Strategies for a Circular Economy in the Construction and Demolition Sector: Identifying the Factors Affecting the Recommendation of Recycled Concrete

With increasing urbanisation, new approaches such as the Circular Economy (CE) are needed to reduce resource consumption. In Switzerland, Construction & Demolition (C&D) waste accounts for the largest portion of waste (84%). Beyond limiting the depletion of primary resources, implementing recycling strategies for C&D waste (such as using recycled aggregates to produce recycled concrete (RC)), can also decrease the amount of landfilled C&D waste. The use of RC still faces adoption barriers. In this research, we examined the factors driving the adoption of recycled products for a CE in the C&D sector by focusing on RC for structural applications. We developed a behavioural framework to understand the determinants of architects’ decisions to recommend RC. We collected and analysed survey data from 727 respondents. The analyses focused on architects’ a priori beliefs about RC, behavioural factors affecting their recommendations of RC, and project-specific contextual factors that might play a role in the recommendation of RC. Our results show that the factors that mainly facilitate the recommendation of RC by architects are: a senior position, a high level of RC knowledge and of the Minergie label, beliefs about the reduced environmental impact of RC, as well as favourable prescriptive social norms expressed by clients and other architects. We emphasise the importance of a holistic theoretical framework in approaching decision-making processes related to the adoption of innovation, and the importance of the agency of each involved actor for a transition towards a circular construction sector.

Scrutinizing the Circular Economy concept applied at the urban level:A contribution based on the analysis of urban circularity indicators, the categorization ofCircular Economy interventions, and the identification of factors fostering the adoption ofcircular innovation.

Valeria Superti

Problem. Our current economic systems are deemed unsustainable. Although a global issue, the objective of living in a sustainable society is increasingly an urban challenge, as a rising 50% of the world's population currently dwell in cities. To secure a better urban future, integrated and actionable urban knowledge focused on what urban sustainability entails and how to achieve it is needed. In this context, the Circular Economy (CE) concept fosters efficient resource use through value-retention processes and waste minimization. Despite the wide attention on the CE, its interconnectedness with, and contribution to, sustainability, and whether these concepts might support or hinder each other, have not yet been clarified. Besides, knowledge is needed to guide cities towards a CE, for example, by identifying the types of interventions needed to achieve circularity, and the factors affecting the adoption of innovation that can foster it.Aim. This dissertation aims to scrutinize the CE concept applied in urban settings. It is based on a) the analysis of indicators used to assess circular cities, b) the categorization of interventions aimed at achieving a CE, and c) the identification of factors that affect the adoption of recycled products, as one measure towards CE.Approach. Indicators used to assess circularity and sustainability in urban settings were analyzed and compared. Semi-structured expert interviews were performed to iterate a framework that categorizes interventions that foster the achievement of a CE. A behavioral framework was developed that combines insights from the theory of adoption of innovation and behavioral theories, to identify and analyze the factors that can affect architects' decisions to recommend recycled concrete. A survey was used to gather quantitative insights from architects on their beliefs about the selected product.Insights. The results show that the concept of an urban CE is embedded in the broader concept of urban sustainability; however, the use of CE indicator sets entail a more detailed focus on certain thematic groups (e.g., waste production and management), for which more indicators are available in comparison with what offered by urban sustainability indicator sets. To categorize CE interventions, the proposed framework (RISE: Research & Realize, Implement, Support, Enable) offers a tool to guide the achievement of CE targets. In current circularity assessments, specifically in the construction sector, most attention is paid to implementation interventions (e.g., the quantity of material recycled). However, some of them (e.g., recycling strategies) still face barriers. Focusing on one recycling strategy (i.e., recycling concrete aggregates for recycled concrete) we inquired about the factors that affect this product's adoption. A senior position, a high level of knowledge of the material and a specific label, beliefs about the material's lower environmental impact, and prescriptive social norms affect the selected innovation's adoption. Finally, we suggest leveraging specific predictors of behavior to increase the recommendation of recycled concrete.Conclusions. This work contributed to shed light on the CE concept. This research challenged the added value of focusing on a CE rather than sustainability. Furthermore, it put forward a) an integrative perspective on achieving a CE focusing on a systemic approach, and b) a holistic behavioral framework for analyzing innovation adoption.

EPFL2021

Waste Reduction Strategies: A Different Perspective on Waste Flow Modeling and its Application to Concrete and Phosphorus

Anna Minata Cissé

Changing consumption patterns and global population growth lead to ever-increasing waste generation. Human activity and waste generation are irrevocably linked, and the current situation thus calls for a more circular approach to waste management, where wastes become new resources. Industrial ecology offers a variety of waste reduction-favoring concepts. As a first step this project identifies waste-preventing, waste-reducing, end of pipe (EOP) waste management approaches and legislation as classification categories for waste management strategies. Although, according to the waste hierarchy, waste prevention is the most preferable waste management approach, it is the least implemented. To facilitate the identification of waste prevention and reduction potentials, a special waste flow diagram from the waste management perspective is elaborated. The model tends to visualize all waste flows, including by-product valorization along a product's life cycle through the choice of a thematic-geographic system boundary. In a further step the applicability of the waste flow model is tested for concrete-related wastes and phosphorus (P) flows in wastes. The quantification of concrete waste flows for the city of Zurich shows that recycling is well implemented, whereas preferable waste management strategies, prevention and reduction of waste, are hardly put into practice. Scenario modeling is used to show the benefits of these techniques and the comparative LCA for different construction methods and materials identifies waste prevention as most beneficial option. For P, the waste flow model is applied to test its ability to detect P recovery potentials, however no new findings in terms of P-recovery potential are identified. The most compelling result regarding phosphorus is found in the extension to the initial investigation, the mass flow analysis for a wet-chemical and a thermochemical P-recovery procedure from sewage sludge ashes. The analysis shows that for EOP waste technologies, the material output can be bigger than the input due to the extended use of additives. Although all generated by-products can, in this case, be valorized by other industrial activities, this finding highlights the need for more waste prevention-oriented waste management strategies, thus avoiding the necessity to generate high by-product flows in the first place.

2018

Environmental and economic analysis of new construction techniques reusing existing concrete elements: two case studies

Maléna Bastien Masse, Julie Rachel Devènes, Corentin Jean Dominique Fivet, Célia Marine Küpfer

As the most widely used construction material worldwide, concrete is the main cause of greenhouse gas emissions, material depletion, and waste generation by the construction industry. Typically, concrete waste is crushed and, at best, reclaimed into recycled aggregate or used as gravel. This process is energy-intensive and results in a reduction in material properties. In contrast, the direct reuse of concrete elements from obsolete structures offers great potential for significantly reducing the environmental impact of new constructions. To be reused, concrete elements are carefully sawn out of soon-to-be-demolished buildings. Elements are then used without other major transformations for another service cycle in a new assembly. This paper analyses two recent projects in Switzerland that showcase innovative applications of concrete reuse: a post-tensioned segmented arch footbridge and a parking pavement. Both projects reuse blocks extracted from cast-in-place concrete buildings undergoing transformation or demolition. In this paper, environmental and economic analyses provide a comprehensive understanding of the alleviations and costs involved. Results are compared to those of alternatives with conventional construction methods. The two projects reusing concrete globally showcase a drastically lower environmental impacts for comparable or higher construction costs, hence calling for future developments of such new circular construction strategies.

2022

Waste Reduction Strategies: A Different Perspective on Waste Flow Modeling and its Application to Concrete and Phosphorus

Anna Minata Cissé

2018

Valeria Superti

EPFL2021