# Calculation Methods for Construction Material Stocks: A Systematic Review
## 3 Results
### Content Analysis
#### 3.2.1 An Overview of the Analysed Studies  
This review identifies three calculation methods utilized by the studies reviewed for estimation of construction material stock, namely bottom-up, top-down, and demand-driven. Figure 5 shows the type of methods used to estimate the material stock. As shown, the bottom-up methodology has been used more in the studies reviewed compared to top-down and demand-driven methods. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(\mathbf{No}\) & \(\mathbf{Author}\) &
\begin{tabular}{c} **Method** \\ **Applied** \\ \end{tabular} & \(\mathbf{Scale}\) & \(\mathbf{Type}\) of Project & \multicolumn{1}{c}{\(\mathbf{Summary}\)} \\ \hline
30 & [PERSON] et al. [40] & Top-Down & Country & Buildings &
\begin{tabular}{c} The study estimated the presence of PCB \\ plastics in residential and non-residential \\ buildings between 1950 and 1980. \\ The study estimated the material stock \\ and predicted the future construction \\ waste. The study used material intensity. \\ The study estimated the material stock of \\ the non-residential buildings in a city by \\ categorizing the buildings into different \\ types based upon the use and \\ age constructed. \\ The research estimated the material stock \\ and recycling potential of the \\ non-melnick materials in residential \\ buildings, roads, and railways between \\ 2004 and 2009. \\ The study estimated the future material \\ stock dynamics using the existing \\ material stock data. \\ The study analyzed the dynamic type of \\ approach for material stock to find the \\ policies’ results. \\ The study researched the efficiency of the \\ sewage pipes in China using the material \\ stock method and found the sources of \\ inefficiencies. \\ The study found the socio-economic \\ reasons for material stock growth in \\ Japan using the last five decades’ \\ material stock data. \\ Using the existing research to estimate \\ and compare the US and Japan \\ material stock \\ \hline \hline \end{tabular}
\end{table} 
Table 1: \(\mathbf{Cont}\). Figure 5: Methodology used by analyzed studies. Figure 6 shows the scale of the study area researched by the articles. The city level is the smallest study area, while the regional level is a part of the country. The figure shows that most of the studies considered performing material stock calculations at the city and country levels. The investigation of material stocks at regional and continental levels has been done less frequently, highlighting the potential topics for future research. From the review, it is found that the aforementioned methods are employed to evaluate the material stock in two types of projects, namely buildings and infrastructure projects (Figure 7). The building includes both residential and non-residential buildings, similarly, the infrastructure includes roads, pipes, and railway infrastructure. As illustrated, these methods are commonly used for the estimation of material stock in buildings rather than infrastructure projects. It is also revealed that the reviewed studies estimated material stocks associated with both metallic and non-metallic materials. Metallic materials refer to inorganic substances that are morphed via combining metallic elements such as iron, titanium, aluminum, and gold. Steel, aluminum alloys, magnesium alloys, copper alloys, titanium alloys, and carbon steel are examples of metallic materials. Contrarily, non-metallic materials are organic substances that are structurally brittle such as concrete, glass, wood etc. The differences in estimating metallic and non-metallic materials are attributed to gathering data, the study area's size, the assumption made, and the procedures adopted in applying these methods [2]. Regarding infrastructure projects, five articles assessed materials stocks of road projects only. Eleven studies used a much comprehensive approach investigating the materials stock for both building and infrastructure projects.