Browsing by Author "Karahan, Okan"

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Citation - Scopus: 1
Comparison of Mechanical and Physical Properties of Screed With and Without Expanded Polystyrene (EPS) Particles
(Yildiz Technical University, 2022) Kiliç, Fikret Merih; Yorulmaz, Hediye; Özuzun, Sümeyye; Durak, Uğur; İLkentapar, Serhan; Karahan, Okan; Atis, C. D.; 01. Abdullah Gül University; 02.03. İnşaat Mühendisliği; 02. Mühendislik Fakültesi
In this study, in order to observe the mechanical and physical properties of ordinary screed, sandy-lightweight screed and lightweight screed samples, expanded polystyrene (EPS) was used as fine aggregate and lightweight screed systems were produced by replacing sand at 100%, 50% and 0%. Samples of cement dosages of 250, 300, 350 kg/m3 were produced for lightweight screeds, sandy-lightweight screeds and ordinary screeds. Unit weight, water absorption capacity, flexural strength, compressive strength, fire resistance, abrasion and thermal conductivity tests were performed on the produced screed systems. As a result of the research, it was determined that as EPS ratio increases in screed system; unit weights decreased, water absorption rates increased. Besides, the flexural and compressive strengths, fire and abrasion resistance are also decreased. However, it was observed that the thermal conductivity coefficient reduced with the increment of EPS particles in the screed. In normal, sandy-lightweight and lightweight screeds, it was determined that as the cement dosage increased; the unit weights, flexural and compressive strengths, fire and abrasion resistance increased, water absorption capacity and the thermal conductivity coefficient decreased. © 2022 Elsevier B.V., All rights reserved.
Citation - WoS: 104
Citation - Scopus: 120
Dual Effectiveness of Freezing-Thawing and Sulfate Attack on High-Volume Slag-Incorporated ECC
(Elsevier Sci Ltd, 2013) Ozbay, Erdogan; Karahan, Okan; Lachemi, Mohamed; Hossain, Khandaker M. A.; Atis, Cengiz Duran; 01. Abdullah Gül University
This study investigated the dual effect of freeze-thaw cycles with sodium sulfate solution on the performance of non-air-entrained Engineering Cementitious Composites (ECCs) with high volumes of slag. ECC specimens containing three different levels of slag content as a replacement for cement (55%, 69% and 81% by weight of total cementitious material) were exposed to aggressive sodium sulfate solution under freezing-thawing cycles. The load-deflection response associated with ultimate mid-span deflection and flexural strength/stiffness was determined, along with crack development behavior. For comparison purposes, the freezing-thawing resistance (in water) of control ECC specimens was also evaluated. Modified point count method air-void parameters, compressive strength, porosity, water absorption and sorptivity tests were also conducted on the virgin ECC specimens (those not exposed to freezing-thawing cycles in water or aggressive sodium sulfate solution). The test results for the virgin specimens revealed that increased slag content (S/PC) improved the ductility, hardened air content, water absorption, porosity and sorptivity of ECC, while marginally decreasing the compressive and flexural strengths. Freeze-thaw cycles in water or sodium sulfate solution showed that the ductility of ECC specimens decreased remarkably, irrespective of slag content and applied freezing-thawing process. Reduction in mass loss was at minimal levels and no significant behavior change was monitored between the specimens undergoing freeze-thaw cycling in water and the aggressive sodium sulfate solution. Moreover, the decrease in flexural stiffness was more evident than the reduction of the flexural strength for all ECC mixtures. Crown Copyright (c) 2012 Published by Elsevier Ltd. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 6
Effect of Nano-SiO2 on Strength and Hydration Characteristics of Ternary Cementitious Systems
(Springer Heidelberg, 2023) Yorulmaz, Hediye; Uzal, Burak; Karahan, Okan; Durak, Ugur; Ilkentapar, Serhan; Atis, Cengiz Duran; 01. Abdullah Gül University; 02.03. İnşaat Mühendisliği; 02. Mühendislik Fakültesi
This paper shows results of laboratory study on the effects of nano-SiO2 on Portland cement-fly ash systems. It is aimed to improve performance of fly ash-cement systems, particularly at early age, with the inclusion of nano-SiO2. In order to observe the effects of nano-SiO2 particles on the strength and hydration kinetics of fly ash blended cementitious systems, binary and ternary systems were prepared by adding 0.25-1.5% nano-SiO2 by weight of blended cements. Workability, setting time, water absorption capacity, fire resistance, compressive strength and isothermal calorimeter tests were conducted on the cementitious systems. The results indicate that increasing quantity of fly ash increased workability, setting time, water absorption capacity of cementitious systems, whereas the increasing quantity of nano-SiO2 reduced these values. Significant increment in compressive strength were observed, especially at early ages of fly ash-cement systems with nano-SiO2 addition, compared to fly ash added systems, which may compensate for the decrease in compressive strength caused by fly ash. Nano-SiO2 addition accelerated hydration reactions at early age. By partially eliminating the negative effects of fly ash with nano-SiO2, high rates of fly ash can be used in cementitious systems, thus forming more sustainable systems.
