Introduction to Micro Silica Understanding its Composition Types and Properties

In the world of construction materials, there are a variety of substances that are used to enhance the strength and durability of structures. One such material that has gained popularity in recent years is micro silica, also known as silica fume. This fine, powdery material has become a staple in the construction industry for its numerous beneficial properties. In this blog post, we will delve into the world of micro silica and explore its composition, properties, and applications in construction.

 

What is Micro Silica?

 

Micro silica is a by-product of the production of silicon metal and ferrosilicon alloys. It is obtained through the reduction of high-purity quartz with coal in an electric arc furnace. During this process, the silicon and oxygen in the quartz react to form silicon dioxide gas, which is then collected and condensed into a fine powder known as micro silica.

 

Composition of Micro Silica

 

Micro silica is primarily composed of amorphous silica particles, with a typical particle size range of 0.15 to 5 microns. These particles are extremely small, about 100 times smaller than a grain of cement, and have a spherical shape. This unique morphology gives micro silica its high surface area, which can range from 15,000 to 30,000 square meters per kilogram.

 

Apart from silica, micro silica also contains trace amounts of other elements such as aluminum, iron, calcium, magnesium, and potassium. The exact composition of micro silica may vary depending on the source of the raw material and the production process.

 

Chemical Composition of Micro Silica

 

Micro silica is composed of silicon dioxide (SiO2), which is the primary component of sand, and is also found in various minerals such as quartz and granite. However, unlike sand, micro silica has a very high SiO2 content, ranging from 85% to 97%. It also contains small amounts of other oxides such as aluminum oxide, iron oxide, and calcium oxide, which give it its unique properties.

 

Sources of Micro Silica

 

Micro silica is a by-product of the production of silicon and ferrosilicon alloys, which are used in the manufacturing of electronic devices and steel, respectively. It is produced by heating high-purity quartz in an electric arc furnace, which produces silicon and carbon monoxide. The silicon then reacts with oxygen, resulting in the formation of micro silica.

 

Types of Micro Silica

 

Here are the four main types of micro silica: undensified, densified, slurry and condensed microsilica. Each type has its own unique characteristics and uses, making it important to understand the differences between them.

 

Undensified Microsilica

 

Undensified microsilica is the most common type of microsilica used in the construction industry. It is obtained in a powder form and has a density of around 200-300 kg/m3. This type of microsilica is often used as a partial replacement for cement in concrete mixes. It improves the strength and durability of concrete by filling in the voids between cement particles and reducing the pore size of the concrete.

 

Densified Microsilica

 

Densified microsilica is produced by densifying or compacting undensified microsilica. It has a higher density (around 600-700 kg/m3) and is available in both powder and granular form. Densified microsilica is commonly used in high-performance concrete to improve its strength, durability, and resistance to chemical attacks. It is also used in the production of refractory materials and as an additive in rubber and plastic products.

 

Slurry Microsilica

 

Slurry microsilica is a combination of undensified microsilica and water. It is widely used as a shotcrete admixture for tunneling, mining, and slope stabilization. Slurry microsilica is also used as a grout admixture to improve its stability, strength, and impermeability. It is an excellent material for repairing and strengthening existing concrete structures due to its ability to penetrate and fill cracks.

 

Condensed Microsilica

 

Condensed microsilica, also known as silica fume pellets, is obtained by condensing the vapor of undensified microsilica. The pellets have a higher density (around 500-700 kg/m3) and are available in various sizes and shapes. Condensed microsilica is used as a filler in polymer composites, in the production of high-strength concrete, and as an additive in refractory and ceramic materials.

 

Properties of Micro Silica

 

The small particle size and high surface area of micro silica give it some unique properties that make it an ideal additive for concrete and other construction materials. Let's take a closer look at some of the key properties of micro silica:

 

1. High Strength

 

One of the most significant advantages of using micro silica in construction materials is its ability to increase the strength of the final product. The high surface area of micro silica allows it to fill in the gaps between cement particles, resulting in a denser and stronger concrete. This is particularly beneficial in high-stress applications, such as bridges, tunnels, and high-rise buildings.

 

2. Improved Durability

 

Micro silica also improves the durability of concrete by reducing its permeability. The fine particles of silica fill in the pores and capillaries in the concrete, making it less susceptible to water and chemical penetration. This, in turn, increases the lifespan of the structure and reduces maintenance costs.

