Analysis of Flow and Stock of Sand and Gravel in Shenzhen Buildings and Associated Environmental Impact

There is a rapidly spread sand and gravel supply shortage to meet increasing construction material needs. A considerable quantity of sand and gravel are stored in the built environment and have the value of being a secondary material resources. Using the bottom-up material flow analysis (MFA), this study estimates the flow and stock of sand and gravel in Shenzhen buildings and evaluates associated environmental impact from the material production stage. The results show that the consumption of sand and gravel in Shenzhen buildings exceeded 439 million tons (Mt) from 1979 to 2019, with an average annual consumption of 10.9 Mt. Equivalently, 598 kilotons (Kt) of the embodied carbon emissions were generated in the production stage of the sand and gravel. The cumulative outflow (measured by the generation of demolition waste) of sand and gravel exceeded 150Mt, accounting for 34% of the total consumption. Moreover, the sand and gravel stocks in Shenzhen buildings have boomed to 302 Mt in 2019 (23 t/cap), and show characteristics of fast inflow and slow outflow. This study helps understand the dynamic metabolism of sand and gravel in buildings and forms the data basis for further research in urban sand and gravel resources, waste management, and environmental strategy.