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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.

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.

The increasing interest in the field of conservation of existing masonry structures pushed to the development of new retrofitting technologies in the recent past. One of the most promising is the use of Fabric Reinforced Cementitious Mortar (FRCM), which consists of an open-grid within an inorganic matrix. The effectiveness of the FRCM-application is well-demonstrated in literature by several experimental investigations regarding different structural members, including columns and shear wall. The success of FRCMs is manly related to durability aspects, since the grid is generally non-metallic, the compatibility of the inorganic matrix with the substrates, the easy application, the low weight and spatial impact, the possible installation in damp areas and at high temperatures. The interaction between the substrate, the mortar-based matrix and the open-grid make challenging the theoretical prediction of the mechanical behavior of the FRCM-retrofitted structures. For this reason, the analytical formulations for the proper design of FRCM-strengthening are still an open research problem, referring to both short and long term conditions. The present paper reports and discusses design-oriented relationships for FRCM-confinement and in-plane FRCM-strengthening of masonry elements; the proposals are intended to satisfy the requirements of simplicity and accuracy needed for code-finality.

Externally bonded (EB) steel reinforced grout (SRG) composites have the potential to improve the flexural and shear performance of existing concrete and masonry structural members. However, one of the most commonly observed failure modes of SRG-strengthened structures is due to composite debonding, which reduces composite action and limits the SRG contribution to the member load-carrying capacity. This study investigated an endanchorage system for SRG strips bonded to a concrete substrate. The end anchorage was achieved by embedding the ends of the steel cords into the substrate. Nineteen single-lap direct shear specimens with varying composite bonded lengths and anchor binder materials were tested to study the effectiveness of the end-anchorage on the bond performance. For specimens with relatively long bonded length, the end-anchorage slightly improved the performance in terms of peak load achieved before detachment of the bonded region. Anchored specimens with long bonded length showed notable post-detachment behavior. Anchored specimens with epoxy resin achieved load levels significantly higher than the peak load before composite detachment occurred. For specimens with relatively short bonded length, the end-anchorage provided a notable increase in peak load and global slip at composite detachment. A generic load response was proposed for SRG-concrete joints with end anchors.