Ultra-High-Performance Fibre-Reinforced Cementitious Composite (UHPFRC) has been developed to design lightweight structures and enhance existing designs. As the environmental footprint of the construction industry must be significantly reduced, the potential to lower environmental impacts of structures using UHPFRC needs to be explored. While the greenhouse gas emissions of a volume of UHPFRC are higher than that of the same volume of concrete, UHPFRC enables the reduction in the amount of material required in structural designs and improves the durability of structures. The environmental impacts of structural designs must thus be compared on the cradle-to-grave use cycle of the design at a project scale. In this study, a methodology is proposed to evaluate the ecological burdens of several bridge designs involving various structural elements in UHPFRC. The method proposes an analysis over three time horizons: first, the construction phase, then including the scheduled maintenance, and finally, adding the elimination. A case study of a short-span bridge in Switzerland is used to assess three alternatives of bridge designs: a conventional reinforced-concrete structure, a composite timber–UHPFRC bridge, and a full-UHPFRC solution. The results show that timber–UHPFRC structures can significantly reduce the environmental impacts of bridge designs, showing promising results in terms of sustainable development. The use of the methodology supports bridge owners in assessing the environmental impacts of structural designs.

The reuse of structural components in new buildings has great potential to reduce the environmental impacts of the construction sector but remains uncommon practice. An obstacle to its wider implementation is the lack of robust assessment methods and decision-making tools that consider the full spectrum of benefits and drawbacks. This paper proposes a multi-criteria decision framework that builds on a simulated set of design alternatives with varying ratios of reused and new structural components. A set of performance criteria is presented, addressing procurement risks, construction technique complexity, environmental impacts, and project costs. As the independent criterion evaluations often deliver conflicting results, a multi-criteria decision analysis helps identify the most appropriate solution. The design of a steel Pratt truss is used as a case study to demonstrate the applicability of the framework. Different alternatives with reuse rates above 65% are recommended for each preference scenario, reducing between 35 and 45% of adverse environmental impacts in comparison to an equivalent design made of new elements only. The study underpins the principle that there is no trivial and unique best option when designing with reused components. Multi-criteria decision analyses applied to structures with varying reuse rates constitute a promising tool to support decision-makers.

Practices that reuse concrete pieces in new building or infrastructure projects are currently diversifying as concrete reuse gains more and more relevance for sustainability. The present research provides a yet missing identification of the main approaches to these practices and introduces a new set of criteria to compare them. Five types of sourced concrete pieces are identified, three resulting from careful deconstruction and two from demolition. The study shows that approaches allowing the best re-utilization rate of the structural capacities of the concrete pieces are less compatible with current demolition practices, in contrast to approaches reusing debris. The reuse of wall and slab panels, beams, and columns is a promising approach as it implies a low to medium level of constraints on the new design while recovering the capabilities of discarded reinforced concrete equivalently. A few dozen built precedents have already applied this approach to precast components, but applications reusing cast-in-place concrete are lacking, despite considerable CO₂ emissions reduction.

Carefully extracting reinforced concrete (RC) elements from soon-to-be demolished structures and reusing them directly as load-bearing elements in new buildings is an emerging circular low-carbon resource-management strategy. As floor construction typically accounts for a large share of a building’s upfront carbon footprint, designing floors with reused RC elements is a promising, yet little explored, approach to lower a building’s embodied carbon. This paper presents the concept, design, construction and assessment of a new load-bearing floor system for an office building made with reused saw-cut RC pieces and reused steel profiles. The system reuses the existing properties of widely discarded construction materials – RC and steel – and is dismountable. To demonstrate the system’s technical feasibility and assess its structural and environmental performance, a 30-m² prototype – FLO:RE – is designed, built with elements reclaimed from local demolition sites, tested and finally dismantled. Reclaimed material property testing and prototype load testing confirm the structural-design safety. A Life-Cycle Assessment shows unprecedentedly low upfront embodied carbon, with results as low as 15 to 5 kgCO₂e/m², i.e., 80–94% reductions compared to conventional new RC flat slabs. This research demonstrates the untapped technical and environmental potential of reusing saw-cut RC elements in bending in structurally performant floor systems. Through this novel ultra-low-carbon solution, the study supports the efficient use of existing resources and calls for considering soon-to-be demolished RC and steel structures as potential mines of suitable quality materials ready to be reused locally.

As floors account for a significant share of a building’s embodied carbon, designing low-carbon floors is crucial to mitigating construction’s environmental impact. This research presents a multi-criteria comparison of four concrete floor systems: two widely used conventional systems —flat concrete slabs and timber-concrete composite slabs—and two novel systems —concrete thin shells and systems reusing concrete and steel elements. Six qualitative and quantitative criteria (embodied carbon, total depth, self-weight, waste use, deconstruction ease, supply ease) are used to compare the systems. Additionally, the study examines the sensitivity of key embodied carbon parameters such as material selection and transportation distance. Compared to flat slabs, the novel systems and timber-concrete composite slabs achieve embodied carbon reductions of up to 80 % and 40 %, respectively. While no system outperforms all criteria, the novel solutions surpass flat slabs in all aspects except supply ease and total depth. Since embodied carbon is not yet restricted in Swiss construction, flat slabs remain advantageous and largely prevalent due to their slenderness and ease of construction. To meet carbon reduction targets, the authors call for further supply-chain and business-model investigations and optimisation of the novel systems.