 

3. Reduced Heat of Hydration

 

The process of cement hydration, which is responsible for the hardening of concrete, generates heat. In large concrete structures, this heat can cause thermal cracking, reducing the strength and durability of the structure. Adding micro silica to the concrete mix can significantly reduce the heat of hydration and prevent these cracks from forming.

 

4. Increased Chemical Resistance

 

Micro silica has a high resistance to chemical attack, making it an ideal additive for structures that are exposed to harsh environments. It can protect the concrete from the damaging effects of acids, sulfates, and other chemicals, increasing its lifespan and reducing maintenance costs.

 

5. Improved Workability

 

Despite its small particle size, micro silica can improve the workability of concrete. It acts as a lubricant, making the concrete easier to mix and place. This is particularly useful in self-consolidating concrete, where the absence of coarse aggregates can make the mix difficult to handle.

 

Physical Properties of Micro Silica

 

1. Particle Size: The average particle size of micro silica is about 100 times smaller than cement particles, ranging from 0.1 to 1 micron.

 

2. Specific Surface Area: The high surface area of micro silica (15,000 to 30,000 m2/kg) makes it highly reactive and pozzolanic.

 

3. Density: The density of micro silica ranges from 200 to 700 kg/m3.

 

4. Chemical Composition: Micro silica is mostly composed of silicon dioxide (SiO2), with small amounts of other oxides such as aluminum, calcium, and iron.

 

Features Of Micro Silica

 

Here are the best features of Micro Silica:

 

• Fine dust
• High reactivity
• Pozzolanic
• High Surface Area
• Low density
• Chemical resistance
• Heat reduction

 

Applications of Micro Silica in Construction

 

Now that we have a better understanding of the composition and properties of micro silica, let's explore its applications in the construction industry:

 

1. Concrete

 

The most common use of micro silica is in concrete. It is added to the concrete mix in a quantity of 5% to 10% by weight of cement to improve its strength, durability, and workability.Micro silica manufacture particularly in high-performance concrete, where strength and durability are critical.

 

2. Shotcrete

 

Shotcrete, also known as sprayed concrete, is a construction method that involves spraying concrete onto a surface. Micro silica is often added to the shotcrete mix to improve its adhesion, strength, and durability. This makes it a popular choice for applications such as tunnel linings, retaining walls, and slope stabilization.

 

3. Refractory Materials

 

Refractory materials are used in high-temperature applications, such as furnaces and kilns, where conventional materials would melt or break down. Micro silica is added to these materials to enhance their strength and resistance to thermal shock.

 

4. Cement and Mortar

 

Micro silica is also used in the production of cement and mortar. It improves the strength and durability of these materials, making them suitable for various applications, such as masonry, plastering, and tile fixing.

 

5. Oil and Gas Well Cements

 

Micro silica is added to oil and gas well cements to improve their compressive strength and resistance to chemicals found in oil and gas wells. This makes it an essential additive for the construction of oil and gas wells.

 

Examples of Successful Projects Using Micro Silica

 

1. Burj Khalifa, Dubai: The world's tallest building, Burj Khalifa, used micro silica in its concrete mix to increase its strength and durability.

 

2. Golden Gate Bridge, San Francisco: Micro silica was added to the concrete used for the pillars of the Golden Gate Bridge, making it more resistant to corrosion from seawater.

 

3. Gotthard Base Tunnel, Switzerland: The longest railway tunnel in the world, Gotthard Base Tunnel, used micro silica in its concrete to withstand high pressure and prevent water seepage.

 

Advantages of Micro Silica -

 

• Strengthens Concrete: Micro silica makes concrete stronger by filling in tiny gaps, making it more durable.
• Reduces Permeability: It makes concrete less porous, reducing the chance of water and chemicals seeping through.
• Improves Workability: It makes concrete easier to work with, making construction smoother and faster.
• Increases Longevity: Structures built with micro silica last longer due to increased resistance to wear and tear.
• Enhances Bonding: It improves the bond between concrete and steel, making structures safer and more reliable.
• Reduces Heat of Hydration: Micro silica lowers the heat generated during concrete curing, preventing cracks.
• Minimizes Shrinkage: It reduces the risk of concrete shrinking, which can cause cracks and structural issues.
• Enhances Abrasion Resistance: Concrete with micro silica is more resistant to abrasion, ideal for high-traffic areas.
• Improves Chemical Resistance: It protects against chemical corrosion, increasing the lifespan of structures in harsh environments.
• Environmentally Friendly: Micro silica is often a byproduct of industrial processes, so using it in concrete reduces waste and environmental impact.

