The Urban-Industrial metabolism: contribution of waste recycling to the circular economy objectives within the construction sector

Abstract

The construction and buildings sector is facing an urgent need to reduce GHG emissions and ensure efficient resource utilization while minimizing waste in order to comply with climate change policies and circular economy initiatives. Alkali-activated materials, as an alternative binder to CO2-intensive conventional cement, show potential in utilizing waste streams from urban environments in their production technology, thereby reducing CO2 emissions. This study examines two waste streams generated in Switzerland: incineration ashes from municipal solid waste treatment facilities and mineral wool waste from building stock renovation and demolition activities. Geospatial analysis is combined with LCA methods to assess optimal scenarios for waste recycling, utilizing a multi-objective optimization framework based on mixed integer linear programming. The objectives are to minimize the environmental impacts and costs associated with alternative supply chain networks, thereby identifying optimal locations for waste pre-treatment and concrete manufacturing. The proposed scenarios demonstrate reductions of 56% in global warming potential and 29% in costs when compared to the business-as-usual scenario of conventional cement concrete use and waste landfilling. Results show that recycling of urban waste streams in alternative concrete can reduce GHG emissions of industry and heavy transportation sectors by 0.46 mt. CO2 eq. by year 2030, equivalent to 23% and 4% of the Swiss carbon budget reduction targets for these sectors.