## 2 Research Methodology
### Quantification Method of the Carbon Dioxide Emissions  
Based on the sources of carbon dioxide emissions during the construction of slab systems in a building, Equation (1) describes the total emissions:  
\[E_{Total}=\sum\
olimits_{i=1}^{3}E_{i} \tag{1}\]  
where, \(E_{Total}\) is the total carbon dioxide emissions during the construction stage in kg CO\({}_{2}\) eq., \(E_{i}\) is the carbon dioxide emissions from the \(i\)th stage during the process of construction, and in this study, \(i\) is from 1 to 3. Equations (2)-(4) describe the quantification method for calculating the carbon dioxide emissions during the construction phase of the three slab systems:  
\[E_{1}=\sum M_{j}\times f_{j} \tag{2}\]  
where \(E_{1}\) is the carbon dioxide emissions of all building materials (in kg CO\({}_{2}\) eq. ), \(M_{j}\) is the amount of building materials j (in m\({}^{3}\) for ready-mixed concrete, kg for rebars and expanded polystyrene for void formers, and m\({}^{2}\) for forms and steel decking), and \(f_{j}\) the carbon dioxide emissions factor of building material \(j\) (in kg CO\({}_{2}\)/unit). The value of the carbon dioxide emissions factors may vary dependent upon the country. In this study, data on the carbon dioxide emissions factors of building materials are limited to South Korean data. The carbon dioxide emissions factors in this study were adopted from the South Korean National Life Cycle Inventory Database [48]. Table 1 presents the related carbon dioxide emissions factors (\(f_{j}\)) of five dominant materials for the construction of slab systems for the current study. \[E_{2}=\sum\
olimits_{i=1}^{3}\sum\
olimits_{j=1}^{j}L_{c}\times N_{t}\times f _{trans} \tag{3}\]  
where \(E_{2}\) is the total carbon dioxide emissions from the transportation of building materials to the construction site (in kg CO\({}_{2}\) eq. ), \(L_{c}\) is the amount of fuel consumed in the transportation stage (in litres), \(N_{t}\) is the number of vehicles used to transport the building materials, and \(f_{trans}\) is the carbon dioxide emissions factors of each type of vehicle to transport the building materials. The consumed amount of fuel was computed by the distance between the supplier's location and the construction site (km), and the fuel efficiency of the transportation method (km/L). In addition, the number of vehicles required to transport the building materials was calculated by the amount of construction materials, and the capacity of the transportation methods. Table 2 summarises the distance and the type of transportation of this study: \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Material** & **Unit** & \begin{tabular}{c} **CO\({}_{2}\) Emission Factors** \\ **(kg CO\({}_{2}\) eq./unit)** \\ \end{tabular} & **Source** \\ \hline \hline \begin{tabular}{c} Ready-mixed concrete \\ Rebars \\ \end{tabular} & kg & \(3.48\times 10^{2}\) & \\ \begin{tabular}{c} Forms \\ \end{tabular} & \begin{tabular}{c} m\({}^{2}\) \\ kg \\ \end{tabular} & \
\begin{tabular}{c} \(1.49\times 10^{2}\) \\ \(1.91\times 10^{1}\) \\ \(1.91\times 10^{1}\) \\ \(1.90\times 10^{1}\) \\ \end{tabular} &
\begin{tabular}{c} National Life Cycle \\ Inventory Database [48] \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Carbon dioxide emissions factors of building materials. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Materials** & **Distance (unit: km)** & **Type of Transportation** \\ \hline \hline
**Ready mixed concrete** & 25 & Concrete mixer \\
\begin{tabular}{c} Reinforcing bars \\ \end{tabular} & 220 & 11.5-ton lorry \\
**Steel decking** & 252 & 11.5-ton lorry \\
**Forms** & 90 & 4.5-ton lorry \\
**Void formers** & 170 & 1.5-ton lorry \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Distance of suppliers and transportation methods. The carbon dioxide emissions from the construction equipment usage on site was determined by the fuel consumed by the equipment and machinery.