Properties of Silica Fume related to its applications

Silica fume has been recognized as a pozzolanic admixture that is effective in greatly enhancing mechanical properties.

The addition of silica fume to concrete improves the latter's durability by reducing permeability and refining pore structure, leading to a reduction in the diffusion of harmful ions and the calcium hydroxide content, resulting in greater resistance to sulfate attack.

Because of its extreme fineness and very high amorphous silicon dioxide content, silica fume is a very reactive pozzolanic material. As the Portland cement in concrete begins to react chemically, it releases calcium hydroxide. Silica fume reacts with this calcium hydroxide to form additional binder material known as "calcium silicate hydrate", which is very similar to the calcium silicate hydrate formed from Portland cement.

Cement reaction:
2 (3 CaO SiO2) + 6 H2O = 3 CaO SiO2 3 H2O + 3 Ca(OH)2

Pozzolanic materials consume lime and form even more CSH binder phases:
3 Ca(OH)2 + SiO2 = 3 CaO SiO2 3 H2O

A = Ca(OH)2
B = CSH
C = CASH