WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Citation - WoS: 9Citation - Scopus: 9Reaction Kinetics and Properties of Pumice-Based Geopolymer Systems Cured at Room Temperature(Elsevier Sci Ltd, 2023-12) Kucukyildirim, Enver; Yorulmaz, Hediye; Durak, Ugur; Ilkentapar, Serhan; Uzal, Burak; Karahan, Okan; Atis, Cengiz DuranThis 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.Article Citation - WoS: 108Citation - Scopus: 124Dual Effectiveness of Freezing-Thawing and Sulfate Attack on High-Volume Slag-Incorporated ECC(Elsevier Sci Ltd, 2013-02) Ozbay, Erdogan; Karahan, Okan; Lachemi, Mohamed; Hossain, Khandaker M. A.; Atis, Cengiz DuranThis 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.Article Citation - WoS: 32Citation - Scopus: 35A New Parameter Influencing the Reaction Kinetics and Properties of Fly Ash Based Geopolymers: A Pre-Rest Period Before Heat Curing(Elsevier, 2021-03) Durak, Ugur; Ilkentapar, Serhan; Karahan, Okan; Uzal, Burak; Atis, Cengiz DuranIn 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.