Yardımcı, Mert Yücel
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Yardimci, Mert
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Yardımcı, Yücel
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Yardimci, M.
Mert Yücel YARDIMCI
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Yardımcı, Y.
Yardımcı, Mert Yücel
Yardımcı, Mert
Mert Yücel Yardımcı
Yardimci, Mert Yuecel
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Mert Y. Yardımcı
Yardımcı Mert Yücel
Mert Yücel, Yardımcı
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Yardimci, Mert
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Yardımcı, Yücel
M. Y. Yardımcı
Yardimci, Yucel
M. Y. YARDIMCI
Yardımcı, M.
Mert Y. Yardimci
Yardimci, Y.
M. Y. YARDiMCi
YARDIMCI Mert Yücel
YARDiMCi Mert Yucel
Yardimci, M.
Mert Yücel YARDIMCI
Yücel Yardimci M.
Yardimci Mert Yucel
Yardımcı, Y.
Yardımcı, Mert Yücel
Yardımcı, Mert
Mert Yücel Yardımcı
Yardimci, Mert Yuecel
Yardimci, Mert Yucel
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Doç.Dr.
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mert.yardimci@okan.edu.tr
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Scholarly Output
17
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16
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0
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1
17 results
Scholarly Output Search Results
Now showing 1 - 10 of 17
Article Citation Count: 25Enhancing thixotropy and structural build-up of alkali-activated slag/fly ash pastes with nano clay(Springer, 2021) Dai, Xiaodi; Ren, Qiang; Aydin, Serdar; Yardimci, Mert Yucel; Lesage, Karel; De Schutter, Geert; İnşaat Mühendisliği / Civil EngineeringThis study investigates the influence of nano clay on the rheological properties of alkali-activated cement pastes having different GGBFS/FA ratios. The thixotropic index, structural build-up, dynamic yield stress and heat evolution of fresh AAC pastes with addition of nano clay are studied. Test results showed that nano clay had a strong influence on the thixotropy/structural build-up and dynamic yield stress of AAC pastes depending on the GGBFS/FA ratio of the mixture. It was found that the pastes with lower GGBFS/FA ratio exhibited higher thixotropic index, but lower dynamic yield stress in the presence of nano clay. This study reveals the importance of GGBFS/FA ratio in the presence of nano clay for obtaining AAC mixtures with low dynamic yield stress for a better flowability and high thixotropy/structural build-up for stability.Article Citation Count: 7Accelerating the reaction process of sodium carbonate-activated slag mixtures with the incorporation of a small addition of sodium hydroxide/sodium silicate(Elsevier Sci Ltd, 2023) Dai, Xiaodi; Ren, Qiang; Aydin, Serdar; Yardimci, Mert Yucel; De Schutter, Geert; İnşaat Mühendisliği / Civil EngineeringThis paper investigates the possibility of accelerating the slowly progressive early reaction process of sodium carbonate-activated slag mixtures by adding a small amount of sodium hydroxide or sodium silicate to the so-dium carbonate activator. The reaction process of sodium carbonate-activated slag mixtures was evaluated by isothermal calorimetry and ultrasonic wave technology. Test results showed that adding a small amount of so-dium hydroxide or sodium silicate to the sodium carbonate activator significantly accelerated the reaction process, resulting in shortened setting times and enhanced mechanical properties. Only 1% Na2O contribution from sodium hydroxide addition can lead to a 2-d compressive strength of 20 MPa for sodium carbonate -activated slag mixtures. In addition, the 28 days compressive strength was significantly higher than the sole sodium carbonate activator. The addition of sodium hydroxide or sodium silicate also considerably influenced the rheological behavior of the sodium carbonate-activated slag mixture, enhancing the structural build-up rate and transforming the shear-thinning behavior to Bingham or shear-thickening behavior. A more well-packed microstructure was observed in the mixtures with the addition of sodium hydroxide; however, more micro -cracks were observed in the mixtures with a small incorporation of sodium silicate.Article Citation Count: 47Rheology, early-age hydration and microstructure of alkali-activated GGBFS-Fly ash-limestone mixtures(Elsevier Sci Ltd, 2021) Dai, Xiaodi; Aydin, Serdar; Yardimci, Mert