Geopolymer Synthesis with Low Sodium Hydroxide Concentration
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RESEARCH PAPER
Geopolymer Synthesis with Low Sodium Hydroxide Concentration Evren Arioz1 · Omer Arioz2 · O. Mete Kockar1 Received: 21 May 2018 / Accepted: 27 December 2019 © Shiraz University 2020
Abstract In this study, fly ash was utilized to synthesize geopolymer by activating with 4 M sodium hydroxide. Samples were cured at 120 °C for 6, 15 and 24 h, and they were aged for 7, 28 and 90 days. The degree of reaction was determined, and leaching tests were performed on all geopolymer samples according to US EPA TCLP method. The microstructural properties of samples were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and scanning electron microscope (SEM) techniques. Increase in both curing and aging durations resulted in higher compressive strength values. The results of leaching tests indicated that the metals were successfully immobilized. The major bonds of geopolymers were observed in FTIR spectrum. The intensity of the Al–O and Si–O asymmetric bonds increased with increase in curing duration. In XRD diffractograms, it was observed that all of the geopolymer samples had amorphous structure containing mainly two crystal phases. FTIR, XRD and SEM results revealed that geopolymerization was achieved in these synthesis conditions despite low molarity. Keywords Geopolymer tests · Fly ash · Alkali activation · Compressive strength test · Leaching test · Microstructural properties
1 Introduction The energy consumption is increasing gradually due to increase in World’s population. It is expected that the energy demand will increase at a rate of 40% between 2007 and 2030 reaching 16.8 million tons of equivalent petroleum (Torgal and Jalali 2011). In coal burning thermal power plants, a million tons of fly ash occurs each year due to coal combustion to meet the industrial and domestic energy demand (Alvarez-Ayuso et al. 2008; Swanepoel and Strydom 2002; Ahmaruzzaman 2010). Fly ash is captured from flue gases by electrostatic precipitators or bag filter systems (van der Merwe et al. 2014). The excessive amount of fly * Evren Arioz [email protected] Omer Arioz [email protected] O. Mete Kockar [email protected] 1
Department of Chemical Engineering, Faculty of Engineering, Iki Eylul Campus, Eskisehir Technical University, 26555 Eskisehir, Turkey
AAcademy RMC, Eskisehir, Turkey
2
ash creates serious environmental problems (Swanepoel and Strydom 2002; Ahmaruzzaman 2010). Worldwide, 600 million tons of ash is produced annually but 75–80% of it is classified as fly ash. Furthermore, 30–40% of this amount is utilized throughout the world, but unfortunately the rest is disposed in landfills (Alvarez-Ayuso et al. 2008; Al-Degs et al. 2014; Fernández-Jimenez et al. 2006; Hassan and Arif 2019). On the other hand, fly ashes are suitable source materials for geopolymerization because of their contents and structures (Thunuguntla and Rao 2018). The amorphous or glassy silica existing in their structures dissolves in alkaline solution and forms the geopolyme
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