## 3 Results and Discussion
### Carbon Dioxide Emissions from the Utilisation of Construction Equipment on Site  
The construction equipment used in this study were concrete pump trucks and vibrators for ready-mixed concrete, and cranes for the lifting and loading of rebars, forms, steel decking, and void formers on site. The reductions in the amount of total carbon dioxide emissions from the utilisation of construction equipment replacing the ordinary reinforced concrete slab by the flat plate slab and the voided slab systems were 3758 and 4913 kg CO\({}_{2}\) eq., respectively (see Table 10). The carbon dioxide emissions from utilising construction equipment were reduced by 3.6% and 10.1% for the flat plate slab and voided slab systems, respectively. The lowering of carbon dioxide for the flat plate slab and voided slab systems is associated with the reduction in the amount of ready-mixed concrete. In high-rise buildings, the utilisation of concrete pump trucks would be inevitable to convey ready-mixed concrete to the upper floors. In addition, the use of vibrators in concrete work is indispensable during the concrete pouring and curing steps to remove internal bubbles, and to prevent material segregation.  
Moreover, the use of cranes was one of the significant factors to load and lift heavy building materials from the transporting vehicles to the upper floors. In the ordinary reinforced concrete slab, the large number of beams and girders was attributed to be the main factor to the use of a large volume of forms. For this reason, the emissions of carbon dioxide from cranes were higher for this slab system than for the other two slab systems (see Table 10). Similarly, in the voided slab system, the cranes were used to lift steel decking and the void formers. However, the emissions of carbon dioxide were less than for the two other methods, since the weights of both building materials (steel decking and void formers) were lighter than that of the forms in this study. Based on the results, in the emissions of carbon dioxide from the use of construction equipment, as the height of the building increased, it was inevitable to utilise concrete pump trucks and cranes. Hence, it would be important to minimise the lead time and intervals between activities during the construction work. For example, an effective strategy to reduce time waste during the construction process would be the adopting of principles and practices of lean construction [53; 54; 55].  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Materials**} & \multicolumn{3}{c}{**Emissions (kg CO\({}_{2}\) eq.)**} & \multicolumn{3}{c}{**Reduction (kg CO\({}_{2}\) eq.)**} \\ \cline{2-5}  & **ORC** & **FPS** & **VDS** & **FPS-ORC** & **VDS-ORC** \\ \hline
**Ready-mixed concrete** & 10,737 & 11,050 & 9095 & \(-\)313 & 1642 \\
**Rebars** & 1300 & 1198 & 1053 & 102 & 247 \\
**Forms** & 8349 & 4381 & 2714 & 3968 & 5635 \\
**Steel decking** & N.A. & N.A. & 2,535 & N.A. & \(-\)2535 \\
**Void formers** & N.A. & N.A. & 77 & N.A. & \(-\)77 \\
**Total** & 20,386 & 16,629 & 15,474 & 3757 & 4914 \\ \hline \hline \end{tabular}
\end{table}
Table 10: Emissions of carbon dioxide from the construction equipment usage.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Materials**} & \multicolumn{3}{c}{**Method 1**} & \multicolumn{3}{c}{**Method 2**} \\ \cline{2-7}  & **ORC** & **FPS** & **VDS** & **ORC** & **FPS** & **VDS** \\ \hline
**Ready-mixed concrete** & 16,683 & 17,166 & 14,137 & 22,982 & 23,648 & 19,475 \\
**Rebars** & 5362 & 5094 & 4423 & 3650 & 3467 & 3011 \\
**Forms** & 2336 & 1168 & 1168 & 1161 & 1064 & 581 \\
**Steel decking** & N.A. & N.A. & 1839 & N.A. & N.A. & 1129 \\
**Void formers** & N.A. & N.A. & 1090 & N.A. & N.A. & 258 \\
**Total** & 24,381 & 23,428 & 22,675 & 27,793 & 28,179 & 24,454 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Emissions of carbon dioxide for transporting building materials (unit: kg CO\({}_{2}\) eq.).