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This SP is the result of two technical sessions held during the 2017 ACI Spring Convention in Detroit, MI. Via presentations and the resulting collection of papers, it was the intention of the sponsoring committees (ACI Committees 549 and 562 together with Rilem TC 250) to bring to the attention of the technical community the progress being made on a new class of repair/strengthening materials for concrete and masonry structures. These materials are characterized by a cementitious matrix made of hydraulic or lime-based binders, which embeds reinforcement in the form of one or more fabrics also known as textiles. The great variability of fabric architectures (for example, cross sectional area, strand spacing, and fiber impregnation with organic resin) coupled with the types of material used (aramid, basalt, carbon, glass, polyparaphenylene benzobisoxazole (PBO) and coated ultra-high strength steel) makes the characterization, validation, and design of these systems rather challenging. Irrespective of the reinforcement type (synthetic or ultra-high strength steel), the impregnating mortar is applied by trowel or spray-up. It should also be noted that fabric reinforced cementitious matrix and steel reinforced grout, in particular, are very different from other repair technologies such as FRC (fiber reinforced concrete) and UHPC (Ultra High-Performance Concrete) in that they utilize continuous and oriented reinforcement. In a sense FRCM and SRG can be viewed as the modern evolution of ferrocement.

The use of Externally Bonded Reinforcement (EBR) techniques is widely increasing in the last decades to strengthen both masonry and RC constructions. The use of different EBR configurations is well established also in the refurbishment of historical masonry constructions. The performance of different EBR techniques applied on existing historic masonry vaults was investigated in this work by means of in-situ destructive tests. The brick barrel vaults were located in Castel San Pietro, Verona (Italy) and were 5.6 m span, 1.1 m rise and 27 cm thick. The research focuses on inorganic applications by textiles and lime mortar matrix. In one case by steel reinforce grout and in the other with basalt textile reinforced mortar. Another system was based on common organic matrix. In addition to the experimental results of the static destructive tests of each vault that are discussed in order to evaluate the different response of such applications in terms of strengthening and ductility, a discussion on analytical models regarding the cross section and than the entire vaults are also provided with the aim to define the ultimate load reached by a strengthened vault. Such unique in-field opportunity allowed also some considerations in terms of efficacy and workability of mortar matrices.

Fiber-Reinforced Cementitious Matrix (FRCM) composites are becoming a widespread technology for the rehabilitation and strengthening of historic masonry and reinforced concrete structures due to some advantages that allow them to be a suitable alternative to Fabric-Reinforced Polymer (FRP) composites. In this work, a new family of FRCM composites system made of ultra-high strength steel cords installed with either hydraulic lime or cement based mortars named Steel Reinforced Grout (SRG) is presented. This paper briefly introduces to the main properties and mechanical characteristics of SRGs, and introduces case studies on masonry and reinforced concrete structures demonstrating the different field applications of this new and effective strengthening solution.

Unreinforced masonry construction are typically prone to brittle failures due to the nature of their constituent materials, and in many cases their strength is related to the shear strength of the primary walls. In regions affected by intense seismic events, the presence of heritage construction made by poor masonry, strongly enhance this type of vulnerability. The recent earthquakes that occurred in the past ten years in the Eurasian regions drew the attention of researchers and engineers in this sense, since entire cities formed by ancient masonry buildings were affected by extensive disasters and human losses. In order to find an effective solution to these important structural problems, composite materials in forms of Fiber Reinforced Polymers (FRP) were found to be effective and attractive in many cases, showing a good applicability both in reinforced concrete (RC) buildings and masonry construction. In this last case they are well accepted in modern masonry construction, but the use of epoxy resin as matrix and adhesive, combined with high performance fibers (i.e. carbon) have shown some limitations in the field of heritage masonry construction, in which the substrate is very poor. In this perspective two main issues obstacle an effective use of FRP: the mechanical compatibility and the saturation of the surface respect to transpiration of humidity. For these reasons in Europe there are some real applications of heritage masonry buildings in which the use of FRP is not welcome by the authorities that are asked to evaluate the strengthening proposals The problem of the mechanical compatibility is due to the differences between the stiffness and strength of the fibers (typically carbon) and the properties of the masonry substrate which may be 10-3 times those of the fibers. The problem of breathability is due to the fact that polymeric resins create an impermeable jacket which interrupts the cycle of humidity transpiration through the masonry. This may lead to a degradation of the masonry, in the long terms, because of the saline formations. For these reasons the use of a new generation of fibrous materials named as Fiber/Fabric Reinforced Cementitious Matrix (FRCM) was introduced, in order to use long reinforcing fibers into an inorganic matrix based on lime or cement mixes. These new materials have lower mechanical properties respect to FRP composites, but they show higher compatibility with poor masonry. The present manuscript illustrates the results of an extensive experimental campaign, in which masonry panels, made with limestone and poor hydraulic mortar, were tested under diagonal shear forces, until failure. The panels were tested in unreinforced configuration, then different FRCM reinforcement systems were applied and tested to compare the respective results. Both single wall and double wall panels were tested in order to represent different cases found in real applications. Totally thirty specimens were tested. The results, illustrated and discussed in the paper, show the significant increase in terms of mechanical properties that was measured in all cases of FRCMstrengthened walls. Due to the use of different mortars and fibrous systems some differences in terms of failure modes and damage at failure will be shown, even if it is reasonable to believe that for the type of masonry tested herein, all the strengthening methods resulted tremendously effective in terms of load capacity and energy dissipation, without showing a sudden brittle collapse.

An innovative option to reinforce existing masonry buildings or to increase the load-bearing capacity of new ones subjected to lateral loading caused by wind or earth pressure is to apply textile reinforcement in render on the masonry surface or in mortar in the bed-joint. This idea is based on the new material “textile reinforced concrete” (TRC). However, due to the specific characteristics of masonry compared to concrete, it is necessary to find suitable textiles for the use in combination with the masonry unit, mortar and render. To achieve a deeper knowledge on the performance of this composite material, an extensive experimental study is currently carried out. The main objectives are to identify suitable reinforcing materials as well as to describe the load-bearing and deformation behavior of textile reinforced masonry under lateral load and hence to derive a design model. Within this study tests are conducted on small-scale composite specimens under tensile, shear and flexural load, from which the needed parameters for the design model shall be defined. Basic part of these tests is the investigation of the bond behavior between textile reinforcement and mortar/rendering under tensile load, for which a new test method for TRC was implemented. From large scale tests on masonry walls subjected to lateral loading, the effectiveness of strengthening masonry externally with textile reinforced render will be assessed.