Effects of Dry Particle Coating With Nano-and Microparticles on Early Compressive Strength of Portland Cement Pastes
(Tulpar Academic Publishing, 2021) Yorulmaz, Hediye; Özuzun, Sümeyye; Uzal, Burak; İLkentapar, Serhan; Durak, Uğur; Karahan, Okan; Atis, C. D.; 01. Abdullah Gül University; 02.03. İnşaat Mühendisliği; 02. Mühendislik Fakültesi
It is known that nano-and microparticles have been very popular in recent years since their advantages. However, due to the very small size of such materials, they have very high tendency to agglomeration particularly for nanoparticles. Therefore, it is critical that they are properly distributed in the system to which they are added. This paper investigated the effects of dry particle coating with nano-and microparticles to solve the agglomeration problem. For a clear evaluation, paste samples were preferred to detemine the compressive strength. Nano-SiO2 and nano-CaCO3, microCaCO3 and micro-SiO2, also known as silica fume, were selected as particulate additives. It was studied by the addition of various percentages (0.3, 0.7, 1, 2, 3 and 5%) of nano-and microparticles in cementitious systems, replacing cement by weight with and without dry particle coating. Dry particle coating was made by using a highspeed paddle mixer. Portland cement and additive particles were mixed at 1500 rpm for 30 seconds in high-speed powder mixer designed for this purpose. The 3-day compressive strength of the cement-based samples to which particles were added at the specified rates was determined and the effect of the dry particle coating on the early strength was investigated. According to the results, it was observed that the production of paste with the dry particle coating technique gave higher compressive strength compared to the production of paste directly in early period. Especially with dry particle coating, compressive strength increased more than 100% in paste samples containing 0.3% nano-SiO2 compared to direct addition without coating. © 2024 Elsevier B.V., All rights reserved.
Citation - WoS: 19
Citation - Scopus: 36
Fresh, Mechanical, Transport, and Durability Properties of Self-Consolidating Rubberized Concrete
(Amer Concrete inst, 2012) Karahan, Okan; Ozbay, Erdogan; Hossain, Khandaker M. A.; Lachemi, Mohamed; Atis, Cengiz D.; 01. Abdullah Gül University
This paper presents the fresh, mechanical, transport, and durability performances of self-consolidating rubberized concretes (SCRCs). Fresh concrete properties were determined with slump flow, V-funnel, J-ring, and L-box tests. Mechanical, transport, and durability properties were determined by measuring compressive, flexural, and splitting tensile strengths; bond strength characteristics; water porosity; water absorption; water sorptivity; rapid chloride-ion permeability; and freezing-and-thawing and corrosion resistance. SCRC mixtures with a water-binder ratio (w/b) of 0.32; total binder content of 500 kg/m(3) (842 lb/yd(3)); and crumb rubber content of 0, 10, 20, and 30% by fine aggregate volume were produced and tested. Fresh properties testing revealed that the use of crumb rubber as a fine aggregate diminished the filling and passing ability of SCRC. A gradual reduction in mechanical properties was also observed with an increase in crumb rubber content; however, the rate of compressive strength reduction was more evident than that of tensile strength. Despite the fact that water porosity, water absorption, and chloride-ion permeability increased slightly with the use of crumb rubber, a remarkable decrease was observed in the initial and secondary water sorptivity of SCRC. No significant decrease was observed in the freezing-and-thawing and corrosion resistance of SCRC with 10% crumb rubber. Beyond that level, however, durability performance was significantly affected.
