Improvement of Ferrocement Durability by Nanomaterials for Preservation of Pier Luigi Nervi's Structural Heritage

Ferrocement is a construction material which provided to have superior qualities of crack control, impact resistance, and toughness, largely due to the geometrical properties, i.e., uniform dispersion and high specific surface of reinforcement within the material. However, while extensive literature exists on the deterioration mechanisms and maintenance of reinforced concrete structures, little attention has been given to the durability of ferrocement. Given the lack of knowledge of maintenance and repair strategies on ferrocement structures, along with the paucity of literature on deterioration mechanisms taking place in this material, further studies are necessary to define guidelines for diagnosis, structural assessment (including the new need of seismic assessment), structural rehabilitation and remedial actions for durability of ferrocement spatial structural architectures. In this study, the adoption of newly developed nanomaterials, such as ethyl silicate, to improve the durability of ferrocement is investigated. Such nanomaterials are expected to penetrate the cementitious matrix without changing the appearance of the surface. Once penetrated, pozzolanic behavior is displayed forming calcium silicate hydrate and consequently increase durability and mechanical performance. Particular attention was given to the carbonation-induced corrosion of reinforcement, which should be considered as a major concern in ferrocement due to the initially small diameter of the mesh wires (even a small cross-section loss of the wire is of great importance) and the incredibly thin mortar cover (the time required for the carbonation to reach the depth of the steel can be very short). Laboratory tests revealed that ethyl silicate can be effective in reducing the ingress of aqueous substances through the pore structure of the cementitious matrix, although other protective agents (i.e., sodium silicate “waterglass” sealer, and Isobutyl-triethoxy-silane sealer) exhibited better performances with respect to water absorption. The single most conspicuous observation to emerge from the data comparison was that ethyl silicate featured much better performance with respect to carbonation resistance than with respect to water absorption, while the other protective agents were almost ineffective in preventing the penetration of carbonation into the cement mortar matrix. Moreover, the present thesis sheds new light on the sensitive issue of maintenance, repair and conservation of ferrocement architectural heritage. In fact, special focus has been given to the work of the Italian engineer-architect Pier Luigi Nervi, who employed ferrocement in many of his landmarks, combining this extremely versatile material with his prefabrication technique, namely structural prefabrication.Among Nervi’s works, Turin Exhibition Center represents the first large-scale ferrocement construction ever completed. The corrugated vault and the related ribbed apse of the main Hall B, and the refined texture of the vault of the adjacent Hall C represent an international icon of the twentieth century. Unfortunately, the Nervi’s structural masterpiece now exists in a state of semi-neglect and decay; however, a restoration and redevelopment project was drawn up by the Town of Turin and by Politecnico di Torino. Moreover, Politecnico di Torino, in conjunction with PLN Pier Luigi Nervi Project Association, is preparing a submission for a “Keeping it Modern” grant of the Getty Foundation.