Economía circular en la construcción. principios y prácticas

The circular economy in construction is founded on three operational principles: eliminating waste and pollution by design, keeping products and materials in use at their highest level of value, and regenerating natural systems. The scale of the challenge is proportional to the sector's volume: construction annually consumes 3 billion tonnes of raw materials globally (UNEP, 2022), equivalent to 40-50% of all extracted resources. In the European Union, the sector generates 374 million tonnes of construction and demolition waste (CDW) annually, 35% of total waste (Eurostat, 2022), of which only 40% is effectively recycled into materials of equivalent value (upcycling), while 30% is used as low-quality fill (downcycling) and the remaining 30% is sent to landfill. The Ellen MacArthur Foundation (2020) estimates that the comprehensive application of circular principles could reduce the sector's CO2 emissions by 38% by 2050 and generate net raw material savings of 1.4 billion tonnes/year.

The conceptual framework for circularity in construction is organized into strategies ranked by value retention level. The 9R hierarchy (Refuse, Rethink, Reduce, Reuse, Repair, Refurbish, Remanufacture, Repurpose, Recycle) translates into construction practice as: avoiding unnecessary construction through intensified use of the existing stock (office buildings are used an average of 35-55% of the time available, according to JLL 2023), designing buildings with less material (structural optimization), designing for disassembly and component reuse, and finally recycling materials when reuse is not possible. A study by Eberhardt et al. (2022), published in the Journal of Cleaner Production, quantified that design for disassembly can reduce the embodied carbon of an office building by 10% to 45% depending on the proportion of components designed for reuse, with an additional construction-phase cost of 2-8% that is recovered at end of life through the sale of reusable components.

Design for Disassembly (DfD) uses reversible mechanical connections (bolting, interlocking, gravity fixing) instead of irreversible chemical bonds (welding, adhesive, in-situ concrete) to enable the separation and reuse of components at the end of the building's useful life. The Circle office building at Zurich Airport (2020), designed by Riken Yamamoto, applied DfD principles to its steel structure with 4,500 bolted connections that allow the dismantling and relocation of 85% of structural elements. The Triodos Bank project in Driebergen, Netherlands (2019), designed by RAU Architects, was the world's first office building with a complete material passport registered on the Madaster platform: 165,000 objects and 5,500 tonnes of materials inventoried with their composition, location, and estimated residual value, which reaches 8.2 million EUR against a construction cost of 32 million EUR, meaning 25% value recovery at end of life.

Material banks constitute the logistical infrastructure of the circular economy in construction. The Madaster platform, operational in 12 European countries including Spain since 2022, functions as a material cadastre: owners upload their buildings' BIM models and the platform automatically calculates the material inventory, its residual market value, and its life-cycle environmental impact. As of 2024, Madaster registers 15,000 buildings with a total inventory of 120 million tonnes of materials. In Spain, the company Bimaterial has developed a marketplace for reused construction materials that connects demolition sites with new construction projects, with a catalogue of 4,200 lots of materials (structural steel, stone facade, aluminum windows, sanitary fittings) and a transaction volume of 12 million EUR in 2023. The environmental saving from direct reuse is maximum: reusing a steel beam avoids 95% of production emissions (1.8 kg CO2/kg of new steel), compared to the 50-70% saved by recycling in an electric arc furnace.

Concrete, which represents 60-70% of the weight of a conventional building, is the material with the greatest circularity potential by volume. Concrete recycling technology allows the recovery of 100% of coarse aggregate and 50-70% of fine aggregate, although the mechanical properties of recycled concrete with more than 30% recycled aggregate are reduced by 10-20% compared to concrete with natural aggregate. European standard EN 206 (updated in 2021) allows up to 50% recycled coarse aggregate in structural concrete of class up to C30/37, opening a potential market of 80 million tonnes/year of recycled aggregate in the EU. In Spain, ready-mixed concrete consumption was 55 million m3 in 2023 (ANEFHOP), and the rate of recycled aggregate incorporation stands at 5% compared to 15-20% in the Netherlands and Belgium. The European SeRaMCo project (2018-2022) demonstrated the technical and economic feasibility of precast concrete with 100% recycled aggregate from selective demolition, with strengths of 35-45 MPa and costs competitive with conventional concrete when the distance to the recycling point is less than 30 km.

Certified structural timber (FSC or PEFC) is inherently circular when sustainably managed: it sequesters 1.6 tonnes of CO2 per m3 during growth, can be cascaded in reuse (structure to furniture to particleboard to energy), and is biodegradable at end of life. The use of CLT (Cross-Laminated Timber) in Europe grew from 0.5 million m3/year in 2015 to 2.8 million m3/year in 2024 (Timber Online, 2024). Structural steel has the highest recycling rate of all construction materials: 98% of structural demolition steel is recycled (World Steel Association, 2023), and recycled steel in an electric arc furnace emits 0.4 kg CO2/kg compared to 1.8 kg CO2/kg for primary steel from a blast furnace, a 78% reduction. Direct reuse of structural steel profiles, without remelting, saves 95% of energy and emissions, but currently only 5-7% of structural demolition steel is reused due to a lack of traceability and certification of the second-hand material's mechanical properties. The SCI (Steel Construction Institute, 2019) project developed a testing and certification protocol for reused steel that permits its structural use in accordance with Eurocode 3, eliminating the main regulatory barrier.

Circular business models in construction transform the relationship between ownership and use of materials. The Product-as-a-Service (PaaS) model applied to building components allows manufacturers to retain ownership of their products and lease them to the building owner, assuming responsibility for maintenance, renovation, and recovery at end of life. Philips (now Signify) was a pioneer with its "Light as a Service" model implemented at Schiphol Airport headquarters (2015), where Signify retains ownership of the 3,700 luminaires and charges for guaranteed illumination levels, recovering components at end of life for remanufacture. The model has expanded to facades (Schuco offers facades as a service in 8 pilot projects), elevators (KONE has implemented PaaS models in 2,500 units), and office furniture (Interface recovers 74% of installed carpet tiles for recycling). According to Accenture (2020), PaaS models in construction can reduce material consumption by 28-38% because manufacturers optimize durability and maintainability when they retain ownership.

In Spain, the circular economy in construction is at an early stage but with growing regulatory momentum. The Spanish Circular Economy Strategy (Espana Circular 2030) sets a target of a 30% reduction in national material consumption relative to GDP by 2030, and Law 7/2022 on waste and contaminated soil establishes specific CDW recovery targets of 70% by 2025. However, 68% of Spanish construction companies surveyed by the CNC (2023) report having implemented no circular economy practices beyond legal waste management. The barriers are well known: lack of demand for recycled materials (only 3% of public procurement specifications in Spain include circularity criteria), absence of selective deconstruction infrastructure (95% of demolitions in Spain are non-selective), and unfamiliarity with available tools. The market potential is significant: a COTEC Foundation study (2023) estimated that the circular economy in construction could generate 85,000 direct jobs and a business volume of 12 billion EUR/year in Spain by 2030 if the practices already operational in the Netherlands and Denmark are adopted.