International Concrete Abstracts Portal

Fiber reinforced polymer (FRP) composite rebar is a non-metallic concrete reinforcement alternative that has been successfully deployed in hundreds of structural applications globally. The increasing demand for FRP rebar as a metal alternative is driven by its unique value proposition, including lightweight, high strength, magnetic transparency, and most significantly, corrosion resistance. FRP rebar is fabricated through pultrusion, a high throughput composite fabrication process in which, resin-impregnated fiber undergoes rapid cure when pulled through a heated furnace. Considering the open nature of the open pultrusion process, expansion of production capacity for FRP rebar manufacturing demands the use of advanced resins that are free from Volatile Organic Compounds (VOCs), enable high throughput production, and deliver an outstanding translation of fiber properties following cure. In this work, we will present an epoxy system that is inherently VOC Free and is tailored to enable high throughput manufacturing of glass fiber reinforced polymer (GFRP) rebar at scale. Furthermore, the rapid formation of highly crosslinked structures achieved with this resin system during pultrusion is found to enable outstanding fiber property translation resulting in high modulus (>70 GPa) and corrosion resistance (>80 % tensile strength retention without load) that exceeds existing standards such as ASTM D7957.

Fabric-reinforced cementitious matrix (FRCM) is a new class of composite materials that raised great interest in the last years as a promising technique to upgrade, strengthen and rehabilitate concrete or masonry structures. FRCM systems are constituted by a structural reinforcement fabric, consisting of an open grid of perpendicularly connected multifilament yarns (usually made of carbon, glass, or basalt fibers), applied on concrete or masonry structural elements through a cement- or lime-based matrix. In this study, the effects of using different surface treatments on dry carbon yarns have been evaluated, both considering mechanical performances and durability. Three different surface treatments have been investigated, the first two consisting of yarns pre-impregnation with epoxy resin or nano-silica coating while the third one is a process of fibers oxidation. Tensile tests on carbon yarns and pull-out tests have been carried out to evaluate the effects of the treatments both under normal environmental conditions and after artificial exposure in saline and alkaline environments.

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.

Fiber reinforced cementitious matrix (FRCM) composites have gained popularity for strengthening of concrete structures due to their capacity to overcome some drawbacks of fiber reinforced polymer (FRP) composites, mainly related to the use of epoxy resins. Research on the topic has shown that FRCM composites can increase the axial, flexural, shear, and torsional capacity of concrete elements. However, experimental studies are still limited, and an important effort is required to develop accurate and reliable design models to predict the contribution of the system to the capacity of strengthened elements. In this paper, a quantitative review of experimental studies of axially loaded concrete elements confined with FRCM composites is presented. The influence of selected variables on the increase in axial capacity of the strengthened specimens is evaluated. Three available design models for predicting the increase in axial capacity of FRCM-strengthened concrete are assessed using a database compiled by the authors. Results show that confinement with FRCM composites can provide a significant increase in axial strength for both cylindrical and prismatic concrete specimens. Further efforts are needed to improve the performance of models to predict the axial strength and behavior of FRCM-confined concrete.

Experiments were performed on two RC columns taken from a school building that was originally constructed in 1963. The columns were subjected to reverse loading with displacement control under constant axial load. Both columns were designed with a common shear span length of 1200 mm for the validation of shear capacity equations currently used for seismic evaluation. The concrete of both columns exhibited honeycombs. Thus, one column was repaired with epoxy resin injection, and the effect of retrofitting was investigated. The columns did not exhibit significantly different crack patterns. The collapse mechanism of the two columns were shear failure, and the shear force drift angle response was considerably brittle. The observed values of the original column could be predicted by the recommended standard equations for the strength of shear crack and shear capacity. The maximum strength and the initial stiffness of the retrofitted column were 1.18 times and 1.40 times, respectively, of those of the original column. Results indicated that epoxy resin injection improves the seismic performance of columns of the existing buildings.