Particle size distributions of pyrogenic nanosilicas and nanosilica sols, used in cement composites

High attractive surface forces between particles of nanosilicas could lead to significant aggregation of these materials. This study is thus focused on the aggregation status of pyrogenic nanosilicas and nanosilica sols, as two main types of nanosilicas used in concrete. The results show that unlike nanosilica sols, which are in the form of monodispersed particles, serious aggregation of pyrogenic nanosilicas in water occurs. Increasing dispersion forces, particularly the use of ultrasonic waves, has considerable effect in breaking aggregates into smaller aggregates. Increasing the pH was found to be very effective in improving dispersion of nanosilicas and through combined use of high pH and high dispersion forces such as ultrasonic method it is possible to break all the aggregates into primary aggregates.