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Load-bearing unreinforced masonry structures represent a significant proportion of the building stock in several countries worldwide, and include historical constructions that belong to cultural heritage. Because of the limited tensile strength of unreinforced masonry, fiber-reinforced composites are an effective strengthening technique, which has already been widely used, especially in seismic prone areas, to delay the onset of collapse mechanisms of the entire structure or portions of it. Steel reinforced grout (SRG), which consists of steel textiles embedded in a cement or lime based mortar, is a particularly appealing alternative to fiber-reinforced polymer (FRP) composites, as well as to other mortar based composites (i.e., fabric reinforced cementitious matrix, FRCM), especially when applied to masonry structures. This paper sheds light into the retrofitting of masonry structures with SRG, providing an overview of the experimental investigations carried out in the laboratory and in the field on full-scale structural members. SRG proved effective for improving the out-of-plane flexural strength and deflection capacity of masonry walls (for which three or four-point bending tests and shake table tests were performed), the load-bearing and deflection capacity of vaults (tested both in the laboratory and in the field under quasi-static vertical loads), and the compressive strength of columns (subjected in the laboratory to centred axial load). Further research needs are identified, which are considered useful for the development of design guidelines.

The civil engineering community is acquainted with the fact that existing reinforced concrete structures require constant maintenance in order to increase their service life. Nevertheless, maintenance might be not sufficient when a change of use, which entails for an increase of the service loads, damage due to aggressive environment, or the need of withstanding natural and man-made hazards were not taken into account when the structure was designed. Fiber-reinforced composites are a suitable tool to strengthen and thus increase the capacity of the structural element without changing the original configuration and adding mass. Steel reinforced grout (SRG) is a relatively new tool in the realm of fiber-reinforced composites that consists of steel fibers embedded in a cementitious mortar. This paper presents a state-of-the art on SRG that includes a literature review and points out the effectiveness of SRG for flexural strengthening and confinement of concrete members. It also proposes a design approach to strengthen reinforced concrete beams based on the available data on flexural tests on beams, bond tests on SRG-concrete joints, and tensile tests on SRG coupons.

The conservation and the preservation of existing masonry buildings, most of them recognized as cultural heritage, require retrofitting techniques that should reduce the invasiveness and assure reversibility and compatibility with the substrate. In this perspective, the strengthening system should be able to improve the bearing capacity of the structural member and, at the same time, to assure mechanical and material compatibility. The use of Fabric Reinforced Cementitious Matrix (FRCM) composites is now recognized to be suitable for these purposes. Indeed, the inorganic matrix has comparable properties with respect to the existing historical mortars while the fabric has relevant tensile strength. At the same time, these systems assure satisfactory level of reversibility (or at least removability). In this scenario, the present research aims to investigate the FRCM-confinement of masonry columns focusing on the influence of specific parameters, still poorly investigated, in order to deeply understand their effect on the mechanical response. In particular, the experimental variables are: the type of masonry substrate (Tuff and clay brick with lime-based mortar), the type of FRCM system (glass dry mesh + lime-based mortar and steel mesh + lime-based mortar) and the number of plies (1, 2 and 3). In addition, a detailed experimental characterization of the utilized materials has been carried out, including bond tests between the reinforcement and the substrate. The results evidenced that the FRCM is an effective solution for masonry columns confinement once a proper design is performed, taking into account all involved parameters. The different strengthening systems exhibited different failure modes. Generally, a single ply of external reinforcement produced a negligible increase of bearing capacity. Both strengthening systems applied with multi-ply strengthening schemes produced a significant increase in terms of strength and ultimate axial deformation. This benefit was observed for both Tuff and clay masonry columns. Two available design-oriented formulas, reported in the Italian CNR (National Research Council) and ACI (American Concrete Institute) guidelines have been utilized, in order to further investigate their accuracy, mostly in the case of multi-layered reinforcement. The performed comparisons highlight that the two design relationships provide similar and accurate results when referred to the GFRCM (Glass-FRCM) system in 1- and 2-layer configurations, while the predictions appear conservative when 3 layers of GFRCM are utilized, for both masonry types. Considering the SRG (Steel Reinforced Grout) system, the results predicted by the two models are more scattered, mostly when the number of layers increases. In addition, the formulation proposed by CNR appears more accurate in the case of Tuff masonry while the ACI predictions are closer to the experimental results in the case of clay brick masonry.

Steel Reinforced Polymer (SRP) systems, consisting of Ultra High Tensile Strength Steel cords and epoxy resin, are emerging as an effective and cost efficient solution for the externally bonded strengthening of structures. Their applications in civil engineering are more recent than those with Fibre Reinforced Polymers (FRP) employing carbon, glass or aramid textiles, and their mechanical properties still need to be deeply investigated. This paper presents an experimental study on SRP reinforcements comprising textiles with 4, 12 and 18 cord/in density. First, the mechanical properties of both textiles and SRP composites were derived through direct tensile tests. The shear bond behaviour, which is crucial for the effectiveness of most applications, was then investigated on strong and weak concrete, tuff, clay brick and brick masonry substrates, providing information on bond strength, failure mode, load-slip response and effective transfer length. Finally, test results and data available in the scientific literature are collected to calibrate the tuning coefficients for the estimate of the bond strength according to the design relationships provided by the Guidelines on FRP. © 2016 Elsevier Ltd.

Corrosion of steel reinforcement is one of the principal causes of deterioration in concrete structures. Corrosion mechanisms are accelerated by the presence of cracks which represent a preferable way for ingress of water and aggressive agents. Fibers embedded into concrete matrix generally reduce the crack widths of ordinary reinforced concrete structural elements and hence may improve durability of reinforced concrete structures especially of those exposed to aggressive environments. To date quantitative results on the effect of fibers on durability of cracked RC members under service loads is still lacking in the literature. The present research aims at studying the influence of fibers on durability of ordinary reinforced beams exposed in a coastal area under sustained load. Durability tests were performed in order to assess the influence of the presence of fibers on carbonation depth and chloride content.