Basic physical properties of micro silica:
◇ Existing form: amorphous ultra-fine (amorphous) powder
◇ Typical color: gray (the natural state is grayish white, and the color gradually deepens with the increase of density)
◇ Specific surface area: 15~28 m2/g
◇ Loose bulk density: 200~350 kg/m3
◇ Activity index: ≥ 85%
◇ Water demand ratio: ≤ 125%
The main chemical component of micro silica powder is SiO2, with content of 85~97%. Its elements include Fe2O3, Al2O3, CaO, K2O, Na2O, MgO, C, etc.
Comparison of physical properties of micro silica fume with cement, slag and fly ash:
| Project | Silica Fume | Cement | Slag | Fly Ash |
| Proportion(N/m3) | 21000 | 31500 | 29000 | 21000 |
| Density(kg/m3) | 200-300 | 1200-1400 | 1000-1200 | 900-1000 |
| Loss on ignition(%) | 2-4 | – | – | 12 |
| Specific surface area（m2/kg） | 20000 | 200-500 | – | 200-600 |
Micro silica chemical composition in the world:
| Physical and chemical properties | United States | Europe | Canada | Japan | China | Brazil | South Korea | Italy |
| SiO2 (%) | ≥ 85.0 | ≥ 85.0 | ≥ 85.0 | ≥ 85.0 | ≥ 85.0 | ≥ 85.0 | ≥ 85.0 | ≥ 85.0 |
| SO3 (%) | < 2.0 | < 1.0 | < 3.0 | < 3.0 | ||||
| cl (%) | < 0.3 | < 0.1 | < 0.2 | < 0.3 | ||||
| free Cao (%) | < 1.0 | < 1.0 | ||||||
| MgO (%) | < 5.0 | < 5.0 | ||||||
| free Si (%) | < 0.4 | |||||||
| Alkali content (%) | < 1.5 | < 1.5 | ||||||
| Humidity (%) | < 3.0 | < 3.0 | < 3.0 | < 3.0 | < 3.0 | |||
| Ignition loss (%) | < 6.0 | < 4.0 | < 6.0 | < 5.0 | < 6.0 | < 6.0 | < 5.0 | < 4.0 |
| Specific surface area (m2/g) | > 15 | 15-35 | > 15 | > 15 | > 15 | > 15 | ||
| Activity indicators (%) | > 105@7d | > 95@7d> 105@28d | > 85@28d | > 95@7d | > 85@7d | |||
| Particle size ( 45um triage %) | < 10 | < 10 | < 10 | < 5.0 | < 10 | |||
| The average particle size (%) | < 5 | < 5 | ||||||
| Water requirement ratio (%) | < 125 |
The United States, Canada, Norway and other countries have formulated specifications (standards) for the use of silica fume:
| Project Country | SiO2 | SO3 | Loss on ignition | Maximum allowable usage |
| Canada | > 85 | < 1 | < 6 | < 10 |
| United States | > 85 | < 1 | < 6 | < 10 |
| Norway | > 85 | < 1 | – | < 8 |
