Because of established demolition routines and low construction-material production costs that neglect negative externalities, discarded concrete today is crushed and landfilled or downcycled as infill material or recycled aggregates, wasting its embodied carbon, technology, and cultural and structural properties. Addressing the urgent need to improve the sustainability of the construction industry, the thesis investigates a little-known alternative strategy for discarded concrete structures for which demolition is unavoidable: their careful deconstruction into elements, generally with circular saws, and the reuse of the saw-cut elements into new structures after no or minor modifications. The thesis examines the potential of reusing concrete elements to build sustainable structures. The methods include a cross-disciplinary retrospective and prospective characterisation of past and emerging practices of reusing concrete in architecture, and research by design to develop supplementary design methods.
Responding to scattered literature and documentation, the first contribution of the thesis is a critical historical perspective on the reuse of concrete in architecture. Comparing more than 50 built precedents, the analysis highlights the diversity and relative rarity of applications. Results also underline the prevalence of knowledge and precedents reusing precast concrete rather than cast-in-place. Facing this knowledge gap, the second contribution is the documentation and analysis of emerging approaches to reusing cast-in-place concrete. The analysis of two projects reusing blocks in compression confirms considerable environmental benefits compared to conventional practices. The qualitative analysis of a pavilion reusing assemblies highlights the design constraints of reusing such elements. Finally, the analysis points out the untapped research opportunity to develop approaches to reusing cast-in-place flat reinforced concrete elements in bending. Combining this untapped potential with the need to reduce the large contribution of floors to the upfront embodied carbon of buildings, the third contribution is the introduction of two new low-carbon floor systems reusing saw-cut cast-in-place reinforced concrete elements in bending. Their parametric analysis confirms an average reduction of upfront embodied carbon by 80 % compared to conventional new or recycled flat slabs. A 30-m2 mock-up is built to demonstrate the system's technical feasibility. The fourth contribution is the development of criteria and methods to support decision-making when designing with reused structural elements.
The thesis contributes to the research fields of circular design, construction history, and concrete structures in three ways: theoretically - by presenting a critical perspective on an unknown concrete design strategy, methodologically - by providing novel characterisation and design methods to reuse concrete, and conceptually - by introducing original approach conceptualisation for concrete reuse. Through the documentation, analysis, and construction of full-scale case studies, the work broadens practical knowledge and design possibilities for reuse. Overall, findings call for adding concrete reuse to concrete-industry decarbonisation plans and invite researchers, designers, and decision-makers to consider soon-to-be-demolished concrete structures as highly valuable sources of construction materials.