## 1 Introduction
As a result of such technological development and prediction techniques, the environmental impacts associated with energy consumption and GHG emissions from the operation and maintenance stage of a building have tended to decrease. Although the construction phase, which consists of several phases, is relatively shorter than the operation and maintenance phase, its environmental impact should be considered, since large amounts of building materials are used to construct a building in this stage. Since a number of studies have maintained that one of the main sources of environmental impact during the construction stage is the manufacture of building materials [4; 5; 14; 24; 25; 26; 27], the reduction in environmental impact from building materials would be the most effective approach to mitigate the environmental impact and greenhouse gases emissions. [PERSON] et al. [28], for instance, pointed out that replacing traditional building materials, such as concrete, rebars, or bricks, by low embodied carbon ones would lower the environmental impact by almost 50%. Moreover, the application of high-strength materials, such as high-strength reinforcing bars, and reinforced concrete might achieve lower environmental impact, since the amount of utilised building materials is reduced [25; 29; 30; 31]. With the use of high-strength materials, applying recycled materials and by-products from the demolition stage is also suggested as an effective approach to alleviate the environmental burdens from construction work [32; 33; 34; 35]. Moreover, the optimal structural design of a building would be an important stage to determine the construction methods and building materials that lower the environmental impacts from the study of [PERSON] et al. [24]. As discussed above, the mitigation of environmental impacts that occur from the construction phase is mainly focused on the replacement of low environmental impact materials, the optimal structural design of a building, and increasing the use of recycled materials or by-products. However, studies on the improvement of construction techniques or the application of newly developedconstruction methods for reducing the environmental impact are relatively scant, compared to other research topics. In particular, slabs are one of the significant elements for a building; they provide flat surfaces for occupants, as well as transferring various loads through beams, girders, and columns to the ground. While the main focus of research on slabs is to verify the structural performance, including stability against flexural, shear, or seismic loads, and structural design optimisation [36; 37; 38; 39], there are few studies on the evaluation of the environmental impact of different slab systems [3; 40; 41]. For example, [PERSON] et al. [42] evaluated the carbon dioxide emissions from slabs of different thickness and suggested optimal structural design for environmental performance and structural reliability. In order to fill the gap in research, the purpose of this study is to assess and compare the environmental impact of the Ordinary Solid Slab (OSS), the Flat Plate Slab (FPS), and the Voided Slab System (VDS) during the construction phase. The assessed environmental impact indicators in this research cover 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 includes the manufacture of building materials, transportation of the building materials to the construction site, and the utilisation of construction equipment.