Küçükgöncü, Hürmet
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Kucukgoncu, H.
Kucukgoncu, Hurmet
Küçükgöncü, Hürmet
Kucukgoncu, Hurmet
Küçükgöncü, Hürmet
Job Title
Arş. Gör.
Email Address
hurmet.kucukgoncu@agu.edu.tr
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02.03. İnşaat Mühendisliği
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Current Staff
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Sustainable Development Goals
11
SUSTAINABLE CITIES AND COMMUNITIES
3
Research Products
Documents
12
Citations
151
h-index
6
Documents
12
Citations
146
Scholarly Output
12
Articles
12
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305/8
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0
Supervised PhD Theses
0
WoS Citation Count
143
Scopus Citation Count
146
WoS h-index
6
Scopus h-index
6
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0
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2
WoS Citations per Publication
11.92
Scopus Citations per Publication
12.17
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2
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0
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| Journal | Count |
|---|---|
| Journal of Building Engineering | 3 |
| Bulletin of Earthquake Engineering | 2 |
| Construction and Building Materials | 1 |
| Journal of Earthquake Engineering | 1 |
| Niğde Ömer Halisdemir Üniversitesi Mühendislik Bilimleri Dergisi | 1 |
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Now showing 1 - 10 of 12
Article Citation - WoS: 26Citation - Scopus: 20Microstructural Analysis of Low-Calcium Fly Ash-Based Geopolymer Concrete With Different Ratios of Activator and Binder Under High Temperatures(Springer Heidelberg, 2025) Kucukgoncu, Hurmet; Ozbayrak, AhmetGeopolymer concretes have emerged as an alternative to traditional Portland cement concretes with high strength, good durability, well corrosion performance and high-temperature resistance, and being a sustainable and environmentally friendly material. In this study, a comprehensive microstructural analysis of low-calcium fly ash-based geopolymer concrete samples with different alkali activator to binder ratios was conducted after exposure to temperatures ranging from 400 to 800 degrees C. The experimental results of the geopolymer concrete specimens found out significant findings, including a notable loss of mass and an approximate 80% decrease in compressive strength after exposure to 800 degrees C. The microstructural analysis underlined crack formation, voids and porosities in the geopolymer matrix at elevated temperatures, affecting the physical and mechanical properties of the material. The study presents significant insights into the behaviour of low-calcium fly ash-based geopolymer concrete with different binder and alkali activator ratios under high temperatures, revealing the performance of geopolymer concretes in extreme environments and the effect of incompatibility between geopolymer concrete and aggregate due to thermal temperature effects on this performance.Article Citation - WoS: 11Citation - Scopus: 11The Seismic Behaviour of RC Exterior Shear Walls Used for Strengthening of Intact and Damaged Frames(Springer, 2020) Kucukgoncu, Hurmet; Altun, FatihSeveral strengthening techniques such as steel plate bonding, external post-tensioning, steel bracing, or addition of new structural elements have been widely used to improve the seismic behaviour of structures, which suffer from earthquakes. Especially, adding infill walls and shear walls to the structures are preferred because of the added increase in lateral strength and stiffness. Nevertheless, applications of these techniques have some difficulties in terms of labour, cost, usage, and comfort for occupants. Due to these difficulties, the exterior shear wall, instead of an infill wall, is applied to strengthen structures, especially for public buildings like schools, hospitals, etc. In this study, the seismic behaviours of the exterior shear walls used to strengthen intact and damaged frames were investigated experimentally. For this purpose, reinforced concrete shear walls were positioned in parallel to the exterior sides of the damaged and the intact three-dimensional frames. Both frames were tested under cyclic loads. After the investigation, the hysteresis curve, strength envelope, stiffness degradation, and the energy dissipation capacity were obtained to reveal the seismic behaviour of the strengthening exterior shear walls. In addition to these, the differences in behaviours of the shear walls applied to damaged and intact frames were identified.Article Citation - WoS: 7Citation - Scopus: 8Stress and Damage Distribution Analysis of Steel Reinforced Geopolymer Concrete Beams: Finite Element Method and Experimental Comparison Under Varying Design Parameters(Elsevier, 2025) Ozbayrak, Ahmet; Kucukgoncu, Hurmet; Aslanbay, Huseyin Hilmi; Aslanbay, Yuksel GulGeopolymer concrete (GPC) is a sustainable