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Silica Fume: Densified vs. Undensified

Silica Fume: Densified vs. Undensified

Introduction to Silica Fume: Densified vs. Undensified

Silica fume, also known as microsilica, is a byproduct of silicon and ferrosilicon alloy production. This ultra-fine material, primarily composed of silicon dioxide (SiO₂), is renowned for its ability to enhance the properties of concrete. Silica fume is available in two main forms: densified and undensified. Understanding the differences between these forms is crucial for selecting the right type for specific construction applications.

Physical Differences

The primary distinction between densified and undensified silica fume lies in their physical characteristics.

Densified Silica Fume

Densified silica fume is created by agglomerating the fine particles into larger, more manageable clusters. This densification process makes the silica fume easier to handle, transport, and mix with other materials. The densified form typically has a bulk density ranging from 300 to 600 kg/m³. The agglomerates can be broken down during mixing, ensuring the fine particles are well-dispersed throughout the concrete mix.

Undensified Silica Fume

Undensified silica fume retains its original fine particle size, with a bulk density of around 200 to 300 kg/m³. These particles are extremely small, about 100 times finer than average cement particles. The undensified form is highly reactive and offers superior performance enhancements for concrete. However, its low bulk density can make handling and transportation more challenging compared to the densified form.

Chemical Differences

While the chemical composition of densified and undensified silica fume is fundamentally similar, their physical forms can influence their reactivity and performance in concrete.

Chemical Composition

Both densified and undensified silica fume primarily consist of amorphous silicon dioxide, usually more than 85-95%. They also contain minor amounts of impurities such as carbon, iron oxide, and alumina. The high silicon dioxide content is responsible for the pozzolanic properties that improve concrete strength and durability.


The undensified form, due to its finer particle size and higher surface area, tends to be more reactive than the densified form. This increased reactivity allows undensified silica fume to contribute more effectively to the pozzolanic reaction, leading to enhanced concrete properties. However, once densified silica fume is adequately dispersed in the mix, it can achieve similar chemical performance.

Production Differences

The production processes for densified and undensified silica fume differ primarily in the post-collection treatment.

Undensified Silica Fume Production

Undensified silica fume is collected directly from the flue gases produced during the manufacturing of silicon or ferrosilicon alloys in electric arc furnaces. The collected fume is then processed to remove impurities and ensure a consistent particle size distribution.

Densified Silica Fume Production

The production of densified silica fume involves an additional step after the initial collection. The fine particles of undensified silica fume are subjected to a densification process, where they are agglomerated into larger particles through controlled conditions of temperature and pressure. This process increases the bulk density, making the densified form easier to handle and transport.

Application Differences

The choice between densified and undensified silica fume depends on the specific requirements of the construction project.

Densified Silica Fume Applications

Densified silica fume is often preferred in applications where ease of handling, storage, and mixing are critical. It is commonly used in:

  • Ready-mix concrete plants: Its higher bulk density simplifies storage and batching processes.

  • Precast concrete: Facilitates efficient mixing and uniform distribution within the mix.

  • Concrete repair materials: Enhances the properties of repair mortars and grouts.

Undensified Silica Fume Applications

Undensified silica fume is ideal for applications that demand the highest performance enhancements in concrete. It is typically used in:

  • High-performance concrete (HPC): Maximizes strength and durability for critical infrastructure projects.

  • Marine structures: Provides superior resistance to chloride penetration and corrosion.

  • Industrial floors: Enhances wear resistance and durability in harsh environments.


Understanding the differences between densified and undensified silica fume is essential for optimizing concrete performance in various construction projects. While both forms offer significant benefits, the choice depends on the specific handling, chemical, and performance requirements of the project.

For construction projects that demand high-quality and durable concrete, incorporating the right form of silica fume is crucial. VALO Concrete is dedicated to providing top-notch concrete solutions tailored to your needs. Contact us today to learn more about how we can help you achieve outstanding results with our expert concrete services. Send us your inquiry and let us assist you in bringing your vision to life with the best silica fume options.


Contact VALO Concrete now and discover the power of silica fume for your next project!

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