## 2 Research Methodology
### Goal and Scope Definition  
The goal of this study is to assess the environmental impacts of three different slab systems, which are the OSS, the FPS and the VDS for apartment buildings in South Korea. Slabs are one of the significant structural members for buildings. They not only transfer various loads through beams, girders, and columns to the ground, but also provide flat surfaces for building occupants. Since constructing high-rise commercial or residential buildings is common in urban areas around the world, the role of slabs has grown to facilitate more storeys. When the construction of slabs is carried out during the construction phase, a vast amount of concrete and reinforcing bars is required. Conventionally, slabs would require a large number of beams and girders to secure the structural stability of buildings or facilities. While the conventional method of constructing slabs would require vast amounts of building materials, such as concrete and reinforcing bars, the self-weight of the building itself would be increased as a result of the input amount of building materials. It is reported that there are several disadvantages in terms of the conventional construction method of slabs, such as extended construction period and costs, as apply to high-rise building construction. In order to sort out such difficulties resulting from application of the conventional slab system, new methods for slab systems have been introduced and applied to high-rise buildings. The FPS and the VDS are alternative approaches for slab systems, which make it possible to reduce the amount of building materials as well as the construction period and costs, compared to the ordinary solid slabs.  
In this study, the system boundary for assessing the environmental impact is the construction phase (i.e., cradle to pre-operation) for the three slab systems. This includes embodied emissions from the production of building materials, emissions due to transportation of the manufactured materials to the construction site, and emissions from the utilisation of machines and equipment (see Figure 2). Six environmental impact indicators, which are 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), were selected for assessing the environmental impacts of three slab systems. GWP refers to the average temperature rise level of the surface of the Earth, which is a parameter of the climate changes causing the ecosystem changes in soil and water. AP indicates the fate and deposition caused by acidifying substances, such as SO\({}_{2}\), NH\({}_{3}\), and NO\({}_{x}\) on soil, water, organisms, ecosystems, and materials. This is mainly affected by the circulation of pollutants and would threaten the survival of living organisms on the Earth. EP is the polluted state of aquatic ecosystem, such as algal growth and red tides, since the biomass in the water is grown by over-fertilisation of water and soil. ODP is a measure of the density decrease in the ozone layer that is located in the stratosphere as a result of trichlorofluomethane (R-11 or  
Figure 1: Life cycle assessment.  
CFC-11). This would be harmful effects on human skin through the increased exposure to Ultraviolet Ray (UV) radiation. POCP refers to the formation of ozone with photochemical oxidation of Volatile Organic Compounds (VOCs) and Carbon Monoxide (CO) and would affect damage to ecosystems and human health. ADP is the decreasing of natural resource availability, including fossil fuel resources and minerals. This means the amount of non-renewable resources on the earth is being reduced.