and eco-friendly alternative to ordinary Portland cement-based concrete (OPC). However, its application in reinforced concrete structures remains limited due to insufficient research on structural performance. This study examines the effects of tensile reinforcement ratio, sodium silicate/sodium hydroxide ratio, and curing method on GPCreinforced concrete (GPC-RC) beams. Experimental and numerical bending tests were performed on GPC and OPC beams with similar tensile reinforcement and strength properties. Load- displacement and moment-curvature relationships were obtained and compared, while stress and stiffness behaviors were analyzed numerically. The results show that curing methods and reinforcement ratios significantly influence GPC beam behavior. In GPC samples, numerical and experimental displacement and load values differed by approximately 10 % at both yield and ultimate points. For OPC, these differences were 35 % and 14 % at the yield point and 17 % and 25 % at the ultimate point. GPC exhibited distinct stress and damage distribution characteristics compared to OPC. The finite element models were statistically validated, confirming their consistency with experimental results. These findings contribute to the understanding of GPC's structural behavior and provide guidance for its design and optimization in reinforced concrete applications.Article Citation - WoS: 1Citation - Scopus: 2Equivalent Stress Block Parameters for Fly Ash-Based Geopolymer Concrete Structural Elements(Ernst & Sohn, 2025) Ozbayrak, Ahmet; Kucukgoncu, HurmetResearch on the design of structural members made from geopolymer concrete (GPC) remains limited. This study investigates the applicability of equivalent rectangular stress block parameters, traditionally used for reinforced concrete design, in GPC structural elements. We conducted experimental tests on 20 columns (16 GPC, 4 Ordinary Portland Cement [OPC]) and 15 beams (12 GPC, 3 OPC) produced using fly ash-based GPC and standard OPC. These tests involved subjecting the specimens to various loading conditions to measure their ultimate compressive strength and strain. The findings demonstrate that these factors significantly influence the stress block parameters in GPC samples. Notably, parameters k(1) and k(3) were compatible with ACI 318 and Eurocode 2 standards, with deviations within acceptable limits, supporting GPC's potential for use in conventional reinforced concrete frameworks. The study also reveals that GPC columns and beams have higher balanced reinforcement ratios than OPC, due to GPC's increased deformation capacity and strain values. According to the results, the average balanced reinforcement ratio of GPC column specimens is 30% higher than that of OPC, while that of GPC beam specimens is 6% higher. Variations in alkaline activation and curing methods did not significantly impact the equivalent stress block parameters. The change between the average equivalent stress block parameters obtained from GPC and OPC beam samples varies between 1% and 5%, while the change in column samples is around 1%. Although the longitudinal reinforcement ratios in the tests are variable, the averages of the calculated equivalent stress block parameters are close. The experimental results align with numerical analysis, emphasizing GPC's suitability as an alternative material in structural applications. These findings provide a basis for incorporating GPC into existing design standards, with adjustments for its distinct mechanical behavior.Article Structural Behavior of Geopolymer Reinforced Concrete Beams: Experimental, Numerical, and Code-Based Assessment(Springer, 2025) Ozbayrak, Ahmet; Kucukgoncu, HurmetThis study experimentally investigates the flexural performance of heat-cured low-calcium fly ash-based geopolymer concrete (GPC) beams reinforced with ribbed steel bars, focusing on the effects of reinforcement ratio, alkaline activator concentration (SS/SH), and curing regime. Fifteen full-scale beams, including twelve GPC and three OPC specimens, were tested under four-point loading to evaluate load-deflection and moment-curvature behavior. Despite a lower compressive elastic modulus, the results showed that GPC beams exhibited comparable or superior cracking and ultimate moment capacities relative to OPC beams. Increasing the reinforcement ratio enhanced load capacity but reduced ductility in both systems, with GPC beams showing more brittle post-yield behavior. Numerical models based on OPC parameters were developed in SAP2000 to compare with experimental GPC moment-curvature data, revealing good agreement in the linear range but notable differences in post-yield response. The study also examined the microstructure of failed GPC beams via SEM, XRD, and EDX analyses to correlate matrix morphology with mechanical behavior. Finally, moment capacities calculated according to ACI 318 and TS 500 provided conservative estimates, supporting the safe applicability of current