System dynamics modeling to assess the environmental impact of building demolition and concrete waste recycling process

Bangkok, like other fast-growing countries, experiences a high surge of migration to the city to seek work and life opportunities. This results in a high demand for residential units. Many new infrastructures are built, and outdated housing units are demolished to satisfy the needs of the rapidly increasing population and developing economy. These result in high construction and demolition waste, generating various environmental problems, such as illegal dumping, pollution, and resource depletion. The demolition waste from the building demolition comprises several components, the majority of which is concrete. Concrete waste recycling is encouraged to raise environmental concerns and minimize environmental impacts. This research study aims to develop the system dynamics (SD) model to compressively assess the environmental impacts of concrete waste in Thailand's townhouse demolition and concrete waste recycling process. Eight impacts, including primary energy consumption, CO2eq emission, noise, dust, heat, material saving, landfill consumption, and landfill saving, are listed in the literature. Based on the interviews with the experts, four combinations of demolition tools are considered for the townhouse demolition. The simulation results reveal that Combination 4 (i.e., the use of excavators and hydraulic splitters) is the most effective combination for townhouse demolition to reduce the environmental impacts in the long term as it generates the lowest CO2eq emission, energy consumption, noise, and dust. If demolition robots are not available, Combination 1 (i.e., the use of excavators, jackhammers, and flame cutters) offers the lowest environmental impacts in the demolition process. Concrete waste achieved from the demolition process (using the demolition tools in Combination 1, as demolition robots in Combination 4 are yet available) is further examined with the recycling processes and environmental impacts associated with those processes. The results show that the CO2eq emission and energy consumption impacts, which are global impacts, are most severe in the transportation process. Increasing the truck capacity assists in reducing energy consumption from fewer trips, resulting in less CO2eq emission. Electric trucks may also help minimize the overall impacts as they release no CO2eq emissions. The results also reveal that the impacts, like material saving and landfill saving, can be improved through concrete waste recycling. Increasing the capacity of the recycling plant increases the material and landfill savings and reduces landfill consumption. All these bring a better final environmental impact. The results of the study offer insights for decision-makers in the construction industry, aiding them in making suitable choices regarding demolition tools and strategies to mitigate long-term environmental impacts. It assists in a better understanding of the processes related to building demolition and concrete waste recycling and the environmental impacts involved in the whole process.