International Concrete Abstracts Portal

Embedded Through-Section (ETS) method is a shear rehabilitation technique for concrete structures involving pre-drilling vertical holes into a reinforced concrete member and installing FRP bars to be bonded using epoxy adhesive. Due to the lack of reliable models for predicting the ETS FRP bond behaviour, developing an accurate model to predict the maximum pull-out force of the ETS technique was deemed a knowledge gap. In this study, the main parameters used in an analytical bond-slip model proposed by the authors were obtained empirically and evaluated against the existing experimental results in the literature. To be able to calculate the maximum pull-out force for ETS FRP bars with different materials, a fracture mechanics-based bond model was defined in terms of the joints' geometrical and material properties, to allow the model to predict the performance of any FRP type with any concrete compressive strength. By using data in the available literature on FRP ETS pull-out tests, statistical analysis was utilized to fit the parameters against experimental data. The proposed model was able to produce superior analytical predictions of the experimental test data when compared to the existing bond models for ETS FRP bars.

Three bridge barriers were tested under pseudo-static loading to assess the effectiveness of a dowelling repair technique for restoring the capacity of damaged glass fiber-reinforced polymer (GFRP) reinforced systems. Barriers were 1500 mm (59.1 in.) wide and tested with an overhang of 1500 mm (59.1 in.). One barrier was entirely reinforced with steel reinforcement with the layout and geometry common in Alberta, Canada for highway applications. A second barrier replaced all steel reinforcement with GFRP bars. The third barrier simulates repair where the barrier is damaged and needs to be replaced by removing the barrier, drilling holes, and using epoxy to dowel GFRP bars into the deck. All barriers failed by concrete splitting at the barrier/deck interface which is attributed to the complex interaction of stresses from the barrier wall and overhang. The steel reinforced barrier was strongest but had slightly lower energy dissipation than the GFRP reinforced barriers. The repaired GFRP reinforced barrier had very similar response to the baseline GFRP reinforced barrier but reached a slightly larger capacity. Previously completed finite element models showed similar general responses and failure modes but larger stiffnesses and strengths than the tests which requires further investigation.

This study evaluates the bond performance of concrete epoxy bonds using an image segmentation-based image processing technique. The Concrete Epoxy Interface (CEI) plays a crucial role in the structural performance of FRP-repaired concrete as it transfers stresses from the concrete to the epoxy. By employing the image segmentation technique, the performance of the CEI is assessed through the ratio of Interfacial Failure (IF) to other failure types, namely cohesive failure in Epoxy (CE) and Cohesive cracks in Concrete (CC). The effects of sustained loading duration on CEI bond performance are quantitatively analyzed using 21 single-lap shear (SLS) specimens and 28 notched 3-Point Bending (3PB) specimens. The findings highlight vital conclusions: CE is the least failure mode in SLS and 3PB specimens. In contrast, CC is the predominant failure mode, indicating the susceptibility of the concrete substrate in FRP-repaired concrete. Moreover, IF generally increases with longer sustained loading durations in 3PB specimens but decreases with increased loading duration in SLS specimens. The study also demonstrates the effectiveness of the image segmentation approach in evaluating CEI performance in 3PB specimens, where color distinguishes epoxy, FRP, and concrete substrate.

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.