Microsilica in Concrete – Types, Properties, and Practical Applications

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Microsilica in concrete improves its strength and durability as it provides more uniform distribution and a greater volume of hydration products, and decreases the average size of pores in the cement paste.

Microsilica, also known as silica fume or condensed silica fume, is a mineral admixture composed of very fine solid glassy spheres of silicon dioxide. It is usually found as a by-product in the industrial manufacture of ferrosilicon and metallic silicon in high-temperature electric arc furnaces.

Added to that, Microsilica reduces the rate of carbonation and decreases permeability to chloride. As a result, microsilica concrete is able to strongly protect reinforcement and embedments from aggressive agents.

Types of Microsilica

Microsilica comes in three forms which are:

1. Powdered microsilica  
2. Condensed microsilica
3. Slurry microsilica

Effects of Microsilica on Concrete

1. Effects on Fresh Concrete

• It reduces segregation possibilities, so it can be used as pumping aid.
• It almost eliminates bleeding, consequently finishing work shall begin early.
• Workability and consistency of concrete decreases.

 2. Effects on Hardened Concrete

The addition of microsilica improves different aspects of hardened concrete which include:

• Compressive strength, hence flexural and tensile strength are improved as well.
• Bond strength
• Abrasion resistance
• Reduces permeability; therefore, it helps in protecting reinforcement steel from corrosion.
• Impact and cavitations resistance.
• Sulphate Resistance
• Heat Reduction
• Chemical Resistance

Properties of Microsilica

1. Microsilica is a grey; nearly white to nearly black powder.
2. Spherical particles less than 1mm in diameter.
3. The bulk density of microsilica is based on the degree of densification and varies from 130 to 600 kg/m³.
4. The specific gravity of microsilica ranges between 2.2 to 2.3

Advantages

1. Reduces thermal cracking caused by the heat of cement hydration.
2. Improves durability to attack by sulphate and acidic waters. 
3. Reduces the early age temperature rise.
4. Silica fume is cheap; therefore, it is cost-effective.
5. It reduces the overall slab weight and cost
6. Addition of microsilica decreases efflorescence due to the refined pore structure and increased consumption of the calcium hydroxide.

Practical Use of Microsilica in Concrete

1. Silica Fume Waterproof Concrete
2. High Strength Concrete
3. Shotcrete
4. Specifying for Durability
5. It is used in elastomeric, polymer, refractory, ceramic and rubber applications.