# Calculation Methods for Construction Material Stocks: A Systematic Review
## 3 Results
### Content Analysis
#### 3.2.2 Material Stock Calculation Methods
While in 2055, the inflow and outflow would become equal. Factors influencing the growth of material stock have been analyzed by different studies. For instance, [PERSON] (2018) aimed to find the material stock and its spatial and temporal distribution in China between 1997 and 2016. The study analyzed the possible increase of material stocks due to the changes that occurred in economic and population factors. Using the government sources data, the study compiled the total material stock. The results showed that the material stock increased more than 4.0 times during this time and spatially decreased from the coastal areas to the inland. The results also suggest that affluence is a major factor in increasing material stock. Similarly, [PERSON] et al. (2017) studied the material stock accounting for 10 materials in 6 major cities in Beijing, Tianjin, and Shanghai and probed the driving factors between 1978 and 2013. The study was conducted by a logarithmic mean division index decomposition method. It showed that the material stock growth was rapid during the 1980s, steady in the 1990s and again accelerated after the 2000s. The reason for such a fluctuation lay with a decoupling phenomenon between material stock and economy that was mostly caused by a decline in material intensity. Regarding the infrastructure projects, [PERSON] et al. (2017) estimated the material stock of Vietnamese roads between 2003 and 2013 using the bottom-up method. To this end,the study combined multiple data sources such as the federal and provincial government highway departments, contractors, and the roads' historical design in order to compute the total material stock. The results showed that 40% of the domestic material stock consumption was related to expanding and maintaining the material stock. Moreover, the material stock was assessed to be in the range of 1321 million metric tons in 2003 to 2660 million metric tons in 2012. Although the application of such an approach may increase the accuracy of calculations, it can be time-consuming since it involves massive data collections. In another study, [PERSON] et al. [46] used the bottom-up material stock method to estimate the municipal water and sewage waste management system efficiency between 1980 and 2050. A dynamic model using the inflow and outflow of materials was first developed and further combined with the average material intensity to estimate the material stock. The results were indicative of an increase in the annual water supply capacity over the last 30 years from 11 to 100 km\({}^{3}\), while the sewage capacity increased from 1.1 to 50 km\({}^{3}\). Furthermore, it was conclusively stated that the material stock might increase more than double by 2050, which in turn requires 3.3 Gigatons (GT) of construction materials containing 170 Megatons of Iron and Steel and 400 Megatons of cement. The development of a road network on GIS can be a promising measure toward an accurate estimation of material stock of roads due to its capacity to capture real-life scenarios. For instance, [PERSON] et al. [14] attempted to estimate the material stock of roads in Beijing. The study was conducted by making an integrated model that covered all types of roads, intersections, and ancillary facilities using the GIS. GIS was employed to avoid the issue of double-counting. The results showed that the total stock of roads was 159 million tons, of which 80% was stored in roads while 20% in ancillary facilities. It was also shown that Macadam was the largest stock with 111 million tons. In another study, [PERSON] et al. [36] developed a more comprehensive model by using sensitivity analysis. They also included the inflows and outflows of material aiming to build a highway based on material metabolism (flows of construction material spatially over time). The results showed that the total material stock in the entire highway system was 1933.57 Megatons in 2013, where stones, fly ash, lime, cement, mineral powder, and asphalt comprised 99.8% of the stocks. Similarly, [PERSON] et al.