mechanical action causing material degradation of a
component
Note 1 to entry: For the purposes of this document, the term "environment" mainly refers to the marine environment
and related influence factors.
3.3
category of location
conventionally defined typical exposure conditions of a component or structure
Note 1 to entry: Exposure can mean in the open, under seawater, in an aggressive salt spray environment, etc. The
typical exposure conditions include the atmospheric zone, splash zone, tidal zone and submerged zone.

4 Fundamental
4.1 Transfer mechanisms
Transfer mechanisms, including gravity, condensation and drainage, either promote or prevent the
transfer of environmental influences into the agents (e.g. moisture, oxygen and temperature) that cause
environmental action on or within the components of the structural system.
4.2 Environmental action
Environmental action, such as corrosion, decay or shrinkage, result from chemical, electrochemical,
biological (e.g. insect attack), physical (e.g. UV) or mechanical action that causes material deterioration or
deformation. The environmental action considered in this document is chloride-induced corrosion.
NOTE The influence factor under different environmental actions is outlined in Clause A.1.
4.3 Exposure zone
The term "exposure zone" refers to a specific zone within the surface area of a concrete element that is
exposed to the marine environment. The category of location is standardized in relation to the effects of
environmental action.
The workflow of the exposure zone division method includes investigation (Clause 5), exposure zone division
(Clause 6) and exposure zone determination based on environmental action measurement of standard
specimens (Clause 7). For any component of marine structures, the method requires an understanding of
the transfer mechanisms (4.1) and environmental action (4.2) leading to the difference in each exposure
zone (4.3).
NOTE 1 The spatial location is divided into the horizontal platform and vertical platform according to the respective
directions. Both the horizontal platforms and vertical platforms consist of several different exposure points.
NOTE 2 The horizontal platforms are categorized based on their minimum distance from the coastline, while the
vertical platforms are segmented according to the elevation of the structural element relative to the mean sea level
(see Clause A.2).
5 Investigation
5.1 Investigation object
The objects of investigation are reinforced concrete structures in an open field.
5.2 Investigation content
The investigation focuses on the design tide level, the astronomical tide level and the coastline limit. Both
the design tide level and the astronomical tide level include high water level and low water level.
The high tide level is defined by the high tide cumulative frequency corresponding to 10 % of the tide level, which
is referred to as "high tide 10 %". Similarly, the low tide level is based on the tide level with a low tide cumulative
frequency of 90 %, which is referred to as "low tide 90 %". To determine these cumulative frequencies, data is
collected from several years of recorded tidal levels or, at the very least, from daily hourly measurements over
one year. Additionally, the coastline limit is determined by the long-term measured boundary created by the
high tides of the mean spring tide, which is used to calculate the distance from the shore.
6 Exposure zone division
The exposure zone of the marine environment is established either by determining it in accordance with
Clause 7 or, where this is not possible, by estimating it in accordance with Clause A.2. Both methods of
exposure zone division represent a generalized approach and have uncertainties and limitations.

An exposure zone is identified based on the environmental factors that impact the reinforcement within the
concrete. These environmental factors represents the specific effects experienced within an exposure zone
over a designated exposure time.
When estimating the exposure zone by comparing local environmental conditions with typical descriptions
of marine environments, misinterpretations can sometimes occur. These errors arise when generalized
descriptions do not accurately reflect the unique characteristics of the local environment.
The exposure zone estimation approach can be used if experimental data is not available (see Annex A). The
exposure zone determination approach can be used if experimental data is available (see Annexes B, C and D).
Annex A outlines the process for estimating typical exposure zones.
Annex B gives a case of exposure zone determination with the corrosion potential of the reinforcement.
Annex C gives a case of exposure zone determination with the surface chloride ion concentration.
Annex D gives a case of exposure zone determination with the concrete electrical resistivity.
7 Exposure zone determination based on environmental action measurement of
standard specimens
7.1 Specimen fabrication
To accurately capture the environmental action in different exposure zones, all concrete specimens are
prepared uniformly, thereby eliminating the influence of material and structural size on the measurement
of environmental action. For instance, the dimensions and material composition of the specimens adhere to
[4]
standards including EN 197-1, ISO 22965-1, ISO 22965-2 and ISO 6935-2.
To fabricate the concrete specimens, a thin layer of organic coating (e.g. glue, varnish or lacquer-like
cellulose acetate dissolved in acetone) is applied to prevent chloride ingress. This coating is applied to the
surface of the reinforced concrete specimens, where the dry coating thickness does not exceed 20 mm. The
coating is deliberately applied in a manner that does not cover the entire surface area of the test specimen,
intentionally leaving an exposure zone for the exposure test.
7.2 Specimen placement
The specific placement of the reinforced concrete specimens is shown in Figure 1. The purpose of the
exposure test is to quantify the effect of environmental action on the reinforcement inside the concrete over
the same exposure time.
For the exposure test, each specimen is positioned on a horizontal platform with the exposed surface
oriented skyward or the specimen is positioned on a vertical platform with the exposed surface oriented
towards the tides and currents of the open sea. To prevent the effects of tides, typhoons, ocean currents, etc.
on the specimens, fixed brackets are added to the test specimens. The duration of exposure is a minimum
of 90 days. The long-term properties of chloride penetration and reinforcement corrosion can be fully
quantified by setting up one-year exposure tests.

(a) Vertical platform (b) Horizontal platform
Key
Δh spacing between specimens in the vertical direction
h elevation from mean sea level
Δd spacing between specimens in the horizontal direction
d distance from coastline
Figure 1 — Placement of reinforced concrete specimens
7.3 Test procedure
The procedure for collecting test data is as follows:
a) Two or three test areas are arranged on each test specimen.
b) Four or five test points are set in each test area.
c) Testing is carried out at each test point and test values are recorded.
d) The exposure platform and exposure time (the time interval from sample placement to taking sample)
of each specimen are recorded.
7.4 Exposure zone determination
The environmental action on the reinforcement inside the concrete has measured indicators such as the
surface chloride ion concentration, the concrete electrical resistivity and the corrosion potential of the
reinforcement.
The corrosion potential of the reinforcement can directly quantify the effect of environmental action on
reinforcement corrosion. As the corrosion of reinforcement within the concrete specimen leads to significant
changes in the measured corrosion potential, accurate corrosion potential data can only be obtained if
the exposure duration is sufficiently extended. Therefore, when the corrosion potential does not change
significantly, the exposure zone can be divided by the surface chloride ion concentration and the concrete
electrical resistivity. Measuring concrete electrical resistivity is non-destructive, but the testing accuracy
is low. Therefore, when the engineering demands high accuracy for exposure zone division, the surface
chloride ion concentration can be used for regional division.
[9]
ASTM C876-15 provides guidance on the corrosion potential of the reinforcement inside the concrete
measurements and interpretation.
ISO 1920-11 provides guidance on surface chloride ion concentration measurements and interpretation.

References [10] and [11] provide guidance on concrete electrical resistivity measurements and
interpretation.
A measured indicator is selected according to the actual conditions to detect the corresponding test results.
Based on the test results, the boun
...