With the aging and deterioration of infrastructure, the need for repair, strengthening, and rehabilitation of existing structures continues to increase. Climate change makes extending the service life of our infrastructure critical since any demolition and new construction will trigger substantial amounts of carbon emissions. Research related to repairing and strengthening existing infrastructure is seeing major developments as new green materials and technologies become available. Improved assessment and retrofit of deficient structures, and performance-based design of new structures are also in high demand. Despite the progress, there are many challenges yet to be addressed. The main objective of this Special Publication is to present results from recent research studies (experimental/numerical/analytical) on the retrofit and repair of structural elements along with the assessment, analysis, and design of structures. Several of these papers were presented at the ACI Fall Convention “Seismic Repair/Retrofit/Strengthening of Bridges at the Element or System Level: Parts 1 and 2.” The presented studies cover various aspects of structural retrofitting and strengthening techniques including the use of rubberized engineered cementitious composite for enhancing the properties of lightweight concrete elements, high-performance concrete jacketing to strengthen reinforced concrete piers/columns, and the behavior of fiber-reinforced-polymer-wrapped concrete cylinders under different environmental conditions. Additionally, the research explores the behavior of concrete-filled FRP tubes under axial compression, innovative bridge retrofit technologies, and retrofit techniques for deficient reinforced concrete columns. There is also a focus on evaluating the seismic response of retrofitted structures, designing guidelines for seismic retrofitting using tension-hardening fiber-reinforced concrete, strengthening unreinforced masonry walls with ferrocement overlays, and developing seismically resilient concrete piers reinforced with titanium alloy bars. The seismic response of a retrofitted curved bridge was also presented where elastomeric bearings of the as-built bridge were replaced by high damping rubber bearings as a part of the seismic retrofit. Recommendations for nonlinear finite element analysis of reinforced concrete columns under seismic loading are also presented to simulate their behavior up to collapse. Overall, the presented studies in this Special Publication demonstrate the potential of new materials, methods, and technologies to improve the performance of various structural elements under different loading conditions, including seismic and environmental loads. These studies are expected to help our practitioners and researchers not only develop more effective and sustainable methods for repairing and strengthening of structures but also improve their analysis and design skills.

Unreinforced masonry (URM) structures are very common in South Asian countries. They can sustain vertical loads but are vulnerable against lateral loadings. This paper presents review of previously performed research on wall unit, reduced scale model and full-scale model of URM structures retrofitted with ferrocement. Researchers of Bangladesh, over the last five years, have implemented ferrocement overlay retrofitting on URM structures using indigenous materials. The research covered examining the performance of unit wall (without frame), half scale wall, full scale wall, and half scale room of retrofitted URM. The present study describes the differences in the experimental set ups and loading patterns of these studies, examines the lateral loading capacity determined in these studies and compares the failure patterns observed in the tests to the theoretically predicted ones. Finally, the paper compares performance in terms of load bearing capacity, cumulative energy consumption and stiffness degradation per cycle. It is found that previous studies were consistent in showing that ferrocement retrofitting using 18-gauge wire having mesh opening of 12.5 mm [0.5 in] x 12.5 mm [0.5 in] can improve the load bearing capacity of a wall by 40-50%, and the energy consumption before failure increases 1.4 times the reference unreinforced structure.

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.

This paper reviews progress spanning a period of about four decades during which the author was intimately involved in research and teaching in three distinct yet related fields of civil engineering: prestressed concrete, fiber reinforced concrete, and ferrocement and thin cementitious products. In retrospect and for each area, key contributions are mentioned, milestones recalled, and prospects for the near future envisioned. Issues related to partial prestressing, external prestressing, high performance fiber reinforced cement composites, strain-hardening FRC composites, 3D textiles and the like are addressed. Technical advances are webbed with some personal milestones as well. Important research issues to address in the near future are pointed out.

The main advantage of textiles as reinforcements in cement-based composites is in the enhancement of mechanical behavior. Textile-reinforced concrete (TRC) has emerged as a novel composite with various potential applications in non-structural and, more recently, structural building materials, including thin and slender elements, repair, and strengthening of existing structural members. The wide variety of textile production methods allows great flexibility in textile design, which enables controlling of textile geometry, yarn geometry, and orientation of yarns in various directions. This diversity is advantageous in the development of cement-based composites and allows engineering of the performance of the final products for the desired requirements. Recognizing the increasing research interest in thin fiber-reinforced cement-based composites using fabrics and hybrid systems (fabrics + chopped fibers) and their emerging industrial applications in the last years, there has been a close communication and collaboration between ACI Committee 549, Thin Reinforced Cementitious Products and Ferrocement, and RILEM TC 201, Textile Reinforced Concrete (TRC), in the area of TRC. Following two two-part technical sessions, held at the 2005 ACI conventions in New York and Kansas City, ACI Committee 549 sponsored the technical session “Design and Applications of Textile Reinforced Concrete” at the ACI Fall 2007 Convention in Puerto Rico. Seven papers were presented by invited international experts from Germany and co-authored by members of RILEM TC 201. This Special Publication (SP) contains seven papers that provide insight into the state-of-the-art design and application of TRC. The topics of the papers cover the following: materials aspects related to serviceability; strength and damage accumulation; TRC for flexural strengthening of reinforced concrete structures – structural behavior, design model, and application for a concrete shell; use of TRC as a subsequently applied waterproof structure; application of TRC for lightweight structures; and sandwich panels with thin-walled TRC facings for structural exterior walls and nonstructural façades. The papers included in this publication have been peer reviewed by international experts in the field according to the guidelines established by the American Concrete Institute. The future of thin fiber and textile-reinforced cementitious systems depends on their ability to compete with existing solutions and to identify new applications. Efforts are required in the areas of process, design, and implementation in industrial and full-scale applications of TRC. On behalf of ACI Committee 549, the editor would like to thank all the authors for their contributions and the reviewers for their assistance and valuable suggestions and comments.