EFFECT OF SILICA FUME ON PORE STRUCTURE AND CHLORIDE DIFFUSIVITY OF LOW POROSITY CEMENT PASTES

This paper presents the results of an experimental investigation on the effect of silica fume on pore structure and diffusivity of low porosity cement pastes. For cement pastes with w/c ratios in the range of 0.20 to 0.30, a 10 % replacement of the cement with silica fume only reduced the total porosity to a small extent. However, a refinement of the pore size distribution took place in such a way that the content of larger pores was reduced for decreasing w/c ratio. For pure portland cement pastes the effect of a certain constant change of w/c ratio on the chloride diffusivity was substantially higher at high w/c ratios than at low w/c ratios. A 10 % replacement with silica fume reduced the chloride diffusivity for all w/c ratios so much that the effect of w/c ratio became less important.