Evaluating the Carbonation of Concrete by TOC Solid Sample Measurement System

Importance of the Topic

Concrete carbonation, the reaction of carbon dioxide with alkaline cement components to form calcium carbonate, is a primary deterioration mechanism in reinforced concrete structures. Quantitative evaluation of carbonate formation is essential for material development, durability assessment and quality control in construction and infrastructure maintenance.

Study Objectives and Overview

This application note demonstrates the use of a Total Organic Carbon (TOC) solid sample measurement system to quantify inorganic carbon (IC) in a standard cement sample. The objective is to compare IC levels immediately after sample opening and after three months of air exposure, illustrating the kinetics of carbonation under ambient conditions.

Instrumentation Used

• TOC-LCPH Total Organic Carbon Analyzer
• SSM-5000A Solid Sample Combustion Unit

Methods and Instrumentation

Approximately 50–100 mg of powdered cement was weighed into a sample boat and mixed with 0.1 mL of deionized water. Phosphoric acid was dispensed to release CO₂ from inorganic carbon, and the sample was combusted in an IC furnace at 200 °C. Evolved CO₂ was carried by oxygen (500 mL/min) into the TOC analyzer. A single-point calibration using powdered sodium carbonate (11.3 % C) established the response curve.

Results and Discussion

Immediately after unsealing, IC was below the quantitative detection limit (0.0045 %). After three months of air exposure, the IC concentration rose to 1.005 %, corresponding to a 1 % increase in carbonate content. Replicate measurements showed a coefficient of variation under 2 %, confirming excellent repeatability. These results highlight the sensitivity of IC measurement for detecting early carbonation stages compared with conventional visual methods.

Benefits and Practical Applications

• Rapid, quantitative assessment of concrete carbonation without complex sample preparation.
• Ability to analyze up to 1 g of solid sample minimizes errors from inhomogeneity.
• Numerical evaluation of subtle changes supports research in admixture performance and durability studies.
• Determination of total carbon (TC) or IC allows calculation of TOC by difference.

Future Trends and Applications

Advancements may include automated sample handling for higher throughput, integration with micro-combustion modules for trace analysis, and coupling with isotope ratio mass spectrometry for provenance studies. Expanded applications could cover carbon footprint assessment of building materials and real-time monitoring of carbonation in field samples.

Conclusion

The TOC solid sample measurement system provides a precise, reproducible method for quantifying carbonation in cementitious materials. The observed increase in inorganic carbon after air exposure demonstrates its effectiveness for tracking material aging and durability. This approach offers a robust tool for both research and quality control in concrete technology.

References

Shimadzu Application News No. O56. 2021.