International Concrete Abstracts Portal

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 interest in retrofit/rehabilitation of existing concrete structures has increased due to degradation and/or introduction of more stringent design requirements. This work focuses the attention on the shear capacity of reinforced concrete beams strengthened with different FRCM (Fiber Reinforced Cementitious Matrix) systems. The shear performances of strengthened beams are analyzed by experimental results available in the literature. To evaluate the influence of the main factors (geometrical and mechanical) on the structural response on FRCM shear strengthened reinforced concrete beams, a critical discussion of experimental results is given. A semi-empirical analytical model, able to predict the shear capacity of strengthened beams, is proposed and its predictions were compared with those furnished by both Code models (ACI model, CNR DT model, fib model) and experimental results. A numerical procedure founded on a FE model is, also, developed and adopted to simulate the shear response of FRCM shear strengthened reinforced concrete beams. The effectiveness of the numerical procedure is, then, verified by a comparison in terms of both load-displacements response and shear capacity with experimental results.

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.

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.

Steel reinforced grout (SRG) systems consist of high strength steel cords or fabrics embedded in a mortar or grout matrix; these are typically utilized as external reinforcement of existing reinforced concrete (RC) or masonry structures. Despite extensive experimental investigations conducted so far, reliable answers concerning their tensile, bond strength, strain to failure and stiffness properties seem still incomplete mainly due to their heterogeneous nature; this represents a limit for the design, standardization process and applications of such a system. These limiting aspects are also of a major interest in comparison with similar strengthening systems, namely textile reinforced matrix (TRM), in which the reinforcing system is typically made of a fiber reinforced polymer (FRP) bi-directional grid rather than steel cords. This study deals with an experimental investigation on the tensile behavior of SRG and TRM systems, focusing on the mechanical aspects related to the different scales of the strengthening system itself, i.e. reinforcement and composite system. The tensile tests are carried out on two different SRG systems manufactured with two different matrix types. Typical glass TRM systems are also considered in this study for comparison purposes. Based on the experimental outcomes, some analytical interpretations are provided.