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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.

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.

Textile-reinforced concrete (TRC) is a composite material resulting from the combination of finegrained concrete and textile reinforcement, widely used to strengthen existing structures. In addition, TRC is an alternative to obtain lighter and thinner structures. However, the behavior of these structures depends on the properties of the matrix and fiber used, as well as on the interface between these two phases. In this work, the interface properties of SBR-based carbon textile-reinforced concrete as supplied and after sand-coating treatment are evaluated through pullout tests. Then, to assess the bending behavior of structural members, four-point bending tests were performed on I-section beams using textiles with and without surface treatment. To analyse the evolution of cracking, digital image correlation (DIC) technique was used. The effectiveness of epoxy-sand treatment surface in textile reinforcement improve the bond between textile as well matrix as the failure mode of TRC beams and was confirmed by improved interface properties, i.e. a stiffer and stronger interface was obtained. In addition to the improved crack pattern, it was observed smaller and less spaced cracks.

In 2017, the Rilem Technical Committee 250-CSM coordinated a Round Robin initiative, in which 19 research institutions tested 28 Fabric Reinforced Cementitious Matrix (FRCM) composites, with the support of 11 industrial partners. Two years after the publication of the first papers on the results of this wide investigation, it is still worth further analysing its outcomes to highlight the fundamental properties of mortar-based reinforcements and give an overview of the various available fabrics and matrices, which are currently used in structural rehabilitation activities. Equally, a better understanding still needs to be gained on the causes of the variability observed in test results. These include the quasibrittle behaviour of the inorganic matrix and its sensitivity to manufacturing, curing and handling. Test implementation, such as gripping method and measuring techniques, also plays a crucial role in the reliability and repeatability of experimental outcomes.

Fabric reinforced cementitious matrices (FRCM) or textile reinforced concrete (TRM) are being developed for various practical application areas by number of research groups. The properties of the composite depend on the properties of fabric and matrix and the matrix-fabric interface. Fabric-reinforced cementitious matrices provide high strength and toughness composite for applications in construction industry. In this experimental study, mechanical properties of glass and carbon fabric reinforced Ultra High-Performance Concrete (UHPC) as well as the performance of FRCM with lower strength mortar were investigated. Glass fabrics, sand coated SBR and only SBR coated carbon fabrics were used as reinforcements. In this context, compressive strength tests on matrices and, tensile tests on composites were performed. Fibermatrix interfaces were examined and effects of the interface on the composite mechanical properties were also evaluated by scanning electron microscopy. Main result obtained from the study indicates that: the characteristic values of composites produced with ultra-high strength cementitious matrix under tension were higher than the characteristic values of composites produced with lower strength matrix. The difference is higher in the composite with carbon fabric. This difference is attributed to the higher strength and higher adherence of the fiber-matrix interface in the high strength matrix composite.