Citation - WoS: 121
Citation - Scopus: 132
Influence of Admixtures on the Properties of Alkali-Activated Slag Mortars Subjected to Different Curing Conditions
(Elsevier Sci Ltd, 2013) Bilim, Cahit; Karahan, Okan; Atis, Cengiz Duran; Ilkentapar, Serhan; 01. Abdullah Gül University
This paper presents the influence of shrinkage-reducing (SHR) and superplasticizing and set-retarding admixtures (SSRe) on the properties of slag pastes and mortars activated by liquid sodium silicate with different dosage and modulus ratio. Properties in the fresh and hardened state for these binders were investigated by means of measuring some properties including setting time, flowability, flexural strength, compressive strength, carbonation and shrinkage. In this study, fifteen pastes and mortars were prepared. Liquid sodium silicate was used to activate the slag at two sodium concentrations, 4% and 6% by mass of slag. Liquid sodium silicate and sodium hydroxide were blended to obtain 0.75 and 1 modulus ratio of SiO2/Na2O. Results showed that although the higher percentage of sodium in the activator produced a higher strength, workability and setting times rapidly decreased with the higher sodium concentration due to instantaneous reaction and quick hardening of slag activated by liquid sodium silicate. None of the admixtures generally had an impact on the setting times of alkali-activated slag (AAS) pastes. SSRe admixture increased the flow rate of AAS mortars while SHR admixture partially affected the flow values of AAS mortars. SHR admixture exhibited a slight decrease in the carbonation depths of AAS mortars. SSRe and particularly SHR chemical admixtures reduced the shrinkage of AAS mortars. However, the shrinkage values of AAS mortars still were higher than those of ordinary Portland cement (NPC) mortars. Curing conditions had a significant effect on the mechanical behavior in the hardened state of AAS mortars compared to NPC mortars. (C) 2012 Elsevier Ltd. All rights reserved.
Citation - WoS: 6
Citation - Scopus: 6
The Influence of Cement Kiln Dust on Strength and Durability Properties of Cement-Based Systems
(Springer Heidelberg, 2022) Hakkomaz, Hadiye; Yorulmaz, Hediye; Durak, Ugur; Ilkentapar, Serhan; Karahan, Okan; Atis, Cengiz Duran; 01. Abdullah Gül University; 02.03. İnşaat Mühendisliği; 02. Mühendislik Fakültesi
There are very few studies in the literature on the usage of CKD in cementitious systems. This article presents the laboratory study results on the influence of cement kiln dust (CKD) on the properties of mortar made with cement kiln dust and Portland cement. The article aims to prevent CKD's (known as a hazardous waste product) damage to nature by utilizing CKD in cementitious systems and contributing to sustainability by reducing cement amount in the cementitious system. For this purpose, 5%, 10%, 15%, and 20% of CKD were replaced with cement and binary cementitious systems were formed. For all mortar mixes, the water/binder ratio was kept constant at 0.5, and the sand/binder ratio was 3. Workability, dry unit weight, water absorption ratio and porosity, flexural strength, compressive strength, abrasion, carbonation, and high-temperature resistance tests were performed on the mortar specimens. Based on the results of laboratory work, it was observed that the replacement of CKD with cement reduces the workability of fresh mortar. Compressive and flexural strengths of CKD-added mixtures were found to be equivalent or insignificantly lower than that of the control sample. The addition of CKD had a negligible effect on water absorption and porosity of samples. Besides, the residual compressive strength determined after the elevated temperature test for the sample made with CKD were found to be equivalent or higher compared to the control sample. Present laboratory studies showed that utilization of CKD in cementitious mortar system is feasible in terms of testing conducted.
