## 4 Conclusions  
The purpose of this study was to assess the various environmental impacts from the construction stage of the ordinary solid slab (OSS), the flat plate slab (FPS) and the voided slab system (VDS). The assessed environmental impact indicators were the Global Warming Potential (GWP), Acidification Potential (AP), Eutrophication Potential (EP), Ozone Layer Depletion Potential (ODP), Photochemical Ozone Creation Potential (POCP), and Abiotic Depletion Potential (ADP). In this study, the construction phase was confined to the manufacture of building materials, transportation of the building materials to the construction site, and the utilisation of construction equipment. A process-based quantitative model was adopted to calculate the six environmental impact indicators, and the comparative results were analysed to demonstrate the significant characteristics of the environmental impacts at the construction of slab in an apartment building in South Korea. The quantitative environmental assessment results during the construction phase of slab systems would provide a significant contribution to the reduction in environmental impacts. The conclusions of this study may be summarised as follows:  
1. In this study, the construction phase was divided into the manufacture of building materials, transportation of the building materials, and usage of construction machinery. The total environmental impacts from all the environmental indicators were the highest in the manufacture of building materials, followed by the transportation of building materials, and the use of construction machinery.
2. The assessment results show that among the three slab systems, the environmental impacts from the OSS are the highest, while those of the VDS are the lowest. Along with the assessment of total environmental impacts, the variation of the environmental impacts by replacing the OSS with the FPS and the VDS was examined.
3. As the slab system of the studied building was replaced, the environmental impact indicators showed a decreasing tendency.
4. Replacing the OSS with the VDS showed the highest reduction ratio for all of the environmental impact indicators. This study also considered the environmental impact assessment results from each building material for the three different slab systems.  
(5) Based on the results of the environmental impact reductions from the three slab systems, the VDS would show the least environmental impact in all indicators.  
The assessment results of this study should be used to conduct further research regarding the comparison of the environmental impacts of the whole life stage of a building, including construction, operation and maintenance, and demolition. Moreover, only major building materials for the construction of slab systems were dealt with in this study. Further research that takes into account all of the building materials would be useful to assess and compare the potential benefits from selecting among the alternative slab systems.  
[PERSON] designed the research method and calculated the quantities of building materials. [PERSON] conducted the structural analysis and the life cycle assessment from three slab systems in this research. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Research Foundation of Korea (NRF) grant number NRF-2019R1A6A3A01091459.  
This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government Ministry of Education (No. NRF-2019R1A6A3A01091459).  
We declare that there are no conflicts of interests between the authors of this research.