Desafíos y soluciones en el aprovechamiento de estructuras y materiales existentes

Leveraging existing structures and materials faces technical barriers arising from the uncertainty surrounding the mechanical properties and chemical composition of aged materials. Concrete produced before 1970 exhibits characteristic strengths ranging from 10 to 25 MPa, compared with the 25-50 MPa typical of modern concrete, with coefficients of variation of 25-35% according to studies by the FIB (Fédération Internationale du Béton, 2021). Carbonation in concrete advances to depths of 15 to 40 mm in structures 50-80 years old, reducing the alkaline protection of the reinforcement and triggering corrosion that diminishes the effective steel cross-section by up to 15-30%. Detection of these deterioration mechanisms requires techniques such as half-cell potential measurement (ASTM C876) and chloride profile determination via potentiometric titration (EN 14629:2007).

Steel structures predating 1950 used steels with heterogeneous compositions — carbon contents of 0.15% to 0.35%, phosphorus up to 0.12%, and sulfur up to 0.08% — which hinder weldability and strength calculation under current standards. The SCI P427 (Steel Construction Institute, 2018) guide establishes sampling protocols requiring a minimum of 3 test specimens per 50 tonnes of existing steel to determine chemical composition and mechanical properties. In Spain, the Structural Code (Royal Decree 470/2021) introduces for the first time a specific chapter on the assessment of existing structures, requiring an increased partial safety factor of 1.35 for existing steel (compared with 1.05 for certified new steel) when sufficient test data are unavailable.

Buildings constructed before 1990 may contain multiple hazardous substances whose management constrains reuse possibilities. Asbestos, widely used in Spain between 1960 and 1984, is present as fiber cement in roofing (2.6 million tonnes installed, according to estimates from the Observatorio del Amianto, 2022), pipe insulation, vinyl floor tiles, and fireproofing mastics. Asbestos removal requires companies registered with RERA (Registro de Empresas con Riesgo de Amianto), with costs ranging from 15 to 60 euros/m² for fiber cement roofing and 80 to 250 euros/m² for pipe insulation, according to data from ANAVRE (Asociación Nacional de Víctimas del Amianto, 2023).

Lead-based paints, used in interiors until their EU ban in 1992 (Directive 89/677/EEC), contain lead concentrations of 1,000 to 50,000 ppm and require encapsulation or specialist removal at costs of 25 to 75 euros/m². PCBs (polychlorinated biphenyls) present in capacitors of fluorescent light fittings manufactured before 1986 and in joint sealants of 1960s-70s concrete buildings require hazardous waste management at costs of 800 to 2,500 euros per tonne. Directive 2011/65/EU (RoHS) and the REACH Regulation (EC 1907/2006) impose restrictions affecting the reuse of materials containing these substances. The total cost of hazardous substance management can represent between 8% and 20% of the overall budget for a deep renovation, according to the report Decontamination Costs in Building Renovation by the JRC (2020).

Material passports represent the most promising regulatory solution for overcoming information barriers to the reuse of existing materials. The Madaster platform, operational in the Netherlands, Germany, Belgium, Switzerland, and Norway, records the identity, location, quantity, and quality of every material and component in a building, generating a calculated residual value that facilitates end-of-life reuse decisions. In 2023, Madaster had 5,200 registered buildings and a catalogued material value of 12 billion euros. The proposed revision of the Energy Performance of Buildings Directive (recast EPBD, 2024) introduces the mandatory building renovation passport, which will include information on reusable materials.

The standard ISO 20887:2020 (Sustainability in Buildings — Design for Disassembly and Adaptability) establishes design principles for disassembly that facilitate the future reuse of components. Key technical recommendations include: use of reversible mechanical connections (bolts rather than welds), separation of functional layers (structure, envelope, services, finishes) with service lives of 50-100, 20-30, 15-20, and 5-10 years respectively, and permanent material labeling with QR or RFID codes. The BAMB (Buildings as Material Banks) project developed material passport protocols for 300 pilot buildings and estimated that their widespread application could reduce construction and demolition waste in the EU by 25-30%, with a recoverable material value of 18 billion euros annually.

Selective deconstruction — the orderly disassembly of a building to maximize the recovery of reusable components — achieves landfill diversion rates of 90-95%, compared with 50-70% for conventional demolition with post-sorting. The Park 20|20 project in Hoofddorp (Netherlands), a 100,000 m² business park designed entirely according to Cradle to Cradle principles, uses material leasing contracts in which manufacturers retain ownership of facades, raised floors, and furniture, guaranteeing their recovery at end of use. The system has demonstrated that 92% of the park's materials can be reused or recycled in closed loops, with an estimated residual value of 35 million euros on a total investment of 200 million.

In Brussels, the regional regulation RRU (Règlement Régional d'Urbanisme) has required since 2019 a pre-demolition reuse inventory for all demolitions of buildings exceeding 1,000 m². The inventory, carried out by accredited professionals, identifies components with direct reuse potential (doors, windows, radiators, timber beams, flooring) and their estimated market value. In the first 4 years of implementation, the mandatory inventory has diverted 28,000 tonnes of components into reuse circuits, generating a second-hand market valued at 14 million euros annually, according to data from Bruxelles Environnement (2023). The Belgian experience has inspired similar initiatives in Amsterdam (mandatory since 2021 for demolitions exceeding 500 m²) and in Paris, where the Loi Anti-Gaspillage (AGEC, 2020) makes the pre-demolition resource survey mandatory from 2024 for buildings exceeding 1,000 m².