Silica Fume (Microsilica)

Silica fume, also known as microsilica, (CAS number 69012-64-2, EINECS number 273-761-1) is an amorphous (non-crystalline) polymorph of silicon dioxide, silica. It is an ultrafine powder collected as a by-product of silicon and ferrosilicon alloy production and consists of spherical particles with an average particle diameter of 150 nm. The main field of application is as pozzolanic material for high-performance concrete.

Microsilica is a very active pozzolanic material that easily reacts with CH and water and becomes the secondary form of CSH. Through the pozzolanic reaction, micro silica can absorb a large amount of CH and the production of CSH also fills the capillary pores. This process is able to reduce the porosity and permeability of concrete as well as the possibility of chemical reaction of CH with other ions to form harmful products.

In this way, the durability of concrete increases to a great extent. It has been shown that microsilica can greatly enhance the resistance of high-performance concrete against alkaline aggregate reaction and chloride distribution. Currently, this material is widely used in the production of high-performance concrete around the world.


Because of its extreme fineness and high silica content, silica fume is a very effective pozzolanic material.Standard specifications for silica fume used in cementitious mixtures are ASTM C1240, EN 13263.
Silica fume is added to Portland cement concrete to improve its properties, in particular its compressive strength, bond strength, and abrasion resistance. These improvements stem from both the mechanical improvements resulting from the addition of a very fine powder to the cement paste mix as well as from the pozzolanic reactions between the silica fume and free calcium hydroxide in the paste.

The addition of silica fume also reduces the permeability of concrete to chloride ions, which protects the reinforcing steel of concrete from corrosion, especially in chloride-rich environments such as coastal regions and those of humid continental roadways and runways (because of the use of deicing salts) and saltwater bridges.