Microsilica, also referred to as silica fume or condensed silica fume, offers significant enhancements to the strength and durability of concrete. This is achieved through its ability to promote a more uniform distribution and increased volume of hydration products, while simultaneously reducing the average size of pores within the cement paste. Microsilica consists of finely solid glassy spheres composed of silicon dioxide and is typically obtained as a by-product during the production of ferrosilicon and metallic silicon in high-temperature electric arc furnaces.
One of the key benefits of incorporating microsilica into concrete is its ability to slow down the process of carbonation. Additionally, it effectively decreases the permeability of concrete to chloride, which is particularly important in protecting reinforcement and embedments from aggressive agents. By reducing the rate of carbonation and enhancing resistance to chloride penetration, microsilica concrete provides a robust shield for the reinforcement and embedments, resulting in improved durability and longevity of the concrete structure.
Types of Microsilica
Microsilica is available in three different forms: powdered microsilica, condensed microsilica, and slurry microsilica. Powdered microsilica refers to microsilica in a finely ground powder form. Condensed microsilica, on the other hand, is microsilica that has been processed to form small, spherical particles with a high density. Lastly, slurry microsilica is microsilica that has been mixed with water to create a fluid suspension. These different forms of microsilica provide versatility and flexibility in its applications, allowing it to be used in various industries such as construction, oil and gas, and even in the production of high-performance concrete.
Effects of Microsilica on Concrete
1. Effects on Fresh Concrete
The utilization of this particular technique significantly decreases the potential for segregation, making it an effective aid for pumping operations. Moreover, it virtually eliminates bleeding, thereby enabling an earlier start to finishing work. However, it should be noted that the workability and consistency of the concrete tend to decrease as a result of employing this method.
2. Effects on Hardened Concrete
The inclusion of microsilica in hardened concrete brings about enhancements in various important aspects. Firstly, it significantly improves the compressive strength of the concrete, leading to a subsequent improvement in flexural and tensile strength as well. This means that the concrete becomes stronger and more resistant to bending and pulling forces.
Another area that benefits from the addition of microsilica is bond strength. Microsilica helps to enhance the bond between the concrete and other materials, resulting in improved adhesion and overall structural integrity.
Concrete infused with microsilica also exhibits enhanced resistance to abrasion, making it more durable and capable of withstanding wear and tear caused by friction and contact with rough surfaces.
Furthermore, the permeability of the concrete is reduced when microsilica is added. This reduction in permeability is significant as it aids in protecting the reinforcement steel within the concrete from corrosion. By limiting the passage of water and harmful substances, microsilica contributes to the long-term durability of the concrete.
Additionally, microsilica improves the concrete’s resistance to impact and cavitation. It enhances its ability to withstand sudden forces or impacts, as well as the formation of cavities due to rapid changes in pressure.
The inclusion of microsilica also grants the concrete increased resistance to sulphate attacks, making it suitable for environments where sulphate exposure is a concern.
Moreover, microsilica helps in reducing heat within the concrete. This property is particularly beneficial in applications where temperature control is important, such as in hot climates or structures subjected to high thermal loads.
Finally, microsilica enhances the concrete’s chemical resistance. It improves its ability to withstand the corrosive effects of certain chemicals, ensuring the longevity of the structure in environments where exposure to such substances is expected.
Overall, the addition of microsilica brings about a multitude of advantages to hardened concrete, encompassing improved strength, bond, abrasion resistance, permeability reduction, impact and cavitation resistance, sulphate resistance, heat reduction, and chemical resistance.
Properties of Microsilica
Microsilica is a powder that can range in color from nearly white to nearly black. It consists of spherical particles with a diameter of less than 1mm. The bulk density of microsilica depends on how densely it is packed and can vary from 130 to 600 kg/m3. Its specific gravity ranges between 2.2 and 2.3.
Advantages
Silica fume effectively prevents thermal cracking from cement hydration heat, enhances resistance to sulphate and acidic water attacks, and reduces early age temperature rise. It is a cost-effective solution due to its affordability. Furthermore, the addition of microsilica reduces both the weight and cost of the slab. Its inclusion also decreases efflorescence by refining the pore structure and increasing the consumption of calcium hydroxide.
Practical Use of Microsilica in Concrete
Silica fume is utilized in waterproof concrete, high-strength concrete, and shotcrete applications. It is also commonly specified to enhance durability. Additionally, it finds application in elastomeric, polymer, refractory, ceramic, and rubber products.
