Silica Fume

Silica Fume

Silica fume, also referred to as microsilica or condensed silica fume, is a byproduct material that is used as a pozzolan. This byproduct is a result of the reduction of high-purity quartz with coal in an electric arc furnace in the manufacture of silicon or ferrosilicon alloy. Silica fume rises as an oxidized vapor from the 2000°C (3630°F) furnaces.

SILICA FUME

Silica fume, also referred to as microsilica or condensed silica fume, is a byproduct material that is used as a pozzolan. This byproduct is a result of the reduction of high-purity quartz with coal in an electric arc furnace in the manufacture of silicon or ferrosilicon alloy. Silica fume rises as an oxidized vapor from the 2000°C (3630°F) furnaces. When it cools it condenses and is collected in huge cloth bags. The condensed silica fume is then processed to remove impurities and to control particle size. Condensed silica fume is essentially silicon dioxide (usually more than 85%) in noncrystalline (amorphorous) form. Since it is an airborne material like fly ash, it has a spherical shape. It is extremely fine with particles less than 1μm in diameter and with an average diameter of about 0.1 μm, about 100 times smaller than average cement particles.

Condensed silica fume has a surface area of about 20,000 m2/kg (nitrogen adsorption method).For comparison; tobacco smoke’s surface area is about 10,000 m2/ kg. Type I and Type III cements have surface areas of about 300 to 400 m2/kg and 500 to 600 m2/kg (Blaine),respectively. The relative density of silica fume is generally in the range of 2.20 to 2.5. Portland cement has a relative density of about 3.15. The bulk density (uncompacted unit weight) of silica fume varies from 130 to 430 kg/m3(8 to 27 lb/ft3). Silica fume is sold in powder form but is also available in a liquid. Silica fume is used in amounts between 5% and 10% by mass of the total cementitious material. It is used in applications where a high degree of impermeability is needed and in high strength concrete. Silica fume must meet ASTM C 1240 & ACI 234 (1994)provide an extensive review of slag.