Pore structure and surface area of hardened cement pastes containing silica fume

Specific surface areas and pore structure studies were carried out on the hardened cement pastes containing various amounts of silica fume after being hydrated for different ages. Nitrogen adsorption and desorption 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 silica fume as hydration proceeded. The variations of the nitrogen surface area, the total pore volume and the mean hydraulic radius of the total pore system accessible to nitrogen molecules are discussed and the results are related as much as possible to the formed hydrates.