International Concrete Abstracts Portal

The compressive strength of glass fiber-reinforced polymer (GFRP) rebars is investigated and a new test method is proposed. The program consists of three test series. In Test Series 1, the strengths and weaknesses of the test methodology outlined in ASTM D695-15 were explored. Specimens with varying length-to-diameter ratios were prepared and tested. Premature failure was observed, and longitudinal splitting was the dominant failure mode. Test Series 2 aimed to prevent failure initiation at the ends by using steel clamps. The clamps confined the specimen ends and prevented failure propagation. The compressive strengths showed an average of around 70% the tensile strength. In Test Series 3, an advanced fixture was designed to overcome the limitations of the previous series by including clamping parts and vertical steel bars. Three different loading speeds were employed, and an average compressive strength of 75% of the tensile strength was found. The tests were followed by a statistical analysis indicating a significant difference between the results of the three test methods. The proposed test method offers a practical and reusable approach for evaluating the compressive strength of GFRP rebars. However, further analysis is recommended for a more comprehensive understanding of the compressive behavior of these rebars.

This study explores technological advancements enabling the utilization of GFRP bars in concrete structures, particularly in coastal areas. However, GFRP bars often encounter reduced bend strength at specific bend locations, which may pose a challenge in their practical application. Various properties such as the strength of bent GFRP bars are crucial for quality assurance, yet existing testing methods stated in ASTM D7914M-21 and ACI 440.3R-15 have limitations when applied to different GFRP bent shapes. Furthermore, those methods require special precautions to ensure symmetry and avoid eccentricities in specimens. To address these challenges, CSA S807:19 introduced a simpler standardized testing procedure that involves embedding a single L-shaped GFRP stirrup in a concrete block. However, the specified large block size in CSA S807:19 Annex E may pose difficulties for both laboratory and on-site quality control tests. Therefore, CSA S807:19 Annex E (Clause 7.1.2b) permits the use of a customized block size, as long as it meets the bend strength of the FRP bars without causing concrete splitting. To date, very few prior research has explored the use of custom block sizes. Therefore, this study aims to thoroughly investigate the strength of bent FRP bars with custom block sizes and without block confinement. Such an investigation serves to highlight the user-friendliness and efficiency of the CSA S807:19 Annex E method. The study recommends two block sizes: 200x400x300 mm (7.87x15.75x11.81 in) for bars <16 mm (0.63 in) diameter and 200x200x300 mm (7.87x7.87x11.81 in) for bars <12 mm (0.39 in). Additionally, the study cautions against using confinement reinforcement, especially with smaller blocks, as it could interfere with the embedded bent FRP bar. Furthermore, the study suggests incorporating additional tail length to mitigate the debonding effects resulting from fixing the strain gauges to the bent portion of the embedded FRP bar. By exploring these modifications, the study seeks to enhance the effectiveness of the testing procedure and expand its practical application for both laboratory and on-site quality assurance. The findings hold implications for the reliable testing of GFRP bars' strength, advancing their use as reinforcement in concrete structures.

The first phase of this work uses experimental evidence to critique some shortcomings of the so-called improved double-lap bond shear tests regarding their limited application to wet layup fiber-reinforced polymer (FRP) and their inapplicability to pultruded FRP laminates. Even in the case of the wet layup FRP, the study provides some evidence of high chances of obtaining undesirable fiber rupture that preclude the use of the results as reliable means for interpreting the FRP-concrete bond-slip models. Further proposed modifications to overcome these challenges are provided by designing a convertible bond tester applicable to both wet layup and pultruded FRP laminates. Apart from the application of the apparatus to FRP-concrete bond assessment under pure double shear, it proved to be applicable to conducting mixed-mode bond tests. The second phase of the work upgrades the so-designed test apparatus to make it convertible to bond testing of other variants (near-surface mounted [NSM] FRP bars/strips, fiber-reinforced cementitious mortar [FRCM], etc.) of strengthening systems without developing a different apparatus for each. The apparatus allows testing the NSM FRP-concrete bond in a novel manner compared to the traditional practice. Also, given the absence of mixed-mode studies for FRCM, the apparatus provides a pioneer means of conducting the same.

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.

This paper presents the crack monitoring of reinforced concrete beams strengthened with fiber reinforced polymer (FRP) sheets. Emphasis is placed on the development of a smart FRP bonded material that can measure the crack opening of a reinforced concrete beam strengthened by FRP. The reliability measured by a conventional digital image correlation (DIC) and by the proposed smart FRP is employed to assess the contribution of the FRP to control the crack. The monitoring process is based on a large set of experimental database consisting of 19 test beams. The effect of FRP to control the crack opening is studied depending on the steel ratio, FRP ratio and the level of damaged of RC beams when FRP is applied. The results were compared with the theoretical values of crack width and spacing predicted using the Eurocode 2 (EC2) formula, calibrated for non-strengthened RC elements. The corresponding results were compared in order to clarify the effect of external bonded FRP on the cracking behaviour of RC beams.