Existing buildings are often in need of strengthening interventions, and several technical solutions have been recently developed for this purpose. Among them, the use of textile-reinforced mortar (TRM) composites has gained consensus as a technically viable and economically convenient option. Moreover, TRM has the potential to be employed as a reversible and sustainable strengthening technique for masonry buildings. In this context, the present paper aims to investigate the mechanical properties of TRM systems consisting of sustainable phases, such as lime-based matrices and natural fabrics produced by waiving fibers obtained from plants, such as Jute or Flax. This class composite system can be referred to as natural TRM and is denoted by the acronym NTRM. The present study moves from the geometric and mechanical characterisation of fibres and fabrics and, after having also investigated the properties of the mortar, it reports the results of tensile tests carried out on specimens of the NTRM systems under consideration, with the main aim of providing the empirical bases of the relationships between the geometric and physical properties of the constituents and the resulting mechanical response of the composite system. The obtained results show that the considered Flax-TRM system has an apparent composite behavior, as its response to tension is clearly characterised by the well-known three stages corresponding to the elastic response, the formation of cracks, and the reinforcement response up to rupture. Conversely, the Jute-TRM system needs to be further improved in terms of balance between the properties of the matrix and the internal reinforcement. Further studies will be devoted to this specific aspect and, more generally, to investigating the relationships between constituents’ properties and the NTRM behavior.

In recent years, the development of alternative and more sustainable technologies for reinforced concrete structures has been attracting more and more interest, given the increasing need to reduce the impact that the construction sector has on the environment. Furthermore, 3D concrete printing (3DCP) technology falls into this context, allowing the optimization of the quantities of employed raw material to be used while at the same time allowing the possibility to design more complex elements’ shapes. In the view of improving the sustainability of construction sector, the present study aims at experimentally investigating the characteristics of the fresh and hardened states of concrete mixtures incorporating different percentages of replacement of the fine aggregate with recycled aggregates of different nature. As such, the key innovative aspect of the present study is the possible investigation of cement-based mixtures produced with 100% recycled fine aggregates (both derived from concrete waste and brick elements) without affecting either the fresh or hardened mechanical properties of the resulting Recycled Aggregate Concrete (RAC) mixtures. Furthermore, in order to make this study linked to 3D printing technology, extruded concrete elements were realized and tested through a process designed to simulate the automated 3D concrete printing process: in fact, the RAC mixtures were designed in order to obtain an adequate workability and compressive strength typically adopted for ordinary 3D printed mixtures. Although some adjustments and further analyses are required in order to optimize the shape retention and stability, as well as the well-known problem of the 3D mixtures being linked to anisotropic behavior, the obtained results unveil that it was possible to observe promising characteristics for the mixes containing recycled aggregates (i.e., consistency index at the fresh state above 150 mm and compressive strength at 28 days above 50 MPa), which were in any case suitable for the creation of 3D printed structural concrete elements and can be further confirmed with future studies in order to validate their possible buildability.