On a general level, the Dutch government wants to have a fully circular economy by 2050 by reducing the use of primary materials and carbon dioxide emissions. As the consideration and integration of concepts such as sustainability and circular economy are becoming increasingly popular in the civil engineering sector, it might be time to re-consider certain activities. From both scientific and practical points of view, it is concluded that currently a great deal of research is focused on stimulating concepts such as sustainability and circular economy in the “early stages” of the lifecycle such as procurement, design, and construction stages. However, the aforementioned concepts are not yet elaborately researched in stages after construction, such as the maintenance stage. However, in the Dutch context, there are hundreds of existing civil engineering assets, that need to be maintained daily. As the Dutch government has certain goals, it is important to see how maintenance strategies for existing civil engineering assets can be affected in the case when sustainability and circular economy are considered. This research aims to explore the integration of concepts such as sustainability and circular economy within the maintenance stage of existing civil engineering assets. As a result of this research, a tool is developed in Microsoft Excel. This tool referred to as “Maintaining sustainably and circularly in a collaborative way” can be used by actors involved in the maintenance stage. It is possible to apply the tool in the following two phases, namely (1) the pre-contractual phase and (2) the execution phase for maintenance works. With the help of indicators, the actors involved can (re)consider aspects such as the (current) maintenance strategies, and the requirements for maintenance contracts. The tool can help to overcome certain identified barriers such as knowledge gaps on sustainability and circular economy within the maintenance stage, and diffused collaboration among parties involved in a certain process. For this research, two important constraints to mention are: (a) The developed tool is currently only applicable for sluices and bascule bridges (in Dutch: beweegbare bruggen), and (b) the focus of this research is solely on performance-based contracts for maintenance works. As an approach to conducting the research, the “Double Diamond Methodology” is applied. This is a design-thinking research approach. In the first part of the diamond, literature is reviewed and semi-structured interviews are conducted. The results of the literature review and the interviews led to the requirements that should be used as a basis for developing the tool. In the second part of the diamond, the tool was developed and tested via validation sessions.

The rapidly growing infrastructure sector has a detrimental effect on climate change. The infrastructure sector is responsible for approximately 10% of worldwide emissions. In the past years, sustainability became more important in the procurement of infrastructure projects. One of the ways to implement sustainability in infrastructure projects is by award criteria in the tender phase of the project, called EMAT criteria, which stands for Economically Most Advantageous Tender. In this way, the client or procurer can determine the added value of the quality per contractor. So, the EMAT criteria is a way of tendering through the best quality/price ratio. Selecting a suitable subcontractor and supplier will considerably improve the professional services capabilities of the main contractor. Approximately 80 – 90 percent of large infrastructure projects are subcontracted. This means that to have a transition towards a sustainable sector, the subcontractors and suppliers must help too. This research, therefore, aims to generate insight into how the EMAT criteria influence the selection of subcontractors and suppliers A literature study and case study with three cases were performed in this research. The results of the case study show that the EMAT criteria influenced the selection of subcontractors and suppliers, especially when it comes to sustainability. The EMAT criteria are an incentive for the contractor to look at the sustainability level and development of the subcontractors and suppliers. When the client asks for sustainability in the tender through EMAT criteria, the contractor will use sustainability as one of the selection criteria for subcontractors and suppliers. Moreover, the importance of the EMAT criteria (read the percentage of deduction of the tender bid) influence the trade-offs between the selection criteria as well. When the deduction for sustainability in the EMAT criteria is higher, the more important the sustainability selection criteria will be in the trade-offs for subcontractors and suppliers. It is recommended to the client and the contractor to have dialogue sessions with each other about the measurement of the sustainable EMAT criteria and the responsibility for the monitoring of this. Making clear how sustainability is measured and what is needed to monitor it, will stimulate the contractors, subcontractors, and suppliers of the infrastructure sector to be more sustainable in the future. Furthermore, the use of equally weighted sustainable EMAT criteria makes it easier for the contractor to select the most sustainable subcontractor or supplier. A final recommendation towards the clients of infrastructure projects is that sustainability should be part of EMAT, or part of all present and future contracts in general if we are to achieve sustainability goals for the infrastructure sector, but mostly for the ambitious goals in the Netherlands.

The construction sector's reliance on raw materials and the generation of waste necessitate a shift from the unsustainable linear economy to a circular economy (CE). Adopting Product-Service System (PSS) business models is crucial for achieving this transition. However, contractor companies in the building sector face barriers to implementing PSS, and there is limited knowledge about PSS in this context. This study aims to understand the state-of-the-art in PSS, assess barriers, and propose potential solutions specifically for contractor companies in the building sector. A qualitative research method was employed, including a literature review and semi-structured interviews. The literature review encompassed 774 studies, with 45 meeting the inclusion criteria. Semi-structured interviews were conducted with professionals in the building construction sector to supplement the literature findings. This study highlighted that PSS in the building sector has the potential to enhance sustainability and circular economy efforts by promoting economic growth, reducing resource consumption, and minimizing waste. The practical implementation of PSS in the building sector is hindered by challenges such as technological and supply chain changes, lack of financial support, organizational restructuring, establishing new customer relationships, developing new contracts, and adopting new economic models. Insufficient policies and regulations further impede PSS adoption. Nonetheless, this study highlights that sustainability, circularity, and CO2 reduction can drive the adoption and implementation of PSS. The research identified 41 barriers to PSS adoption through the literature review and 20 barriers through interviews grouped into ten categories. These barriers encompass customers, supply chain financial, organizational, resource, knowledge, regulation or policy, environmental, social, and technology-related challenges. To overcome these barriers, nine potential solutions were proposed, including effective leadership, separated business units, training existing personnel, hiring additional personnel, cultivating long-term relationships, horizontal and vertical integration, leveraging knowledge and experience from other sectors, and learning by doing. This study contributes to understanding PSS in the building sector and provides recommendations for practice and further research. By implementing these solutions, contractor companies in the building sector can overcome barriers to PSS adoption and increase their chances of successful implementation. The study offers guidance for efficient resource allocation and prioritization of solutions based on their effectiveness in addressing specific barrier categories. Future studies can explore customers' perspectives, conduct in-depth research on specific barrier categories, and focus on specific building systems or products to investigate potential barriers and solutions.

The global shift toward a circular economy, vital for tackling climate change and resource security, necessitates the integration of circular principles in the construction sector. Urban planning, significant in shaping the built environment, offers an opportunity for implementing these principles comprehensively. However, limited implementation in area development projects is observed due to ambiguity in design themes, timing of strategy definition, and lack of coordination in urban planning. This research addresses these gaps, focusing on integrating circularity in different urban area development phases. The methodology employed a qualitative case-based design study involving a literature review and comparative case study. It identified eleven crucial circular design themes through a systematic literature review. Furthermore barriers, accelerators, and lock-in moments in area development processes were identified through the comparative case stud. These findings have been combined, resulting in the development of eleven phase-wise guidelines for circular area development processes. These guidelines, validated through stakeholder input, encompass change management elements and recommendations for overcoming barriers, thereby optimizing the incorporation of circular design strategies. The guidelines, usable in all process stages, strike a balance between clarity and flexibility, enhancing stakeholder engagement and decision-making. However, further research is recommended to generalize findings, explore the practical application of evaluation sessions, and address technological barriers hindering the transition to a circular economy.