Citation - WoS: 1
Citation - Scopus: 1
The Influence of Cement Kiln Dust on Strength and Durability Properties of Cement-Based Systems
(Springer Heidelberg, 2022) Hakkomaz, Hadiye; Yorulmaz, Hediye; Durak, Ugur; Ilkentapar, Serhan; Karahan, Okan; Atis, Cengiz Duran; 01. Abdullah Gül University; 02.03. İnşaat Mühendisliği; 02. Mühendislik Fakültesi
Citation - WoS: 71
Citation - Scopus: 76
Influence of NaNo SiO2 and NaNo CaCo3 Particles on Strength, Workability, and Microstructural Properties of Fly Ash-Based Geopolymer
(Ernst & Sohn, 2020) Durak, Ugur; Karahan, Okan; Uzal, Burak; Ilkentapar, Serhan; Atis, Cengiz Duran; 01. Abdullah Gül University; 02.03. İnşaat Mühendisliği; 02. Mühendislik Fakültesi
The influence of nano SiO2(NS) and CaCO3(NC) particles on the properties of class F fly ash based geopolymer mortar activated with different sodium ion concentrations have been investigated. Mortar mixture proportions were 1:3:0.3 for binder, sand, and water, respectively. Nano SiO2 and CaCO3 particles were replaced with a binder by weight basis at the ratios of 1, 2, and 3% in the mixtures. Sodium concentrations amount used were 8, 10, and 12% Na+ of binder content. Geopolymer mortar samples were cured at 60, 75, and 90 degrees C in a furnace for 24, 48, and 72 hr. After the heat curing process, flexural, and compressive strength tests were performed. The changes in the microstructure of geopolymer due to influence of nanoparticles were examined by utilizing isothermal calorimetric studies on geopolymer paste, and field-emission scanning electron microscopy (FESEM). Based on laboratory work results, it was concluded that for all sodium ion concentrations, the addition of nano SiO2 and CaCO3 particles improved the flexural and compressive strengths after 24 hr heat curing. However, the favorable effects of nanoparticles on strength properties tend to disappear after 48 and 72 hr heat curing. The results of isothermal calorimetric studies showed that nano SiO2 and CaCO3 particles accelerated the geopolymeric reactions at an early age. FESEM results showed that additions of nanoparticles made the microstructure of geopolymer products more intense and compact.
Nanotanecikler İçeren Yüksek Miktarda Doğal Puzolan Katkılı Çimentolar: Özellikler, Hidratasyon ve Hamur İç Yapısı
(TUBİTAK, 2015) Uzal, Burak; Korkanç, Mustafa; Karahan, Okan; 0000-0002-3810-7263; AGÜ, Mühendislik Fakültesi, İnşaat Mühendisliği Bölümü; Uzal, Burak; 01. Abdullah Gül University; 02.03. İnşaat Mühendisliği; 02. Mühendislik Fakültesi
Çimento sektörü dünya genelinde atmosfere salınan CO2 gazının %7’sinden tek başına_x000D_ sorumludur. Çimento sektörü odaklı CO2 emisyonlarının azaltılabilmesinde en etkin yol,_x000D_ çimentolardaki mineral katkı kullanım oranının yükseltilebilmesidir. Bunun önündeki en büyük_x000D_ engel göreceli olarak yüksek miktarda mineral katkılı çimentoların geç priz süreleri, düşük_x000D_ dayanımları ve yüksek büzülme eğilimleridir. Son yıllarda nanoteknolojiye olan ilgi artışıyla_x000D_ beraber, nanotaneciklerin çimento sistemlerinde kullanımına yönelik çalışmalar dikkat_x000D_ çekmektedir._x000D_ Bu projede yüksek miktarda doğal puzolan içeren çimentolara nanotanecik ilavesinin, farklı_x000D_ doğal puzolan tiplerine de bağlı olarak, bu çimentoların hidratasyonu, hamur iç yapısı ve_x000D_ özellikleri üzerindeki etkisi irdelenmiştir. Yirmi üç farklı doğal puzolanik malzemeden türlerini_x000D_ en iyi şekilde yansıtacak şekilde seçilen bir zeolit, bir pomza ve bir volkanik tüfün her birisi,_x000D_ ağırlıkça %50 oranında Portland çimentosuna ikame edilerek katkılı çimentolar hazırlanmıştır_x000D_ (toplam 20 farklı çimento kompozisyonu). Bu çimentolara %1 ve %2 oranlarında nanoCaCO3 ve nano-SiO2 tanecikleri ilave edilerek, çimentoların hidratasyonu, hamurların iç_x000D_ yapısı ve harç özellikleri incelenmiştir. Bu kapsamda izotermal kalorimetreyle hidratasyon_x000D_ kinetiği, taze hamurların vizkositesi, termal analizle sertleşmiş hamurların kalsiyum hidroksit_x000D_ ve bağlanmış su içerikleri, elektron mikroskobuyla iç yapı gözlemleri, harçların dayanımları_x000D_ ve büzülme (rötre) ölçümleri gerçekleştirilmiştir._x000D_ Yapılan deneysel çalışmaların sonucunda nanotanecik ilavesinin, yüksek miktarda doğal_x000D_ puzolan içeren çimentoların başta hidratasyon kinetiği (reaksiyon hızı ve açığa çıkan_x000D_ hidratasyon ısısı) olmak üzere, iç yapısını mikro ve nano düzeyde modifiye ettiği tespit_x000D_ edilmiştir. Çimento harçlarında %19’a varan oranlarda basınç dayanımı artışları ile_x000D_ büzülmelerde belirgin düşüşler gözlenmiş ve bu durumun nanotanecik ilavesiyle hamur iç_x000D_ yapısının gözenek boyut dağılımında meydana gelen yoğunlaşmayla ilgili olduğu_x000D_ değerlendirilmiştir.
