# Experimental Methods to Evaluate the Carbonation Degree in Concrete--State of the Art Review
## 4 Conclusions  
The present study reviews and evaluates the applicability of different methods for carbonation degree measurement in concrete in both qualitative and quantitative ways, summarized in Table 3. Most approaches studied have shown comparable findings when a careful selection of the techniques of analysis and investigation criteria has been made. However, quantitative determination of the degree of carbonation seems to be critical for the accurate calculation of the CO\({}_{2}\) penetration capacity of a sample by accelerated carbonation, while all qualitative methods could provide modifications in the alkalinity of the pore solution of the specimen. Phase analysis methods are used instead of pH indicator for carbonation level determination as a way of limiting the drawbacks of conventional methods in detecting different zones from the external to central parts of the sample, while the phenolphthalein test does \begin{table}
\begin{tabular}{p{128.0 pt} p{128.0 pt} p{128.0 pt} p{128.0 pt}} \hline \hline
**Methods** & **Concept** & **Advantages** & **Drawbacks** \\ \hline I. & Qualitative methods & & & \\ \hline pH indicator & Evaluation the change in pH level & Simple and effective. Inexpensive. & Difficult to detect partial carbonated area. Outcome is partly depended on the experience and skill of examining staff. Destructive test \\ \hline Image analysis & Characterization of carbonation based on image analysis. & Uncomplicate to determine the carbonation front width. Allow to study deeply into the newly transformed phases of the carbonated sample. Rapid measurement. & High cost. Restrictions in depth exploration of the interior of structure. \\ \hline \hline Phase analysis & & & \\ \hline TGA & Investigation the weigh loss of profile ground powder of sample at the temperature range 450–900 \({}^{\circ}\)C. & Accurate measurement of chemical constituent at the different carbonated level. & Problems associated with the sampling (small mass). \\ XRD & Observation the intensity, the disappearance and generation of the diffraction peaks created by carbonation reaction. & & \\ \hline FTIR & Passing infrared light across the sample to observe relative intensity of the absorption bandwidths associated with the creation of chemical compositions during carbonation process. & Detect the main phases of typical carbonation reaction products. Therefore, partial carbonated area is easy to detect. Rapid measurement, time-saving. & \\ \hline Ultrasonic phase velocity & Detecting the change in the frequency of ultrasonic wave interacted with surface of sample. & Non-destructive test. Sensitivity to microstructure changes. & It is difficult to investigate the inner area of concrete. \\ \hline II. & Quantitative methods & & \\ \hline phenolphthalein & Degree of carbonation was evaluated by calculating the rate of the carbonated areas and the total fresh broken area of sample analyzed. & Simple and fast. & The data is not high enough to accurate quantitation. \\ \hline CO\({}_{2}\) uptake & Accurate estimation of CO\({}_{2}\) absorption content & Able to accurate evaluation of the carbonation degree in accordance with the carbonation time. & Complicated task due to the absence of a definite calculation method. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Experimental methods for determination the carbonation degree: Content, pros and drawbacks. not seem appropriate because the quantity of real CO\({}_{2}\) uptake all along the carbonation process has been overlooked. Based on the review, the following recommendations are given:  
* Using suitable indicators is highly recommended as a straightforward and simple approach. Even if quantitative methods have been applied, pH indicators were also used to detect the carbonated zones. All the pH measurement methods gave similar findings; thus, the authors suggest the easiest and cheapest pH measurement method: phenolphthalein.