Overview
ISO 1920-12:2015 specifies an accelerated carbonation method for evaluating the carbonation resistance of concrete. The procedure uses controlled exposure to elevated carbon dioxide levels to measure the depth of carbonation on cast specimens (cubes or prisms) after preconditioning, exposure and penetration assessment using phenolphthalein. It is intended to compare the carbonation resistance of different concretes of the same strength class under the same environmental conditions, not to set contractual performance limits.
Key topics and technical requirements
- Specimens: Two cubes (min. 100 mm cross-section) for single-time measurements, or two prisms (100 × 100 × 400 mm) when repeated measurements on the same specimen are required. Minimum specimen dimension must be ≥ 4 × maximum aggregate size.
- Curing and conditioning: Standard curing for 28 days (water bath ~20 ± 2 °C or 27 ± 2 °C in hot climates), then 14 days in laboratory air (≈ 18–29 °C, RH 50–70 %). Alternative regimes must be recorded.
- Exposure conditions: Storage chamber with CO2 at (3.0 ± 0.5) % by volume, temperature (22 ± 2) °C (or 27 ± 2 °C in hot climates), and RH (55 ± 5) % (or 65 ± 5 % in hot climates). Active control and monitoring of CO2, temperature and RH are recommended.
- Sealing: Non-exposed faces are sealed (paraffin wax or equivalent) so carbonation occurs only on two vertical faces.
- Exposure period: Reference exposure is 70 days at the elevated CO2 level. Minimum total test time under reference conditions is ~112 days (28 d curing + 14 d conditioning + 70 d exposure).
- Measurement: After splitting specimens, phenolphthalein solution (1 g phenolphthalein in 100 ml: 70 ml ethanol + 30 ml deionized water) is sprayed on the freshly-split surface. Carbonation depth is measured perpendicular to the exposed face with precision 0.5 mm. Results reported as single-point, face, specimen and mean depths.
- Reporting: Record curing, conditioning, exposure chamber parameters, any deviations from reference conditions and methods used to maintain RH/CO2.
Applications and users
- Who uses it: Materials and durability laboratories, concrete producers, R&D teams, structural designers, durability consultants, specification writers and academics.
- Practical uses: Comparing mixes (cement type, SCMs, admixtures), validating durability improvements, supporting mix selection for reinforced concrete structures, research on carbonation mechanisms and mitigation strategies, quality control in development of low-permeability or high-durability concretes.
Related standards
Keywords: ISO 1920-12:2015, carbonation resistance, accelerated carbonation method, concrete testing, phenolphthalein, CO2 chamber, depth of carbonation, concrete durability.