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Problem statement: Numerous data and information on pozzolanic reaction and microfiller properties of silica fume were derived from laboratory investigation on silica fume in undensified form. Currently, due to low bulk density of undensified silica fume which poses problem in transportation and handling of the material, silica fume are commercially supplied in densified form. Densification process used to increase bulk density of fresh silica fume has resulted in agglomeration of the silica fume particles hence altering its effective particle size and distribution which may affect its hydration and microfiller properties. However, very few studies have been performed to study hydration properties of cementitious mixtures containing Densified Silica Fume (DSF) as supplementary binder. Approach: Characterization of physical and chemical properties of DSF was performed. Compressive strength of high performance mortar mixtures containing DSF as partial cement replacement material at various level of replacement ranging between 0-25% was assessed. Water absorption and intrinsic air permeability of hardened mortars was evaluated at the age of 28 days. Results: Incorporation of DSF at replacement level up to 25% produced mortar with higher 28 days compressive strength as compared to the control mortars. Reduction in 28 day water absorption and intrinsic air permeability of mortar was observed for mortar containing DSF up to 15% by weight of binder. Conclusion: DSF was determined to have large median particle size of 28.21 µm and high amorphous silica content. Incorporation of DSF in mortar increases water demand of mix to achieve constant workability. Optimum level of cement replacement using DSF to ensure best compressive strength performance was found to be 7.5% by total weight of binder

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