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.