Environmental Perspectives on Urban Material Stocks used in Construction Granular Materials

Abstract: The peoples demand of functions and services in cities is the driver for energy and material flows. Most people in the world are now living in urban areas. In order to achieve a sustainable development of cities, both resource use and environmental impact have to be reduced. For construction activities, an important aspect is to increase the reuse of construction materials. From a resource perspective, the urban demand for construction of buildings, infrastructure and other facilities results in materials accumulated in constructions but also in other applications and in landfills. The materials can be described as the urban material stock where some materials are used and others are not used, i.e. wasted. There are many cases where material stocks are used for construction purposes. For example, used concrete and bricks, excavated soil and rock from construction projects and other wasted materials such as rubber from tires can be crushed, shredded and sorted to granules and used in many different construction applications. Different perspectives can be applied when assessing the environmental impacts of using stocked material in construction. The overall aim of this thesis is to study the environmental impacts of using granular soil, rock and rubber in construction. For soil and rock, the aim is to study the environmental impact of material management in urban areas. For granular rubber, the aim is to study the environmental impact of artificial turf from a life cycle perspective and from different infill materials of recycled and new rubber and plastics. The literature of excavated soil and rock was reviewed in order to identify and quantify the material flows and greenhouse gas (GHG) emissions from the management of soil and rock materials. For artificial turf and the different infill materials, a life cycle approach was used to quantify the energy use and GHG emissions. A chemical analysis of potential chemical leaching from the different infill materials to water was conducted in order to compare potential local emissions to water. Based on the results, it was concluded that the knowledge about the urban flows of excavated soil and rock is lacking in terms of patterns, quantities, qualities and its environmental performance. A resource perspective is missing in the literature. However, the recycling of soil and rock can reduce resource use and GHG emissions. It was suggested that models are developed that take into account future material demand and availability to soils and rock. From such information it would be able to assess sustainable management practices and the possibilities of sharing materials between urban construction projects in order to reduce resource use and environmental impact. It was concluded that for the life cycle of artificial turf, the production of construction materials contributes largely to energy use and GHG emissions. Differences in terms of energy use and GHG emissions for the production of infill materials are large. The production of new material required more energy and resulted in more GHG emissions than using recycled rubber. The potential release of substances from infill materials to water were shown to be possible for all infill materials analyzed. Previous assessments of local environmental impacts of using infills generally concludes that the impacts are small. These assessments are primarily focused on infill of recycled tires. It is therefore concluded that environmental assessments of local impact should include all infill types. Environmental assessments of using stocked materials in construction should take into consideration the material applications´ significance for the environmental impacts at a higher system level. Broader system boundaries in environmental assessments will reduce the risk for sub-optimizations when taking decisions on how materials should be used in construction.