Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
Browse
6 results
Search Results
Article Citation - WoS: 8Citation - Scopus: 8Very High Early Strength Calcium Aluminate Based Binary and Ternary Cementitious Systems: Properties, Hydration and Microstructure(Taylor & Francis Ltd, 2023-06-16) Saydan, Murat; Keskin, Ulku Sultan; Uzal, BurakCalcium aluminate cement (CAC) is a cement type that has superior properties such as rapid strength gain, high resistance to high temperatures and harmful chemicals. However, the result of the using of CACs in the production of structural elements occur strength decreases at later ages as a result of a series of chemical reactions called 'conversion reactions' seen in these cements. In this study, the hydration kinetics and the crystalline and amorphous structures formed as a result of hydration were investigated in CAC containing different amounts and types of main oxides-based binary and ternary systems. Considering the results obtained, the main hydration product seen in these specimens was ettringite. Unlike many studies in the literature, metastable structures which cause conversion reactions, such as CAH(10), C(2)AH(8), have not been observed. Instead of conversion of the phases, ettringite needles were became thin and elongate which causes the paste structure porous and thus causing expansion and strength reduction at the later stages of hydration in some mixtures produce high amounts of ettringite. On the other hand, it is understood that the formation of stratlingite was limited strength decreases in systems where high silica fume is used.Article Citation - WoS: 79Citation - Scopus: 83Influence of NaNo SiO2 and NaNo CaCo3 Particles on Strength, Workability, and Microstructural Properties of Fly Ash-Based Geopolymer(Ernst & Sohn, 2020-05-06) Durak, Ugur; Karahan, Okan; Uzal, Burak; Ilkentapar, Serhan; Atis, Cengiz DuranThe 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.Article Citation - WoS: 34Citation - Scopus: 38Green Building Envelope Designs in Different Climate and Seismic Zones: Multi-Objective ANN-Based Genetic Algorithm(Elsevier, 2022-10) Himmetoglu, Salih; Delice, Yilmaz; Aydogan, Emel Kizilkaya; Uzal, Burak; Kızılkaya Aydoğan, EmelIn recent years, the major component of green building designs adopted by governments in order to reduce CO2 emissions as well as energy consumption is the green building envelope. The green envelope has the most important share in terms of thermal energy consumption, environment, and indoor comfort criteria. Determining the most suitable building envelope combination in the building life cycle is an important problem for designers. This study presents a new multi-objective approach that determines the most suitable green envelope designs for the buildings in different climate and earthquake zones, taking into account CO2 emissions, heating/cooling energy consumption, and material cost in terms of life cycle cost analysis. To this end, EnergyPlus building performance simulation program, artificial neural network (ANN), and genetic algorithm are used together. After the heating and cooling energy consumption, CO2 emissions, and material cost values are obtained for a certain number of the envelope alternatives with the EnergyPlus, ANN models that learn the working mechanism of EnergyPlus are trained according to these values. An ANN-based genetic algorithm procedure is developed to search the whole envelope alternative space by using the trained ANN models with EnergyPlus. The proposed approach allows searching in a very short time the whole alternative space, which is almost impossible to scan with EnergyPlus by reducing the time spent and the number of alternatives required for the design and simulation processes of the green building envelope. The proposed approach is performed for a design-stage city hospital structure in Turkey. Window type, the internal/external plaster, wall, and insulation materials along with the thicknesses of these materials, which consist of 46 different variables, are determined as envelope attributes for four different climate and seismic zones. The green building envelope designs obtained with the proposed approach are entered into EnergyPlus and the consistency of the results is compared. ANN models with an average accuracy of over 97% are developed. Without the CO2 emission cost in the life cycle cost, the mean absolute percent error (MAPE) values for each region are 0.67%, 0.6%, 0.58%, and 1.78%, respectively. With the CO2 emission cost in life cycle cost, the MAPE values for each region are 0.96%, 0.88%, 0.86%, and 0.43%, respectively. According to the obtained results, there is a consistency of over 99% between EnergyPlus and the proposed approach.Article Citation - WoS: 8Citation - Scopus: 8Effect of Nano-SiO2 on Strength and Hydration Characteristics of Ternary Cementitious Systems(Springer Heidelberg, 2023-05-31) Yorulmaz, Hediye; Uzal, Burak; Karahan, Okan; Durak, Ugur; Ilkentapar, Serhan; Atis, Cengiz DuranThis 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.Article Citation - WoS: 15Citation - Scopus: 16Effect of Duration and Type of Grinding on the Particle Size Distribution and Microstructure of Natural Pumice With Low Pozzolanic Reactivity(Elsevier, 2023-10) Taj, Khalilullah; Ilcan, Huseyin; Teksin, Eray; Argin, Gizem; Ardog, Mehmet Kemal; Uzal, Burak; Sahmaran, Mustafa; Ardoğa, Mehmet KemalPumice, with low pozzolanic reactivity, was ground for 1, 3, and 6 h with a laboratory ball mill in dry conditions and it was ground for 1 h in wet conditions via an industrial-scale ball mill. Based on derivative particle dis-tribution, grinding for longer periods led to the disappearance of bimodal distribution and the development of unimodal distribution. Furthermore, the phase characterization, assessed through XRD, demonstrated appre-ciable changes in intensities of the peaks of quartz and dachiardite. The extension of grinding time resulted in a significant uptake at the early-age lime consumption and evolution of hydration heat. According to SEM images, the number of particles between 10 and 20 & mu;m was less in the powder ground for 3 and 6 h. Moreover, it was found that the prismatic shapes of raw pumice tended to transform to spheroid shapes after prolonged grinding, and the smooth surfaces of pumice particles became more rugged.Article Compatibility of Superplasticizers With Natural Pozzolan Blended Cement: Multi-Criteria Compatibility Index Through Rheology and Hydration Kinetics(Taylor & Francis Ltd, 2025-08-09) Argin, Gizem; Uzal, BurakAn effective technique to decrease carbon dioxide emissions in the cement industry is the partial replacement of clinker with supplemental cementitious materials (SCMs). Given the restricted supply of by-product SCMs such fly ash, blast furnace slag, and silica fume, natural pozzolans provide viable options in the manufacturing of blended cement. In cementitious systems with natural pozzolans, the use of superplasticizers is essential to compensate for the reduced workability caused by their higher water demand. This study investigates the compatibility of different superplasticizer types, administered at similar dosages, with Portland cement containing 40% natural pozzolan, focusing on paste rheology and hydration kinetics. A Multi-Criteria Compatibility Index (MCCI) was created to provide a comprehensive and quantitative evaluation of compatibility between natural pozzolans and different types of superplasticizers, utilizing rheological and hydration kinetics within a weighted scoring framework. The assessment findings indicated that PMS displayed the best overall compatibility, principally owing to its improved hydration properties, but PNS revealed enhanced performance in rheological characteristics. PCA demonstrated restricted compatibility in both categories. The MCCI framework delivered a balanced and thorough comparison unattainable by single-parameter studies, providing a solid methodological foundation for future study on SCM-admixture compatibility.