properties of silica fume
Silica fume, also called microsilica, is an amorphous. Silica fume powder that is collected by a specially designed dust collector after smelting ferrosilicon and industrial silicon. The average particle size of the silica fume is 0.1-0.15μm, which is a few percent of the average particle size of the cement. It has a specific surface area of 15 -27 m2/g with extremely surface active.
Physical and chemical properties of silica fume
1.The appearance of silica fume is gray or gray white powder, refractoriness >1600℃; Volume weight: 200-250kg/cbm.
2.The fineness of silica fume: the fineness of silica fume less than 1µm is accounted for 80%. Average particle diameter of 0.1-0.3µm; specific surface area: 20～28m2/g; Its fineness and specific surface area are about 80%-100% times of cement, 50 to 70 times of fly ash.
3.Particle morphology and mineral phase structure: during the formation process of silica fume, amorphous phase spherical particles are formed in the amorphous phase due to the surface tension during the phase transformation process. And the surface is smooth, some are spherical particles. Agglomerates stick together. It is a kind of volcanic ash material with large specific surface area and high activity. It is mixed with micro silica powder that can play a role in lubrication.
After the micro silica powder is mixed into the concrete, it can be fully dispersed and filled between the voids of the cement particles to make the slurry more dense. The volcanic ash activity index of the micro silica powder can reach 110 and the effective substitution coefficient is 3-4. It has strong absorption capacity for Ca(OH)2 formed a well-developed calcium silicate gel, which greatly improves the strength of concrete. The practical applications of silica fume as following:
- Increase strength: when the blending amount is 5-10%, the compressive strength of niobium can be increased by 10-50%. And the flexural strength is increased by more than 10%.
- Increase density: when 10% silica fume is added, the impermeability is increased by 5-8 times, and the anti-carbonization ability is increased by more than 4 times.
- Increase frost resistance: the enthalpy of 10% micro silica powder is reduced by 1-2% after 300-500 freeze-thaw cycles, while ordinary sputum, after25-50 cycles, the relative dynamic modulus has been reduced by 36%-73%.
- Increase anti-wear and anti-cavitation: micro silica powder is 0.5-2.5 times better than ordinary anti-wearing ability. And cavitation resistance is increased by 3-16 times. It is a good material for anti-wear repair and protection of hydroelectric power station, reservoirs and dams.