From sink to stock : the potential for recycling materials from the existing built environment

Abstract

This thesis examines the prospect for new local recycling schemes for concrete and masonry waste within an existing urban environment. Using Lisbon, Portugal as a case study, I propose three context-specific material recycling scenarios to make use of mineral construction waste generated as city's aging residential building stock is replaced over the next 30 years. The objective of the work is to explore whether the existing stock, as it is overturned, can feed the future built environment and to what degree. What happens to construction waste when obsolete buildings are demolished? In the case of Lisbon, most of it is used as backfill or disposed in landfill. Little of the mineral waste's material value is recovered. Nonetheless, the urban built environment maintains the alluring prospect of being a source for our impending resource needs. The concept of urban mining and the circular economy movement bolster this proposition as a path towards more efficient, localized resource use within cities. I compare the three recycling proposals, along with standard landfill disposal, in terms of greenhouse gas emissions, land use, and cost. The results show that from both an environmental and economic standpoint, recycling is not always the optimal solution. The impacts depend not only on the recycling processes and end uses, but also the avoided and added burdens consequent to changes in the existing system. Through this analysis, I identify both the limiting factors and potential opportunities for improvement in the current paradigm of material use and reuse in construction, in Lisbon and beyond.