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Date of Publication:2021-01-01

Journal:Zhongguo Gonglu Xuebao/China Journal of Highway and Transport

Volume:34

Issue:10

Page Number:234-244

ISSN No.:1001-7372

Abstract:Coal-based synthetic natural gas slag (CSNGS) is a potential new resource for producing geopolymer, however, few studies have reported the utilization of CSNGS in geopolymer area. The present paper, the geoploymers were fabricated by using the milled CSNGS powder and sodium hydroxide or potassium hydroxide solution. Firstly, the effects of different factors on the strength of the CSNGS geopolymers were studied by a compressive test. Secondly, X-ray diffraction (XRD), field emission scanning electron microscope-energy dispersive spectrometer (SEM/EDS), and Fourier transform infrared spectroscopy (FT-IR) were carried out to investigate the microstructural properties and the reaction mechanism of two kinds of CSNGS geopolymers, and the effects of different alkali metal cations on the properties of geopolymers were also analyzed. The findings show that the peak intensity of crystals in the CSNGS decreases and the silicon-to-aluminum ratio (Si/Al) increases due to the increase of thermal curing temperature, which may cause an increase of geopolymer strength. It is also found that under proper thermal curing conditions, when the concentration of the activator is 6-9 mol•L-1, the two kinds of CSNGS geopolymers can obtain high mechanical strength. The SEM analysis shows that a highly denser microstructure is formed by a number of sodium aluminosilicate hydrate (N-A-S-H) or potassium aluminosilicate hydrate (K-A-S-H) gels attributing to a high heat curing temperature and an appropriate activator concentration, which leads to a satisfactory mechanical strength of the CSNGS geopolymer. In addition, the alkali-activated effect of NaOH solution on CSNGS is better than that of KOH solution. This is not only because the binding capacity of sodium ions and negative ions are stronger than that of potassium ions, it more effectively maintains the charge balance in the geopolymer framework, but also because sodium ions areeasierthan potassium ions to form geopolymer gels with two or three SiO4 tetrahedrons bridging a single AlO4 tetrahedron, which makes the material form a dense and uniform microstructure. The highest strength of the geopolymer studied in this paper are 36.1 MPa (NaOH) and 27.8 MPa (KOH), respectively. In general, it is feasible to produce geopolymer by the CSNGS. © 2021, Editorial Department of China Journal of Highway and Transport. All right reserved.

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