Error Factors in Quantifying Inorganic Carbonate CO₂ in Concrete Materials

In this study, CO2 quantification was performed on various concrete binder and aggregates by back titration, ther-mogravimetric method, and combustion-infrared absorption method, and their mutual consistency and error factors due to material characteristics were investigated. The back titration measures CO2 directly and is considered the suitable method for both materials, although the effect of sulfide was a concern. On the other hand, the TGA method was revealed to have the possibility of underestimating or overestimating the CO2 determination because the oxidation of sulfides in blast furnace slag, combustion of unburned carbon in fly ash, and dehydration of clay minerals in aggregate overlapping with the temperature range of calcination of calcium carbonate. In the combustion-infrared absorption method, elemental or organic carbon encapsulated in aggregate particles may underestimate or overestimate the CO2 content. In blended cement, sulfur compounds may interfere with the infrared absorption of CO2 and overestimate the amount of CO2. Based on these results, back titration was considered the most suitable method for determining CO2 for concrete materials. It is essential to understand the characteristics of each sample contained and select appropriate methods for CO2 quantification of concrete materials and concrete.