Abstract: The effects of the ratios of H_2O/FA (fly ash), NaOH/FA, water glass/FA and calcium compounds addition on setting time of geopolymers were investigated. The hardened products were examined by scanning electron microscope (SEM) and the activating solutions were analyzed by nuclear magnetic resonance (~(29)SiNMR). As a result, the final setting times of geopolymers prolonged from 120 min to 280 min as the ratio of H_2O/FA increases from 0.29 to 0.36. The setting time of geopolymer was prolonging with the ratio of NaOH/FA increasing. The trend of compressive strength of geopolymers was the same as that of setting time. When the ratio of NaOH/FA was 0.1, the final setting time sample was longest with 200 min and the compressive strength was highest with 70 MPa. The ratio of Na_2SiO_3/FA has a little effect on setting time. It was found that slag shortened the setting time by providing heterogeneous nucleation centers. The setting time of geopolymers can be adjusted by the ratio of H_2O/FA, NaOH/FA and slag.

Key words: geopolymer%fly ash%setting time%compressive strength