Yucel; Qiang, R. E. N.; Lesage, Karel; De Schutter, Geert; İnşaat Mühendisliği / Civil EngineeringIn this study, the effects of limestone powder on the rheological behavior, pore solution chemistry, mechanical properties and microstructure of alkali-activated cements have been investigated. The results exhibit that, with the increasing content of limestone powder in the ternary alkali-activated system, the structural build-up of the mixture increases earlier. It was observed that flow curves of pastes fit the Bingham model well. With the increasing content of fly ash in the ternary mixtures, the plastic viscosity decreased as expected by the particle packing effect and the increased water film thickness as well as the spherical shape of fly ash particles. As a result of the higher specific surface and improved nucleation provided by the limestone powder, the reaction process was enhanced and accelerated for the mixtures with higher limestone powder contents. The calcium and alumina concentrations in the pore solution rapidly evolved at first for a certain time, but decreased afterwards. The significant influence of the Ms value of the activator was observed on the evolution of the elemental concentrations. Microstructure analysis revealed that the early age reaction product is C-A-S-H for the slag mixtures incorporating limestone or fly ash. The compressive strength of the ternary mixtures decreased with the incorporation of limestone powder due to the inert character of the limestone powder.Article Citation Count: 0Early structural build-up behavior, setting mechanism, and nanostructure of alkali-activated GGBFS mixtures(Wiley, 2024) Dai, Xiaodi; Aydin, Serdar; Yardimci, Mert Yuecel; Reekmans, Gunter; Adriaensens, Peter; De Schutter, Geert; İnşaat Mühendisliği / Civil EngineeringThe initial changes in the microstructure of alkali-activated slag cement (AAS) characterize the rheological behavior, initial structuration, and setting times of the mixture. In this study, the relationships among the rheological behavior, solidification process, and nanostructure changes of sodium hydroxide-activated slag (NH-AAS) and sodium silicate-activated slag (SS-AAS) pastes over time are investigated by small amplitude oscillation shear test, isothermal calorimetry, scanning electron microscopy analyses, and 1H-29Si cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy (CP MAS NMR) and 29Si MAS NMR spectroscopy. Test results showed that the NH-AAS reaches its initial setting time following a continuously proceeding structuration process, whereas the SS-AAS reaches its initial setting with an abrupt increase in the structuration process. At their initial setting times, the NH-AAS and SS-AAS mixtures release similar heat and reach a similar reaction degree. The SS-AAS mixture had more N-A-S-H formation than C-A-S-H at the initial setting time. On the other hand, the amount of C-A-S-H was similar to N-A-S-H in the NH-AAS mixture. The gradual N-A-S-H gel degradation to form C-A-S-H was observed during the acceleration period for the SS-AAS mixture.Article Citation Count: 2Fresh and hardened state properties, reaction kinetics and microstructure of sodium sulfate/sodium hydroxide - Activated slag mixtures(Elsevier Sci Ltd, 2023) Dai, Xiaodi; Aydin, Serdar; Yardimci, Mert Yucel; De Schutter, Geert; İnşaat Mühendisliği / Civil EngineeringThis study investigated the impact of incorporating sodium hydroxide (NaOH) on the properties of ground granulated blast furnace slag (GGBFS) activated by sodium sulfate (Na2SO4). Specifically, the rheological properties, setting behavior, reaction kinetics, mechanical performance, and microstructure of the mixtures were examined. Results indicated that using only Na2SO4 as the activator resulted in mixtures with long setting times and no compressive strength at early ages. However, the addition of NaOH to the Na2SO4 activator significantly improved the reaction kinetics of the GGBFS. By optimizing ratio between NaOH and Na2SO4, mixtures with improved workability, faster structuration, reasonable setting times, and desirable mechanical properties were achieved. The superior mechanical properties were attributed to a well-packed microstructure consisting of C -(A)-S-H, ettringite, and hydrotalcite in the binary NaOH-Na2SO4 activator systems.Article Citation Count: 0Effect of temperature on the fresh and hardened state properties of alkali-activated slag/fly ash mixtures(Springer, 