## 3 Data Collection for the Case Study of Natural Carbonation  
### Data Description of Inspection Reports  
The natural carbonation data were collected from bridge inspection reports of three regions in Korea. Typically, bridge managers conduct periodic inspections and report the test results. In this study, 242 inspection reports of RCS structures were collected from three regions. Table 1 lists the reports collected from each region. Region A was a relatively densely populated downtown area, Region B was a low-density coastal area, and Region C was an island.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Region** & **Number of Reports** & **Characteristics** & **Area (km\({}^{2}\))** \\ \hline Region A & 137 & \begin{tabular}{c} High-densely \\ downtown area \\ \end{tabular} & 600 \\ \hline Region B & 22 & \
\begin{tabular}{c} Low-density \\ coastal area \\ \end{tabular} & 1850 \\ \hline Region C & 166 &
\begin{tabular}{c} Low-density \\ island \\ \end{tabular} & 10,550 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics and number of inspection reports collected from different areas.  
Figure 3: Example of weight matrix of the masking method.  
The data reported for the carbonation analysis were extracted from the inspection and diagnosis reports. Each inspection report contained carbonation information; however, its format differed depending on the inspection company. In this study, carbonation data were manually extracted from inspection reports. A total of 1379 carbonation data points were extracted, which included 588 superstructures and 791 substructures. Table 2 lists the additional data collected with respect to carbonation. The construction year, inspection year, and concrete strength data directly associated with carbonation were extracted. Furthermore, we collected information related to the bridge, such as bridge length, maximum span length, width, and live load, to estimate bridge constructability. Although these variables were not theoretical factors involved in carbonation, they indirectly predicted the quality at the time of construction [36; 41; 42; 43]. Figure 4 illustrates the carbonation depth of bridges with respect to service life. As indicated in the figure, the dispersion of the carbonation depth for service life was high, contrary to the theoretical equation. This was attributed to field bridges being exposed to conditions different from those of the laboratory environment. For instance, differences were observed in environmental conditions according to region, the quality of concrete based on the completed environment, and the history of environmental conditions as per the year of construction.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Classification** & **Factors** & **Average** & **Min** & **Max** \\ \hline \multirow{3}{*}{Carbonation-related factors} & Service life & 24.79 & 5 & 47 \\ \cline{2-5}  & Year of construction & 1989.65 & 1969 & 2010 \\ \cline{2-5}  & Concrete strength & 23.42 & 18 & 35 \\ \hline \multirow{3}{*}{Indirect factors} & Length & 83.19 & 5.2 & 261 \\ \cline{2-5}  & Maximum span length & 17.70 & 5 & 55 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Data extracted from the inspection reports.  
Figure 4: Carbonation depth according to regions: (**a**) Region A; (**b**) Region B; and (**c**) Region C.