Geopolymers are inorganic polymers which can be produced by the reaction between silico aluminate oxides and alkali silicates in alkaline medium. Materials containing silica and alumina compounds are suitable for geopolymer production. These can be primary materials or industrial wastes, i. e. fly ash, metallurgical slag and red mud. ud In this paper, the results of the systematic experimental series are presented which were udcarried out in order to optimize the geopolymer preparation process. Fly ash was ground for uddifferent residence time (0, 5, 10, 30, 60 min) in order to investigate the optimal specific udsurface area. NaOH activator solution concentration also varied (6, 8, 10, 12, 14 M). udFurthermore, sodium silicate was added to NaOH as a network builder solution. In this last udserie different heat curing temperatures (30, 60, 90°C) were also applied. After seven days of udageing the physical properties of the geopolymer(compressive strength and specimen uddensity)were measured. Chemical leaching tests on the rawmaterial and the geopolymers were udcarried out to determine the elements which can be mobilized by different leaching solutions. It udwas found that the above mentioned parameters (fly ash fineness, molar concentration and udcomposition of activator solution, heat curing) has great effect on the physical and chemical udproperties of geopolymer specimens. Optimal conditions were as follows: specific surface area udof the fly ash above 2000 cm2/g, 10 M NaOH, 30o C heat curing temperature which resulted in 21 MPa compressive strength geopolymer.
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