Purpose: The construction industry is responsible for great amounts of resource consumption, waste generation and both carbon and greenhouse gas emissions in the European Union. The currently still predominant linear mindset of take-make-consume-dispose must shift to reduce the industry’s environmental impact and enable the transition towards a circular construction industry. Circular material hubs facilitate more circularity by collecting, processing, and redistributing secondary building components to make them available for another life cycle. In literature, little can be found about the system circular material hubs are embedded in and their connection to architects. This study investigates the system of circular material hubs in the Netherlands, its challenges, opportunities, and potential future developments in the transition towards a circular construction industry. A special focus is placed on the role of architects within this system, as a circular construction industry also needs designers to include secondary building components in designs. The Netherlands is one of the top nations in the reuse of secondary raw materials and therefore provides as an exemplary setting for this exploratory research.
Methodology: An exploratory, qualitative research approach was chosen. Fourteen semi-structured interviews were conducted with representatives from circular material hubs, architects, as well as experts in the fields of circular economy, circular construction industry and construction logistics. Practitioner interviews aimed at identifying practices performed within the system of circular material hubs, and detecting challenges, opportunities and potential future developments as perceived by practitioners in the field. Expert interviews were conducted to validate the information gathered through literature review and practitioner interviews.
Findings: The research found four practice bundles which are important for the system of circular material hubs. These practice bundles are acquisition practice, processing practices, sales practices, and material harvesting practices. Within these practice bundles, different practices and performances of these practices were identified. The practices influence each other. Which building components are acquired influences which processing practices need to be performed. The type of building component also influences the sales practice as different building components target different groups of clients and are sold through different communication channels. It is also crucial whether the building components are sold offline or online. The online marketplace of Insert was found to be particularly helpful, as it is specifically designed for the construction industry and used by circular material hubs as well as architects. This shows the influence of the choice of communication channel on a circular design practice and scouting practices. By providing as much information as possible about the secondary building component at hand, circular material hubs also facilitate a circular design practice. Additionally, challenges, opportunities, and potential future developments of the system of circular material hubs were identified. Challenges the system faces are related to uncertainty and irregular assortment, guidelines, costs, and the provision of guarantees, while opportunities are governmental decisions, the provision of information and the use of shared online marketplaces. Missing collaborations are both a challenge and an opportunity. Future developments are primarily related to changes in the provision of secondary building components.
Research limitations: The limitations of this study are that social practice theory was not applied to the entire research as it is not suitable for the assessment of challenges, opportunities, and potential future developments. A greater variety of circular material hubs, not in number but in their field of activity, could present a different view on the system. Semi-structured interviews also always have certain limitations. Identifying the practices while they are being performed could also have led to more in-depth results.
Originality/value: By providing a comprehensive view on the system of circular material hubs in the Netherlands, this research helps to understand the dynamics within the system and allows the identification of potential interventions based on the practices that constitute the system.

The construction industry's substantial consumption of materials, CO2 emissions, and construction and demolition waste underscore the pressing need for change. One promising solution is the reuse of secondary building components, which has the potential to signifi-cantly mitigate these environmental impacts. Circular Building Hubs (CBHs) have emerged as a novel business concept that could facili-tate the collection and processing of these components, thereby promoting their reuse. However, effectively scaling up their operation-al secondary building component supply processes (supply processes) requires changes in the practices embedded in these processes. Therefore, this exploratory research aimed to identify the extend to which constraining and enabling factors influence the scalability of core practices embedded in supply processes of these CBHs. The core practices are those considered to be essential for the CBH concept. As such, it intended at contributing to new and more comprehensive understanding on the effects of these factors and thereby contrib-ute to the development and scaling up of these processes. Hence, the main research question is as follow: ‘What are core practices em-bedded within the secondary supply processes for circular building hubs, and to what extent are involved constraining and enabling factors influencing the scalability of these practices?’ This research adopts a qualitative case study research approach, centered around a conceptual framework based upon Social Practice Theory (SPT) and hypothesized supply processes. This study incorporates semi-structured interviews with seven experts, four observations, and one focus group discussion (FGD), all conducted in the Netherlands. The results conclude that throughout 10 different supply processes, 37 different core practices are performed that contribute to the supply of secondary building components for CBHs. Furthermore, the research revealed that these core practices are affected by at least 29 constraining and 26 enabling factors. The research categorizes the influence of factors on core practices as low, medium, or high impact based on quantitative data from CBH supply process experts. The FGD emphasized that constraining and enabling factors affecting core practices in CBHs are highly complex and context-dependent. These factors are influenced by various contextual aspects, business strategies, and specific project conditions. In conclusion, there is no one-size-fits-all solution, highlighting the importance of customized strategies to address constraining factorsand enhance enabling factors for scaling core practices within the supply process-es of CBHs. Further research is required on exploring CBHs with diverse historical backgrounds to identify new constraining and ena-bling factors specific to their context.

A tool that contributes to solving the cultural barrier of the lack of knowlegde about circularity in conventional members of project teams. Using three case studies an evaluation tool is developed. With gathering circular project dynamics, validating them and integrating them into the evaluation tool. The tool intends to help members of project teams to learn about the integration of project dynamics for circularity in construction projects to stimulate the realization of circular ambitions. But also intends to stimulate organizational level learning to benefit the transition towards circular economy.