Silica fume, also known as microsilica, It is an amorphous (non-crystalline) polymorph of silicon dioxide, silica. It is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production. Silica fume is an ultrafine material with spherical particles less than 1 μm in diameter, the average being about 0.15 μm, which have supperpower activity index.This makes it approximately 100 times smaller than the average cement particle. The bulk density of silica fume depends on the degree of densification in the silo and varies from 100 (undensified) to 720 kg/m3. The main field of application is concrete, grouts and mortars as well as refractory,cearamic ,etc.