Effect of sodium sulphate on the hydration of granulated blast furnace slag blended portland cement

Study of the hydration of granulated blast furnace slag (GBFS) has attracted attention for a number of years. It is not only due to the potential of cost saving but the GBFS blends have some engineering advantages also as compared to concrete made of portland cement only, such as lowered heat evolution , lower permeability and greater durability in aggressive environments. Investigations on GBFS blended cements have been reviewed by a number of researchers t .? GBFS alone has no hydraulic property but when mixed with portland cement, it hydrates and develops strength. Slag may be activated by reaction with a solution of high pH (alkaline). However, the characteristics of slag vary from source to source and slags obtained from different sources may be sensitive to different activators. In spite of a large number of studies. 13, the mechanism of activation is not fully understood. The addition of some salts (which are almost neutral in water) to GBFS portland blended cement in smaller amounts, results in the acceleration of hydration. This may be due to activation of GBFS . The detailed study of the hydration in the presence of such salts is needed. In this paper the effect of Na2S04 on the hydration of GBFS blended portland cement is reported and the mechanism discussed.