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Yayın Corrosion and Chloride Diffusivity of Reinforced Concrete Cracked under Sustained Flexure(Turkish Chamber Civil Engineers, 2020) Özyurt, Nilufer; Soylev, Tayfun Altug; Özturan, Turan; Pehlivan, Ahmet Onur; Nis, AnilThis research discusses the chloride diffusivity of concrete as well as corrosion performance of rebars in cracked and uncracked states. Prismatic concrete specimens with two water-to-cement ratios, two concrete cover thicknesses with and without steel fibers were used. Three-point flexural loading was applied to form cracks and cracks were sustained by a bolt system. Half-cell potential and corrosion rate measurements were carried out following wetting drying cycles in chloride environment which were continued for 80 weeks. The positive effects of lower water-to-cement ratio and greater cover depth were found to be surpassed by existence of cracks in concrete.Yayın Effect of Alkali Content and Activator Modulus on Mechanical Properties of Alkali Activated Mortars(2020) Pehlivan, Ahmet OnurAlkali activation is a promising method of reducing cement production considerably without further significant investments. Utilizationof these materials are of extreme importance when environmental aspects such as CO2 emissions and energy consumptions areconsidered. In this article, effect of activator modulus and alkali content on fresh behavior and mechanical properties were investigated.12 M NaOH solution and sodium silicate solution with a modulus of 3 were used. Water-to-binder ratio was selected as 0.5 for allspecimens where binder content was calculated as the total of slag content plus activator solids. Slag content was 500 kg/m3 for allmixtures. Mechanical tests were conducted on 40 x 40 x 160 mm prismatic specimens. Results indicate that mechanical propertiesof alkali activated mixtures are highly dependent on both parameters hence proper optimization of these two parameters becomescompulsory. In this study, it is concluded that alkali content (Na2O/slag) should be selected 9% and whereas activator modulus shouldbe leveled near a value of 1.5. Flexural properties were also highly affected from optimization of these parameters and similar findingsare deduced. Early strength evaluations are highly dependent on activator modulus. Workability of the mixture was also assessed andit should be noted that flowability of mixture was adversely affected with the increasing activator solids content.Yayın Effect of novel synthesized nanoeggshell on the properties of cementitious composites(Japan Concrete Institute, 2020) Pehlivan, Ahmet Onur; Karakuş, Selcan; Karapınar, Işıl Sanrı; Özsoy Özbay, Ayşe Elif; Yazgan, Ahmet Utku; Taşaltın, Nevin; Kilislioğlu, AybenIn this study, a novel synthesized form of nanoeggshell is introduced and its use in cementitious composites is proposed as a green, safe and low-cost additive. The nanoeggshell was characterized using FTIR, SEM, BET and viscometer techniques and results showed that the ultrasonic effect was a major factor for the structure of synthesized hierarchical 3D flower-like nanoeggshell. The intrinsic viscosity, voluminosity, and shape factor of nanoeggshell were calculated to understand rheological properties of the structure. Different error functions were used to find the optimum. Regarding the effect of the novel 3D flower-like nanoeggshell on the mechanical properties of mortar, four different cement mor-tar mixtures were prepared with varying percentages of nanoeggshell (0%, 0.1%, 0.5% and 1%). It is concluded that compressive strength of the mixtures increased with the increasing amount of nanoeggshell additive. Additionally, flexural strain capacity was improved with the additive due to bridging effect in the cement matrix, thus induced higher ductility. In addition, better workability was noted in the mixtures with nanoeggshell. As a result, the introduced 3D flower-like nanoeggshell is a novel potential nanomaterial that can be used as an effective additive for improving the mechanical properties of cementitious composites.Yayın Effect of silica fume and basalt fibers on the fracture parameters of magnesium phosphate cement incorporating fly ash(Pontificia Univ Catolica Chile, Escuela Construccion Civil, 2022) Pehlivan, Ahmet OnurMagnesium phosphate cements are implemented for several purposes demonstrating significant mechanical properties in limited durations. However, brittle behavior of this material needs utmost concern and tensile performance may be enhanced with the proper application of fibers increasing both ductility and energy absorption capacity. This research studies the effect of basalt fibers (BF) and silica fume (SF) on the fracture parameters of magnesium phosphate cement (MPC). MPC mortar mixtures were prepared with different SF (0, 5, 10%) and BF amounts (0, 0.5, 0.75, 1 % by wt.). Also fly ash was adopted with a constant ratio for all mixes. Compressive strength and splitting