design codes to heat-cured GPC beams. These findings demonstrate that GPC, when properly proportioned and cured, is a viable structural alternative to OPC for reinforced concrete members.Article Citation - WoS: 27Citation - Scopus: 29Determination of Stress-Strain Relationship Based on Alkali Activator Ratios in Geopolymer Concretes and Development of Empirical Formulations(Elsevier Science Inc, 2023) Ozbayrak, Ahmet; Kucukgoncu, Hurmet; Atas, Oguzhan; Aslanbay, Huseyin Hilmi; Aslanbay, Yuksel Gul; Altun, FatihFly ash-based geopolymer has recently gained attention of researchers due to its potential application, as well as being an alternative binder with low emissions compared to ordinary Portland cement (OPC) in concrete production. Studies which are conducted on the design and mechanical properties of structural members produced from fly ash geopolymer concrete (GPC) are very important in terms of increasing the use of this concrete. The aim of this study is to obtain experimental data on the effect of sodium silicate/sodium hydroxide (SS/SH) and alkali activators/fly ash (AA/FA) ratios on the mechanical properties of a low calcium heat-cured fly ash geopolymer. In addition, it is to reveal the similarities and differences of OPC and GPC by comparing the mathematical formulations in existing regulations and concrete models with experimental data. Thus, geopolymer cylinder concrete samples were produced using 15 different mixtures with SS/SH ratios of 1.5, 2.5 and 3.5, while AA/FA ratios of 0.4, 0.5, 0.6, 0.7 and 0.8. At the end of the study, the optimum SS/SH ratio was obtained as 2.5. A decrease in the AA/FA ratio increases the compressive and splitting tensile strength, while an increment increases the ductility and consuming energy. In addition, the relationship between the experimental data and the splitting tensile strength and modulus of elasticity formulations depending on the compressive strength given in other studies and regulations as a part of literature was investigated, and then, two alternative empirical formulations considering the ratios of alkali activators were proposed at the end of the regression analysis. When the stress-strain relationship of OPC concrete models and GPC mixtures were compared, the closest unconfined concrete model for GPC concrete was the Hognestad model.Article Citation - WoS: 1Citation - Scopus: 1Experimental and Numerical Analysis of Damage and Crack Behavior in Geopolymer and Ordinary Portland Cement Reinforced Concrete Columns(Elsevier, 2025) Ozbayrak, Ahmet; Kucukgoncu, Hurmet; Aslanbay, Yuksel Gul; Aslanbay, Huseyin HilmiThis study evaluates and compares the structural behavior of reinforced concrete columns produced with geopolymer concrete (GPC) and ordinary Portland cement (OPC) under eccentric axial loading, aiming to investigate GPC's potential as a sustainable alternative. A total of twenty columns with varying longitudinal reinforcement ratios, curing methods, eccentricities, and geopolymer formulations were experimentally tested. Displacement measurements at each load increment were obtained using a total station, allowing crack pattern tracking at key stages such as first cracking, yielding, and ultimate failure. These observations were schematically documented using AutoCAD. Additionally, finite element models were developed in ABAQUS using the Concrete Damage Plasticity (CDP) model, with material parameters calibrated based on experimental compressive and tensile strengths, elastic modulus, and fracture energy. Results indicated that increasing eccentricity reduces axial load capacity while increasing lateral deformation. While the reinforcement ratio did not significantly affect axial strength, it increased displacement demand. Due to their distinct microstructural characteristics, GPC columns exhibited greater deformation capacity and narrower, more localized crack patterns than OPC columns. Furthermore, the sodium silicate/sodium hydroxide (SS/SH) ratio and curing duration significantly influenced the structural response of GPC. Numerical simulations showed strong agreement with experimental results regarding load-displacement behavior and damage distribution. These findings demonstrate that GPC can serve as a reliable and sustainable alternative to OPC in structural column applications, provided its specific material properties are considered in design and analysis.Article Sargısız Betonun Mekanik Özelliklerinin TBDY 2018 ve Diğer Modellerle Analitik ve Deneysel Karşılaştırılması(2023) Küçükgöncü, HürmetBetonarme elemanların davranışlarının anlaşılabilmesi için betonarmeyi oluşturan malzemelerin gerilme-şekil değiştirme davranışlarının bilinmesi gerekmektedir. Sargısız beton malzemesinin gerilme-şekil değiştirme davranışının tahmin edilebilmesi için pek çok matematiksel model geliştirilmiştir. Türkiye Bina Deprem Yönetmeliği 2018 (TBDY 2018) de de sargısız betonların gerilme-şekil değiştirme bağıntılarına yer verilmektedir. Ancak bu matematiksel