Dosages of Silica Fume in Concrete Industry

Silica fume acts as a filler and as a cementitious material in concrete. The small silica fume particles fill spaces between cement particles and between the cement paste matrix and aggregate particles. The silica fume also combines with calcium hydroxide to form additional calcium hydrate through the pozzolanic reaction. Both of these actions result in a denser, stronger and less permeable material.

Adding Silica Fume to concrete render more durability, improve resistance to corrosion and as discussed above reduce concrete permeability. In case of shotcrete application provide less rebound.

Dosages:

10% to 15%	High strength structural columns
10%	Flatwork
8% to 10%	High durability / Low permeability such as bridge decks or parking structures
8% to 15%	by weight of cement but as an addition not replacement

Silica Fume has been used as an addition to concrete up to 15 percent by weight of cement, although the normal proportion is 7 to 10 percent. With an addition of 15 percent, the potential exists for very strong, brittle concrete. It increases the water demand in a concrete mix; however, dosage rates of less than 5 percent will not typically require a water reducer. High replacement rates will require the use of a high range water reducer.