Properties and Applications of Silica Fume

Silica fume, commonly known as microsilica, is an ultrafine powdery material formed by the rapid oxidation and condensation of SiO₂ and Si gases generated during the smelting of ferrosilicon alloys and industrial silicon in air. Its particle size reaches the micron level (1–2 μm).

Classification of Silica Fume

Silica fume is available in two forms:

undensified microsilica   (uncompacted silica fume) and densified microsilica fume.

(1) Uncompacted silica fume: Collected directly from dust collectors. It has low bulk density, large volume, low transportation efficiency, and generates significant dust during application.

(2) Densified silica fume: Produced by agglomerating raw micro-silica fume into small granules using densification technology, facilitating transportation and application. The cohesion of these small granules is weak, allowing them to disperse easily and uniformly during concrete mixing.

Applications and Mechanisms of Silica Fume

Mainly used in monolithic refractories, especially low-cement castables

Main mechanisms:

(1) Improve fluidity

(2) Enhance compactness

(3) Increase strength at both ambient and high temperatures

(4) Reduce cement dosage and lower costs

Used in the concrete industry

(1) Reduce water demand and improve compactness: silica fume fills internal pores

(2) Enhance compressive strength: resulting from improved compactness

(3) Improve impermeability

Therefore, the addition of silica fume extends the service life of concrete.