It is a highly reactive, amorphous SiO 2 spherical particle with a particle size 1/100 of that of cement particles, which can fill in between cement particles and also react with hydration products to produce gels, as well as with materials with alkaline substances to produce gels.

Application of silica fume in concrete: modification mechanism and function of silica fume After mixing into cement concrete, it can fill in the cement particle gap well and make the paste more dense. In addition, it combines with free Ca(OH)2 to form a stable calcium silicate hydrate 2CaO ?SiO 2?nH2 O, which has a higher gel strength than Ca(OH)2 crystals.