Role of particle size on the mechanical and microstructural properties of fly ash-based geopolymer

Geopolymers are amorphous inorganic polymers that can be synthesized by utilizing aluminosilicate source materials and alkaline solutions. Geopolymer materials show excellent mechanical properties compared to conventional materials. Various process parameters affect the mechanical properties, and among them, the particle size distribution of aluminosilicate source materials plays an important role. This study addresses the challenge of improving the mechanical and microstructural properties of fly ash-based geopolymer by investigating the role of particle size. Instead of mechanical milling of fly ash powders, various-sized powders were collected, analyzed, and used to synthesize geopolymer specimens. In this present investigation, sodium hydroxide solutions and sodium silicate solutions were used as an alkaline activator, where the concentration of sodium hydroxide solution was 14 molar. The ratio of sodium hydroxide solutions to sodium silicate solutions and the liquid to solid was maintained at 1 and 0.3, respectively. The synthesized geopolymer specimens are tested with the universal testing machine. The highest compressive strength and flexural strength values of 43.87 MPa and 5.44 MPa were achieved under ambient curing for 28 days. The formation of a larger quantity of sodium alumino-silicate hydrated (N-A-S-H) gel is attributed to an enhancement in mechanical strength, including flexural and compressive strength. The specimen that achieves the highest mechanical strength is analyzed using techniques such as Fourier transform infrared spectroscopy, Field emission scanning electron microscope, and Transmission electron microscope, respectively. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.