## 3 Results and Discussion
### Discussion
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**ODP (kg CFC11 eq/m2)**} & \multicolumn{3}{c}{**POCP (kg C2H4 eq/m2)**} & \multicolumn{3}{c}{**ADP (kg Sb eq/m2)**} \\ \hline  & **OSS** & **FPS** & **VDS** & **OSS** & **FPS** & **VDS** & **OSS** & **FPS** & **VDS** \\ \hline Ready-mixed & \(1.35\times\) & \(1.26\times\) & \(8.63\times\) & \(3.41\times\) & \(5.98\times\) & \(2.1\times\) & \(7.50\times\) & \(6.99\times\) & \(4.79\times\) \\ concrete & \(10^{-5}\) & \(10^{-5}\) & \(10^{-5}\) & \(10^{-6}\) & \(10^{-1}\) & \(10^{-2}\) & \(10^{-1}\) & \(10^{-1}\) & \(10^{-1}\) \\ Rebars & \(3.03\times\) & \(2.82\times\) & \(2.59\times\) & \(9.94\times\) & \(2.30\times\) & \(8.50\times\) & \(8.13\times\) & \(7.56\times\) & \(6.96\times\) \\  & \(10^{-7}\) & \(10^{-7}\) & \(10^{-7}\) & \(10^{-3}\) & \(10^{-1}\) & \(10^{-3}\) & \(10^{-2}\) & \(10^{-2}\) & \(10^{-2}\) \\ Forms & \(1.75\times\) & \(1.65\times\) & \(1.17\times\) & \(2.07\times\) & \(6.61\times\) & \(1.38\times\) & \(1.39\times\) & \(1.31\times\) & \(9.25\times\) \\  & \(10^{-6}\) & \(10^{-6}\) & \(10^{-6}\) & \(10^{-2}\) & \(10^{-4}\) & \(10^{-2}\) & \(10^{-1}\) & \(10^{-1}\) & \(10^{-2}\) \\ Steel materials & N.A. & N.A. & \(1.34\times\) & \(10^{-8}\) & N.A. & \(4.40\times\) & N.A. & N.A. & \(3.60\times\) \\  & & & & & & & & & \\ Steel decking & N.A. & N.A. & \(5.00\times\) & \(10^{-4}\) & N.A. & N.A. & \(1.00\times\) & \(10^{-3}\) & N.A. & \(1.02\times\) \\  & & & & & & & & & & \(10^{-4}\) \\ Void formers & N.A. & N.A. & \(9.44\times\) & \(10^{-8}\) & N.A. & N.A. & \(9.44\times\) & \(10^{-8}\) & N.A. & N.A. & \(4.34\times\) \\  & & & & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: The environmental impacts of building materials (continued). be one of the useful methods to reduce the environmental impact from concrete. In further research, a comparison of the normal and by-products added to ready-mixed concrete, as well as application of high-strength concrete and rebars should be carried out to enhance the reduction in environmental impacts during the manufacture of building materials. In this study, the transportation of building materials is the second largest environmental impact source for all three slab systems. Mitigation of the environmental impacts from transportation requires selection of the proximate manufactures to the construction site, in order to reduce the fuel consumption during the procurement management process. Furthermore, it is necessary to minimise the lead time during the transportation of building materials to minimise the environmental impacts caused by fuel consumption. A number of studies have claimed that imported building materials would be beneficial to the economic perspective of building projects. However, imported materials would have a negative impact on the environment, since the transportation distance would be increased, as well as the use of additional transportation methods. Further research should be conducted to verify the relation between the environmental performance and economic effectiveness. This study was carried out only for the construction of different slab systems and did not address the environmental impacts from various types of building, as well as entire construction projects. In order to fill such research gaps, further research that considers various types of buildings, such as commercial buildings and apartments, as well as the entire life cycle of buildings, should be carried out. Moreover, the numbers of examples in this study that were chosen were only one case for each slab system. In order to verify the environmental performance and sustainability of the voided slab systems against the ordinary reinforced concrete slab or flat plate slab, the number of samples for each slab system should be increased in future studies to enhance the results of this study.