What is Silica Fume?

Updated: Oct 27

What is Silica Fume, what is it used for, and how does it work?

Without realizing it, you probably come into contact each day with a product containing some form of Silica Fume. From driving over bridges to flying from an airport, Silica Fume is a vital material that impacts our lives every day. What is Silica Fume and why is it so important?

SIO2 Smoke is produced from the processing of certain raw materials, such as woodchips, quartz, and coal, through the operation of a furnace. As this smoke is lifted and vented through the furnace stack, residue from the smoke sticks to the stack. This residue is called Silica Fume. Silica Fume can be used as hydrophilic or hydroponic. Once seen as a bothersome by-product that had to be removed and disposed of industry realized this residue had certain properties that strengthened concrete and lengthened life expectancy in corrosive environments. Silica Fume Concrete is 100 to 150 times smaller than a cement particle and can fill the interstitial voids creating a filler effect. The packing effect strongly reduces the concretes porosity and permeability.

According to the Silica Fume Association, “Silica fume is a byproduct of producing silicon metal or ferrosilicon alloys. One of the most beneficial uses for silica fume is in concrete. Because of its chemical and physical properties, it is a very reactive pozzolan. Concrete containing silica fume can have very high strength and can be very durable. Silica fume is available from suppliers of concrete admixtures and, when specified, is simply added during concrete production. Placing, finishing, and curing silica-fume concrete require special attention on the part of the concrete contractor.”

Silica Fume is a pozzolan, which in and of itself has no cementing properties, however, when added to calcium hydroxide creates a pozzolan reaction creating additional calcium silicate hydrates (CSH) which produces cement with excellent cementing makeup. High-performance concrete containing silica fume is one of the more important advanced materials necessary in the construction and enhancement of critical infrastructure. Silica fume delivers increased toughness and resistance to abrasion and corrosion, improving sustainability and life-cycle cost efficiency. Silica Fume Concrete’s fine and amorphous particles react with cement alkalies which reduces their content in the concrete before hardening, thus protecting the concrete against an alkali reaction.

Silica Fume Concrete increases component packing and adhesion, which directly affects the mechanical properties, specifically regarding the strength of the concrete. Adding Silica Fume Concrete decreases pore size as the concrete reduces porosity. As aggressive agents attempt to permeate the concrete leading to corrosion, Silica Fume Concrete reduces and prevents penetration by these destructive agents, as well as reduces water movements and internal pressures leading to irreversible degradation. This is critical when concrete is used in environments such as in harbors, airports, bridges, heavy impact areas, chemical areas, parking decks, de-icing areas, and coastal buildings where conditions are demanding and lead to corrosion.

Silica fume is a byproduct from the production of silicon or ferrosilicon metal. Silica fume is a mineral admixture, a very fine powder of spherical particles that average 0.1 to 0.3 microns in diameter with a surface area of 17 to 30 m2/g. Silica fume is used in a variety of cementitious concrete, grouts and mortars, refractory, elastomer, and polymer applications. Silica fume powder is gray to off-white in color

When silica fume is used in concrete, shotcrete, and repair products, it performs as a filler, improving the physical structure by occupying the spaces between the cement particles, and as a reacting chemical (pozzolanic) to create greater strength and durability to concrete.

Silica Fume originates from the oxidation of the SiO gas produced during the fabrication of Silicon, Ferrosilicon alloys, and CaSi alloys in electric furnaces. The SiO2 formed is then condensed into spherical particles and recovered in baghouse filters.

Silica Fume consists of individual ultrafine particles of silicon dioxide with a high specific surface and an average diameter of 150nm which gives Silica Fume its high pozzolanic properties.

Silica Fume is an amorphous product. Its color ranges from white to dark grey and is available in densified and undensified forms.