tensile strength results indicated that addition of SF into mixtures extensively developed the matrix structure and improvements were noted with the increasing SF content. The inclusion of BF enhanced the flexural behavior although there were significant improvements in the fracture energy as well as the double-K parameters. Improvements in the tensile capacity of specimens with high BF were prone to the amount of SF percentage such that inclusion of 1 % BF performed best with 10 % SF added mixtures. Load-CMOD (crack mouth opening displacement) curves obtained from notched three-point tests were given for all specimen series and parameters were calculated according to the double-K criterion. Addition of BF resulted in higher toughness values however presence of SF was very significant in establishing appreciable development in toughness values. Brittleness index was implemented to establish clear conclusions on the findings and best performance was seen for specimens with 10% SF and 1% BF.Yayın Evaluation of the Microstructure and Mechanical Properties of Biopolymer-Based Cementitious Composites with Silver Nanoparticles(Asce-Amer Soc Civil Engineers, 2023) Pehlivan, Ahmet Onur; Karapinar, Isil Sanri; Karakuş, Selcan; Özsoy Özbay, Ayşe Elif; Yazgan, Ahmet UtkuThis study investigated the effects of using silver nanoparticles (Ag NPs) on the microstructure and mechanical properties of cementitious composites. Ag NPs were synthesized with an ultrasonic irradiation method using konjac gum-polyethylene glycol (KG/PEG) and locust gum-polyethylene glycol (LG/PEG) and characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX), high-resolution transmission electron microscopy (TEM), and Fourier-transform infrared (FTIR) analyses. To identify the effect of the Ag NPs on the mechanical properties of mortar, four different cement mortar mixtures were prepared with varying percentages of Ag NPs (0%, 0.5%, 1%, 2%, 3%, 4%, and 5% by weight). Clear improvements were observed in the 7- and 28-day compressive and flexural strengths of nanocomposites with Ag NPs. A thorough microstructure investigation using SEM, EDS, XRD, and thermogravimetric analysis (TGA) was presented, and the relationship between microstructure and the mechanical properties of cementitious composites including Ag NPs was discussed.Yayın Improvement of mechanical strength of mortars by different morphological zinc oxide nanoparticles(Ice Publishing, 2022) Yazgan, Ahmet Utku; Karakuş, Selcan; Pehlivan, Ahmet Onur; Karapinar, Isil Sanri; Özsoy Özbay, Ayşe Elif; Taşaltın, Nevin; Kilislioğlu, AybenThis study presents novel nano-mixtures containing zinc oxide (ZnO) nanoparticles (NPs) to enhance the mechanical properties of cement mortars. Different morphological ZnO NPs were synthesised through the green sonochemical method, using tragacanth gum/Kappa carrageenan (TG/kappa-C) and tragacanth gum/chitosan (TG/CS) as biopolymer matrices. The ZnO NPs were characterised using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy, X-ray diffraction, Zetasizer and Brunauer-Emmett-Teller techniques. The intrinsic viscosities of TG/kappa-C-ZnO and TG/CS-ZnO NPs were investigated to determine the miscibility of the polymeric blends in aqueous solution as affected by sonication time and composition ratios. The average diameters for the spherical and prism-like ZnO NPs were around 266 nm and 355 nm, respectively. Seven different cement mortar specimens containing TG/kappa-C-ZnO and TG/CS-ZnO NPs were prepared in ratios of 0, 0.1, 0.5 and 1% by weight, and the flexural and compressive strengths of the specimens were determined at the ages of 7 and 28 days. The results indicate that there is a significant improvement in the mechanical performance of different morphological ZnO NP-based cement mortar composites. In comparison, it was observed that specimens containing TG/kappa-C-ZnO NPs had much better results than TG/CS-ZnO NPs. Moreover, the workability problem encountered by using only ZnO NPs has been overcome with the presented biopolymers used in this study.Yayın Improvement of the mechanical properties of cementitious composites by the novel synthesized borophene nanosheets(Sage Publications Ltd, 2022) Karapinar, Isil Sanri; Pehlivan, Ahmet Onur; Özsoy Özbay, Ayşe Elif; Yazgan, Ahmet Utku; Taşaltın, Nevin; Karakuş, SelcanThis study is the first investigation focused on the preparation of novel synthesized borophene nanosheets and their use in cementitious composites. The two-dimensional beta borophene was prepared by a facile and low-cost sonication process including ultrasonic cavitations. To understand the effect of the novel synthesized borophene nanosheets, varying ratios of 0, 0.5, 1, 2, 3, and 5 wt% of cement were incorporated in cement composites and improvements on the mechanical strength, workability, and toughness were identified. Also, for the microstructure evaluation, several advanced characterization techniques including SEM, EDS, XRD, and TGA were