Specific surface areas and pore structure studies were carried out on
the hardened cement pastes containing various amounts of silica fume a
fter being hydrated for different ages. Nitrogen adsorption and desorp
tion isotherms were determined for all pastes at the boiling point of
nitrogen, from low pressures to the saturation pressure. The effect of
content of silica fume on the properties of the silica fume-Portland
cement pastes was discussed. The specific surface areas as well as the
total pore volume were found to decrease with increasing amount of si
lica fume as hydration proceeded. The variations of the nitrogen surfa
ce area, the total pore volume and the mean hydraulic radius of the to
tal pore system accessible to nitrogen molecules are discussed and the
results are related as much as possible to the formed hydrates.