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Microsilica
Also known as silica fume, is a fine powder consisting of amorphous silicon dioxide (SiO2) that is a by-product of silicon and ferrosilicon alloy production. It is widely used as a mineral admixture in concrete, where its sub-micron, spherical particles fill voids, enhance packing density, and react with calcium hydroxide to form additional calcium silicate hydrate (CSH) phases. This pozzolanic reaction significantly increases concrete’s strength, durability, and resistance to chemical attack.
Composition and Function in Concrete:
Composition:
● Primary Constituent: Silicon Dioxide (SiO2).
●; Content:; Typically ranges from 85% to 98% by mass.
● ;Physical Characteristics:; The particles are spherical 6and
extremely fine, with an average diameter of about 0.15
micrometers (150 nm), making them about 100 times smaller
than average cement particles. This gives it a very high specific
surface area, which contributes to its high reactivity.
Function:
Microsilica improves concrete performance through two main
mechanisms:
● Pozzolanic Reaction: As a powerful pozzolanic material,
Microsilica reacts chemically with calcium hydroxide, a by-
product of cement hydration.
This reaction forms additional Calcium Silicate Hydrate (C-S-H)
gel, significantly enhancing the concrete's strength and density.
● Filler Effect (Micro-Filler): Due to its microscopic size, Microsilica
fills tiny voids between cement particles and the aggregate
interface, resulting in a denser, more compact, and less porous
cement paste. This action also improves the bond by eliminating
the weak Interfacial Transition Zone (ITZ).
Applications and Benefits
Microsilica is critical for producing High-Performance Concrete (HPC), and has various industrial uses.
Construction & Cementitious Materials Application & Benefits:
● High-Performance Concrete (HPC): Very low permeability to water and chloride intrusion 18, extremely high electrical resistivity (mitigating corrosion), and superior resistance to chemical attack.
● High-Strength Concrete: Achieves compressive strengths up to 20,000 psi (140 MPa), high modulus of elasticity, and high early strengths for fast-track construction.
● Shotcrete: Reduces rebound loss, increases bonding strength, and realizes material cost savings.
● Cementitious Repair: Used as a component in pre-packaged bagged products for concrete, mortar, or grout repair.
● Wallboard: Used in commercial gypsum and concrete wallboard products for increased performance and durability.
Specialized Industrial Uses: Application & Benefits:
● Oil & Gas Well Grouting: Improves flow characteristics, dramatically decreases permeability (controlling gas migration), and contributes to lightweight grout systems.
● Refractory & Ceramics: Improves particle packing, enhances strength at high temperatures, and reduces permeability to avoid penetration by gas, slag, and metal.
● Fiber Cement: Increases bonding strength, decreases permeability to water intrusion, and increases compressive strength.
● Elastomers/Polymers: Used as a highly effective reinforcing filler in rubber or plastic.
● Agriculture: Used in the defluorination process for dicalcium phosphate production (used in animal feed).
Packing
● Densified & packed in jumbo bags each of 1000 – 1500 kg.
● Bulk in silo trucks.
Test Results
| Items | Unit | Test Results | Explain |
|---|---|---|---|
| SiO2 | % | 98.34 | ASTM 1240-15 |
| H2O (Moisture) | % | 0.30 | ASTM 1240-15 |
| Loss on Ignition (L.O.I) | % | 0.50 | ASTM 1240-15 |
| Accelerated Pozzolanic Strength Activity Index (7 days) | % | 125 | ASTM 1240-15 |
| Specific Surface Area | m2/g | 2.2 | ASTM 1240-15 |
| Percent Retained On 45μm | % | 3 | ASTM 1240-15 |
| Bulk Density | kg/m3 | 320 | ASTM 1240-15 |
| PH Value | 8.2 | ASTM 1240-15 | |
| Conclusion | Complies with the requirements of ASTM C 1240 standard | ||
1- COA SSF-97U / Standard: ASTM C 1240
Chemical Component
| Items | Unit | Test Results | Explain |
|---|---|---|---|
| SiO₂ | % | 98.34 | ASTM 1240-15 |
| H₂O (Moisture) | % | 0.30 | ASTM 1240-15 |
| Loss on Ignition (L.O.I) | % | 0.50 | ASTM 1240-15 |
| Accelerated Pozzolanic Strength Activity Index (7 days) | % | 125 | ASTM 1240-15 |
| Specific Surface Area | m²/g | 2.2 | ASTM 1240-15 |
| Percent Retained On 45μm | % | 3 | ASTM 1240-15 |
| Bulk Density | kg/m³ | 320 | ASTM 1240-15 |
| PH Value | – | 8.2 | ASTM 1240-15 |
Complies with the requirements of ASTM C 1240 standard.
