# Experimental Methods to Evaluate the Carbonation Degree in Concrete--State of the Art Review
## 3 Quantitative Methods
### CO\({}_{2}\) Uptake  
Different views on the relationship between the depth and degree of carbonation exist in the literature. [PERSON] [84] believed that the carbonation degree is entirely indepen  
Figure 8: Signals from non-carbonated and carbonated cement paste [81]. The number in the graphs presents the ratio of water and cement. dent from carbonation depth through study or the carbonation degree of concrete over a four-year exposure duration. The evidence for this is that, at the position where the carbonation depth reaches maximum, the amount of CO2 is not at maximum. This means that carbonation degree is not influenced by carbonation depth. The carbonation degree is mainly governed by the amount of CO2 uptake once the concrete is in touch with a CO2-rich environment. Therefore, accurate estimation of CO2 absorption content from accelerated carbonation conditions is vital to accurately predict and quantify carbonation stages in actual concrete structures. However, CO2 uptake measurement in cement-based materials is a very complicated task due to the absence of a definite calculation method. The theoretical, semi-empirical and empirical models could constitute calculation bases. The CO2 uptake method relates to an amount of CO2 absorbed in the sample that could be calculated in multiple ways. Some studies [69; 87; 88; 89] reported that the carbonation degree could be governed by the uptake of CO2 within the carbonation process. This mass was calculated based on the content of CO2 in the sample at different durations of the exposure process. The usage of this method could give a relatively accurate evaluation of the carbonation degree in accordance with the carbonation time. However, this method seems to suit the pure CO2 environment (CO2 concentration in the storage chamber ~100%) with a short carbonation duration. For example, [PERSON] et al. [90] investigated the carbonation degree in the first two hours of the carbonation of concrete and assessed that a degree of carbonation of 16% was obtained through the measurement CO2 uptake of 8%. As can be seen, in quantitative measurement, the calculation of the carbonation degree is varied and relies on the view of the CO2 diffusion mechanism in concrete. Quantitative assessment of the carbonation degree of the cementitious composite has been calculated based on CO2 uptake content and was identified differently, as shown in Table 2. Several researchers have calculated the carbonation degree of concrete based on the CO2 uptake content calculated in TGA analysis. Besides, some other methods were also employed for the measurement of CO2 amount such as XRD [91; 92], nuclear magnetic resonance NMR [17; 58; 93], mercury intrusion porosimetry MIP [94; 95], or estimation using the mass gain method in early-age carbonation [96]. \begin{table}
\begin{tabular}{l l l} \hline \hline
**Equation of the Carbonation Degree** & **Feature** & **Ref.** \\ \hline  & - & CO2 uptake is based on the ratio of the original mass of the reacting compounds \\  & & to that of mass basis. \\ CO2 uptake & - & CO2 uptake maximum capacity is calculated hypothetically from the stoichiometric composition of the \\  & & reacting mixtures. \\ \hline  & - & CO2 is determined by the proportion of \\  & & CO2 in the carbonated areas absorbed \\ CO2 in the carbonation zone & - & Maximum CO2 uptake is regarding \\ Maximum CO2 uptake & - & content of CO2 emissions at \\  & & clinker calcination. \\ \hline  & - & CO2 content based on the mass loss in the \\ CO2 content in fully carbonated zone – CO2 content after carbonation * 100\% & temperature range of 500–900 \({}^{\circ}\)C, \\  & according to TGA analysis. \\ \hline  & - & CO2 based on the mass loss in the \\ CO2 content in carbonated zone – CO2 content in uncarbonated zone * 100\% & temperature range of 550–1000 \({}^{\circ}\)C, \\  & according to TGA analysis. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Several mathematical models for carbonation degree calculation by means of CO2 content.