modellerin dayanım, süneklik ve yük altında enerji tüketebilme kapasitesi açısından benzer özelliklerdeki deneysel numunelerden farkının tespit edilmesi oldukça önemlidir. Böylece sargısız beton modellerin, analitik yaklaşımlarının doğruluğu belirlenebilmektedir. Betonarme yapısal elemanların özellikle kesit davranışı araştırılırken ya da yük altında kesit tasarımları yapılırken söz konusu modellerin sergilediği davranışı bilmek büyük kolaylıklar sağlamaktadır. Bu nedenle, bu çalışmada TS 500 yönetmeliğinde yer alan beton sınıfları ve dayanımlarına uygun olarak üretilen numuneler basınç testine tabi tutulmuş, sonrasında ise bu dayanım sınıflarına ait sargısız beton davranışı için literatürde sık kullanılan matematiksel modeller ve TBDY 2018 de yer alan bağıntılar kullanılarak gerilme-şekil değiştirme grafikleri elde edilmiştir. Bu grafiklerden yararlanılarak süneklik ve enerji tüketebilme kapasitesi gibi mekanik özellikleri, TBDY 2018 ve diğer matematiksel modellerle, deneysel verilerden elde edilen değerler karşılaştırılarak farklılıkları ortaya konulmuştur. Buna göre göz önüne alınan beton modellerinin güçlü ve zayıf yönleri belirlenmiş ve kullanılan beton sınıfına ait dayanımın da modellerin performansı üzerinde etkili olduğu sonucuna varılmıştır.Article Citation - WoS: 50Citation - Scopus: 53Comprehensive Experimental Analysis of the Effects of Elevated Temperatures in Geopolymer Concretes With Variable Alkali Activator Ratios(Elsevier, 2023) Ozbayrak, Ahmet; Kucukgoncu, Hurmet; Aslanbay, Huseyin Hilmi; Aslanbay, Yuksel Gul; Atas, OguzhanBy growing population and rapid urbanization, demand for concrete increases exponentially. Researches on use of fly ash material in waste product class for concrete production are important to produce concrete more environmentally friendly. However, there is a need for more research to use geopolymer concrete (GPC) in every field where ordinary Portland cement concrete (OPC) is used. Therefore, it is crucial to experimentally investigate thermal properties as well as me-chanical properties of geopolymer concrete. As investigated thermal properties, the main factor affecting strength development of GPC is alkali activator ratios. In this study, GPC prism samples with nine different compositions, produced by various alkali ratios. After flexural strength tests, they were cut into cubes and exposed to 400 degrees C, 600 degrees C and 800 degrees C, then they were subjected to compressive strength tests. Results obtained from different AA/FA and SS/SH ratios were eval-uated as mechanical properties at ambient temperature and physical, mechanical and micro-structural properties at elevated temperature. An empirical formula, which considers the effect of activator ratios, was proposed to calculate flexural strength depending on compressive strength of samples at ambient temperature. As an increase of SS/SH and AA/FA ratios, compressive strength increased, while flexural strength decreased. The increase in AA/FA ratio decreased compressive strength of samples exposed to high temperatures, while increase in SS/SH ratio did not deter-mine at elevated temperatures. There is an inverse change with AA/FA ratio and parallel change with SS/SH ratio between compressive strengths of samples at ambient temperature and exposed to high temperature.Article Numerical Analysis and Experimental Comparison of Stress and Stiffness Parameters of Steel Reinforced Geopolymer Concrete Columns(Elsevier Sci Ltd, 2026) Ozbayrak, Ahmet; Kucukgoncu, Hurmet; Aslanbay, Huseyin Hilmi; Aslanbay, Yuksel Gul; Altun, FatihDespite extensive research, Geopolymer concrete (GPC) lacks reinforced concrete construction and design specifications. Developing such specifications requires comprehensive studies to promote the use of GPC, which is known for its superior performance and environmental benefits compared to ordinary Portland cement concrete (OPC). This study numerically investigated and compared the behavior and strength of fly ash-based geopolymer-reinforced concrete columns with the experimental results. Comparisons with OPC were made based on existing specifications. Herein, FEM analyses were conducted on 16 GPC and 4 OPC columns under eccentric axial compressive loads. Parameters such as eccentricity, reinforcement ratio, curing method, and activation solution ratios were varied. According to average numerical results, the GPC columns have 7% more moment capacity and 30% more curvature values than OPC. Moreover, GPC columns absorbed more energy than OPC columns. Also, GPC columns have higher axial load and bending moment carrying capacities than OPC for numerical results. Error analysis between FEM and experimental data revealed a strong correlation, with MAPE values of 8.88% (axial load) and 7.20% (moment) for GPC columns, confirming the reliability of the numerical model. ACI 318 and Eurocode 2 specifications were deemed applicable for GPC columns, provided axial loads are limited per TEC 2018.
