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.

Predicting the development of cracking processes in structural elements made of reinforced concrete (RC) or other cementitious composites is still a challenging task. Although well‐established experimental procedures are widely adopted with the aim to gain empirical knowledge of the aforementioned processes, no similar consensus has been reached about mechanical modeling. Actually, the simulation approaches available in the literature are based either on computationally demanding 3D finite element models or on simplified 1D solutions obtained through alternative numerical strategies, such as finite difference schemes. The present paper proposes a simplified FEM model based on 1D spring elements, which aims at obtaining a reasonable balance between simulation accuracy and computational effort. The incremental‐iterative scheme driving the nonlinear solution procedure is described in detail and some comparisons with experimental results on RC tensile members are proposed with the aim of validating the proposed model. Moreover, the promising results obtained in this paper inspire the future developments of the research towards the numerical simulation of the cracking behavior of other inorganic‐matrix composites, like textile reinforced mortars (TRM), subjected to tensile actions.

The present paper proposes the results of a multi-scale experimental campaign aimed at investigating the mechanical and structural response of Textile Reinforced Mortar (TRM) systems incorporating natural fibers and natural textile, also referred as Natural Textile Reinforced Mortar (nTRM), for existing masonry structures which can represent a promising alternative to conventional composites, combining structural effectiveness with environmental sustainability. More specifically, the natural TRM composite systems under investigation analyzed herein consider the possible combination of pre-treated flax textiles and short fibers (made of either jute or flax) employed as spread reinforcement. As a matter of principle, the application of hybrid (i.e., combination of textile and short fibers) is proposed as a possible strategy to optimize the overall amount of reinforcement by reducing the optimal number of textile layers while improving mechanical performance through the crack-bridging effect of the short fibers. The mechanical response of the proposed systems is evaluated through four-point bending tests meanwhile diagonal compression tests on reinforced masonry walls are executed to evaluate the structural response of the masonry elements. The results provide insight into the role of fiber type, fiber treatment and reinforcement configuration on strength, ductility, and crack control. The proposed approach highlights the potential of flax- and jute-based hybrid natural TRM systems as effective strengthening solutions for masonry structures, offering a material-efficient alternative to conventional synthetic reinforcement systems.