The present work aims to define the mechanical behavior of a new composite material for the preservation and enhancement of the vast historical and architectural heritage particularly vulnerable to environmental and seismic actions. The new composite represents a novelty in the landscape of the fibrous mortars and consists of natural hydraulic lime (NHL)-based mortar, strengthened by Sisal short fibers randomly oriented in the mortar matrix. The developed mortar ensures the chemical-physical compatibility with the original features of the historical masonry structures (especially in stone and clay) aiming to pursue the effectiveness and durability of the intervention. The use of vegetal fibers (i.e., the Sisal one) is an exciting challenge for the construction industry considering that they require a lower level of industrialization for their processing, and therefore, their costs are considerably lower, as compared to the most common synthetic/metal fibers. Samples of Sisal-composite are tested in three-point bending, aiming to estimate both their bending stress and fracture energy. Tensile and compressive tests were also performed on the composite samples, while water retention and slump test were performed on the fresh mix. At last, the tensile tests on the Sisal strand were performed to evaluate the tensile stress of both strand and wire. An original mechanical interpretation is proposed to explain two interesting phenomena that arose from the analysis of experimental data. The comparison among the performances of unreinforced and reinforced mortar suggests that the use of short fibers is recommendable as coating in the retrofitting interventions alternatively to the long uni or bi-directional fiber strands adopted in the classic fibrous reinforcement (i.e., FRCM). The proposed composite also ensures mix-independent great workability, excellent ductility, and strength, and it can be considered a promising alternative to the classic fiber-reinforcing systems. As final remarks, the use of fiber F1 (length of 24 mm) with respect to fiber F2 (length of 13 mm) is more recommendable in the retrofitting interventions of historical buildings, ensuring higher strength and/or ductility for the composite.

Recent seismic events prompted research to develop innovative materials for strengthening and repair of both modern and historic masonry constructions (buildings, bridges, towers) and structural components (walls, arches and vaults, pillars, and columns). Strengthening solutions based on composite materials, such as the Fiber Reinforced Polymers (FRP) or the Fiber Reinforced Cementitious Matrix (FRCM), have been increasingly considered in the last two decades. Despite reinforcement made of short-fibers being a topic that has been studied for several years from different researchers, it is not yet fully considered for the restoration of the masonry construction. This work aims to experimentally investigate the enhancement of the mechanical properties of lime-based mortar reinforced by introducing short glass fibers in the mortar matrix with several contents and aspect ratios. Beams with dimensions of 160 mm × 40 mm × 40 mm with a central notch were tested in three-point bending configuration aiming to evaluate both the flexural strength and energy fracture of the composite material. Then, the end pieces of the broken beams were tested in Brazilian and compressive tests. All the tests were performed by a hydraulic displacement-controlled testing machine. Results highlight that the new composite material ensures excellent ductility capacity and it can be considered a promising alternative to the classic fiber-reinforcing systems.

This paper focuses on the simulation of irregular stone masonry by the lattice discrete particle model (LDPM), which simulates the fracture and failure behavior of quasi-brittle heterogeneous materials by modeling the interaction among coarse material heterogeneities. LDPM is formulated at the length scale of the masonry stones whose interaction is described through constitutive equations featuring softening in tension and strain hardening in compression. The numerical results relevant to diagonal compression tests show that the intrinsic stochastic character of LDPM can quantify the variation of the mechanical properties of irregular masonry resulting from random stone size and stone-size distribution. Furthermore, the paper presents an analysis of the size effect on irregular stone masonry structures. This was obtained by simulating the shear behavior of geometrically similar samples of different sizes. The simulations demonstrate that increasing structural size leads to a significant reduction of both structural strength and structural ductility. The magnitude of the predicted size effect suggests that, contrary to typical experimental results on reduced size samples, real irregular masonry structures must be considered as perfectly brittle.