silica fume is also called microsilica. To make concrete compressive strength.

Microsilica - Physical Properties

Particle Size

Most particles are sub-micron. Average particle diameter is 0.15 microns, about 100x smaller than cement

grains.

Particle Shape Smooth, spherical particles.

Density (Specific Gravity)

Approximately 2.2 (cement is typically 3.1)

Specific Surface Area

Ranging from 15 000 to 30 000 m2/kg (measured by nitrogen-absorption - BET)

Microsilica - Chemical Properties

Minimum 85% SiO2 (normally 90+%)

Amorphous Reactive Silica

Pozzolanic - reacts with Ca(OH)2