## 2 Research Method  
### Quantifying the Construction Waste  
There are many approaches to estimating the approximate amount of construction waste generated on site. According to the United States Environmental Protection Agency (USEPA) [33], the amount of construction and demolition (C&D) waste can be estimated using the waste-weight-per-construction-area method. This method would be able to determine the average waste generation per building area (kg/m\({}^{2}\)), as shown in Equation (1),  
\[w=A\times g \tag{1}\]  
where \(w\) is the total weight of construction waste (kg), \(A\) is the area of the building constructed (in m\({}^{2}\)), and \(g\) is the average construction waste generation per building area (in kg/m\({}^{2}\)). This method has been applied to estimate the amount of C&D waste in various countries and regions such as the US states of Florida [34] and Massachusetts [35], as well as South Korea [7]. Despite of the ease of estimating the amount of construction waste, it would be difficult to calculate and compare the amount of construction waste generation by utilising the different construction methods. New construction methods have been evolving in ways to develop new structural systems, to reduce the use of construction materials, and to minimise the amount of works on site. In particular, it might be difficult to evaluate the amount of construction waste generation based on the waste-weight-per-construction-area method from the new construction methods, where the use of building materials changes. This current research work presents a comparison to quantify different construction waste streams arising from the different structural systems for the slab in a commercial building. Since the different structural systems can lead to different amounts of building materials being used, there would be a limitation when seeking to assess the level of waste generation for each structural system based on the waste-weight-per-construction-area method. In this study, the amount of waste generation during the construction phase was calculated based on the quantities and the material loss rate of each building material in order to estimate the quantity of construction waste by the changes in the application of different structural systems for the slab of the studied model. The profile of building materials including the name of products, unit, and material loss rate were classified by reviewing the bill of quantities for all four construction methods (see Table 1). In this study, the amount of waste generated during the construction phase was only considered involving the major building materials for the slab system, since the only differences among the solid slab, flat plate slab systems, and the void slab system were the structural design of the slab while other design parameters were identical except the slab systems. Once the quantities of the building materials had been determined based on the bill of quantities, the amount of the produced waste during the construction phase from each structural system was calculated as shown in Equation (2)  
\[WG_{n}=\sum_{i=1}^{n}Q_{i}\times L_{i} \tag{2}\]  
where \(WG_{n}\) is the total amount of the construction waste for structural system \(n\) (in kg), \(Q_{i}\) represents the amount of the building material \(i\) (in kg), and Li refers to the material loss rate of the building material \(n\). As stated in the previous section, the major building materials for quantifying the construction waste were ready-mixed concrete, rebars, forms, spacers for solid slab, flat plate slab, and the void slab system. The void slab system required additional building materials, which were void formers, steel decking, and anchoring metal materials.