presented and the relationship between the microstructure and mechanical properties of cementitious composites modified with borophene nanosheets was discussed. As a result of this study, with the incorporation of the borophene nanosheets, clear improvements were achieved for the 28 day compressive and flexural strengths of the specimens within a range of 5-19% and 4-13%, respectively. The findings also indicated that borophene nanosheets contributed to the formation of a denser microstructure of the corresponding cement composites. Thus, within this study, the utility of as-prepared borophene nanosheets in cementitious composites is proved and proposed as a two-dimensional potential nanomaterial candidate to be used in cementitious composites.Yayın INVESTIGATION OF FRACTURE PARAMETERS OF CONCRETE INCORPORATING BASALT FIBERS(Serban Solacolu Foundation, 2021) Pehlivan, Ahmet OnurConcrete is a brittle material that should be enhanced with better tensile strength and toughness capacity. Concrete matrix is generally reinforced with fibers which are extremely helpful inhibiting the crack propagation and supplying the ability of strain accumulation into concrete matrix. In this study, an environment friendly type of fiber was introduced into concrete for the investigation of mechanical properties and fracture characteristics by size independent double-K fracture parameters asserted in the literature. Effect of basalt fibers with different lengths and contents were investigated under notched three-point bending tests and relevant parameters obtained and calculated, were compared for two distinct parameters: fiber length (6, 12, 24 mm) and content (0, 0.1%,0.3%, 0.5%, 1%). Shorter fibers confronted dispersion problems when used in higher content whereas 12 mm fiber specimens performed more stable results. Fracture energy dissipation was found to be linearly increasing with increasing fiber content and also longer fibers were found to be more efficient. Double-K fracture parameters were found to be resourceful when considering toughness and ductility of the material besides these parameters indicated useful information regarding the precracking and post-cracking behavior of concrete. SEM investigations were also conducted to monitor the bonding between basalt fibers and concrete matrix.Yayın Mechanical Properties of Cement Mortars Incorporating Zero-Valent Iron Nanoparticles(Asce-Amer Soc Civil Engineers, 2022) Özsoy Özbay, Ayşe Elif; Karapinar, Isil Sanri; Yazgan, Ahmet Utku; Pehlivan, Ahmet Onur; Karakuş, Selcan; Taşaltın, Nevin; Kilislioğlu, AybenIn this study, the effects of zero-valent iron (ZVI) nanoparticles (NPs) on the mechanical performance of cementitious composites were investigated. For this purpose, the use of a novel nanomaterial containing ZVI NPs blended with carboxymethyl cellulose (CMC) and SiO2 was introduced. CMC/SiO2-ZVI NPs were prepared by a green and low-cost sonochemical method at room temperature and characterized using scanning electron microscopy/energy dispersive X-ray spectroscopy, thermal gravimetry analysis, Brunauer-Emmett-Teller, and X-ray diffraction techniques. The values of intrinsic viscosities of CMC/SiO2-ZVI NPs were examined to determine the optimal miscible condition as affected by the different mass ratios of CMC/SiO2 and sonication time. Then, eight different cement mortar specimens containing CMC/SiO2 and CMC/SiO2-ZVI NPs were prepared in ratios of 0.2%, 0.5%, 1%, and 2% by weight, and flexural and compressive strengths of the specimens were determined at the ages of 7 and 28 days. The microstructure of the specimens was also evaluated. Comprehensive results proving the improvement in the mechanical properties have been obtained in the specimens containing 1% and 2% CMC/SiO2-ZVI NPs. (C) 2021 American Society of Civil Engineers.Yayın Mechanical properties of magnesium phosphate cement incorporating basalt fibers(Stowarzyszenie Producentow Cementu, 2021) Pehlivan, Ahmet OnurIn this experimental study, the effect of basalt fibers on the mechanical properties of magnesium phosphate cement [MPC] was investigated. Compressive strength, splitting tensile strength, flexural strength and modulus of elasticity, were introduced. It was observed that mechanical properties were significantly enhanced with the addition of silica fume, especially splitting tensile and flexural strength were enhanced with the increase of basalt fibers. However, for mixtures without silica fume addition, high content of fibers adversely affected the mechanical properties. Silica fume addition was found to be significant in increasing the bonding mechanism between basalt fibers and the MPC matrix. Thus, combined usage of silica fume and basalt fibers was found to be effective. A molar ratio of magnesia to ammonium dihydrogen phosphate of 8 was observed to have better results with respect to a molar ratio of 6, however, this distinction was not very apparent, when silica fume was added to both mixtures.
