Silica fume

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Silica fume, also known as microsilica, is a byproduct of the reduction of high-purity quartz with coke in electric arc furnaces in the production of silicon and ferrosilicon alloys. Silica Fume is also collected as a byproduct in the production of other silicon alloys such as ferrochromium, ferromanganese, ferromagnesium, and calcium silicon (ACI Comm. 226 1987b). Before the mid-1970s, nearly all silica fume was discharged into the atmosphere. After environmental concerns necessitated the collection and landfilling of silica fume, it became economically justified to use silica fume in various applications.

Silica fume consists of very fine vitreous particles with a surface area on the order of 215,280 ft²/lb (20,000 m²/kg) when measured by nitrogen absorption techniques, with particles approximately 100 times smaller than the average cement particle. ^[1] Because of its extreme fineness and high silica content, silica fume is a highly effective pozzolanic material. ^{[2] [3]} Silica fume is used as an addition in Portland cement concretes to improve properties. It has been found that silica fume improves compressive strength, bond strength, and abrasion resistance. The improvements in concrete properties from addition of silica fume stem from both the mechanical improvements resulting from addition of a very fine powder to the cement paste mix as well as from pozzolanic reactions betweenthe silica fume and free calcium hydroxide in the paste.^[4] Addition of silica fume also reduces the permeability of concrete to chloride ions, ^[5] which protects concrete's reinforcing steel from corrosion, especially in chloride-rich environments such as those of northern roadways and runways (because of the use of deicing salts) and saltwater bridges.

[edit] References

[edit] External links

• Silica Fume Association