2023) Dai, Xiaodi; Aydin, Serdar; Yardimci, Mert Yucel; Sun, Yubo; De Schutter, Geert; İnşaat Mühendisliği / Civil EngineeringThe effect of ambient temperature on the engineering properties of alkali-activated materials (AAM) needs to be further investigated due to the high variety of activating solutions in the AAM technology. This paper presents the rheological behavior, structural build-up, reaction kinetics and mechanical properties of GGBFS-FA mixtures activated by sodium hydroxide, sodium silicate, sodium carbonate and sodium sulfateinvestigated under different ambient temperature conditions. It was found that the effect of ambient temperature on the rheology and reaction kinetics was highly dependent on the activator type. Under room temperature conditions, the highest and lowest yield stress values were obtained in sodium hydroxide and sodium silicate mixtures, respectively. The increase in temperature did not affect the yield stresses and viscosities of sodium carbonate and sodium sulfate mixtures; however, the yield stresses of sodium hydroxide and sodium silicate mixtures significantly increased. This effect was more pronounced in mixtures with high Ms values. Higher storage modulus values were obtained with an increase in temperature, indicating initial structuration with temperature. The increasing temperature enhanced the compressive strength of alkali-activated GGBFS-FA mixtures. This improvement was more pronounced at early ages for the sodium silicate mixture, and at later ages for the sodium carbonate and sodium sulfate mixtures, while it was very limited in the sodium hydroxide mixture. The SEM images and calorimetric measurements showed the formation of a denser microstructure and enhancement in the exothermic peak with a shorter induction period with an increase in temperature.Article Citation Count: 69Influence of water to binder ratio on the rheology and structural Build-up of Alkali-Activated Slag/Fly ash mixtures(Elsevier Sci Ltd, 2020) Dai, Xiaodi; Aydin, Serdar; Yardimci, Mert Yucel; Lesage, Karel; de Schutter, Geert; İnşaat Mühendisliği / Civil EngineeringIn this study, the effects of water to binder (w/b) ratio on the rheological and fresh state properties of alkali-activated cement (AAC) pastes have been investigated. A mixture of 50% type F fly ash (FA) and 50% ground granulated blast furnace slag (GGBFS) was activated by a mixture of sodium hydroxide and sodium silicate, in three different w/b ratios of 0.32, 0.37 and 0.42. Setting time, ultrasonic pulse velocity (UPV), heat evolution by isothermal calorimetry, flow spread by mini-slump test, rheological properties by means of flow curve and viscoelastic properties such as storage modulus (G') and loss factor (G '') were determined on the paste mixtures. The results showed that the higher w/b ratio led to structural build-up with higher rate compared to lower w/b ratios. GGBFS provided the main contribution to the increase of storage modulus in the early stage of hybrid mixture of GGBFS and FA. The dynamic yield stress, plastic viscosity and thixotropic index values decrease with an increase in w/b ratio of AAC mixture. The setting times of AAC mixtures were found to be less dependent on the w/b ratio as compared to ordinary Portland cement mixtures. (C) 2020 Elsevier Ltd. All rights reserved.Master Thesis Polikarboksilat eter ve naftalin sülfonat formaldehit esaslı kimyasal katkılı betonlarda redoz uygulamasının betonun taze ve sertleşmiş hal özelliklerine etkileri(2021) Beritan, Mehmet Reşat; Yardımcı, Mert Yücel; İnşaat Mühendisliği / Civil EngineeringBaşlangıçta plastik kıvamda olan taze beton çimento ile suyun hidratasyonunun bir sonucu olarak zamanla katılaşarak sertleşir. Taze beton katılaşmaya başlayana kadar taşıma, pompalama, yerleştirme, sıkıştırma ve yüzey düzeltme işlemleri için belirli bir süre kıvamını korumalıdır. Ancak taze beton uzun taşıma mesafeleri ve karışım suyunun bir kısmının buharlaşması gibi çeşitli nedenlerle şantiyeye ulaştığında kıvamını kaybetmiş olabilir. Kaybedilen kıvam beton halen transmikserde iken yeniden akışkanlaştırıcı kimyasal katkı eklenmesi (redoz) yoluyla telafi edilmektedir. Bu çalışmada iki farklı tip akışkanlaştırıcı kimyasal (polikarboksilat eter ve naftalin sülfonat formaldehit) ve mineral (uçucu kul ve öğütülmüş yüksek fırın cürufu) katkı kullanılarak üretilmiş betonlarda 90 dakika sonra meydana gelen kıvam kayıplarının tek dozda