Global warming is primarily driven by the emissions of carbon dioxide resulting from human activities. The construction industry, driven by urbanization and population growth, plays an important role in this due to its resource-intensive nature. Buildings account for nearly 40% of global energy consumption and one third of associated greenhouse gas emissions. Additionally, the government’s goal for the Netherlands is to reduce greenhouse gas emissions by 55% in 2030 and to achieve climate neutrality in 2050. The focus to reduce CO2 emissions used to be on lowering operational energy emissions, but due to the increase in energy-efficient and net-zero buildings this focus is now shifting. As operational emissions drop, materials' emissions gain importance, shifting environmental studies toward reducing embodied energy.
One potential solution to address this challenge of reducing carbon emissions is the adoption of circular economy principles in the construction industry. Circular strategies, such as reduce, reuse, recycle, and recover, have the potential of minimizing waste, reducing resource consumption, and reducing CO2 emissions. However, it is unclear how these strategies compare to each other in terms of their carbon footprint.
Therefore, this research aims to assess and compare the embodied carbon benefits of the circular 4R-strategies with different structural materials in the building industry. Through life cycle assessments (LCAs) of case studies spanning a 40-year lifespan, the study evaluates the effectiveness of downsizing, reuse, and recycling strategies in reducing emissions. A 5% reduction in material use led to a 5-10% decrease in emissions, while a 10% reduction yielded a 9-16% reduction. The implementation of a moderate reuse strategy has been demonstrated to result in reductions in emissions ranging from 16% to 24% for timber and steel structures. Moreover, the results showed that it is possible to achieve significant emission savings of around 60% to 70% through the implementation of an extensive reuse strategy, where a greater proportion of materials are reused. The effectiveness of recycling strategies in reducing emissions varies considerably, with potential emission reductions of between 55% and 70% for concrete, between 27% and 70% for steel structures and between 12% and 37% for timber. The effectiveness of this strategy is highly dependent on the maximum percentage of recycled content the material in question can have.
A comparative analysis reveals that timber generally offers superior CO2 reduction over concrete and steel in the short term. However, concrete with an effective circular strategy and a lifespan of around 80-100 years can outperform a timber building with a lifespan of 40 years. Concrete with high recycled content and steel with significant reuse show notable CO2 reduction potential. Tipping points for concrete and steel structures occur around 80 years, where concrete becomes more favourable than steel due to lower replacement rates.
The research contributes to practice through the integration the study’s outcomes in design guidelines and a mathematical optimization decision model, that facilitate informed decision-making among clients, managers, architects, and suppliers during early design phases.