From Green Concrete to Policy and Stakeholders: A Transdisciplinary Approach to a Circular Built Environment in Luxemburg

The built environment is a critical component of global sustainability efforts as it represents quite a significant waste and energy toll, but the transition to more circular and sustainable construction practices has not been a smooth sail. This research aims to bridge part of the knowledge gap by investigating some of the technical and non-technical barriers to circular economy practices in Luxembourg's construction sector. Initially rooted in material science and examining the effect of additions of secondary raw materials as substitutes to ordinary Portland cement in concrete, the project expands through a transdisciplinary lens to understand the broader social, political, and economic influences on circular construction practices.

The material technology – investigating green concrete

The first phase of this research focused on developing more sustainable cement blends by incorporating secondary waste materials such as gravel wash muds and clays originating from the quarries in and around Luxembourg in the Greater Region and classified as industry waste. These materials were tested for their chemical and mineralogical properties to determine their potential as supplementary cementitious materials. Further research on environmental impacts of the additions and the properties of concrete were studied by other partner universities in the context of project CO2REDRES funded by Interreg Greater Region.

Key Findings:

• The laboratory tests confirmed the viability of using secondary waste materials in concrete mixtures.
• Some of these materials outperformed traditional Portland cement, with certain mixes showing up to 20% cement replacement while still maintaining or exceeding the strength of reference mortar.
• Despite the promising results, these innovations have not seen widespread adoption in the industry.

Transition to Social Science: Understanding Stakeholders and Policies

After the successful completion of the experimental phase, the project broadened its scope to examine why sustainable materials, such as those studied in phase 1, and circular building techniques are not more widely adopted in Luxembourg. This phase shifted from a purely engineering and material technology focus to a more holistic, interdisciplinary analysis of the social, political, and economic factors influencing the construction sector.

This approach employed a qualitative research methodology, gathering data from field practitioners engaged in circular economy practices within the built environment to explore both the barriers and opportunities. An initial outcome was the creation of a stakeholder map, which analyzed their interactions, highlighting conflicts and synergies that might affect the sector's transition. By mapping the relationships and power dynamics among various actors, the research aimed to uncover the underlying reasons for the slow uptake of circular construction practices, focusing on the flow of information and collaboration among stakeholders based on insights from the interviews.

On the policy side, the research explored the interplay between Luxembourg’s circular economy goals and the construction sector’s current practices. This involved examining existing policy frameworks and assessing how well they align with circular economy principles, as perceived by the interview participants. The research also sought to identify where policy adjustments could foster more sustainable practices, based on the challenges and opportunities highlighted in the interview data.

Additionally, the research explored how participants understand the concept of circularity, and how their interpretations shape their vision of the future of the built environment. This involved analyzing the different lenses through which circularity is viewed in relation to sustainability, concluding with experts' future visions for the sector.

Conclusions

The outcomes of this research serve as an invitation to rethink the way we approach the built environment, offering new perspectives and identifying untapped opportunities for transforming construction practices. These insights aim to move the sector toward a nature-positive and regenerative circularity that not only enhances the performance of structures but also improves the satisfaction of users and inhabitants, all while respecting the balance of natural ecosyst