Microsilica in Concrete – Types, Properties and Uses

Microsilica is a chemical compound which is produced while manufacturing ferrosilicon and silicon alloys. It is also called ‘silica fume’, and appears as a very fine substance made of microscopic sphere-shaped particles. Microsilica mainly contains silicon dioxide (SiO2).

It has excellent high surface area and exceptional pozzolanic properties. These characteristics make it ideal to add microsilica in concrete and improve the concrete’s inherent properties.

In this blog, you will learn everything you need to know about Microsilica in concrete, including its types, properties, and uses.

Characteristics of Silica Fume

Microsilica has certain characteristics that make it truly unique, and incredibly efficient in producing high-quality concrete products.

Some of the most prominent characteristics of microsilica are –

High Surface Area – Microsilica has an extremely high surface area. It is normally between 15,000 and 30,000 m²/kg.

Small-sized Particles – The average size of the microsilica particle is around 0.1 microns, which is at least 100 times less than the size of cement particles.

Density – Thanks to its microscopic particles, the density of microsilica is between 200 kg/m³ and 300 kg/m³.

Amorphous Structure – Microsilica is amorphous, unlike crystalline silica. This characteristic enhances the reactivity of microsilica in concrete.

Composition – Microsilica is made up of 85% to 98% SiO2. This unique chemical composition makes microsilica extremely reactive with the calcium hydroxide found in cement.

Types of Microsilica

There are several types of microsilica available. These are categorized according to their production process and intended use.

The most popularly types of microsilica are –

Raw Microsilica

This is the non-densified form of microsilica. It has a high surface area but low bulk density.

Dense Microsilica

This type of microsilica is made by compressing the silica particles till their bulk density gets enhanced. This form of silica fume is more efficient to transport and handle.

Pelletized Microsilica

This form of microsilica is manufactured into small pellets, depending on specific use. However, this type of microsilica has smaller surface area which makes it less reactive.

Slurry Microsilica

This type of microsilica is made by mixing water till the substance turns thick. This form of microsilica is used for some specific construction projects.

Effects of Microsilica on Concrete

Now that you know the different types of silica fume, let’s find out the effects of microsilica on concrete.

Adding microsilica to concrete affects several properties of the concrete mix, such as –

Less Porosity

The microscopic particles of microsilica are ideal to fill tiny pores and small gaps on the surface of the concrete. It also reacts with the calcium hydroxide in cement and forms Calcium Silicate Hydrate (C-S-H). These processes effectively make the concrete less porous and reduce its permeability. This way, the concrete becomes highly resistant to water seepage and chemical spills.

Higher Strength

As the fine particles of microsilica efficiently cover tiny pores and the gaps between cement particles it also creates a dense and impervious layer over the concrete surface. This way, microsilica enhances the flexural, tensile and compressive strength of the concrete structure.

Better Workability

Adding superplasticizers to microsilica improves its overall workability, despite the high surface area which may otherwise reduce average workability of the concrete mix.

Higher Heat-Resistance

Mixing microsilica in concrete makes the concrete ideal to work even at high ambient temperature. This makes the compound excellent for fire-resistant and refractory applications. 

Improved Durability

Microsilica also extends the lifespan of buildings and makes them more durable by making it highly resistant to alkali-silica reaction (ASR) and sulfate attack.

Use of Microsilica in Concrete

Mixing microsilica in concrete makes it extremely useful for various purposes, such as –

Marine construction

Microsilica-laced concrete protects the structures against corrosion from chloride. This makes the concrete well-suited for offshore platforms, ports, jetties, and other marine structures.

HPC (High Performance Concrete)

Adding microsilica enhances the concrete’s strength significantly. This makes it ideal for use in construction projects that prioritize durability and higher strength. HPC is widely used for constructing heavy load-bearing structures, such as skyscrapers, dams, bridges, etc.

Precast components

Microsilica, when mixed with concrete, also provides exceptionally high-quality finish and also ensures consistency in performance.

Industrial areas

The higher strength and extended durability makes the concrete minimized dust, and enhances the concrete’s resistance to wear-and-tear from heavy loads. Hence, microsilica-based concrete is extremely useful in building floors in industrial settings.

Subways/Tunnels

The higher resistance to water seepage and chemical corrosion also make microsilica-laced concrete an excellent choice for constructing tunnels and subways.

How Microsilica Works in Concrete?

There are two main ways that microsilica works to enhance the concrete’s inherent properties.

1 – Pozzolanic Reaction

During cement hydration, calcium hydroxide is formed, which reacts with microsilica to create C-S-H (Calcium Silica Hydrate). This reaction enhances the durability and strength of the concrete structure.

2 – Filler Effect

The other way that microsilica works in concrete is through the ‘filler effect’. In this, the microscopic particles of microsilica successfully enter any small pores and even fill the gaps between cement particles. This enhances the concrete’s density, which significantly improves the structure’s strength and water-resistance.

Mixing and Placing Considerations

Follow the below-listed tips from construction experts for the best mixing and placing practice for microsilica-mixed concrete –

Ideal Quantity

According to experts, you should add around 5% – 15% microsilica, according to the cement volume to achieve the desired properties in the concrete mix.

Add Superplasticizers

Adding superplasticizers to the concrete mix helps improve its workability, thanks to the large surface area of microsilica-based concrete.

Proper Mixing

Make sure to mix the microsilica in concrete till the clumped cement particles get dispersed uniformly throughout the concrete mix.

Correct Hydration

You can use any high-quality water-reducing agent in the concrete to achieve the required water-to-cement ratio, with no adverse effects on its workability.

Perfect Placement

It is recommended by experts to place the mixed concrete swiftly and follow ideal curing practices. This will help to avoid cracks in the concrete and ensure maximum compressive strength of the concrete structure.

Microsilica Applications

Microsilica-laced concrete is widely used in the following applications worldwide –

1 – Repairing

Microsilica is extremely useful in repairing mortars. It effectively restores the structural integrity of the structure, and also prolongs its life-span.

2 – Power plants

Concrete mixed with microsilica gives concrete structures minimal porosity and significant durability. This is an excellent choice of building material to construct nuclear power plants.

3 – Skyscrapers

The higher compressive strength attained by concrete from mixing microsilica makes it the ideal choice for foundations, beams and columns of high-rise buildings.

4 – Industrial plants

Adding microsilica to concrete makes the concrete extremely resistant to damage from heavy loads, constant use, chemical spills, thermal cycling and extreme temperatures. These properties make microsilica-laced concrete an excellent choice for industrial structures.

5 – Hydraulic construction

The microsilica-concrete mix has higher resistance to corrosion and lowest porosity, which makes it best-suited for use in hydraulic construction, such as canals, dams, etc.

Conclusion

Microsilica in concrete has revolutionized the global construction industry in several ways. Its ability to produce stronger, more durable and reliable structures make the microsilica-concrete mix ideal for various uses, including new construction and repairing existing buildings.

To ensure the best results, it is recommended to buy high-quality microsilica construction chemicals only from reliable manufacturers, such as Sakshi Chem Sciences Pvt. Ltd.

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