The Role of Water in the Synthesis of Fly Ash-Based Geopolymer


  • Hongsheng Cheng Center of Innovative Materials for Sustainability, School of Science, Mae Fah Luang University
  • Darunee Wattanasiriwech Center of Innovative Materials for Sustainability, School of Science, Mae Fah Luang University
  • Suthee Wattanasiriwech Center of Innovative Materials for Sustainability, School of Science, Mae Fah Luang University


Fly Ash Based Geopolymer, Compressive Strength, Apparent Density


Water has played an important role in controlling geopolymerization and thus mechanical properties of final geopolymer products. Effects of internal water and atmospheric water on formation of fly ash-based geopolymers and their properties were systematically studied in this research. The initial water amount was varied from 29 to 44 wt%. To investigate the effect of the atmospheric water, curing was designed into 3 successive steps. The samples were first activated at 60 °C in a water saturated-atmosphere for 24 h. Then they were cured at 40 °C for 3 days in two atmospheres; water saturated- or open, prior to curing at 40 °C in an open atmosphere for another 3 days. Microstructure was examined using a scanning electron microscope. Porosity and apparent density were measured following ASTM C 642-06. The results showed that porosity of the samples increased with increasing the initial water content. The initial water content, however, had only minor effect on the apparent density. Curing in the water saturated-atmosphere resulted in a significantly improved compressive strength possibly due to the milder water evaporation. Compressive strength increased with decreasing the initial water contents according to lowered porosity contents. In conclusion, the samples with 29 wt% water content cured in the water saturated - atmosphere showed the highest compressive strength of 34 MPa. This geopolymer paste showed promising potential in construction industry as a cement paste replacement.


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