yeniden katkı ekleyerek telafi edilmesinin (redoz) betonun taze birim hacim ağırlığı, hava miktarı, priz süresi ve 2, 28 ve 90 günlük basınç dayanımlarına olan etkileri laboratuvar koşullarında deneysel olarak incelenmiştir. Taze ve sertleşmiş beton örneklerden elde edilen sonuçlar betonun üretildiği kimyasal katkıyla yapılan redoz işleminin betonun 90 dakikada kaybedilen kıvamını geri kazandırdığını ancak redozun betonun priz sürelerinin uzamasına ve hava miktarlarının hafifçe artmasına neden olduğunu ortaya koymuştur. Öte yandan, redoz işleminin betonun erken ve ileri yaş basınç dayanımına önemli bir etkisinin olmadığı belirlenmiştir. Anahtar sözcükler: Kimyasal katkılar, redoz, işlenebilirlik, kıvam kaybı, taze beton priz süresi, basınç dayanımı.Article Citation Count: 2Effect of the steel fibre hook geometry on the flexural properties of high strength steel fibre reinforced concretes under static and impact loading(Gazi Univ, Fac Engineering Architecture, 2019) Kizilirmak, Cengiz; Aydin, Serdar; Yardimci, Mert Yucel; İnşaat Mühendisliği / Civil EngineeringIn recent years, steel fibre producers have produced new generation steel fibres with high strength and multiple hooked-end geometry (4D and 5D). The studies on the mechanical properties of steel fibre reinforced concretes containing 4D and 5D fibres under the static loading conditions are very limited and there is no published study on the performance of these new generation fibres under flexural impact loading yet. In this study, the effects of the dosage and the aspect (length/diameter) ratio of 4D and 5D fibres on the flexural strength and fracture energy of high strength concrete under static and impact flexural loading conditions have been investigated comparatively with the conventional single-hook-end 3D fibres. The experimental results showed that the flexural strength and the fracture energy of fibre reinforced high strength concrete significantly improved with the increase in the fibre volume, and by using multiple hooks-end steel fibres with sufficiently high tensile strength. For the fibres with aspect ratio of 65, significantly higher flexural strength and fracture energy values have been obtained for 5D hook geometry as compared to conventional 3D fibres, while 4D fibres did not improve these engineering properties probably due to their relatively insufficient fibre strength for this aspect ratio. It has been revealed that the effect of the 4D steel fibre on the mechanical properties of high strength concrete was more pronounced in higher aspect ratio fibres. The increase of fibre aspect ratio for 3D steel fibres negatively affected the fracture energy of concrete. As compared to static loading, 1.4 to 2.6 times higher flexural strength and 1.2 to 3.0 times higher fracture energy values were obtained under impact loading. The best performance under flexural impact loading has been obtained from steel fibre reinforced high strength concretes with 5D fibres having aspect ratio of 65 and 4D fibres having aspect ratio of 80.Article Citation Count: 38Rheology and microstructure of alkali-activated slag cements produced with silica fume activator(Elsevier Sci Ltd, 2022) Dai, Xiaodi; Aydin, Serdar; Yardimci, Mert Yucel; Lesage, Karel; De Schutter, Geert; İnşaat Mühendisliği / Civil EngineeringThe effects of silica fume and sodium silicate-based activators (SFA and SSA, respectively) with different Ms (SiO2/Na2O) values on the setting behavior, rheological, mechanical, and microstructural properties of alkaliactivated slag cement (AASC) were investigated. Setting time test results showed that the setting time of AASCs activated by SFA prolonged significantly with an increase of Ms value opposite to SSA activation case. From the rheological point of view, SFA-activated mixtures exhibited a slower structural build-up in the early stage and better workability retention than SSA-activated mixtures. In addition, SFA mixtures showed lower drying shrinkage and slightly higher mechanical properties as compared to SSA mixtures. Microstructure analysis revealed that the mixture produced by SFA with Ms value of 1.2 had less micro-cracks and a well-packed microstructure as compared to the mixtures produced by SSA. The overall evaluation of the test results revealed that SFA could be more economical and sustainable alternative to SSA with its lower cost, much lower CO2 emissions, and more favorable engineering properties.
