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Silica Fume

Silica fume (sf) is the byproduct of the manufacture of silicon for the computer industry. It is a very finely divided material, many hundreds of times finer than cement. It reacts with lime and water in a similar way to Fly ash, also known as pulversided fuel ash (pfa), to produce a binder.

It is added to concrete mixes to increase compressive strength and reduce permeability.Typically it is used in a concentration of 5% to 10% of the weight of cement.

Concrete Society Technical Report 61, Enhancing reinforced concrete durability, gives information on the effects of silica fume on the rates of carbonation and chloride ingress.

Silica fume seen under electron microscope
Acknowledgement: The Concrete Society

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TR61 Enhancing reinforced concrete durability

TR74 Cementitious materials