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Abstract
This paper investigates the properties of geopolymer obtained by alkali-activation
of fly ash (FA), i.e. the influence of characteristics of the representative group
of FA (class F) from Serbia, as well as that of the nature and concentration of various
activators on mechanical and microstructural properties of geopolymers. Aqueous solutions
of Ca(OH)(2), NaOH, NaOH+Na(2)CO(3), KOH and sodium silicate (water glass) of various
concentrations were used as alkali activators. It was established that the nature
and concentration of the activator was the most dominant parameter in the alkali-activation
process. In respect of physical characteristics of FA, the key parameter was fineness.
The geopolymer based on FA with the highest content of fine particles (<43 microm),
showed the highest compressive strength in all cases. Regardless of FA characteristics,
nature and concentration of the activator, the alkali-activation products were mainly
amorphous. The formation of crystalline phases (zeolites) occurred in some cases,
depending on the reaction conditions. The highest compressive strength was obtained
using sodium silicate. Together with the increase of sodium silicate SiO(2)/Na(2)O
mass ratio, the atomic Si/Al ratio in the reaction products was also increased. Under
the experimental conditions of this investigation, high strength was directly related
to the high Si/Al ratio.