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.

An innovative option to reinforce existing masonry buildings or to increase the load-bearing capacity of new ones subjected to lateral loading caused by wind or earth pressure is to apply textile reinforcement in render on the masonry surface or in mortar in the bed-joint. This idea is based on the new material “textile reinforced concrete” (TRC). However, due to the specific characteristics of masonry compared to concrete, it is necessary to find suitable textiles for the use in combination with the masonry unit, mortar and render. To achieve a deeper knowledge on the performance of this composite material, an extensive experimental study is currently carried out. The main objectives are to identify suitable reinforcing materials as well as to describe the load-bearing and deformation behavior of textile reinforced masonry under lateral load and hence to derive a design model. Within this study tests are conducted on small-scale composite specimens under tensile, shear and flexural load, from which the needed parameters for the design model shall be defined. Basic part of these tests is the investigation of the bond behavior between textile reinforcement and mortar/rendering under tensile load, for which a new test method for TRC was implemented. From large scale tests on masonry walls subjected to lateral loading, the effectiveness of strengthening masonry externally with textile reinforced render will be assessed.

In this study, the behavior of concrete compressive members confined by steel reinforced grout (SRG) is investigated. An experimental study was carried out to understand the behavior of short concrete prisms with a square cross-section confined by SRG subjected to a monotonic concentric compressive load. Test parameters considered in this study are the density of steel fibers, number of layers, corner condition, number of overlapping faces, and length of the reinforcement. The effectiveness of the confinement is evaluated in terms of peak stress with respect to unconfined prisms. SRG confinement is shown to improve the compressive strength of concrete prisms relative to the unconfined condition. An increase in the number of confinement layers results in an increase in the compressive strength and energy absorption.

A shake table investigation was carried out on a full-scale U-shaped masonry assemblage to study the effectiveness of Steel Reinforced Grout (SRG) for the improvement of the out-of-plane seismic capacity of masonry walls. Natural accelerograms were applied with increasing scale factor up to failure. A first session of tests was performed on the unreinforced specimen, that collapsed by out-of-plane overturning. Steel tie bars were then installed to prevent overturning. In this case, severe damage developed due to bending. Finally, the wall was retrofitted with horizontal strips of Ultra High Tensile Strength Steel cords, externally bonded to the masonry with lime based mortar, and steel connectors. SRG led to a significant improvement of the seismic capacity, strongly limited damage development, and entailed small modifications of the dynamic properties of the specimen. Since the reinforcement had a thickness of less than 10mm, it is suitable for applications within the plaster layer during the maintenance work of the façades without modifying their appearance.

The use of Fiber Reinforced Polymer (FRP) strengthening systems for reinforced concrete (RC) members represents nowadays an effective alternative to traditional strengthening techniques. Recently, a new class of composites have emerged known as Steel Reinforced Grout (SRG), consisting of steel fibers embedded in an inorganic matrix and applied by using manual techniques and traditional handcraft. An experimental campaign was recently carried out that aims at assessing the performance and effectiveness of SRG strengthening systems to improve the flexural behavior of RC slabs. The present work uses the experimental results to validate the numerical prediction of a FEM code, developed by the authors, to analyze the flexural behavior of SRG-strengthened slabs. The cross-sectional response is obtained using a fiber-model equipped with a plasticity model for rebars, a continuumdamage model for SRG, and a plastic-damage model for concrete. Overall, the numerical predictions are in good agreement with the experimental results. The model reproduces with acceptable accuracy the nonlinear behavior of the tested strengthened beams, as well as the failure point both in terms of failure modes and ultimate strength and displacement. In some cases, slight differences can be found between the numerical and experimental results. These differences are discussed in this work.