Silica Flour is a byproduct in the carbothermic reduction of high-purity quartz with carbonaceous materials like coal, coke, wood-chips, in electric arc furnaces in the production of silicon and ferro-silicon alloys.
Because of its extreme fineness and high silica content, silica flour is a very effective pozzolanic material.
Silica flour is added to Portland cement to improve its properties. In particular, its compressive strength, bond strength, and abrasion resistance. These improvements stem from both the mechanical improvements resulting from addition of a very fine powder to the cement paste mix as well as from the pozzolanic reactions between the silica flour and free calcium hydroxide in the paste.
Addition of silica flour also reduces the permeability of concrete to chloride ions. This 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 de-icing salts) and saltwater bridges.