Citation - WoS: 27
Citation - Scopus: 30
A New Parameter Influencing the Reaction Kinetics and Properties of Fly Ash Based Geopolymers: A Pre-Rest Period Before Heat Curing
(Elsevier, 2021) Durak, Ugur; Ilkentapar, Serhan; Karahan, Okan; Uzal, Burak; Atis, Cengiz Duran; 01. Abdullah Gül University; 02.03. İnşaat Mühendisliği; 02. Mühendislik Fakültesi
In this study, the influence of a pre-rest period before heat curing (as a new parameter), on the physical properties, flexural and compressive strength, and microstructure of geopolymer mortars and pastes produced with alkali activation of fly ash were investigated. In this context, geopolymer mortar and paste samples were prepared and pre-rested under laboratory conditions for 0, 1, 2, 3, 7, 14, and 28 days before heat curing. After the pre-rest period, the samples were subjected to heat curing at 75 degrees C in an oven, for 2 days. Mortar and paste samples exposed to a pre-rest period while in the fresh state before heat curing were compared with control samples without pre-resting. Water absorption, porosity, specific gravity, capillarity, flexural strength, compressive strength, and abrasion resistance tests were conducted on the geopolymer mortar samples. A reaction kinetics study using an isothermal calorimeter, XRD, and SEM analyses were performed on the geopolymer paste samples for microstructural investigations. Based on the results obtained, it was observed that the mechanical strength of the samples subjected to the pre-rest period before heat curing increased considerably compared to the reference (without pre-resting) samples. In addition, because of pre-resting, the capillarity coefficient, water permeability, and porosity of the samples decreased compared to the reference samples, and it was concluded that pre-resting improves durability-related properties. Moreover, the reaction kinetics and SEM analysis results, supporting the above findings, showed that a pre-resting period increases the geopolymeric reaction products and causes a denser microstructure.
Citation - WoS: 4
Citation - Scopus: 4
Reaction Kinetics and Properties of Pumice-Based Geopolymer Systems Cured at Room Temperature
(Elsevier Sci Ltd, 2023) Kucukyildirim, Enver; Yorulmaz, Hediye; Durak, Ugur; Ilkentapar, Serhan; Uzal, Burak; Karahan, Okan; Atis, Cengiz Duran; 01. Abdullah Gül University; 02.03. İnşaat Mühendisliği; 02. Mühendislik Fakültesi
This research investigated the kinetics of pumice-based geopolymer systems and their physical and mechanical properties. The effect of the Na2SiO3/NaOH ratio of geopolymer systems on the rate of heat evolution and total heat of reaction were examined via isothermal calorimetry of geopolymer pastes prepared with Na2SiO3/NaOH ratios of 2.5, 3, and 3.5. Hardened pastes were also studied with thermo-gravimetric analysis to determine weight loss. In addition, the unit weights and compressive strengths of the pastes prepared using pumice were measured. Although the hydration process starts the earliest in pumice-based geopolymer pastes with a Na2SiO3/ NaOH ratio of 2, they have the lowest total hydration temperature. Na2SiO3/NaOH ratio of 2.5 by mass, shows higher weight loss obtained from TGA results. The compressive strength of the paste sample, prepared with a Na2SiO3/NaOH ratio of 3.5 by mass, was the highest, with 36.30 MPa at 28d. Depending on the Na2SiO3/NaOH ratio, it is thought that as the amount of Na2SiO3 increases in the samples, silica gel formation increases in later ages.