DD CEN TS 12390 — Testing Hardened Concrete Standard Series (Freeze-Thaw and Carbonation)

🏗️ DD CEN/TS 12390 is a CEN Technical Specification issued by BSI in the Draft for Development (DD) series, supplementing the European hardened-concrete testing family EN 12390. The two documents in this series cover test methods for two durability indicators: freeze-thaw scaling resistance and relative carbonation resistance. UK participation was entrusted by Technical Committee B/517 (Concrete) to Subcommittee B/517/1 (Concrete production and testing), and the documents are classified under ICS 91.100.30 (Concrete and concrete products). Both are provisional documents subject to review no later than 3 years after publication to decide on conversion into formal European Standards.

⚠️ The BSI committee responsible for the UK voting decision has concerns about the practical applicability of Part 9 (freeze-thaw): although the TS gives no performance values, its criteria derive from extreme Nordic freeze-thaw experience. Many UK concretes that perform adequately in the prevailing environmental conditions would fail these criteria by a substantial margin, so the UK concluded that modifications to the test method are required.

1. Series Overview and Application Context 📌

Concrete durability is the decisive factor in whole-life structural cost. In cold regions, surface scaling from freeze-thaw cycles is the most common deterioration mode for pavements, bridges, and marine structures; in de-icing salt environments, the combined salt-frost action markedly aggravates scaling. Carbonation, in turn, lowers the pore-solution pH and weakens the steel passivation film, preconditioning reinforcement corrosion. The main EN 12390 family focuses on basic properties such as strength and density; these two parts provide test methods for these two critical durability indicators for use in durability design and acceptance.

2. Series Structure and Document List 📋

Standard	Edition	Subject	Durability Indicator
DD CEN/TS 12390-9	2006	Freeze-thaw resistance — Scaling	Frost/salt-frost surface scaling
DD CEN/TS 12390-10	2007	Determination of the relative carbonation resistance	Carbonation depth / rate

3. Part 9: Freeze-Thaw Scaling Test 🔧

Part 9 specifies a method for determining the amount of scaling from hardened concrete surfaces under repeated freeze-thaw cycles. Key points include:

Specimen preparation: cast and cure specimens; the test surface is exposed to water or a salt solution (simulating de-icing salt conditions).
Freeze-thaw cycling: apply repeated cycles within the specified temperature range and rate for a prescribed number of cycles.
Scaling measurement: periodically collect and weigh the scaled material to obtain a cumulative scaling curve (g/m²) versus cycle number.
Interpretation: evaluate freeze-thaw scaling performance by cumulative scaling, compared against a reference concrete.

💡 De-icing salts (e.g., NaCl) raise the saturation equilibrium near the pore-solution freezing point and generate osmotic pressure and thermal shock; scaling typically occurs in the mortar layer nearest the surface. The standard prescribes the orientation and sealing of the test surface to keep results comparable.

4. Part 10: Determination of Relative Carbonation Resistance 🔍

Part 10 gives a method for determining the relative carbonation resistance of concrete: cured specimens are placed in a controlled CO₂ concentration, temperature, and relative humidity environment for accelerated carbonation; at specified ages the specimens are split and the carbonation depth is measured by phenolphthalein indicator colour change. Comparison of the depth with that of a reference concrete yields the “relative carbonation resistance”, used to compare the carbonation resistance of concretes with different mix designs and supplementary cementitious materials (fly ash, slag, etc.).

⚠️ An accelerated carbonation environment cannot fully represent natural exposure: excessively high CO₂ concentrations shift hydration products and pore-structure evolution away from reality. The indicator suits relative comparison and should not be directly extrapolated to predict corrosion-initiation time in real environments, which requires service-life modelling.

5. Engineering Practice 🛠️

🔍 Mix optimization: compare frost and carbonation resistance when screening SCM types and dosages.
🔧 Durability acceptance: run dedicated tests for concrete in special environments (cold regions, de-icing salt pavements, coastal).
📊 Service-life input: carbonation depth data calibrate carbonation-induced corrosion models (e.g., the fib model).
📋 Reporting and audit: archive test conditions, cycle parameters, and scaling data to guarantee traceability.

6. Frequently Asked Questions ❓

❓ Q: Why does Part 9 focus on surface scaling?
A: Scaling reduces the section, exposes aggregates, and accelerates further frost and salt attack; it is the dominant frost-damage form for roads and marine structures, so it is used as the evaluation indicator.

❓ Q: Why does the UK have reservations about Part 9?
A: The UK climate is mild and most in-service concretes perform well, but many would “fail” the severe Nordic criteria. The UK recommended a reference concrete with known satisfactory performance or different test conditions/acceptance criteria, and considers the method itself to require modification.

❓ Q: How is the accelerated carbonation period determined?
A: Follow the CO₂ concentration and curing age prescribed by the standard; measure carbonation depth on specimens cut at different ages, fit the k·√t relationship to determine the carbonation coefficient, and compare.

🔍 Q: Do the two documents give performance values?
A: No. The TS specifies test methods only, not performance requirements; limits are agreed in national codes, project technical specifications, or documents of the EN 206 type.

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