2- Grade: 92D
Chemical Component
| Item | Unit | Specification | Typical Value |
|---|---|---|---|
| SiO₂ | % | 92 min | 93.6 |
| Cl | % | 0.1 max | 0.010 |
| Al₂O₃ | % | 1.0 max | 0.41 |
| Fe₂O₃ | % | 1.0 max | 0.32 |
| K₂O | % | 1.0 max | 0.68 |
| MgO | % | 1.0 max | 0.41 |
| C | % | 3.0 max | 1.86 |
| H₂O | % | 3.0 max | 0.96 |
Physical Data
| Item | Unit | Specification | Typical Value |
|---|---|---|---|
| Loss on Ignition | % | 6 max | 2.4 |
| Coarse particles > 45µm | % | 10.0 max | 2.8 |
| PH- Value | – | 6–8 | 7 |
| Bulk Density | kg/m³ | 500–700 | 680 |
3- COA SSF-95U / Standard: ASTM C 1240
Chemical Component
| Items | Unit | Test Results | Explain |
|---|---|---|---|
| SiO₂ | % | 96.65 | ASTM 1240-15 |
| H₂O (Moisture) | % | 0.20 | ASTM 1240-15 |
| Loss on Ignition (L.O.I) | % | 0.97 | ASTM 1240-15 |
| Fe₂O₃ | % | 0.058 | ASTM 1240-15 |
| CaO | % | 0.72 | ASTM 1240-15 |
| MgO | % | 0.35 | ASTM 1240-15 |
| K₂O | % | 0.38 | ASTM 1240-15 |
| Na₂O | % | 0.33 | ASTM 1240-15 |
| TiO₂ | % | 0.008 | ASTM 1240-15 |
Complies with the requirements of ASTM C 1240 standard.
4- Silica Fume Grade 85
Chemical Component
| Item | Unit | Specification | Typical Value |
|---|---|---|---|
| SiO₂ | % | 85 min | 88.6 |
| Chrome | % | 1.0 max | 0.21 |
| Al₂O₃ | % | 1.0 max | 0.53 |
| Fe₂O₃ | % | 1.0 max | 0.35 |
| K₂O | % | 1.0 max | 0.81 |
| MgO | % | 1.0 max | 0.43 |
| C | % | 3.0 max | 1.8 |
| H₂O | % | 3.0 max | 0.93 |
Physical Data
| Item | Unit | Specification | Typical Value |
|---|---|---|---|
| Loss on Ignition | % | 6 max | 2.3 |
| Coarse particles > 45µm | % | 10.0 max | 2.5 |
| PH- Value | – | 6–8 | 7 |
| Bulk Density | kg/m³ | 500–700 | 680 |
How is Micro Silica Produced?
01
Microsilica is a mineral composed of ultrafine, amorphous glassy spheres of Silicon Dioxide (SiO2), which is a byproduct of producing Silicon metal or Ferrosilicon alloys. The individual particles are extremely small, approximately 1/100th the size of an average cement grain.
02
Silicon metal and alloys are produced in electric furnaces. The raw materials are quartz, coal, and woodchips. The Microsilica is formed when SiO2 gas, given off as the quartz reduces, mixes with oxygen in the upper parts of the furnace.
03
Here, the SiO2 is oxidized to SiO2, condensing into the pure spherical particles of Microsilica that form the major part of the smoke or fume from the furnace.
04
The fumes from the furnace are drawn through cooling pipes, through a pre-collector and cyclone, to remove coarse particles that may have been carried over from the furnace-and then blown into specially designed baghouse filters where they are collected.
05
The quality of the raw materials and the operation of the furnaces determine the purity of the Microsilica. Although the material is collected as a very fine powder with a bulk density in the region of 200kg/m3, it can be processed to densify it, making the B/D around 250-700kg/m3.
Contact Us
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- +86 138 0115 7116
- info@gxmicrosilica.com