Abstract:
In this paper the effect of sodium oxide concentration, the water-to-binder-solids ratio,
temperature, and the duration of elevated temperature curing on the compressive strength of
alkali-activated fly ash cement pastes was investigated. Alkali concentration varied between
3% and 15% Na2O of fly ash mass. An increase in Na2O from 3% to 9% greatly improved the
compressive strength of the pastes from 26.1 MPa to 50.8 MPa at 28 days. A further increase in
Na2O up to 15% did not provide an increase in the strength, but a decrease was observed, as
well as higher strength variation. The paste activated with 9% Na2O had the highest strength at
28 days and a low standard deviation, and 9% Na2O was thus considered as the best value in the
present study. The temperature and the duration of elevated temperature curing were found
to be critical factors affecting the compressive strength at early age, but their effect decreased
significantly in the long term. The water-to-binder-solids ratio affected the compressive
strength considerably. An increase in the water-to-binder-solids ratio of the pastes from 0.18 to
0.29 resulted in a decrease in the compressive strength from 49.3 MPa to 21.3 MPa.
