Il ripristino del Béton Brut. Tecnologie e materiali a confronto. The restoration of the Béton Brut. Comparison between technologies and materials

The reinforced concrete was immediately identified as the ideal material to achieve a more secure, functional and durable construction and housing model, but also to define a new architectural style. The architects of the Modern Movement and the Brutalists will use it to emphasize the formal and expressive aspects of their language and to give shape to complex visions that are difficult to achieve with other materials. Le Corbusier, Niemeyer, Kahn, Wright, Scarpa, Nervi, Savioli, are just some of the architects who, aware of the mechanical properties, have experienced and enhanced their formal potential. In the rapid rise of the material, however, are partly traced the reasons of its partial defeat: a speculative frenzy linked to excessive confidence in the standardization of the construction process, the inadequacy of labour and the lack of a specific regulatory framework have led to disregard quality and accuracy of the building, dramatically reducing the performance and durability of the reinforced concrete. Serious situations of building decay distinguish a few decades after their construction, many masterpieces of modern architecture, putting in crisis both the formal values of the architectural image and the same mechanical stability. Today the knowledge, the technologies and the materials on the market allow the realization of visible concrete products with formal performances, mechanical resistance and durability of unquestionable quality: the research is oriented towards products that, thanks to innovative mix design, allow to reduce the problems due to high operating stresses, inadequate installation and particularly aggressive environmental contexts (SCC, fibres-reinforced, TIO2, etc.). The same applies to the maintenance and restoration of existing structures: passivating materials for reinforcement and cement mortars with compensated shrinkage allow intervening on concretes, guaranteeing their original performance. However, when the recovery intervention also aims to restore the original architectural quality, perhaps by redesigning the veins of the wood imprinted on the facades or by recalibrating the original colouring tones on smooth and polished surfaces, the knowledge, technologies and materials at our disposal do not always appear adequate. The contribution aims to provide, through the story of case studies, a state of the art on innovative materials and specific technologies for the restoration of architectural reinforced concrete.