The present work studies and compares the flexural properties of fly ash geopolymer with varying molarity of sodium hydroxide (NaOH). Different molarities of NaOH solution (6M, 8M, 10M, 12M and 14M) are used to prepare the alkali activator (a mixture of NaOH and sodium silicate). The fly ash geopolymer were synthesised by using the solid/liquid ratio of 2.5 and sodium silicate/NaOH ratio of 2.5. The samples were cured at 60°C for 6 hours. The flexural test and microstructural analysis of fly ash geopolymer are performed after 28 days. Generally, the flexural strength of fly ash geopolymer increases when the molarity of NaOH increases. The 12M geopolymer has the highest flexural strength and a more densified microstructure is observed.