 

Disadvantages of Micro Silica, You Need to Know

 

• High Cost: It can be expensive to use in construction projects.
• Handling Difficulties: Micro silica can be challenging to handle and mix due to its fine particles.
• Health Risks: Inhaling microsilica dust can be harmful to health, causing respiratory issues.
• Limited Supply: There may be shortages of micro silica in some regions.
• Potential Set Time Issues: It can accelerate the setting time of concrete, which may require adjustments in construction schedules.
• Surface Bleeding: Excessive use can lead to surface bleeding, affecting the appearance and finish of concrete.
• Sensitive to Moisture: Microsilica can absorb moisture, affecting its performance if not stored properly.
• Compatibility Issues: It may not be compatible with all types of concrete mixes.
• Requires Expertise: Proper handling and application require expertise, which may not always be available.
• Environmental Concerns: Extraction of raw materials for microsilica production can have environmental impacts.

 

Production of Micro Silica

 

The production of micro silica begins with the smelting of quartz, coal, and wood chips in electric arc furnaces. These raw materials are heated to extremely high temperatures, causing them to react and form a vapor. This vapor is then rapidly cooled, causing it to condense into tiny particles of micro silica.

 

The resulting micro silica particles are about 100 times smaller than a grain of cement, giving it a large surface area and high reactivity. This makes it an ideal pozzolanic material, as it can react with the free lime in cement to form additional calcium silicate hydrate (C-S-H) gel, which is responsible for the strength and durability of concrete.

 

Once the micro silica is produced, it is collected and stored in silos for further processing and packaging. It can be used in its raw form or processed into a densified form, depending on the application. 

 

Types of Micro Silica Production Methods

 

1. Direct method:

 

This is the most common production method of micro silica. In this method, high-purity quartz or quartzite is reduced in an electric arc furnace, as described above. The resulting silicon metal is then collected, cooled, and ground to produce micro silica. The main advantage of this method is that it produces a high-quality micro silica with a consistent chemical and physical composition.

 

2. Indirect method:

 

In this method, the production of micro silica starts with the production of silicon metal or ferrosilicon alloys. The gases produced during the reduction process are then cooled, collected, and processed to produce micro silica. The main advantage of this method is that it utilizes the byproduct gases, making it a more sustainable production method.

 

3. Precipitated method:

This method involves the reaction of silica compounds, such as sodium silicate or silicon tetrachloride, with a mineral acid to produce a gel-like precipitate. The precipitate is then filtered, washed, and dried to produce micro silica. This method is commonly used to produce high-purity micro silica for specialized applications, such as in the electronics industry.

 

Challenges in Using Micro Silica

 

While micro silica offers a wide range of benefits, its use also presents some challenges that need to be addressed:

 

1. Handling and Storage

 

Due to its small particle size, micro silica is highly susceptible to moisture absorption. This can lead to clumping and clogging during storage and transportation, making it difficult to handle. Special measures, such as storing it in a dry environment and using air-tight containers, must be taken to prevent moisture from affecting its properties.

 

2. Health and Safety

 

Micro silica contains a high percentage of amorphous silica, which can pose a health risk if inhaled. It is essential to take necessary precautions, such as wearing a mask and gloves, while handling micro silica to avoid any respiratory or skin irritation.

 

3. Cost

 

Micro silica is a by-product of the production of silicon metal and ferrosilicon alloys, which are used in various industries. This means that its availability and cost can vary, depending on the demand for these industries. The cost of micro silica may also be higher than other additives, making it a less viable option for some construction projects.

 

Future of Micro Silica in Construction Industry

 

Micro silica is currently being widely used in the construction industry for its numerous benefits. It has been shown to improve the strength and durability of concrete, reduce the risk of cracking and deterioration, and increase its resistance to harsh environmental conditions. With the growing demand for sustainable and high-performance construction materials, the use of micro silica is expected to increase in the future.

 

Moreover, ongoing research and development in the field of nanotechnology have led to the development of nano-silica, which is an even finer form of micro silica with a particle size of less than 100 nanometers. This has opened up new possibilities for the use of micro silica in various applications, such as self-healing concrete and high-strength, lightweight construction materials.

 

In Conclusion

 

Micro silica or silica fume is one of the most versatile and beneficial additives in the construction industry. Due to its unique properties, it can be used to enhance the strength, durability and workability of many different building materials. However, there are some challenges associated with the use of micro silica, including proper handling and storage, as well as potential health risks. However, the advantages of micro silica far exceed its costs, making it one of the most popular additives in modern construction projects.