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Sponsors: ACI Committee 549, Rilem-MCC Editors: Barzin Mobasher and Flávio de Andrade Silva Several state-of-the-art sessions on textile-reinforced concrete/fabric-reinforced cementitious matrix (TRC/FRCM) were organized by ACI Committee 549 in collaboration with RILEM TC MCC during the ACI Fall 2019 Convention in Cincinnati, OH, and the ACI Virtual Technical Presentations in June 2020. The forum provided a unique opportunity to collect information and present knowledge in the field of TRC and FRCM as sustainable construction materials. The term TRC is typically used for new construction applications whereas the term FRCM refers to the repair applications of existing concrete and masonry. Both methods use a textile mesh as reinforcement and a cementitious-based matrix component and, due to high tensile and flexural strength and ductility, can be used to support structural loads. The technical sessions aimed to promote the technology, and document and develop recommendations for testing, design, and analysis, as well as to showcase the key features of these ductile and strong cement composite systems. New methods for characterization of key parameters were presented, and the results were collected towards the development of technical and state-of-the-art papers. Textile types include polymer-based (low and high stiffness), glass, natural, basalt, carbon, steel, and hybrid, whereas the matrix can include cementitious, geopolymers, and lightweight matrix (aggregates). Additives such as short fibers, fillers, and nanomaterials were also considered. The sessions were attended by researchers, designers, students, and participants from the construction and fiber industries. The presence of people with different expertise and from different regions of the world provided a unique opportunity to share knowledge and promote collaborative efforts. The experience of an online technical forum was a success and may be used for future opportunities. The workshop technical sessions chairs sincerely thank the ACI staff for doing a wonderful job in organizing the virtual sessions and ACI TC 549 and Rilem TC MCC for the collaboration.

Textile Reinforced Concrete (TRC) has emerged in recent years as a new construction material, which is seriously considered as substitutes for traditional composite materials. However, the practical utility and design of innovative materials like TRC is hindered by the lack of standardized specifications, including required lap splice length of textile fabrics. This study aims to investigate the structural behavior of TRC members subjected to uniaxial tensile force, therefore providing knowledge for further research on determining overlap length.

Fabric-reinforced cementitious matrix (FRCM) composites are promising structural materials representing the extension of textile reinforced concrete (TRC) technology to repairing applications. Recent experiences have proven the ability of FRCMs to increase the mechanical performances of existing elements, ensuring economic and environmental sustainability. Since FRCM composites are generally employed in the form of thin externally bonded layers, one of the main advantages is the ability to improve the overall energy absorption capacity, weakly impacting the structural dead weights and the structural stiffness and, as a direct consequence, the inertial force distributions activated by seismic events. In the framework of new regulatory initiatives, the paper aims at proposing simplified numerical approaches for the structural design of retrofitting interventions on existing reinforced concrete structures. To this purpose, the research is addressed at two main levels: i) the material level is investigated on the uniaxial tensile response of FRCM composites, modeled by means of well-established numerical approaches; and ii) the macro-scale level is evaluated and modeled on a double edge wedge splitting (DEWS) specimen, consisting of an under-reinforced concrete substrate retrofitted with two outer FRCM composites. This novel experimental technique, originally introduced to investigate the fracture behavior of fiber-reinforced concrete, allows transferring substrate tensile stresses to the retrofitting layers by means of the sole chemo-mechanical adhesion, allowing to investigate the FRCM delamination and cracking phenomena occurring in the notched ligament zone. It is believed that the analysis of the experimental results, assisted by simplified and advanced non-linear numerical approaches, may represent an effective starting point for the derivation of robust design-oriented models.

A fundamental challenge for today and the future is the preservation of existing constructions. In addition to repair and maintenance measures, the effective strengthening of existing structures is of central importance to this issue. According to current regulations, a large number of existing reinforced concrete (RC) structures show deficits in their shear capacity, which is often limited by their existing shear reinforcement. The application of thin carbon reinforced concrete (CRC) layers can be a suitable and effective alternative to previously used strengthening methods. In this study, two RC T beam types, which differed in cross-section, were strengthened with CRC. The essential parameters of the strengthening layers were varied, and the influence of these changes on the load-bearing behavior and shear capacity of the T-beams was analyzed. Compared to non-strengthened test specimens, load increases of about 40% were achieved in the CRC-strengthened T beams.

Externally bonded fiber-reinforced cementitious matrix (FRCM) composites are applied to the tension side of reinforced concrete (RC) beams to increase their flexural strength. Composite action is often prematurely lost because of the debonding of the composite, which for most of the available FRCMs occurs at the matrix-fiber interface. The bond behavior is studied at the small-scale by means of single- and double-lap direct shear tests. An alternative small-scale test configuration is the beam test. Beam tests can be performed using a single notched prism with a composite strip attached to the face where the notch is located (notched beam test) or by two prisms connected by a cylindrical hinge on one side and by a composite strip on the opposite side (modified beam test). As the scientific community is discussing the best test configuration, the goal of this paper is to shed light on the differences between the two test methods. In this paper, an FRCM composite comprising polyparaphenylene benzo-bisoxazole (PBO) fibers, which exhibits debonding at the matrix-fiber interface, is subjected to single-lap shear and modified beam tests. Load responses and failure modes are compared in an attempt to provide guidance on the selection of the test method.