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    Effect of graphene oxide-coated jute fiber on mechanical and durability properties of concrete mixtures
    (Elsevier Sci Ltd, 2024) Ozen, Suleyman; Benlioglu, Arif; Mardani, Ali; Altin, Yasin; Bedeloglu, Ayse
    Various methods are applied in order to improve the mechanical properties of concrete and to provide ductility. The most common method is the addition of fiber to cementitious systems. The fibers used in cementitious systems are divided into two categories: artificial and natural. Natural fibers are preferred due to their lower production cost, lower environmental impacts such as lower carbon emissions and fossil fuel consumption, biodegradability, lower density and ease of manufacturing. On the other hand, graphene-derived materials have been proven to improve the mechanical and interface properties between fiber and matrix. In this study, the effect of surface treatment of jute fibers with various chemical treatments and graphene oxide coating on the mechanical and some durability performances of concrete mixtures was investigated. For this purpose, the surface of jute fibers was roughened with graphene oxide coating. Within the scope of the experimental study, different fiber concrete mixtures were prepared by adding jute fibers of 30 and 50 mm length to the mixture at 0.25 and 0.5 % of the total volume in addition to the fiber-free control mixture. The fiber was used in 2 different ways, both without any treatment and by coating the surface with graphene oxide. Slump tests were performed on the concrete mixtures produced. The 28-day hardened concrete specimens were tested for compressive strength, flexural strength, modulus of elasticity, ultrasonic pulse velocity and depth of water penetration under pressure. The resistance of the concrete specimens at 300 and 600 degrees C high temperatures and after 300 cycles of freeze-thaw was determined by examining their compressive strength. In addition, the microstructural properties of the jute fiber specimens were examined using Scanning Electron Microscopy (SEM).
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    Tensile behavior of C/GFRP-steel hybrid rebars: Effect of volume fraction and helical angle with a proposed analytical model
    (Elsevier, 2026) Senaysoy, Safa; Yilmaz, Ayten Nur Yuksel; Bedeloglu, Ayse; Altin, Yasin; Sakcali, Gokhan Baris
    This study examines the tensile properties of hybrid rebars consisting of a steel core wrapped with layers of Carbon Fiber-Reinforced Polymer (CFRP) or Glass Fiber-Reinforced Polymer (GFRP). The mechanical performance of the Steel-FRP composite bars (SFCBs) was evaluated through axial tensile tests considering two primary parameters: (i) the longitudinal FRP volume fractions (33 %, 40 %, and 47 %) and (ii) the helical wrapping angles (0 degrees, 30 degrees, and 60 degrees). Although SFCBs have gained increasing attention as an alternative to fully FRP or conventional steel reinforcement, the combined influence of fiber volume fraction and helical orientation on their tensile response has not been clearly established. Experimental findings demonstrated the influence of fiber volume fraction and helical angle on the tensile properties of SFCBs. Specimens coated with carbon exhibited greater strength than those coated with glass, especially at larger wrapping angles, while the glass-coated SFCB specimens demonstrated a wider range of deformation capability. The specimen with a 47 % volumetric fraction and a 60 degrees helical wrap exhibited a 21.8 % increase in yield stress compared with that of the steel bar, whereas its glass-fiber counterpart exhibited a 15.9 % increase. Maximum strength was significantly higher in carbon-SFCB rebars than in glass-SFCB ones. In contrast, glass-SFCB rebars showed 59 % higher ultimate strain. As the volume fraction increased, the influence of the helical angle on ultimate strength decreased. Increasing the helical angle from 0 degrees to 60 degrees enhanced the ultimate strength by up to 32 % in carbon-SFCBs and approximately 12 % in glass-SFCBs at a 33 % volume fraction. An analytical model was proposed to predict a five-zone stress-strain behavior, taking into account the effects of volumetric fraction and helical angle. The proposed model effectively replicated the stress-strain patterns of hybrid rebars in every zone with a satisfactory level of accuracy. Generally, the calculated mean absolute percentage errors for key mechanical parameters such as initial stiffness, yield stress, and fiber-contributed stiffness were below 15 %. This study offers a practical framework for designing SFCBs with customised mechanical properties for sophisticated RC applications.
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    Ti3C2Tx MXene/reduced graphene oxide/cellulose nanocrystal-coated cotton fabric electrodes for supercapacitor applications
    (Springer, 2024) Duygun, Inal Kaan; Bedeloglu, Ayse
    Textile-based electrodes are the most important components of wearable and portable supercapacitors. Ti3C2Tx MXene and reduced graphene oxide (rGO) have a great potential for the fabrication of high-performance textile supercapacitor electrodes. In this work, rGO was synthesized with the presence of cellulose nanocrystal (CNC) and Ti3C2Tx/rGO/CNC dispersions with different rGO/CNC contents were prepared. The plain-woven cotton fabrics were coated by homogenous Ti3C2Tx and Ti3C2Tx/rGO/CNC dispersions (5% wt., 15% wt., 30% wt. and 50% wt. rGO/CNC content) and characterized by X-ray Diffraction, Fourier Transform Infrared spectroscopy and Scanning Electron Microscopy techniques. The electrochemical characterization techniques showed that Ti3C2Tx/rGO/CNC loaded fabric electrodes up to 15 wt.% rGO/CNC content exhibited a high specific capacitance of 501.1 F g(-1) at a current density of 0.3 A g(-1) with low internal electrode resistance, and a good electrochemical stability. The results also showed that MXene/rGO/CNC based high-performance textile supercapacitor electrodes can be prepared by simple drop-casting method.