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.

In the last decade, Fibre Reinforced Cementitious Matrix (FRCMs) became an interesting inorganic alternative to the widespread organic-based Fibre Reinforced Polymers (FRPs). FRCMs are more appealing as retrofitting materials for masonry structures thanks to their generally better compatibility to existing masonry substrates, especially when lime-based matrices are used. In this framework, two FRCMs were tested to evaluate their tensile and shear bond mechanical behaviours, when applied to brick masonry prisms. One FRCM was made of a hydraulic lime mortar coupled with an alkali-resistant glass fibre mesh, while the other was made of a latex-modified cement mortar coupled with a carbon mesh. Tensile tests and single lap shear tests were performed to characterize the relevant strengths of the two FRCMs. The objective was the definition of the basic design parameters for the appraisal of the two FRCMs as strengthening inorganic composite materials for masonry structures. In this paper, the experimental results will be presented and discussed with the definition of the tensile and bond design strengths of the two FRCMs. An example of application with related normalized cost estimations is also provided; it showed that the best trade-off of mechanical performance and cost-effectiveness was given by the carbon mesh FRCM.

This paper presents the results of an experimental program carried out to study the behavior of brick masonry columns confined by steel reinforced grout (SRG) comprised of continuous steel fiber cords embedded in a cementitious matrix. Short brick masonry columns with a square cross-section confined by SRG jackets were subjected to a monotonic concentric compressive load. Parameters investigated in this study were the area weight of steel fibers and the masonry column corner radius. Results show that the SRG jackets increased the compressive strength of the masonry columns by 26-42% relative to the unconfined masonry columns. The compressive strength of the confined columns increased slightly with increasing corner radius ratio and with increasing fiber area weight.

Repair and strengthening of concrete and masonry structures using fabric-reinforced cementitious matrix (FRCM) and streel-reinforced grout (SRG) are emerging technologies in the industry allowing engineers and contractors to effectively remove deficiencies, improve structural performance and prolong life of existing concrete or masonry structures. FRCM is a composite consisting of one or more layers of cement- or hydraulic-based matrix reinforced with dry fibers in the form of open fabric. Similarly, SRG consists of a matrix reinforced with cords of twisted micro steel wires woven to form a fabric (mesh). Acceptance Criteria AC434 was published to provide guidelines for the evaluation of FRCM/SRG strengthening of concrete and masonry structural elements because the building codes in the USA do not have requirements for testing and determination of structural capacity, reliability and serviceability of this class of composite technologies. AC434 establishes requirements for testing and calculations that can lead to the issuance of a product research reports as evidence of a product’s building code compliance. This paper summarizes and presents the key features of AC434 and its relationship to ACI committee 549.4R, the guide to design and construction of externally bonded FRCM and SRG systems for repair and strengthening concrete and masonry structures.