InCIRC: Opportunities to Close Resource Loops in the Construction Sector of Singapore

Fast urbanization has led to significant extraction of material resources, which end up stocked for a long time in the built environment. While economic growth has usually been directly proportional to trends of increasing resource exploitation, the circular economy (CE) approach is gaining increased attention in the sustainability agenda for its framework focused on decoupling economic growth from the consumption of finite resources. This paradigm shift towards a circular, resource-efficient economy requires a comprehensive knowledge of the flows and material stocks (MS) in buildings and infrastructure. In the case of an import-dependent country like Singapore, the built environment can serve as a valuable reservoir of secondary resources, underlaying fundamental importance for the nation's circular economy ambitions. Assessing the MS in cities has been the focus of several studies for insights into the in-use materials and their potential availability as secondary resources, based on the argument that such estimates will help to create mechanisms for increasing the usage of secondary resources. However, studies often are restricted to building infrastructure, despite the qualitative relevance of roads, a significant driver behind the demand for low-value reuse of construction & demolition waste (CDW) with direct effects over the overall supply and demand of secondary resources. This paper argues that linking supply and demand estimations to the drivers behind downcycling and upcycling of CDW is necessary, in order to unveil realistic opportunities for secondary resource utilization. The primary motivation in this study has been to deploy a bottom-up approach to quantify the entire stock and flows of concrete for buildings and roads within Singapore, in a quest to unveil windows of opportunity where closing resource loops is realistic.

Results show that the concrete stock has grown by 21% on a 3% per year average from 2010-17, in proportion to 6% per year of GDP growth. Concrete stock is expected to grow from 220Mt in 2015 to 307Mt in 2050, which would require 13,4Mt of concrete in 2020, 43,2Mt in 2030, peaking at 310Mt in 2050. In contrast, 70,8Mt of concrete in the building stock are expected to reach their end-of-life (EOL) until 2050, with the most substantial contribution arising from the residential sector. By 2035-50 estimations suggest that local supply of EOL concrete will not be sufficient to sustain the entire construction demand by then. Nonetheless, a surplus scenario is foreseen for the next 15 years (2020-35), way beyond the yearly concrete demands for buildings and roads in the period. This oversupply creates an appealing scenario to increase secondary resource utilization. Hence, the next 15 years are a crucial period in time for Singapore to address the gaps in place for a transition towards the CE.