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 12M 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 x 25 x 285 mm prisms, then immersed in different media consisting of water or 1M to 3M NaOH solutions maintained at varied temperatures of 23, 38 and 80⁰C. The tests done include compressive strength, expansion, 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.