WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Structural Behavior of Geopolymer Reinforced Concrete Beams: Experimental, Numerical, and Code-Based Assessment(Springer, 2025-08-11) 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: 35Citation - Scopus: 29Microstructural Analysis of Low-Calcium Fly Ash-Based Geopolymer Concrete With Different Ratios of Activator and Binder Under High Temperatures(Springer Heidelberg, 2024-06-25) 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: 53Citation - Scopus: 55Comprehensive 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.