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.

To enable a widespread industrial application of carbon reinforced concrete, a reliable characterization of material properties, such as the tensile strength and bond behavior of the composite material, has been established using standard test methods. To allow for an even wider range of application, the fatigue behavior and corresponding appropriate test methods were examined in this paper. A test method along with an experimental setup for determining both static and cyclic tensile behavior is presented. Test results using the proposed methods are shown and discussed. Based on the results of cyclic tests of a reference load combination, load frequency as well as load level were varied and their influence is documented in this paper. Finally, the temperature development during cyclic tests is documented for one test specimen. Based on these results, future research opportunities are presented.

In the last decade, Fibre Reinforced Cementitious Matrix (FRCMs) became an interesting inorganic alternative to the widespread organic-based Fibre Reinforced Polymers (FRPs). FRCMs are more appealing as retrofitting materials for masonry structures thanks to their generally better compatibility to existing masonry substrates, especially when lime-based matrices are used. In this framework, two FRCMs were tested to evaluate their tensile and shear bond mechanical behaviours, when applied to brick masonry prisms. One FRCM was made of a hydraulic lime mortar coupled with an alkali-resistant glass fibre mesh, while the other was made of a latex-modified cement mortar coupled with a carbon mesh. Tensile tests and single lap shear tests were performed to characterize the relevant strengths of the two FRCMs. The objective was the definition of the basic design parameters for the appraisal of the two FRCMs as strengthening inorganic composite materials for masonry structures. In this paper, the experimental results will be presented and discussed with the definition of the tensile and bond design strengths of the two FRCMs. An example of application with related normalized cost estimations is also provided; it showed that the best trade-off of mechanical performance and cost-effectiveness was given by the carbon mesh FRCM.

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.

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.