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Behaviour of fly ash geopolymer binders under exposure to alkaline media
Abstract Alkaline agents are primary binder components of geopolymer systems. In the converse, however, the hardened geopolymer binders can be adversely affected under exposure to strong alkalis. This paper presents an investigation conducted to evaluate the effects of highly alkaline exposure environment on fly ash geopolymer binders. In the study, a combination of sodium silicate and 12 M NaOH solution was used as the alkali activator to prepare a low calcium (Class F) fly ash-based geopolymer binder. Fly ash geopolymer pastes or mortars were cast into 50 mm cubes and 25 × 25 × 285 mm prisms, then immersed in different media consisting of water or 1–3 M NaOH solutions maintained at varied temperatures of 23, 38, and 80 °C. The tests done include compressive strength, expansion, and weight changes. Analytical studies were done using X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, scanning electron microscopy. Leaching analysis of storage solutions was also conducted. Results showed that alkali attack occurred when the concentrations of storage solutions exceeded 1 M NaOH. The severity of attack increased with increase in NaOH concentration and in storage temperature. It was found that the alkali attack causes damage to the polymeric structure of the binder, leading to release of Al and Si. A gel-like substance is formed, causing expansion and microcracking. New crystalline zeolite phases comprising phillipsite, zeolite-P and chabazite, also formed under exposure of the fly ash geopolymer binder to elevated alkali concentrations.
Behaviour of fly ash geopolymer binders under exposure to alkaline media
Abstract Alkaline agents are primary binder components of geopolymer systems. In the converse, however, the hardened geopolymer binders can be adversely affected under exposure to strong alkalis. This paper presents an investigation conducted to evaluate the effects of highly alkaline exposure environment on fly ash geopolymer binders. In the study, a combination of sodium silicate and 12 M NaOH solution was used as the alkali activator to prepare a low calcium (Class F) fly ash-based geopolymer binder. Fly ash geopolymer pastes or mortars were cast into 50 mm cubes and 25 × 25 × 285 mm prisms, then immersed in different media consisting of water or 1–3 M NaOH solutions maintained at varied temperatures of 23, 38, and 80 °C. The tests done include compressive strength, expansion, and weight changes. Analytical studies were done using X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, scanning electron microscopy. Leaching analysis of storage solutions was also conducted. Results showed that alkali attack occurred when the concentrations of storage solutions exceeded 1 M NaOH. The severity of attack increased with increase in NaOH concentration and in storage temperature. It was found that the alkali attack causes damage to the polymeric structure of the binder, leading to release of Al and Si. A gel-like substance is formed, causing expansion and microcracking. New crystalline zeolite phases comprising phillipsite, zeolite-P and chabazite, also formed under exposure of the fly ash geopolymer binder to elevated alkali concentrations.
Behaviour of fly ash geopolymer binders under exposure to alkaline media
Naghizadeh, A. (author) / Ekolu, S. O. (author)
Asian Journal of Civil Engineering ; 20 ; 785-798
2019-04-26
14 pages
Article (Journal)
Electronic Resource
English
Behaviour of fly ash geopolymer binders under exposure to alkaline media
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