NaOH-activated ground fly ash geopolymers, cured at room temperature, were studied in this paper.
Ground fly ash (GFA), with a median particle size of 10.5 lm, was used as source material. NaOH concentrations
of 4.5–16.5 M (M) were used as an alkali activator. Compressive strength tests and microstructure
observations using SEM, EDX, XRD and FTIR were performed. Results indicated that GFA gave higher
strength geopolymer paste compared to original fly ash. Ground fly ash could be used as a source material
for making geopolymers cured at room temperature. An increase in NaOH concentration from 4.5 to
14.0 M increased the strength of GFA geopolymer pastes. Microstructure studies indicated that NaOH
concentrations of 12.0–14.0 M created new crystalline products of sodium aluminosilicate. The compressive
strengths at 28 days of 20.0–23.0 MPa were obtained with the NaOH concentrations of 9.5–14.0 M.
Increasing the NaOH concentration beyond this point resulted in a decrease in the strength of the paste
due to early precipitation of aluminosilicate products.