New materials, models and innovative techniques for the reinforcement of existing buildings

This thesis investigates new materials, models and innovative techniques for the reinforcement of existing buildings, with focus on historical masonry structures and non-seismically designed Reinforced Concrete (RC) joints. The research is divided into two main parts. The first part examines a high performance blended Natural Hydraulic Lime (NHL) mortar developed for the structural reinforcement of historic masonry structures. The proposed mortar contains 40% NHL, a higher percentage than those typically found in commercial products, in order to improve compatibility with old traditional masonry materials. An extensive experimental program was carried out to characterize the microstructure and to evaluate the fresh-state, mechanical and fracture properties. Micro- and nanomaterials—including PolyPropylene (PP) fibers, Carbon NanoTubes (CNTs) and Graphene NanoPlatelets (GNPs)—were added to improve structural build up, thixotropy, mechanical strength and toughness. Microstructural analyses (XRD, TGA, IC, SEM) provided a detailed explanation of the hydration mechanisms of the blended mortar and showed how different \% of NHL influenced the evolution of the microstructure. Moreover, mechanical tests and rheological measurements were also carried out to assess the materials strength, ductility, fracture properties and fresh-state rheology. Then, masonry panels constructed with traditional materials were tested under diagonal compression and the results were compared and supported with validated 3D numerical models. Both experimental and numerical results confirmed that the proposed reinforcing technique can enhances shear strength and ductility while maintaining compatibility with historic masonry structures. The second part of the thesis focuses on the seismic performance of non-seismically designed RC beam–column joints. Full-scale RC wall and corner joints, both unreinforced and reinforced with an external steel plate, were tested under extreme cyclic loading. Experimental results showed that, although the beam-column joints did not include any type of shear reinforcement, all the tested unreinforced specimens showed a surprisingly high structural ductility, even if, according to current design standards, RC joints without transverse reinforcement are typically expected to fail in a brittle shear mode. The addition of external steel-plate reinforcement enhanced the systems ductility by increasing its shear strength and improving its overall deformation capacity. Moreover, detailed 3D finite element models were developed to reproduce the experimental results, evaluate stresses and cracking patterns, and study the effects of concrete strength and plate adhesion. Numerical results were consistent with the experimental observations. Overall, the research provides new insights into the use of high performance blended lime mortars for the structural reinforcement of historical masonry and provides new considerations and a better understanding of the seismic behavior of non-seismically designed RC joints in existing structures. The results contribute to the development of sustainable and effective reinforcement strategies aimed at improving the safety and resilience of the built heritage.